Low-frequency curvilinear transducers with frequencies in the range of 3–6 MHz are best suited for lung ultrasound. Much of the recorded action of the lung begins and ends with the pleura. The pleura, a general term for the parietal pleura, air, and visceral pleura, is the denser outer covering of the lung that moves with the lung. From a sonographer’s perspective, the pleura is the most easily visualized lung structure. Inspecting the pleura sonographically allows for observations of both pleural motion and pleural sonographic disruption.


As the pleura moves, it moves the rest of the lung. This “sliding lung sign” accurately indicates lung motion and successful ventilation. If the pleura is not sliding, the lung, at least on the side of the thorax being inspected, is not ventilating thoroughly. Quick speculations about the causes of a lack of ventilation can be confirmed and treated to save lives. Below are some causes of a lack of ventilation that can be considered when there is no sliding lung sign:[4]


What have been named “A-lines” are the results of a reverberation artifact from the pleura or recurrent mirror images of the pleura that appear under the pleural lining at regular intervals, as shown in Figure 8-2. Disruption of the interstitium of the pleura changes the entire pleural reflection. Because the beam is prevented from uniformly penetrating the pleura, the areas that are disrupted are now seen as “B-lines,” as shown in Figure 8-3. There is no longer a reverberation artifact or A-lines when there are B-lines in motion.


B-lines representing pleural interstitial disruption often represent pulmonary edema or vascular overload, as shown in the right diagram of Figure 8-3. The edema, which collects on the pleural surface, causes “comet tail” artifacts that account for the lines extending the lungs’ entire length. It is often in the realm of intensivists or pulmonologists to ascertain a patient’s intravascular volume. Dr. Lichtenstein was an original contributor to the direct visualization of the inferior vena cava to determine intravascular blood volume. He later discovered that B-lines might more accurately represent intravascular volume overload.


Ultrasound principles allow us to understand that the complete reflection of the waves due to necrotic debris is represented as a bright image on the screen in the area of the lung parenchyma. Nonsonographic clues such as a fever may lead the clinician to speculate that the bright reflection is an infection of the alveolar cells or pneumonia. Since alveoli have such thin walls that allow oxygen to be exchanged, it is often accurately feared that this same thin wall would easily allow infectious organisms to also cross from the alveoli to the bloodstream. Noninfectious obstructions around the alveoli appear as a similar bright reflection of the ultrasound image. This scarring is known as atelectasis and is often considered much less dangerous to the patient.


Due to many factors, it is a slippery slope to write anything about COVID-19. The disease is widespread, the actual effectiveness of isolation is unknown, testing has been inaccurate for the most part, supplies to even care for patients have been limited to an unprecedented extent in most developed countries, and the treatment theories change almost daily.


Far too many patients diagnosed with COVID-19 have had a rapid downhill course and go on to have a painfully long critical care course with a high mortality rate. For the first time in the world, there have been several considerations brought to the forefront. There has been a common consensus that COVID-19 has caused significant shortages of medical supplies both in the United States and worldwide, including those in testing capacity, ICU and hospital bed supply, hospital staff, personal protective equipment (PPE), and mechanical ventilators for affected regions.[5] There is greatly magnified attention on the safety of caretakers of the most critically ill patients. The mental health and well-being of health care professionals have been the focus of increased attention, with persistent evidence of high burnout, psychosocial stress, and mortality rates.[6] There has been a realization of how the increased vulnerability of our underserved population will perhaps impact how medical care is distributed in the future. The prevalence of COVID-19 has had a disproportionate impact on the poor, minorities, and a broad range of vulnerable populations due to its inequitable spread in areas of dense population and limited mitigation capacity resulting from a high prevalence of chronic conditions or poor access to high-quality public health and medical care.[7] There has been a growing need for more research on health equity in order to increase global knowledge and allow cross-national learning of what works for those most in need due to the direct and collateral effects of COVID-19. It has also been demonstrated that a pandemic can quickly destroy many characteristics of our society, affecting the economic, social, and personal habits of people in all countries. The World Health Organization has warned of a mental health burden related to the spread of COVID-19 infection through the global population: stress, worry, fear, and changes in our daily lives (working from home, temporary unemployment, homeschooling, etc.) are all challenging people’s mental and physical health as well as the global health care system and economy.[8]


COVID-19 has been a very humbling condition to deal with for any health care professional. Many patients do well even with a positive COVID test. Many patients found to be COVID-positive on routine screening remain asymptomatic. On the other end of the care spectrum, too many people without major risk factors are experiencing significant acute and chronic symptoms from the virus. Many have died, and a handful of them have been health care workers. The objective predictors of who will do well, such as lab tests and plain X-rays, have been inaccurate in too many cases. Especially in developed countries, diagnosticians can usually rely on numerous pieces of data to arrive at a reasonable treatment plan. At the time of this writing, COVID-19 remains a disease where the outcome can be unpredictable in a most painful manner. Patients with comorbidities are indeed at far greater risk of doing poorly, up to the point of having a much higher mortality rate. Age, congestive heart failure, chronic obstructive pulmonary disease, and dementia significantly increase the chance of doing poorly. The realization that an extensive ICU run for patients with limited life expectancy may not be in the best interest of the patient or a society where ICU resources are limited has been a most painful reality for medical workers to consider.


Lung ultrasound with handheld machines has developed into the most useful serial evaluator of the progression of COVID-19 lung disease. One of the challenges during the COVID-19 pandemic is was that several patients had to undergo ultrasound examinations within a limited amount of time, and those ultrasound tests needed to be completed on easily transportable machines. It was imperative for these machines to have the least number of knobs and small unreachable parts or spaces so that they can be sterilized quickly for immediate use with other COVID-19 patients.


Returning to the earlier chapters, we recall that degrees of brightness represent specific tissue characteristics, such as density. Pleura is one of those highly reflective densities. As the acute phase of COVID-19 disease progresses, distinctive changes may be observed first on lung ultrasound, which warns the clinician that the patient may be quickly worsening. Initially, COVID-19 may begin to change the pleura and cause the patient’s condition to worsen due to pleural thickening and focal fluid collection in some areas. Pleural thickening can be relatively easily seen on lung ultrasound, as shown in Figure 8-4.


As the thickened pleura from COVID-19 becomes even more inflamed, adhesions can develop in specific areas of the lungs. These adhesions may also be focal so that there may be focal areas of impaired ventilation even on the same side of the lung. As COVID-19 disease progresses, there can be focal infiltrates in the posterior and inferior portions of the lung, which are unique and can be identified on an ultrasound as gray areas (these regions appear anechoic on the normal lungs) commonly referred to as “ground glass”. The nature of the infiltrates with “ground glass” is present. The “ground glass” is from inflammation of the bronchioles and alveoli. This type of inflammation is characteristic of COVID-19.


It has been suggested that the ultrasound or CT findings of infiltrates in certain distributions can also be used as a diagnostic test suggesting the need for imploring further specific COVID-19-influenced testing. CT almost always presents a more precise view of the anatomic effects of the COVID virus on a patient. Handheld ultrasound is more accurate in evaluating the physiological effects of COVID-19 on ventilation, especially when considering the sliding lung sign. CT is more expensive and delivers more radiation. It may not be as practical to clean thoroughly to prevent droplet transmission of infection.


As opposed to other serious systemic diseases, progressive lung findings may remain focal or become more diffuse in the lungs. As the disease progresses, a more diffuse systemic condition from adhesions and inflammation may develop. This is known as acute respiratory distress syndrome (ARDS), which often leads to the need for ventilator support for several weeks. Several characteristics of COVID-19 have forced ethical discussions of patient care to very different levels from those for patients with other conditions.


Given the dismal results of cardiopulmonary resuscitation (CPR) in treating patients with COVID and the genuine risk to presumably healthy medical professionals, modifications to CPR have been suggested by many institutions that influence health care actions. These include the following:[9]


Some of the humbling parts of COVID-19 can be seen in the personal experiences of clinicians who have authentic discussions with patients with COVID-19 and the statistics of their success or failure in helping the most ill:


As the pandemic progresses, chronic health outcomes associated with acute COVID are becoming more frequent and are classified under the “long COVID” category. While the acute phase of COVID-19, which is often mild or moderate, usually lasts one to two weeks, the symptoms of long COVID can last for several months and often appear to be nonspecific and not restricted to organ systems. Clarifying the underlying causes and developing a meaningful, effective, and focused diagnostic algorithm are critical. Lung ultrasound will almost certainly be an essential consideration in the care of these patients, and it has been shown to be useful for the diagnosis of COVID-19 in the acute stage of the disease.[18] Clofent et al. were able to show, in their study of 352 adult long-COVID patients with a long-term follow-up of 2–5 months, that lung ultrasound could be implemented as a first-line diagnostic procedure in the treatment course.[19] It was shown that the outcome of lung ultrasound in adults could produce good discrimination between patients with persistent abnormalities compared with high-resolution CT. However, in this population, Clofent et al. found a high rate of interstitial lung disease after acute COVID-19 infection. On the other hand, according to a study conducted on children and adolescents by Gräger et al.,[20] lung ultrasound is not suitable as a standard in the follow-up of long-COVID patients without initial pneumonia or pathological findings in an existing baseline examination. They concluded that better standard examination protocols need to be established for this patient group. Nevertheless, lung ultrasound is an important diagnostic tool for the lung because of its radiation-free nature, rapid availability, and increasing establishment in practice (with increasing experience of the examiners). In summary, much is yet to be discovered from a more adequate evaluation and treatment of worsening patients with COVID-19.


The position of the heart in the thorax is much more variable than often expected. The heart may be in a more superior or lateral placement in the thoracic cavity due to abdominal anatomical abnormalities. Lung conditions, such as emphysema, may present a heart in a vertical orientation due to chronic lung overdistension. In most healthy individuals, the heart may be best seen in a view called the parasternal long axis, where the probe is held at the second or third intercostal space immediately left of the sternum, as shown in Figure 7-1. Directly below the palpated area will be the chamber walls of the left atrium and the left ventricle.


