---
license: cc-by-4.0
tags:
  - mri
  - qsm
  - quantitative-susceptibility-mapping
  - neuroimaging
pretty_name: QSMbly example data
---

# QSMbly example data

One in-vivo subject, used as the "Load example data" dataset in
[QSMbly](https://qsmbly.neurodesk.org/) and fetched by the browser at runtime.

A single 5-echo 3D gradient-echo acquisition at 1 mm isotropic, acquired on a Siemens
MAGNETOM Prisma Fit. Magnitude and phase are split one file per echo, since QSMbly's
loader reads 3D volumes and derives the echo count from the file list.

| | |
| --- | --- |
| Matrix | 184 × 256 × 128, 1 mm isotropic |
| Echoes | 5 — TE 5 / 11 / 17 / 23 / 29 ms |
| TR / flip | 35 ms / 15° |
| Sequence | `gre_bridge_1mm_psn_adapt` (product GRE, GRAPPA R=2) |
| Scanner | MAGNETOM Prisma Fit (XR VA30A) |
| Phase | radians, wrapped |

## Field strength

`MagneticFieldStrength` is **2.8946 T**, the accurate field derived from the scanner's
carrier frequency (`ImagingFrequency` 123.243444 MHz ÷ 42.576384 MHz/T), not the nominal
3.0 T printed on the magnet. QSM scales ppm by this value, so the accurate one is the
correct one to use.

## Echo times

Recovered from the exam-card PDFs shipped with the acquisition and, for the Pulseq
consensus sequence in the wider study, from
[HarmonizedMRI/megre_label](https://github.com/HarmonizedMRI/megre_label). They are not
the DICOM sidecar values, which carry placeholder timings for some protocols.

## Provenance

Packed from the 2026-08-20 QSM harmonization acquisition (MGH bays 4/5) — one subject
scanned on two Siemens 3T scanners under four protocols × 3 runs. The full study is on
OSF at [osf.io/gkemr](https://osf.io/gkemr/); this repo holds the `prisma-bridge-run1`
acquisition only, re-split into per-echo files.

The same acquisition is available to QSMxT users via `qsmxt example`.