# Ultra-low-field brain MRI: test-retest reliability and correspondence to high-field MRI

Contact: [[email protected]](mailto:[email protected])

## Overview

These data were collected as part of a study to assess the test-retest reliability of 64 mT ultra-low-field MRI morphometry, and correspondence to 3T high-field MRI (https://direct.mit.edu/imag/article/doi/10.1162/IMAG.a.930).

Data types included are defaced T<sub>1</sub>-weighted and T<sub>2</sub>-weighted structural MRI images. At 64 mT, images were acquired in multiple orientations and voxel resolutions.

## Methods

### Subjects

23 healthy adults (11 females, 12 males, age = 20 to 69 years). To obtain a sample balanced for age and sex, a minimum of 2 male and 2 female participants were recruited from each of the following 5 age-strata: 20-29 years, 30-39 years, 40-49 years, 50-59 years and 60-69 years.

### MR protocol

MRI data for each participant were acquired during two scanning sessions, held no more than 36 days apart. During the first session, at the Centre for Neuroimaging Sciences (CNS; Institute of Psychiatry, Psychology and Neuroscience, King’s College London), participants were scanned for 45 minutes on a GE SIGNA Premier 3 T high-field scanner with a 48-channel head coil (GE Healthcare, Waukesha, WI), followed immediately by a 1-hour protocol on a Hyperfine Swoop 64 mT ultra-low-field scanner (Hyperfine Inc., Guildford, CT). During the second session, at the Evelina Newborn Imaging Centre (ENIC; St. Thomas’s Hospital, Guys and St. Thomas’s NHS Foundation Trust), participants were scanned for 1 hour on a second Hyperfine Swoop system, identical to the first, and running the same software version (rc8.6.0).

#### 3 T MRI

The 3 T GE Premier high-field protocol is denoted ses-GE. This included T<sub>1</sub>-weighted and T<sub>2</sub>-weighted scans, acquired at 1×1×1 mm<sup>3</sup> resolution.

#### 64 mT MRI

The 64 mT protocols are denoted ses-HFC (Centre for Neuroimaging Sciences, acquired on the same day as ses-GE) and ses-HFE (Evelina Newborn Imaging Centre, acquired during a second session, no more than 36 days later). Both sessions included T<sub>1</sub>w and T<sub>2</sub>w scans, acquired using non-isotropic product sequences (T<sub>1</sub>w: 1.6×1.6×5 mm<sup>3</sup>; T<sub>2</sub>w: 1.5×1.5×5 mm<sup>3</sup>) with high resolution in the axial, sagittal or coronal plane, respectively referred to as AXI, SAG, and COR. Additionally, a research agreement with Hyperfine Inc. enabled acquisition of a custom isotropic sequence (T<sub>1</sub>w: 2.3×2.3×2.3 mm<sup>3</sup>, T<sub>2</sub>w: 2.2×2.2×2.2 mm<sup>3</sup>), referred to as ISO. All scans were acquired on both scanners, except T<sub>1</sub>w ISO scans, which were only acquired during the first scanning session (HFC).