With optimal health, the heart contracts and expands synchronously. The circulation of the blood in the heart is shown in Figure 7-2. Blood enters the right atrium from the inferior vena cava and the superior vena cava. Blood then flows through the tricuspid valve to the right ventricle during cardiac expansion or diastole; this is mostly a passive flow. Blood is then expelled from the right ventricle during systole (or cardiac contraction) through the pulmonary artery and into the progressively smaller pulmonary arteries, pulmonary arterioles, and finally, pulmonary capillaries. Carbon dioxide and oxygen exchange occurs between the pulmonary capillaries and alveolar sacs of the lungs. Freshly oxygenated blood then returns via the pulmonary veins to the left atrium. Blood flows mostly passively from the left atrium, through the mitral valve, and into the left ventricle during diastole. Blood is finally propelled during systole through the aortic valve into the aorta and the body. The heart adapts to different behavioral and physiological stressors.


A commonly performed, more sophisticated ultrasound evaluation of the heart is called echocardiography, often performed by technicians and cardiologists. Echocardiography machines are generally highly sophisticated (and expensive), with the capability and clarity of the views obtained improving over the years.


Some of the most sophisticated machines that are routinely used in echocardiography can evaluate wall motion of specific areas of the heart and perform static measurements of both the opening and closing of the valves that are cycling more frequently than once. Color flow Doppler features in these machines can simultaneously differentiate blood flows going through insufficient valves. These findings help determine what procedures are best for patients with heart disease. Some patient conditions and the ultrasound principles behind the evaluations are described below.


Ischemia is inadequate blood flow through the coronary arteries that may lead to myocardial (cardiac muscle cell) dysfunction or myocardial death. Ischemia typically results in chest pain. Temporary chest pain from reversible ischemia is called angina. Permanent myocardial tissue death from ischemia is called myocardial infarction. It is a common task of primary care providers to determine if the chest pain symptom an individual is experiencing is related to ischemia or another medical cause. Shortness of breath (dyspnea) is also a common symptom of ischemia. The goal is to address angina or reversible ischemia before irreversible global myocardial tissue death. The next step in addressing suspected coronary artery ischemia for patients fortunate enough to access the best health care is coronary artery catheterization. Further diagnosis and treatment with coronary artery catheterization are often done during the same procedure.[1] A coronary artery blockage can be treated with a small open mesh tube called a stent. If indicated, a stent or other procedure to reduce the blockage is completed to restore adequate blood flow.


It is common in the United States to try to diagnose those patients with risk factors and typical chest pain with an evaluation called a stress echocardiogram, also known as a “stress echo” or cardiopulmonary exercise testing with echocardiographic examination. In this test, the patient’s heart rate is increased either by having them exercise on a treadmill or bike or by pharmacological measures to increase heart rate and heart contractility.[2] Pharmacological measures are used for patients with comorbidities, such as orthopedic or neurological conditions that may prevent safe treadmill or bike use. If there is a blockage of a single vessel in a stress echo, the part of the heart that this particular vessel supplies blood to will contract less efficiently. For example, the left main coronary artery (LCA) supplies blood to the anterior part of the heart. In patients with a blockage of their LCA, the anterior portion of the heart will have noticeably less contractility. The reduction of contractility may be coupled with symptoms such as angina or dyspnea during physical movement. The contractility dysfunction that is induced by a rapid heart rate is often followed by cardiac catheterization. A coronary artery bypass grafting during an open-heart procedure may be needed in more severe cases. If so, a large incision is made in the chest to expose the heart. A vessel is removed from the patient’s leg, chest, or arm and grafted around the coronary artery with blockage.


Myocardial muscle function has been assessed for over 200 years, and knowledge of congestive heart failure continues to change. Without imaging, it was hypothesized that heart contractility could be impaired and that the acceptance of incoming blood would be likewise impaired. This was realized to result in increased vascular pressure and fluid leakage in the peripheral interstitium, leading to ankle edema and edema in the lungs.[3] A stethoscope was used to hear the lung edema and probably first noted in an autopsy. Treatment at first involved trying to reduce intravascular volume by using a tourniquet or bloodletting. This was done with some success. One of the first medicines to treat it was a purification of products of the foxglove plant to produce a derivative of digitalis. To this day, medical providers continue to try to decrease intravascular volume and increase cardiac contractility. Digitalis derivatives like digoxin continue to be prescribed for abnormal heart rhythms.


Echocardiography is most important in the initial diagnosis and ongoing care of reduced myocardial contractility. Heart muscle contractility is assessed for quality and calculated as an ejection fraction (EF).[4] This is calculated by measuring the area of the left ventricle during diastole when the left ventricle is at the endpoint of receiving all of the blood prior to the contraction and at the point where the left ventricle has reached end-systole, which is the greatest point of contraction. The blood volumes corresponding to the endpoints during diastole and systole are referred to as end-diastolic volume (EDVol) and end-systolic volume (ESVol), respectively. Stroke volume (SVol) is calculated by subtracting ESVol from EDVol. EF can then be mathematically expressed as follows:[5]


If the left ventricle contains 100 ml of blood at the end of diastole and 40 ml when it fully contracts during systole, SVol is 60 ml, and thus, the EF is 60%. A normal EF percent is considered to be around 55–75%. EF percent measurements are becoming more reliable. This is largely due to software improvements allowing the area of a 3D object to be measured on a 2D screen. The description of a patient having an EF percent of significantly less than 50% gives experienced clinicians a good idea of a patient’s morbidity and mortality.


Heart valves allow blood to travel from one area of the heart to another and prevent “backflow” from its new area to the old area. The four valves evaluated by echocardiography are the aortic valve (between the left ventricle and aorta), the mitral valve (between the left atrium and the left ventricle), the tricuspid valve (between the right atrium and right ventricle), and the pulmonary valve (between the right ventricle and the pulmonary artery). Clinically relevant dysfunction is much more common in the aortic and mitral valves. There are two common types of valvular dysfunction.


Echocardiography evaluates valvular dysfunction by direct visualizations (measuring valve diameter in systole and diastole). This is obtaining static views for those changing most often more frequently than once per second in real time. Indirect measurements are obtained by measuring blood velocity through the valve and watching the color Doppler backflow of blood through valves with regurgitation.


In general, transverse and longitudinal planes (also called sagittal planes) should be obtained of all key anatomic structures and pathologies when performing a diagnostic evaluation. It is always important to know your orientation when visualizing the images. Transducers usually have an indicator on one side at the end of the probe, such as a light, knob, or notch corresponding to the right side of the screen’s image. If you are unsure, just touch one edge of the probe with your finger, and look at the screen to see if you are on the right or left side before imaging. During the evaluation, compare static images, dynamic images, Doppler evaluation, and possible contralateral evaluation. Also, document any masses or fluid collections, such as bursal distension, by indicating the location, size, shape, echotexture, compressibility, and presence or absence of flow with Doppler.[2]


Image optimization is obtained by selecting the proper transducer with appropriate frequencies. In general, a high-frequency linear transducer (10 MHz or higher) will be the appropriate selection for the evaluation of most joints. However, sometimes a curvilinear transducer gives better imaging in larger joints and in the evaluation of most adult hips, which usually require deeper penetration for visualization. Another exception would be the evaluation of superficial detailed structures such as the pulley system of the digits in the hand. A hockey stick transducer (>10 MHz) would be more appropriate for better resolution. Figure 6-1 shows some commonly used transducers in musculoskeletal ultrasound assessment. When evaluating a joint, it is helpful to start by directing your angle of insonation to the bony cortex, which is usually the most distal and hyperechoic structure, to avoid anisotropy.[3]


The normal sonographic appearance of MSK structures often has characteristic ultrasound images that are best visualized in the longitudinal plane. For example, tendons usually appear as a hyperechoic fibrillar echotexture. Ligaments are similar but more compact and connect two osseous structures. Muscle tissue appears more hypoechoic with septations, a pennate (featherlike) appearance in the longitudinal plane, and a starry-night appearance in the transverse plane with dynamic maneuvers. Bone is usually very hyperechoic. It creates a significant acoustic impedance mismatch and therefore is very reflective and appears bright white (hyperechoic) on the image. Adipose tissue and cartilage tend to be hypoechoic. Nerves tend to have both a hypoechoic and hyperechoic honeycomb appearance. The location and function of the structures are always helpful when determining normal anatomy and pathology.


Injuries, inflammation, or infections are divided into acute and chronic and can affect any musculoskeletal structure. Acutely, the sonographic structures tend to be hyperechoic, with possible hypertrophy, hypervascularity, fluid, and disruption of fibers in structures such as tendons. Chronic sonographic images tend to be more hypoechoic, with possible atrophy, scarring, and areas of calcification. Bone abnormalities can also be seen in acute and chronic processes. The normal bone cortex is smooth, uniform, and hyperechoic. A bone fracture can be visualized as a discontinuity of the bone cortex and disruption of the cartilage. Arthritis can have characteristic bone images such as crystal deposits on the cartilage surface in gout and synovial hypertrophy with bone erosions in rheumatoid arthritis.


Sonographic artifacts are not uncommon with MSK ultrasound, some of which have been discussed in earlier chapters. It is vital that the sound beam is perpendicular to the anatomic structure being visualized, or anisotropy can be encountered and give false information. To correct for anisotropy, performing a heel-to-toe maneuver on the long axis and toggling the transducer on the short axis are often helpful to finely tune the ultrasound image.


Figure 6-2 shows the anterior view of the shoulder anatomy. The shoulder is one of the most accessible joints to perform a comprehensive ultrasound evaluation. An ultrasound evaluation can be as reliable as an MRI for a rotator cuff tear. A complete shoulder evaluation should include the rotator cuff’s tendons and muscles, including the subscapularis, supraspinatus, infraspinatus, and teres minor. Also, examine the biceps brachii (with dynamic maneuvers, if indicated for subluxation, dislocation, or impingement), the acromioclavicular joint, the suprascapular nerve (in the suprascapular notch and the spinoglenoid notch), and the posterior glenohumeral joint.[4] Evaluating each anatomic structure in the transverse and longitudinal planes is essential.


