Repeatability of Brain Volume Measurements Made with the Atlas-based Method from T1-weighted Images Acquired Using a 0.4 Tesla Low Field MR Scanner

Abstract

Purpose: An understanding of the repeatability of measured results is important for both the atlas-based and voxel-based morphometry (VBM) methods of magnetic resonance (MR) brain volumetry. However, many recent studies that have investigated the repeatability of brain volume measurements have been performed using static magnetic fields of 1-4 tesla, and no study has used a low-strength static magnetic field. The aim of this study was to investigate the repeatability of measured volumes using the atlas-based method and a low-strength static magnetic field (0.4 tesla).

Materials and methods: Ten healthy volunteers participated in this study. Using a 0.4 tesla magnetic resonance imaging (MRI) scanner and a quadrature head coil, three-dimensional T₁-weighted images (3D-T₁WIs) were obtained from each subject, twice on the same day. VBM8 software was used to construct segmented normalized images [gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) images]. The regions-of-interest (ROIs) of GM, WM, CSF, hippocampus (HC), orbital gyrus (OG), and cerebellum posterior lobe (CPL) were generated using WFU PickAtlas. The percentage change was defined as[100 × (measured volume with first segmented image - mean volume in each subject)/(mean volume in each subject)]The average percentage change was calculated as the percentage change in the 6 ROIs of the 10 subjects.

Results: The mean of the average percentage changes for each ROI was as follows: GM, 0.556%; WM, 0.324%; CSF, 0.573%; HC, 0.645%; OG, 1.74%; and CPL, 0.471%. The average percentage change was higher for the orbital gyrus than for the other ROIs.

Conclusion: We consider that repeatability of the atlas-based method is similar between 0.4 and 1.5 tesla MR scanners. To our knowledge, this is the first report to show that the level of repeatability with a 0.4 tesla MR scanner is adequate for the estimation of brain volume change by the atlas-based method.

Fig. 1.

Repeatability with the atlas-based method. The percentage changes in each ROI are shown with the box plot. The box plot shows median, maximum, and minimum value below inner fence, first and third quartile, and outliers. Analysis of variance revealed a significant difference in average percentage change for all six regions (P < 0.05). In addition, the Tukey–Kramer method revealed significant difference (P < 0.05) for OG vs. GM, vs. WM, vs. CSF, vs. HC, and vs. CPL. The percentage change value was larger for OG than for all the other ROIs. CPL, cerebellum posterior lobe; CSF, cerebrospinal fluid; GM, gray matter; HC, hippocampus; OG, orbital gyrus; ROI, region-of-interest; WM, white matter.

Fig. 2.

The repeatability map for the voxel-based morphometry method. The repeatability maps are superimposed on the template image for each tissue (gray matter, white matter, and cerebrospinal fluid) processed with SPM8. The color bar (top left) indicates the percentage change. R and L are the right and left sides of the subjects, respectively. High-value areas (maximum values) were found near the skull base in the gray matter (3.50%), white matter (3.16%), and cerebrospinal fluid (3.02%) images.