For examination of the patient’s shoulder, developing an approach that allows for the best visualization with dynamic maneuvers is helpful. One approach would be to start by standing in front of the seated patient with their arm at their side, the elbow at 90 degrees flexion, the forearm in supination, and the ultrasound machine on one side of the patient for exam visualization.


The long-head biceps tendon is the first structure to be evaluated, and it works as a good reference point for the anterior shoulder evaluation. The origin of the long-head biceps is the supraglenoid tubercle of the scapula, and the insertion is the radial tuberosity and bicipital aponeurosis. It is innervated by the musculocutaneous nerve. Its action is flexion and supination of the forearm at the elbow joint and flexion of the arm at the shoulder joint. First, look at the transverse position within the bicipital groove of the humeral head with a linear transducer.


The biceps tendon should have a bright, dense, ovoid, and bristle-like appearance. It should be assessed from proximal to distal in the transverse and longitudinal planes, as shown in Figure 6-3. It is essential to evaluate the most proximal area where the biceps tendon courses over the humeral head because this is a common site for pathology. Also, fluid distension within the bicipital tendon sheath often indicates shoulder pathology, since part of it communicates with the shoulder joint. Continue the evaluation distally until the fibrous-appearing band of the pectoralis major inserted into the proximal humerus is visualized. This is sometimes where a bicipital tendon tear can be found separated from the muscle after an injury. Dynamic maneuvers, both active and passive, can be very helpful in the evaluation.


After looking at the bicipital tendon/muscle, return to the point of reference within the bicipital groove of the humerus in the transverse plane. Next, evaluate the subscapularis, which originates at the subscapular fossa and inserts into the lesser tubercle of the humerus. It is innervated by the upper superior and lower inferior subscapular nerves, and the action is for internal rotation of the humeral head. It prevents anterior displacement of the humerus. First, start by moving the transducer medially to the lesser tuberosity to evaluate the rotator interval, which is the space between the anterior margin of the supraspinatus tendon and the superior margin of the subscapularis tendon. The subscapularis tendon/muscle is evaluated by a passive range of motion with external rotation, as shown in Figure 6-4. This brings the subscapularis into the longitudinal (sagittal) plane as it rotates over the humerus. During this dynamic maneuver, also evaluate for coracoid impingement. A limited view of the anterior glenohumeral joint can also be evaluated in this position. The probe is then rotated 90 degrees clockwise in the transverse plane. In this view, the subscapularis will have a characteristic vertical hypoechoic segmented appearance secondary to the musculoskeletal junction, which is usually normal anatomy and not a tear. The evaluation should again include any evidence of effusion, synovial hypertrophy, or tearing.[5],[6]


The next anatomic structure to evaluate in the anterior position of the patient is the acromioclavicular (AC) joint, shown in Figure 6-5. The most straightforward approach is to palpate the AC joint and place the linear transducer on top of it in the transverse plane. Evaluate for widening, such as in a tear or effusion, which is sometimes indicative of rotator cuff pathology.


The next rotator cuff to be evaluated is the supraspinatus, which originates in the supraspinatus fossa and is inserted on the superior facet of the greater tubercle of the humerus. Innervation is by the suprascapular nerve; its action is the abduction of the arm and stabilization of the glenohumeral joint. The best position for the patient to be in is called the modified crass position. In this position (which involves extension, adduction, and internal rotation), the patient is sitting upright with the palm of their hand on the ipsilateral hip and the elbow flexed and pointed posteriorly. This brings the supraspinatus out from under the cover of the acromion. Over 90% of rotator cuff injuries involve the supraspinatus.[7],[8] First, evaluate the supraspinatus tendon in the longitudinal plane, as shown in Figure 6-6. This image is the most essential view and should have a bird’s beak appearance. Next, include the transverse plane view. Evaluate the bony cortex, hyaline cartilage, supraspinatus tendon/muscle, peribursal fat, and the subacromial bursa. Pooling of fluid within the subacromial bursa or restrictive motion of the supraspinatus tendon could indicate subacromial impingement.[9]


It is vital to evaluate the tears of the supraspinatus with the correct description. First, determine if it is a full-thickness tear extending from the articular to the bursal surface or a partial-thickness tear. Partial-thickness tears involve the articular or bursal surface or are localized within the tendon, not extending to either surface. This is called an intrasubstance tear. When evaluating the diameter of the tear, measure along the long and short axis.


Posterior cuff imaging is evaluated next by facing the posterior shoulder, palpating the scapular spine, and placing the transducer below it in an oblique axial plane angled superiorly toward the humeral head. A curvilinear probe is sometimes needed for better penetration, since the posterior shoulder is a deeper structure. The infraspinatus and teres minor tendons are first evaluated in the longitudinal plane from the scapular fossa’s origin to the humerus’s greater tuberosity, as shown in Figure 6-7. The origin of the infraspinatus is the infraspinatus fossa of the scapula, and the insertion is on the middle facet of the greater tuberosity of the humerus. The suprascapular nerve innervates it, and its action is for external rotation and abduction of the arm at the shoulder joint with stabilization of the shoulder joint. The teres minor originates on the lateral border of the scapula and inserts onto the inferior facet of the greater tuberosity of the humerus. It is innervated by the axillary nerve and functions similarly to the infraspinatus.


Next, evaluate the suprascapular nerve in the suprascapular notch and the spinoglenoid notch. Sometimes, turning on the Doppler to better visualize the suprascapular artery is helpful, and right next to it is the suprascapular nerve.


Finally, evaluate the posterior glenohumeral joint, as shown in Figure 6-8. Look for joint effusion, cortical irregularities, and osteophytes, and evaluate the posterior labrum for cysts or tears. Also, this is a good approach for intra-articular glenohumeral joint injections using a posterior approach. This completes the shoulder evaluation.


The entire elbow examination is usually accomplished with a linear transducer. Like all the other joints, the elbow is best evaluated in a quadrant approach: anterior, medial, lateral, and posterior. Figures 6-9 and 6-10 show the anatomical structures of the elbow.


Anteriorly, look at the joint space for narrowing, cortical and cartilage irregularities, synovial hypertrophy, and effusion. Also evaluate the brachialis, biceps, median and radial nerves, and the brachial artery, as shown in Figure 6-11.


Next, the medial elbow evaluation is performed with the elbow in partial extension and the probe in a longitudinal axis, as shown in Figure 6-12. Evaluate the anterior band of the ulnar collateral ligament (UCL). It will have a characteristic triangular homogenous appearance as it spans from its attachment proximally to the humeral trochlea and distally to the olecranon. The common flexor tendon is superficial to the UCL and evaluated carefully at the insertion point of the medial epicondyle, since this is the site of medial epicondylitis. The pronator teres should also be examined for any evidence of tears, effusion, or synovial hypertrophy.[10],[11]


The lateral elbow is next approached with the elbow flexed at 90 degrees and the ipsilateral hand resting in pronation, as shown in Figure 6-13. A longitudinal probe placement is performed to evaluate the bony margins of the capitulum of the humerus and the radial head. Evaluate the radial collateral ligament complex and the common extensor tendon (CET). Closely evaluate the attachment of the CET to the lateral epicondyle, the site of lateral epicondylitis.


Finally, the posterior evaluation is performed with the elbow at approximately 90 degrees of flexion, as shown in Figure 6-14. Evaluate the triceps muscle and tendon, olecranon bursa, and the ulnar nerve within the groove between the medial epicondyle and the olecranon of the ulna. This can be a site for entrapment of the ulnar nerve, which should have an area of 7 mm or less.[12],[13]


The wrist and hand anatomy involve superficial structures; therefore, the best approach is to use a high-frequency hockey stick transducer for better resolution. Figure 6-15 shows the anatomical structure of the wrist and hand.


Start with the palm of the hand facing down. Identify Lister’s tubercle (see Figure 6-17) on the dorsum of the distal radius by digital palpation, and place the transducer on top of it in a transverse plane, as shown in Figure 6-16. This bony prominence separates the second and third extensor tendon compartments of the six in the wrist and helps with identification and orientation. Just radial to Lister’s tubercle is the second compartment containing the extensor carpi radialis brevis and the extensor carpi radialis longus.


With further radial movement, the first compartment on the side of the wrist is identified, which contains extensor pollicis brevis and abductor pollicis longus tendons. The first compartment is the site of de Quervain’s tenosynovitis. Evaluate each compartment from proximal to distal in both planes with active and passive dynamic maneuvers depending on the clinical concerns. Superficial to the compartments is the extensor retinaculum.


The third compartment is on the ulnar aspect of Lister’s tubercle and contains the extensor pollicis longus, as shown in Figure 6-17. Moving further toward the ulna, next to the third compartment, is the fourth compartment, which contains multiple extensor digitorum tendons and extensor indicis. Compartment five contains the extensor digiti minimi, and the sixth compartment contains the extensor carpi ulnaris, as shown in Figure 6-17. Evaluate each for any pathology.


After evaluating each compartment, return to Lister’s tubercle in the transverse plane, and move the probe distally to the radiocarpal joint. The bone just distal to the radius is the scaphoid, and the lunate bone is next to the scaphoid in the ulnar direction. Between the dorsal aspects of both bones is a triangular area that represents the scapholunate ligament, which has a compact hyperechoic fibrillar echotexture, as shown in Figure 6-18. This is a common site for injuries from falls involving extended wrists that could result in a tear of the scapholunate ligament. It is also a common site for ganglion cysts.


Now rotate the hand to evaluate the volar aspect, as shown in Figure 6-19. Evaluate the median nerve, flexor tendons, volar joint recesses, flexor carpi radialis, palmaris longus, and radial artery and the flexor tendons, pulleys, volar plates, collateral ligaments, and joint recesses of the fingers as clinically indicated. The median nerve is found between the flexor carpi radialis and palmaris longus. Place the transducer between these two tendons in the distal wrist crease in the transverse plane, and move the probe proximally as the honeycomb appearance of the median nerve courses radial to the flexor tendons and then moves ulnar and deep between the flexor digitorum superficialis and profundus. If the median nerve has a cross-sectional area of 12 mm2 or greater, this suggests carpal tunnel syndrome. Also, a 2 mm2 or greater difference in the cross-sectional area of the median nerve measured proximally at the level of the pronator quadratus and distally at the level of carpal tunnel has a 99% accuracy for carpal tunnel syndrome.[14]


Finally, individual digits should be evaluated in the transverse and longitudinal planes using dynamic maneuvers as clinically indicated for the evaluation of pathology. There are five flexor tendon pulleys in the fingers, which are named A1–A5 and consist of annular ligament pulleys and cruciate pulleys—that is, the flexor tendon pulley system. The thumb only has two pulleys, which are labeled A1 and A2. When evaluating the pulley system in the digits, the A2 and A4 pulleys are most important in the sagittal plane, as shown in Figure 6-20. If pathology is present, this may demonstrate bowstringing and hypoechoic edema.[15]


Figure 6-21 shows a schematic of the skeletal structure and tendons of the hip. The low-frequency curvilinear transducer is most appropriate for hip evaluation. Start with the anterior evaluation by having the patient supine with the ipsilateral leg in full extension and with slight external rotation, as shown in Figure 6-22.


Superficial to the capsule is the potential space between the capsule and the iliopsoas muscle, which is the iliopsoas bursa. This is the largest bursa in the human body, and an iliopsoas bursitis would be considered an extracapsular effusion. Like hip capsulitis, iliopsoas bursitis can be approached with an injection—but more superficial. The iliopsoas tendon is then evaluated by placing the transducer in the longitudinal plane in line with the femoral shaft and medial. The iliopsoas is a conjoined muscle composed of the iliacus and the psoas major muscles, which attach to the intertrochanteric line of the femur. This is evaluated from proximal to distal in the longitudinal and transverse planes. Also, consider evaluating the femoral vessels and nerve, sartorius muscle, tensor fascia lata tendons and muscles, lateral femoral cutaneous nerve, and rectus femoris tendon and muscles. Dynamic hip maneuvers may also help evaluate for tears, subluxation, or dislocation.[16]


Now have the patient in the lateral decubitus position with the hip to be evaluated up in a flexed 20–30 degree position to examine the gluteus muscles and tendons, as shown in Figures 6-23 through 6-25. The gluteus minimus, which is deep to the gluteus medius, originates from the ilium between the inferior and anterior gluteal lines. It inserts onto both the anterior aspect of the capsule and via its long head onto the anterior surface of the greater trochanter. The gluteus minimus and gluteus medius work together to abduct and internally rotate the hip. Finally, the gluteus maximus starts in the posterior iliac crest and sacrum/coccyx, crosses over the posterior facet, and inserts into the proximal femur, as Figure 6-25 shows. It extends and laterally rotates the hip.


To visualize the tendons in the sagittal plane, rotate the probe 90 degrees and angle the beam anterior to posterior to visualize the gluteus minimus and posterior to anterior to visualize the gluteus medius, as shown in Figure 6-24, and the gluteus maximus, as shown in Figure 6-25.


To evaluate the hamstrings, first identify the ischial tuberosity to locate the origins of the semimembranosus, biceps femoris, and semitendinosus tendons. Locate the conjoined tendons of the biceps femoris and semitendinosus, as shown in Figure 6-26. The semimembranosus lies deep and usually slightly inferior to the conjoined tendons.


Start the evaluation by using a high-frequency linear transducer and having the patient in the supine position. The anterior evaluation starts in the suprapatellar area with the probe in line with the femur, as shown in Figure 6-28.


Evaluate the following structures from deep to superficial, starting with the bony cortex of the femur, the quadriceps muscles and fascial planes, the femoral trochlea, the prefemoral fat pad, the suprapatellar bursa, and the suprapatellar fat pad. Evaluate proximally from the quadriceps muscle to the distal area over the patella in the longitudinal and transverse planes, looking for any pathology such as effusion or tears, as shown in Figures 6-29 and 6-30. It is sometimes helpful to perform toggling and heel-to-toe maneuvers to fine-tune the anatomy and avoid anisotropy.


Next, slide the transducer medially, and evaluate the medial aspect of the knee joint from the femoral to the tibial condyles in the sagittal and transverse planes, as shown in Figures 6-31 and 6-32. Also, evaluate the medial collateral ligament and the medial meniscus in the joint space. As you move the transducer distally, evaluate the pes anserine complex for any evidence of injury or inflammation, such as pes anserine bursitis.


Next, slide the probe to the lateral aspect of the knee joint, and evaluate the joint space of the distal femur and fibular head, as shown in Figure 6-33. In the longitudinal and transverse planes, evaluate the peripheral margin of the lateral meniscus and the lateral collateral ligament from proximal to distal.


Next, scan the infrapatellar area in the longitudinal plane with the bony landmarks proximally of the femur and tibia joint space and distally of the proximal tibia, as shown in Figure 6-34. Keep light pressure on the probe to avoid compressing any possible fluid within the bursa. There are two bursae superficial to the patellar tendon near the patella and one deep to the patellar ligament in the area of the proximal tibia. Evaluate the patellar ligament, sometimes called the patellar tendon, which is the portion of the quadriceps femoris tendon that continues from the patella to the tibial tuberosity.


Finally, the posterior view of the knee is evaluated with the knee slightly flexed at 10–20 degrees, as shown in Figure 6-35. Many structures can be seen in the popliteal fossa, including the popliteal artery and vein. One important area to evaluate is the area between the medial head of the gastrocnemius muscle and the semimembranosus tendon, which is the usual site of a Baker’s cyst. This completes the knee evaluation.


Figure 6-36 shows the anatomical view of the foot and ankle. The ankle and foot can be challenging to evaluate, since many structures require anatomic familiarity and detailed imaging. However, in general, a systematic approach is helpful. As with the other joint evaluations, a quadrant approach works best. Start with the anterior/dorsal evaluation by flattening the foot with an anterior longitudinal plane of the probe across the joint space of the tibia and talus, as shown in Figure 6-37. This provides an excellent focal point to sweep across the ankle joint to evaluate the muscles from medial to lateral: tibialis anterior, extensor hallucis longus, and extensor digitorum longus, as shown in Figure 6-38.


The subtalar joint is often of interest for evaluation and injection purposes. It is found in the longitudinal plane just medial to the lateral malleolus in the talus and calcaneus joint space.


Evaluate from the proximal muscle to the tendon insertion points in the transverse and longitudinal planes as clinically indicated.[17] Dynamic imaging is helpful to evaluate the integrity of the ligament. Now place the probe behind the lateral malleolus in the longitudinal plane with a posterior to anterior angle of insonation to evaluate the peroneus longus, which is superficial to the peroneus brevis. Evaluate both the longitudinal and transverse planes proximally and distally to their insertion points, as shown in Figures 6-39 and 6-40.


Place the probe in the transverse plane behind the medial malleolus to evaluate the medial side of the ankle and foot, as shown in Figure 6-41. Now we can evaluate the cross-sectional area of the structures in the tarsal tunnel. From medial to lateral, we have the Tibialis posterior tendon, flexor Digitorum longus tendon, posterior tibial Artery/Vein/Nerve, and flexor Hallucis longus tendon. Tom, Dick, And Very Nervous Harry is a commonly used mnemonic to recall these anatomical structures. This is important to evaluate for tarsal tunnel syndrome if clinically indicated.[18]


To complete the evaluation, look at the Achilles tendon in the transverse and sagittal planes from the proximal gastrocnemius and soleus muscles to the insertion into the calcaneus, as shown in Figures 6-42 and 6-43.


Finally, evaluate the foot’s plantar fascia in the longitudinal plane, as shown in Figure 6-44. The thickness at the insertion to the calcaneus should not be more than 4 mm, which would be suggestive of plantar fasciitis.


Obstetrics encompasses some of the same considerations as adult diagnostic ultrasound with a critical addition: rapid growth. There is no other time in life when various organs’ functionality is time dependent. The developmental changes in early organ growth are part of the most fascinating differentiation process. What is being observed within a specific imaging procedure in utero, although completely normal, actually changes over time. Broken down further, findings at specific gestational times depend on the level of differentiation an organ has undergone at a specific time in gestational development.


The accuracy of ultrasound is variable, and the issue of diagnostic accuracy is essential to understand for any medical professional. Sensitivity and specificity are commonly used quantitative measures to report such accuracy. For a given test and disease/condition, sensitivity is the ability of the test to correctly identify something being positive. Its specificity for a given test and disease/condition is how well it can distinguish those with disease from those without.[1] Expressed as equations, the calculations may be done as follows:


In recent years more than ever, another consideration is the cost of medical interventions. Clinicians should have a good idea of the impact of the tests that they order:


An example of a standard test is the complete blood count (CBC). The CBC is relatively inexpensive, reproducible among different labs, and often clinically helpful. The sensitivity of the CBC is regarded as relatively high. The specificity is often not very high. On this latter point, an elevated CBC can often be one of the first and most important clues to an impending worsening of an infectious process such as appendicitis. An elevated CBC can also be considered a “false positive” caused by medicines such as steroids or endogenous epinephrine secretion (for example, if the patient recently experienced a traumatic event). In the early stages of pregnancy, a CBC test can help determine various health abnormalities, including anemia and infections.


Maternal-fetal medicine specialists and their specialized technicians understand fetal development and testing rationales to make truly unique diagnoses. It is not unusual for heart development to be assessed weekly or even more frequently when difficulties are suspected, as cardiac problems can develop as gestation progresses. The following basic assessments are commonly performed in obstetrics ultrasound.


The volume of amniotic fluid is calculated by what is called the amniotic fluid index. Even debris (represented by diffuse abnormal reflections in the amniotic fluid) is a harbinger of difficulties. At first glance, the ease of clarity and measurement is heavily influenced by the amount of amniotic fluid. As discussed in the earlier chapters, media, especially fluid, influences the quality of ultrasound wave transmission and reflection. Figure 5-2 shows an ultrasound image at 23 weeks of the fetus, amniotic fluid, and normal fetal morphology. A clear initial view is not necessarily a good sign, since excess amniotic fluid (a condition referred to as polyhydramnios) may make the images easy to obtain but may, more importantly, indicate problems. It has been noted that polyhydramnios represents a high-risk obstetric condition as much as 20% of the time.[2],[3]


Fetal cardiac development (the development of the four chambers) is fascinating. The normal opening between the two upper chambers of the fetus’s heart, the right and left atria, is called the foramen ovale (FO). The FO permits blood flow to bypass the lungs before the infant is born (a fetus gets its oxygen from the placenta, not the lungs). As a result, the heart does not have to work as hard to pump blood where it is not needed. The FO typically closes six months to a year after the infant is born. A patent foramen ovale (PFO) occurs when the FO remains open after birth. A PFO often does not cause any issues.[4] When an infant is born with congenital heart abnormalities, the FO is more likely to remain open.


There is a division of a single atrium and a single ventricle by the growth of a septal wall from the wall of the single cavity in all directions toward the middle. This is a gradual and persistent hole in the septum that grows abnormally, leading to the septum closing, which results in a septal defect. Fortunately, one can detect both an atrial septal defect and/or a ventricular septal defect using ultrasound, as shown in Figure 5-3. Color flow ultrasound Doppler is often helpful, as one can view the flow from one side of the dividing atrial atrium or ventricle to the other side.


Different gestational sizes of different organs in the same fetus can indicate genetic and fetal nutritional problems. Intrauterine Growth Retardation (IUGR) can be either symmetric or asymmetric:


(A) Symmetric indicates a genetic or chromosomal difficulty. The term symmetric refers to the abnormal influence (mostly delayed growth) that affects all organs equally. It is essential to correctly postulate why a symmetric IUGR is often more reversible. Ultrasound-guided intrauterine blood transfusion is often used to improve IUGR in earlier fetal life.


(B) Asymmetric indicates that the head/brain is of the expected size but the baby’s body size and other measures, such as the abdominal circumference, are relatively small. This often indicates poor growth due to inadequate umbilical cord perfusion or anemia.


Spinal vertebra development, or lack thereof, can be the first diagnostic clue to spina bifida. Without normal closure, the thecal sac enveloping the spinal cord in the vertebra may be seen to be bulging outside of the vertebrae. Limb development can be noted to have an abnormally small size or an abnormal shape.


Genital development, more than ever before, may be evaluated before delivery. This is made possible by the higher resolution of high-end obstetric ultrasound machines.


The fetus’s activity can indicate variable states ranging from fetal distress to the infant sleeping. The biophysical profile (BPP) calculates different aspects of fetal motion that indicate fetal well-being. If the fetus has an abnormally low BPP, and especially if the fetus is mature enough to do well outside of the uterus, delivery is often induced or a cesarean is performed.


Prenatal ultrasound has a continuing rapid pace of development with the advent of 3D and 4D technology. The debate regarding both the usefulness of prenatal ultrasound in terms of the wise expenditure of health care dollars and diagnostic accuracy has lagged behind the explosion of technology. We are charmed by babies, and rightfully so. The development of prenatal ultrasound will no doubt continue and will hopefully benefit humanity.


The subject of prenatal ultrasound allows some discussion about the considerations of technological development. With the development of the prenatal ultrasound technique come widespread expectations and assumptions that may not be true. First, with the demonstrable development of a new technology, it is assumed to work for the intended purpose. It is easy for a layperson to believe that such sophisticated modalities would be 100% accurate and, therefore, worth it. For prenatal ultrasound, it would be predicted that a clear picture would allow for not only accurate prenatal diagnosis but meaningful intrauterine treatment of most conditions. The truth of this assumption is variable, depending, of course, on the condition being evaluated. The greatest accuracy of diagnosis has to do with conditions related to abnormality of amniotic fluid volume. The most discouraging levels of accuracy have to do with the detection of heart defects and isolated congenital abnormalities such as a cleft palate. This subject quickly becomes more complex as one progresses into discussions about issues such as the sensitivity index, cumulative Gaussian distribution, and dimensionless statistics.


If abnormalities are accurately discovered, the next hurdle is finding an effective treatment. Routinely in sophisticated medical centers, maternal-fetal medicine specialists and perinatologists perform procedures such as amniotic blood transfusions, fetal ureteral valve repair, and removal/replenishment of amniotic fluid volume due to abnormalities. In individual cases, there have been unbelievable advances and actual lives saved with this sophisticated technology. In our ever-cost-sensitive environment, we must balance this incredible cost against the expenditures of limited dollars for patient education.


The first trimester of pregnancy is when there is the most danger of mishap. Due to the rapid cell division and differentiation of the embryo in unbelievable numbers, even minor “errors” in cellular division may cause the very common event of spontaneous abortion. In the emergency department, it is often an unhappy task for a health professional to explain this issue to patients and their families. It is essential to be careful in doing so due to the tendency of many patients to wonder why a tragedy has occurred and to cast blame on themselves. Without careful explanation, patients who experience spontaneous abortion, or expulsion of an unsuccessful pregnancy through the vagina, may feel that they were at fault when this is not the case.


One can evaluate the earliest pregnancies with many parameters. The serial evaluation of the lab value of the “pregnancy hormone,” beta human chorionic gonadotropin (BHCG), over a few days gives an indication of developmental health. Early in pregnancy, the BHCG should double every 2–3 days. If there is a decrease or no increase in the value, this is a most worrisome sign for embryologic death. Often, early fetal demise will not be 100% certain, and the ultrasound and BHCG evaluation are done serially over a few days. Two ultrasounds without a heartbeat at the appropriate fetal age and an inappropriately declining BHCG are often considered diagnostic for intrauterine fetal death and likely spontaneous abortion.


Ultrasound evaluation can most accurately begin in early pregnancy with a longer, higher-frequency transvaginal probe. Returning to the knowledge of ultrasound physics from earlier chapters, it is crucial to realize why a higher-frequency probe is placed through the vagina and near the cervix. The accuracy of the higher-frequency probe allows a marked improvement in resolution when the reflection is only a short distance. At four to five weeks gestation, we first see the fetal yolk sac, fetal pole, gestational sac, and fetal heartbeat. An irregularly shaped gestational sac or lack of a fetal heartbeat when the embryologic or crown-rump length is greater than five weeks are ominous signs of possible embryological death. It is estimated that up to 50% of pregnancies end in spontaneous abortion, often so early in development that the patient does not recognize the pregnancy.


The other common peril in the first trimester of pregnancy is ectopic pregnancy, or pregnancy outside the uterus. As with intrauterine pregnancies, ectopic pregnancies grow and develop at very fast rates. Figure 5-4 shows an ectopic pregnancy adjacent to the left ovary. Most ectopic pregnancies are in the ovaries, fallopian tubes, or uterine horn. In either event, the pregnancies can “outgrow their blood supply,” rupturing and leading to maternal hemorrhage and potential death.


Sonographic signs of an intact ectopic pregnancy include enlargement in the area of implantation (even a functioning fetal heartbeat) and an “empty uterus” or lack of an intrauterine pregnancy when the BHCG is greater than 1500 international units. A patient with a ruptured ectopic pregnancy classically presents with sudden-onset unilateral pelvic pain and possibly signs of hemorrhagic shock. On the ultrasound, free fluid may be noted most commonly not only in the pouch of Douglas but also in the paracolic gutters or Morrison’s pouch. This is often a surgical emergency; the bleeding must be stopped before maternal death occurs from hemorrhage.


Gestational dating refers to the estimation of the gestation of the pregnancy. This is somewhat helpful when the medical provider evaluates issues such as whether to try to delay a patient in preterm labor or if induction of a patient who continues pregnancy more than 10 days after the estimated date of confinement (EDC) is indicated. Both of these issues have several determining factors. For preterm labor, infant mortality significantly decreases as delivery is delayed in many cases. For postterm situations, having a healthy term fetus more than 10 days after the EDC may pose unnecessary risks. These are complex decisions based on such data. To further complicate the issue, gestational dating may have variable accuracies. Some individuals have little or no prenatal care (i.e., some show up only to the emergency department when they are about to deliver or deliver at home without ever being evaluated by a medical provider). If one does have prenatal care and prenatal ultrasound, gestational dating accuracy remains variable. The facet that introduces the most variability is the gestational age at which the scan is performed. It has been traditionally noted that gestational dating accuracy has an 8% variability of the maturity of the pregnancy.[5] An example is that a 45-day gestation would have an accuracy of ±days, and a pregnancy of approximately 250 days would have an accuracy of ±20 days. This variability may decrease as ultrasound machines become more sophisticated. The principle, however, continues to make sense that as pregnancies mature, the genetic and environmental issues that make us all different have a greater influence on growth.


At approximately 14 weeks gestation, evaluation of organogenesis becomes more useful. As there is fetal growth, there is predictably more accuracy but fewer chances for potential interventions that may help as pathologic damage becomes irreversible. Organogenesis evaluation may differ according to the medical circumstances. Diagnostic capabilities vary according to the operator and machine.


The head, heart chambers, lungs, abdominal organs, genitals, and bones may be more successfully evaluated in the second trimester. While diagnostic accuracy improves, individual organs remain the most difficult to evaluate. Detecting some prenatal heart defects is an area of great interest and some improvement. The most common advantage of prenatal diagnosis of congenital heart defects is that if the condition is known, in more developed countries, the delivery can often be done at a tertiary medical center where there are maternal-fetal medicine specialists, pediatric cardiologists, pediatric surgeons, neonatal ventilators, and other sophisticated options for immediate treatment.


Warda et al.[6] are originally credited with developing regression analysis values to use fetal growth parameters to estimate gestational age. Due to an interesting phenomenon known as “organ sparing,” some organs are more reflective of accurate gestational dating than others. If there is placental insufficiency, the head will continue to grow more normally, but abdominal growth will lag. This increasing discrepancy between fetal head and abdominal growth may lead to the diagnosis of IUGR and indicate induced delivery of a small or preterm infant.


The head measurement is first determined by the biparietal diameter and occipital-frontal circumference. There is a flow pattern of cerebrospinal fluid (CSF) through the brain’s ventricular system and into the spinal cord through the foramen of Magendie and the foramen of Luschka. An obstruction of this flow causes increased back pressure, dilation of the ventricles, and pathologic pressure of the surrounding brain tissue. Many other conditions other than stenosis of the foramina cause hydrocephalus. This abnormality may be seen on prenatal ultrasound first as an increased head size and then as an increased ventricular size. Figure 5-5 shows an ultrasound image of fetal hydrocephalus. Hydrocephalus intervention is most often treated with postdelivery shunt placement, which involves placing a tube in the cerebral ventricles to bypass the obstruction and drain the excess fluid into other body cavities, such as the abdomen, where the fluid may be reabsorbed.


Other than abnormalities in CSF flow, there may be other abnormalities that are represented by an abnormal prenatal head ultrasound. These abnormalities have a wide range of etiologies, including genetic abnormalities, congenital abnormalities, and abnormal growth in an otherwise normal fetus. Genetic abnormalities have to do with abnormal chromosomes primarily due to mutation. Congenital abnormalities usually begin in the prenatal period and are evident at birth.


Cardiac ultrasound accurately predicts congenital abnormalities for many more subtle conditions. The most common congenital heart disease is patent ductus arteriosus, where the fetal ductus arteriosus that diverts the circulation away from the prenatal lungs and into the aorta does not close upon birth. This, of course, is never diagnosed prenatally. Rare but hazardous and sometimes fatal conditions such as transposition of the great vessels or defects of the central cardiac wall (called the septal wall) may be undetected by screening ultrasound exams. The complexity increases when there are combinations of heart defects such as tetralogy of Fallot, including pulmonary stenosis, right ventricular hypertrophy, ventricular septal defect, and an aorta that receives blood from both the right and left ventricle. In developed countries, when a fetal cardiac ultrasound is suspected from a routine prenatal ultrasound, a targeted ultrasound using more specialized machines and more specialized operators is subsequently performed. There may also be noncardiac prenatal ultrasound signs of heart disease, such as fetal hydrops (swelling) for fetal congestive heart failure.


Most intrauterine conditions that are treatable prior to delivery are identified in the abdominal exam. The umbilical cord is utilized as a site of intrauterine blood transfusions (by maternal-fetal specialists) to correct fetal anemia and hypovolemia. This procedure is done under real-time ultrasound and may be genuinely lifesaving as well as preventative of anomalies such as Potter’s sequence.


The fascinating development of the normal kidneys involves the division and migration of one central organ into a right and left kidney. Abnormalities in this separation and division include the persistence of the larger central organ, called a “horseshoe kidney.” Difficulties in renal function, such as nonfunction, may be suspected when the kidney appears small or atrophic. If a kidney is obstructed but functioning, “backward pressure” from the fetal urine may cause the kidney to enlarge, a condition known as hydronephrosis.


Some urinary tract obstructions may be corrected by intrauterine surgery. Posterior urethral valves in the male are the most common correction. When successful, relieving the obstruction prevents further renal damage and restores the average amniotic fluid volume to prevent complications from abnormal pressure.


Evidence of the normal flow of amniotic fluid is indicated by amniotic fluid volume. Contributions to the average amniotic fluid volume are mostly from fetal urine production, with some contributions from umbilical cord filtrate. Detraction from the amniotic fluid volume is mainly from fetal swallowing and fetal aspiration of the amniotic fluid into the lungs.


Oligohydramnios, a condition caused by reduced amniotic fluid volume from the reduced contribution of urine, creates well-known fetal anomalies called Potter’s sequence. This condition is described as including particular fetal facial characteristics, fetal limb abnormalities, and pulmonary hypoplasia. The limb abnormalities are from abnormal pressure.


Polyhydramnios may be from inadequate fetal swallowing of amniotic fluid, inadequate fetal aspiration of amniotic fluid, or fetal gastrointestinal obstruction that prevents amniotic fluid from progressing once swallowed.


The femur length is often considered to be the most reliable indicator of gestational age. Congenital abnormalities of the femur that make this statement not 100% true are rare and often apparent, as the femur abnormality coexists with other skeletal difficulties.


In first discussing the more common screening prenatal ultrasound exams, we have made mention of more targeted exams. Thoracic measurements, measurement of bones other than the femur, more targeted cardiac exams, more central nervous system ventricular evaluations, and fetal neck skin thickness measurements are made. For example, Figure 5-6 shows ultrasound images of a fetus’s face and arms during week 20.


More specific investigation of suspected abnormalities may indicate some conditions that can be corrected prenatally by thrilling advanced treatments such as umbilical cord blood transfusions, correction of amniotic fluid abnormalities, relief of posterior ureteral valve abnormality, or other intrauterine surgeries. As discussed earlier, almost all of these procedures are initiated by the targeted ultrasound.


In 2023, as in every other year in the history of humanity, it remains true that the results of the most sophisticated events in fetal development can be influenced by some of the simplest yet sometimes neglected measures: receiving good prenatal care, ceasing maternal smoking or other substance use, and taking prenatal vitamins. We believe that it is important for future clinicians reading this to never tire of reminding patients to optimize their developing infants’ likelihood of being healthy.


When using ultrasound, risks must be minimized to ensure patient safety. There are two basic rules of medical ethics:[1]


In that case, a procedure is deemed ethical only when it benefits the patient.


Ultrasound is generally considered safe if used properly. While there is no evidence it will physically affect the patient long-term, it should still be noted that it is a form of energy, and even at low levels, some studies suggest that overexposure to ultrasound can lead to potential undesirable effects such as


The damage type and extent mainly depend on the ultrasound wave characteristics such as frequency, intensity level, and exposure time, among other factors.


There are two possible biological effects of ultrasound exposure: (1) thermal (heating) effect and (2) mechanical (cavitation and streaming) effect. These effects can be quantified by reading the mechanical index (MI) and the thermal index (TI) on the ultrasound output display. The MI and TI are on-screen indicators of the potential bioeffects of ultrasound exposure. While imperfect, the TI and MI are considered good thermal and nonthermal risk assessments. These are discussed in detail in the sections below.


As the ultrasound traverses the tissue, it absorbs some of the energy, causing the tissue temperature to increase. The rate at which the energy is absorbed depends on


Higher thermal effects occur in tissues with higher absorption coefficients (such as bones), and lower thermal effects occur in tissues with lower absorption coefficients (such as amniotic fluids).[2] There is a concern that the embryo and fetus are particularly susceptible to heat energy.


The TI is a relative indicator of thermal risk for the likely temperature rise that might be produced after prolonged exposure. A more significant TI value represents a higher temperature and a higher risk. Three kinds of TI values can be displayed on an ultrasound machine depending on the type of application:[3]


The thermal index (TI) is calculated as the ratio of the acoustic power produced by the transducer (Wp) to the power required by the tissue to raise its temperature by 1 degree Celsius (WDeg). In mathematical form:


The index allows sonographers and clinicians to assess the relative potential heating effects associated with ultrasound imaging. A thermal index of 1 indicates the amount of acoustic power required to raise the tissue temperature by 1 degree Celsius. A higher TI value indicates a higher temperature and a higher risk.


In general, tissue heating by ultrasound is related directly to the intensity of ultrasound waves. The rate of increase in temperature is related to the ultrasound intensity and degree of absorption. It is inversely proportional to tissue density and specific heat. The rate at which the tissue absorbs the heat depends on the protein concentration. For example, fat heats much faster than dense tissue such as muscles.


Nevertheless, the tissue temperature rise is also limited by the cooling effects of the blood flow, which makes it more challenging to heat vascular organs (such as the liver and kidney) than bone.[4] Another concern is that the presence of bones increases the likelihood of a temperature rise due to absorption in the bone and the conduction of heat from bone to adjacent tissues. However, TI values of greater than can occur on Doppler ultrasound. Therefore, prolonged pulsed Doppler ultrasound is not recommended for sensitive tissues such as those of the embryo (less than eight weeks), eye, head, brain, and spine.[5]


Oscillations of gas bubbles (cavitation) occur inside tissue due to ultrasound pressure waves. The cavitation effect happens due to the excitation of a stable gas bubble by an acoustic field (noninertial cavitation—the formed bubble oscillates in the acoustic field), and streaming effects result from the movement of complex fluids due to radiation force pressures (inertial, or transient, cavitation—the formed bubble rapidly collapses and produces a shock wave that can be capable of causing biological damage).[6],[7] Bubbles are formed in a liquid when the local pressure falls (rarefaction part of the ultrasound wave) below the vapor pressure of the liquid. This cavitation effect is dependent on the fluid inertia, viscosity, and surface tension. Therefore, it is important to shorten the exposure time to minimize cavitation. Another critical point is that cavitation is likely to occur at lower transducer frequencies. However, cavitation-related bioeffects require the presence of cavitation nuclei (or bubbles) close to cells and physical or chemical interaction between bubbles and cells.


The use of the MI as an indicator is based on the assumption that sound induces oscillations of microbubbles, which can cause an increase in the internal temperature of a water gas bubble.


Nevertheless, tissue viscosity is 100 times greater than that of water such that bubble oscillations are greatly limited. A typical display of soft tissue TI and MI values for a carotid exam is shown in the top right corner of the Doppler image in Figure 4-1.


The risk of cavitation increases with increasing MI values. Other studies suggest that high MI values are associated with the induction of premature ventricular contractions in echocardiography.3 The potential for nonthermal biohazards is likely to increase if the equipment is not used correctly. Such biohazards have been observed in animal tissues with gas bubbles at MI values greater than .[8]3 The bioeffects associated with MI values of or less have been reported in skeletal muscle, fat, myocardia, kidneys, livers, and intestines.[9]


Consequently, unnecessary exposure to tissues such as the neonatal lungs should be avoided. Ultrasound operators should keep the MI values as low as possible when carrying out a diagnosis.


As discussed earlier, the other indicators of thermal effects include the TIS, TIB, and TIC values. The TIS is used when the ultrasound beam passes through soft tissue only, such as in the abdomen and fetal examination during the first trimester. If bones are present, the TIC is used (e.g., in head examinations). The TIB is used if the ultrasound encounters a bone (e.g., in the fetal examination in the second and third trimesters). In addition, the TIS is commonly used for fetal scanning during the first eight weeks of gestation, and the TIB is used after eight weeks. In adults, the TIS is commonly used for eye scanning. In pediatric and adult patients, the TIC is used when examining areas close to skull bone. The TIB is used for all other purposes.


Following the correct electrical safety procedures reduces the possibility of fire, muscle contracture, and tissue burns. Shocks can occur when a person touches electrical wires due to broken insulation in the circuit, which may contract muscles, alter brain function, or lead to ventricular fibrillation. Small currents can harm patients through saline catheters, which convert them to relatively large current densities. To reduce patient susceptibility to electrical hazards, equipment with any broken or uninsulated cables and damaged probes must not be used.


A major concern in the safety of ultrasound has been the exposure of the embryo and fetus during pregnancy examination. Based on current knowledge, there is insufficient information to link diagnostic ultrasound and recognized adverse effects in humans.


The use of diagnostic ultrasound equipment is limited to medical diagnosis only. It can only be used by personnel who are fully trained in the safe and proper operation of the equipment. Other expectations are that the operator should have a complete awareness of machine settings and understand the effect of those machine settings on thermal and mechanical bioeffects. The simple rule that must be followed is that the default power setting protocols should be set at “As Low As (is) Reasonably Achievable” (ALARA) to produce diagnostic quality images. In order to minimize the exposure time on a specific anatomical structure, it is recommended to move or lift the probe when stationary imaging is not necessary. When feasible, it is advisable to avoid imaging fields of view that contain sensitive tissues, including the eye, lungs, and intestines (gas-filled tissues) and fetal calcified structures, such as the skull and spine.


The AIUM, the U.S. Food and Drug Administration (U.S. FDA), and other organizations have issued some guidelines on the use of medical ultrasound in the United States. These guidelines are presented in the sections below.


The AIUM has issued minimum criteria for a complete medical examination of different parts of the body.[10] According to the AIUM guidelines, there are no independently confirmed significant biological effects in the low megahertz frequency range for ultrasound with intensities below 100 mW/cm2. In addition, for focused ultrasound, such effects have not been proven even at higher intensities for exposure times below 500 s. When adjusting controls that influence acoustic output, the AIUM stresses that it is essential to adhere to the ALARA principle and take into account both the duration of transducer dwell and the total scanning time. It is important to be knowledgeable about the MI upper limit, TI upper limit, and associated duration limits for the examination type being conducted. For example, the guidelines established by Harris et al.[11] and endorsed by the AIUM for the recommended maximum duration of ultrasound exposure at a given setting of the TI are presented in Tables 4-1 and 4-2.


Table 4-1: Recommended maximum exposure time and TI ranges for obstetric (including gynecologic when pregnancy is possible), neonatal transcranial, and neonatal spinal examinations.


Table 4-2: Recommended maximum exposure time and TI ranges for adult transcranial, general abdominal, peripheral vascular, neonatal (except head and spine), and other scanning examinations (except the eye).


Even if it is necessary to go beyond the recommended values, an undesirable thermal effect is unlikely to occur in most scanning environments due to attenuating factors such as sensor motion and tissue perfusion. However, it is important to adhere to the ALARA principle so that the duration of the examination is limited to the amount of time needed to obtain a useful diagnostic result.


U.S. Food and Drug Administration Guidelines


Because of the likelihood that ultrasound may have some potential heating and mechanical effects, the U.S. FDA states that the use of ultrasound is not entirely harmless. For this reason, it discourages the nonmedical use of ultrasound devices. The guideline established by the U.S. FDA uses the spatial peak pulse-average intensity (Isppa) and the spatial peak temporal-average intensity (Ispta) in addition to the MI as safety measures for diagnostic ultrasound.[12] Ispta indicates the highest intensity measured at any point in the ultrasound beam averaged over the temporal (time) duration of the pulse, and Isppa represents the highest intensity measured at any point in the ultrasound beam averaged over the pulse repetition period. Table 4-3 lists the highest limit values for these acoustic indicators for diagnostic ultrasound devices.


Table 4-3: U.S. FDA-issued acoustic output exposure level limits.


Other categories that could be included in Table 4-3 are abdominal, intraoperative, pediatric, and small organ (breast, thyroid, testes, etc.). The U.S. FDA also mandates the display of the likelihood of ultrasound-induced bioeffects, known as the Standard for Real-Time Display of Thermal and Mechanical Acoustic Output Indices, on diagnostic ultrasound equipment capable of producing higher thermal or mechanical effects. The U.S. FDA discourages any unapproved use of medical devices without a physician’s order. Such practices may be in violation of state laws or regulations. The operator has the ultimate responsibility for the safe use of ultrasound equipment.


The National Collaborating Centre for Women’s and Children’s Health recommends fetal ultrasound screening between 18 and 20 weeks gestation.[13] The guideline was issued on the basis that there is no evidence to support the need for routine use of ultrasound screening after 24 weeks gestation. The Society of Maternal and Fetal Medicine[14] recommended only one medically indicated ultrasound per pregnancy.


Medical equipment, including ultrasound machines and transducers, may act as both sources and vectors of microbial transmission during examination. Globally, medical equipment–acquired infections are on the increase. Several studies have confirmed the transmission of bacteria and viruses through improper hygienic use of medical equipment. Common transmittable bacteria and viruses that have been identified include Staphylococcus aureus, Pseudomonas, Acinetobacter species, Candida albicans, hepatitis B, hepatitis C, human immunodeficiency virus, and herpes.[15]


Just as with any medical procedure, there is a potential risk for cross infection (patient-to-patient, patient-to-operator, or operator-to-patient) if proper procedures are not followed. The risk of infection is highest in procedures that utilize transducers in intracavities or where body fluids are encountered. These risks are classified into three categories:


The cleaning, disinfecting, and sterilizing of reusable medical and surgical equipment or devices must comply with the manufacturer’s requirements and safety protocols. Routine cleaning must include removing the coupling gel and any visible residue from the probe using the recommended detergent. Disposable gloves must be worn during the cleaning process. Areas that require extensive cleaning or disinfection are the transducer probes and ultrasound machine screens. The keyboard is another critical area that can be easily forgotten during cleaning or disinfection. The choice of the keyboard matters—keyboards similar to those used for computers are not ideal for medical purposes, as it is impossible to clean in between the keys after every medical examination. Most modern ultrasound keyboards now come with disinfectable polyurethane covers, which make them easier to clean.


A simple rule is to regard every patient as a potential source of infection. To prevent the risk of cross infection, the following minimum precautions are recommended in every examination:


While the use of ultrasound in medicine has gained traction over the past two decades, it still faces significant hurdles in some parts of the globe. This is partly due to differences in culture. For example, in some countries, ultrasound is now used for sex-selective abortion.[16] The purpose of this book is not to debate these ethical issues but to bring an awareness of how different societies view the use of ultrasound in medicine.


Clinicians often find themselves in difficult situations, especially when diagnosed anomalies require critical procedures. For example, some fetal abnormalities present ethical dilemmas concerning patient counseling, and abortion issues present challenges in gynecology and obstetrics.


That means clinicians have to play a pivotal role in educating patients about the need to perform these procedures and their benefits to allay the emotional nature of the ultrasound diagnosis or obstetric scanning and the associated implications. In addition, clinicians performing the screening may face dilemmas when diagnosing life-threatening problems with no corrective solutions. In some sections of society, revealing the life span of a patient may not be well received or accepted. That leaves the burden of counseling to the clinicians.


Two-dimensional ultrasound is considered a standard or conventional imaging technique. In 2D scanning, a series of thin slices make up an image, and only one slice can be seen at a time.


Three- and four-dimensional clinical ultrasounds have been around for nearly 25 years. However, their use has lagged behind that of computerized tomography (CT) and magnetic resonance imaging (MRI) due to the difficulty in rendering the data in 3D.[1] However, ultrasound equipment’s increasing computing power has helped resolve complex signal processing tasks needed to render 3D ultrasound data.


Three-dimensional ultrasound is based on the same principles of operation as 2D ultrasound but has an added position-sensing component to produce the effect of a 3D image, as illustrated in Figure 3-1. In 3D ultrasound imaging, echoes are used to form real-like realistic volume images.


A 4D ultrasound shows 3D ultrasound images in motion. Two-dimensional ultrasound images are commonly used because they are less expensive than 3D or 4D. However, many centers now use 3D/4D ultrasound. The most common area of use has been fetal cardiovascular scanning. The 3D/4D technology offers real-time motion-gated cardiac scanning.


A 3D/4D ultrasound offers expecting parents a memorable lifetime opportunity to see the features of their unborn babies. Figure 3-2 shows 2D grayscale and 3D colored images.


Acquiring qualitative and quantitative sonographic volume data such as multiplanar imaging, surface and volume rendering, and semiautomated volume calculation gives 3D/4D an added advantage over 2D imaging. Virtual planes provide extra information that cannot be viewed with a standard 2D technique.[2] The American Institute of Ultrasound in Medicine (AIUM) notes that the ability to take images in any plane in real time has enormous potential use in medical diagnosis.[3] Another advantage is that 3D ultrasound can provide measurements in three planes with acceptable reliability.


A 3D ultrasound uses a series of 2D images covering a volume of a particular area. This allows the images to be rotated and displayed in different orientations. When displayed in real time, or live, they form a 4D ultrasound. Volume acquisition is achieved by using an array of transducers consisting of many 2D frames, one behind the other. Automated mathematical algorithms are then used to process the volume data to produce the desired image, as illustrated in Figure 3-3.


The reconstruction in Figure 3-3 occurs in a matter of seconds such that the spatio-temporal imaging correlation (STIC) acquisition is completed in the presence of the patient. The STIC acquisition mode can be combined with B-mode, color, and power Doppler. From a good STIC acquisition, a sequential plane may be viewed in corresponding transverse and longitudinal planes at any time point, simultaneously.


The B-flow image is a live grayscale depiction of blood flow and cardiac chambers. When applied to 3D fetal echocardiography, the B-flow image shows blood flow in the heart and great vessels in real time.[4]


Four-dimensional imaging involves a 3D image moving in real time, created from a volume of data that allows the live reconstruction of images in different planes and renderings. Rendering is taking voxel-based data and converting it into a viewable image with added depth. Three- and four-dimensional imaging function by reconstructing an image from multiple 2D planes.


The 3D color and power Doppler ultrasound technology can be used in vascular abnormality assessments such as the fetal placental cord and pulmonary vessels. Three-dimensional ultrasound is not yet widely used in many routine medical procedures but has been widely used in gynecology, obstetrics, and biopsy.


The application of 3D/4D ultrasound in biopsy allows for needle tracking in multiple planes simultaneously and imaging of the morphology and proximity of local anesthetic spread around the target nerves.[6] Other specialties in which 3D/4D ultrasound can be applied include dermatology and ophthalmology.


In 2D ultrasound imaging, a series of noncontinuous and presumably representative sections of the imaged organ is used to visualize the anatomy of the organ. Repeated examination is required in order to reconstruct cross sections visually. The absence of quantitative spatial documentation means clinicians must rely on image labels and trust the acquisition technique. Repeated examinations may not produce exact image planes, making comparing serial exams difficult.[7] In addition, every time an organ is examined, it’s likely to give rise to varying measurements of a specific organ or structure, as the imaging process is highly operator-dependent. Volumetric (3D) ultrasound allows volumetric acquisition of anatomic data, which may be needed to examine internal organs such as the liver, gallbladder, gallstones, or kidneys.


In 3D/4D, volume data are obtained in a single image, allowing the operator to view any plane in the volume. The multiplanar rendering mode options also allow for viewing images in real-time motion. Three-dimensional imaging is helpful in examining contours such as those in the facial area, the heart chambers, and the valves. The 4D ultrasound provides a motion video of the 3D structure in real time. Together, 3D and 4D ultrasound have been quite successful in examining the inside or outside of organs, nodules, cysts, or tumors. The 3D ultrasound also offers a more comprehensive image of anatomical structures and pathological conditions. A 3D echocardiography can provide estimates of ventricular volume and function. Comparing 2D and 4D, qualitative 4D ultrasound is considered superior to 2D in real time. However, 4D is inferior to 2D ultrasound for quantitative analysis of movements. For example, 4D evaluation of complex fetal facial activity and expression is better than that of 2D.[8]


Hence 3D and 4D ultrasound imaging allow more accessible and more rapid screening than 2D ultrasound imaging. Irregularly shaped organ volumes can be more accurately visualized using 3D than 2D imaging ultrasound. In addition, 3D measurements are more reproducible than 2D ultrasound and provide the option to rotate the volume, which is often necessary to allow optimal visualization of the geometric structure of the organ under examination and determine the position of the structure in the volume.[9]


The market for small, portable ultrasound machines has flourished over the past decade. They have gained popularity and significant usefulness in the medical sector, especially in the emergency medicine department. There are two specific reasons for this popularity: (1) they are smaller/lighter and portable, which makes the whole process of scanning the patients quicker, more accessible, and safer at the same time, and (2) their portability, ease of use, connectivity, and cleanability make them ideal tools for diverse care settings. Conventional large-sized ultrasound machines are demanding and come with certain limits. For instance, these larger machines are laborious and challenging to sterilize thoroughly in comparison to small handheld machines. Also, a physician performing any intervention with this machine usually requires an extra pair of hands to help set it up and obtain clinical images.


Both laptop and handheld models of portable ultrasound systems are available. There are also a few models that are intermediate between these two. Therefore, portable ultrasound machines can be broadly divided into three categories. The first category is the large, laptop-sized device weighing 12 to 15 pounds. An example of such a device is GE HealthCare’s LOGIQTM e portable ultrasound. The second category involves a smaller device, almost the size of a smaller laptop and weighing about 6 to 10 pounds. An example of such a device is the Sonosite Edge machine.


With technological innovations, even smaller and lighter ultrasound devices with better image quality are now available (such as those manufactured by GE HealthCare, Siemens, and Philips). The third category is the handheld ultrasound device that weighs under a pound. Philips’s Lumify is an example of one such device; it costs around $6,000 to buy or $2,300 per year to lease. This device operates through a simple USB connection of the transducer to a compatible device such as a smartphone. GE HealthCare’s Vscan is a pocket-size ultrasound device that provides real-time gray anatomic and color flow images. It is optimized for physicians to quickly inspect the heart, abdominal organs, and urinary bladder. It can provide insights into areas of obstetrics and gynecology, pleural fluid and motion detection, and pediatrics. A recently extended version of the Vscan handheld ultrasound device can be used to help confirm and monitor the progression of acute respiratory diseases like COVID-19.


While 3D/4D ultrasounds show success in some cases, they have some limitations in their clinical applications. Three-dimensional renderings have demonstrated impressive results in some areas; the interfaces are complex and difficult to interpret. Other significant issues raised by the AIUM[10] are that the protocols and manipulation techniques are not standardized across manufacturers with respect to the terminology of functions and the display, therefore requiring time and effort to perfect operator skill and accuracy. Standardization is also needed in image orientation. Another challenge is that 3D/4D does not solve poor 2D image problems for several reasons: (1) artifacts and orientation can be confusing, and (2) resolution decreases in reconstructed images such that in some cases, 3D/4D images may be inferior to 2D images. Currently, 2D fetal echocardiography with color Doppler has a success rate of up to 92% in diagnosing congenital heart diseases.[11] Research findings have shown that there are limitations to adequate visualization of fetal anatomy with 3D/4D ultrasound if there is inadequate amniotic fluid surrounding the fetus or if the fetus has its face in the posterior position. Another reported limitation with current 3D/4D Doppler ultrasound technology is that endometrial and subendometrial blood flows measured at one time point during IVF treatment were not good predictors of pregnancy.[12]


The AIUM organized a meeting of physicians and scientists to discuss the diagnostic benefits and technical limitations of 3D ultrasound in obstetrics and gynecology and its potential use in various clinical practices now and in the future. Their recommendations, together with the equipment manufacturers and other safety regulations, will be reviewed in the next section.


As shown in Figure 2-1, an ultrasound machine includes the following major components:


Figure 2-2 shows a generalized schematic of ultrasound machines’ mode of operation.


More details about the operations of the components of the ultrasound machine are discussed in the sections below.


In the 19th century, Pierre and Jacques Curie discovered that some materials generate electric potentials in response to mechanical deformation (material shrinks or expands) or stress (the substance is squeezed or stretched)—a phenomenon called the piezoelectric effect, which is illustrated in Figure 2-3. Conversely, the same materials change their shapes when an electric field is applied.


Examples of such materials include silicon oxide, potassium sodium tartrate, barium titanate, and lithium niobate. Bones, tendons, skin, and some man-made polymeric materials can also exhibit the piezoelectric effect. These materials bend in different ways depending on the frequency and their shape, which can result in different vibration modes. The modes are the basis for developing transducers that operate at different frequencies.


A typical ultrasound probe with its components is shown in Figure 2-4. The vibration of crystals in an ultrasound machine’s transducer generates ultrasound, and the transducer can detect the echoes and convert them to electrical signals. A transducer is composed of piezoelectric crystals, which respond to pressure to generate an electric current. The alternating current causes the piezoelectric crystals to vibrate at a desired frequency corresponding to ultrasound waves. The produced ultrasound beam is directed into the tissues by moving the transducer and changing the angle of incidence of the ultrasonic beam. Conversely, when an electric current is applied to the crystals, its shape changes with polarity, producing electrical signals from echoes that are processed to generate a display. Hence the crystals act as transmitters (for a short time) and receivers (most of the time).


Since the air between the tissue and the transducer inhibits the propagation of the ultrasound beam, a conducting gel is usually applied between them.


Figure 2-5 shows a block diagram of an ultrasound imaging system. Two modes are essential in the formation of an ultrasound image. These are the transmission modes that convert an alternating current into mechanical pressure waves. The backscattered pressure waves are picked up by the receiving mode, which converts them into electrical signals. The ultrasound waves that get fully transmitted through any tissues or structures do not produce echoes and appear dark. For example, all fluids appear echo-free and black on the ultrasound image.


The transducer generates pulses and detects backscattered energy from the tissue boundaries, as shown in Figure 2-6. The length of delay between the transmitted and received pulses is used to determine the depth of the tissue boundary or organ under examination.


These piezoelectric signals from the crystals are amplified and converted into a gray or white color on the ultrasound image via a computer program. The difference in tissue reflectivity allows us to see individual structures. When ultrasound hits a dense object, it is wholly reflected, forming a posterior acoustic shadow (a bright and echogenic image). This is because no ultrasound is transmitted, creating an echo void. The computer can calculate the tissue’s depth by measuring the time between when the wave was sent and when an echo was detected.


There are several assumptions about sound waves in ultrasound system operation. These assumptions, when violated, result in the formation of image artifacts, which often make it difficult to distinguish between real and fictitious features in an image. These assumptions are


Artifacts are fictitious portions of images (distortions of the actual anatomy of the tissue). Improper scanning techniques may cause some artifacts, while others result from the physical limitations of the instrument. Such artifacts can be explained using the properties of the ultrasound waves, their propagation through tissue, and the assumptions used in image processing. Typical artifacts include shadowing, beam width, side lobe, reverberation, comet tail, ring down, mirror image, and refraction. They are formed primarily due to multiple echo paths or velocity errors and attenuation errors.


Highly reflective or attenuating tissues reduce the ultrasound beam intensity inside the tissues, leading to obscured images close to or behind them. This shadowing artifact results from refraction that causes echoes to appear darker, like a shadow, due to the ultrasound beam’s decreased amplitude, intensity, and power.