Tissue volume estimation and age prediction using rapid structural brain scans

Abstract

The multicontrast EPImix sequence generates six contrasts, including a T₁-weighted scan, in ~1 min. EPImix shows comparable diagnostic performance to conventional scans under qualitative clinical evaluation, and similarities in simple quantitative measures including contrast intensity. However, EPImix scans have not yet been compared to standard MRI scans using established quantitative measures. In this study, we compared conventional and EPImix-derived T₁-weighted scans of 64 healthy participants using tissue volume estimates and predicted brain-age. All scans were pre-processed using the SPM12 DARTEL pipeline, generating measures of grey matter, white matter and cerebrospinal fluid volume. Brain-age was predicted using brainageR, a Gaussian Processes Regression model previously trained on a large sample of standard T₁-weighted scans. Estimates of both global and voxel-wise tissue volume showed significantly similar results between standard and EPImix-derived T₁-weighted scans. Brain-age estimates from both sequences were significantly correlated, although EPImix T₁-weighted scans showed a systematic offset in predictions of chronological age. Supplementary analyses suggest that this is likely caused by the reduced field of view of EPImix scans, and the use of a brain-age model trained using conventional T₁-weighted scans. However, this systematic error can be corrected using additional regression of T₁-predicted brain-age onto EPImix-predicted brain-age. Finally, retest EPImix scans acquired for 10 participants demonstrated high test-retest reliability in all evaluated quantitative measurements. Quantitative analysis of EPImix scans has potential to reduce scanning time, increasing participant comfort and reducing cost, as well as to support automation of scanning, utilising active learning for faster and individually-tailored (neuro)imaging.

Figure 1

Global tissue volume estimation across contrasts. Comparison of tissue volumes (grey matter, white matter and cerebrospinal fluid) between T₁-w and EPImix (T₁-w) scans with full field of view (A–C) and between EPImix (T₁-w) scans and T₁-w scans with reduced field of view (D–F). (Spearman’s correlation coefficient r_s, p-value, r² derived from Pearson’s correlation).

Figure 2

Voxel-wise tissue volume estimation across contrasts. Correlation between voxel-wise tissue volume estimates from T₁-w and EPImix (T₁-w) scans, and corresponding probability density plots, for grey matter (A, B), white matter (C, D) and CSF (E, F). Only voxels with at least 0.001 mm³ tissue volume in at least 95% of participants are shown.

Figure 3

Grey matter volume as a function of chronological age, using volume estimates derived from (A) T₁-w scans, (B) EPImix T₁-w scans and (C) T₁-w scans with reduced field of view.

Figure 4

Age prediction across contrasts. Predicted age as a function of chronological age for (A) T₁-w scans, (B) EPImix T₁-w scans and (C) T₁-w scans with reduced FoV. (D) Predicted age of EPImix T₁-w scans compared to standard T₁-w scans, and E) EPImix T₁-w scans compared to T₁-w scans with reduced FoV. (Spearman’s correlation coefficient r_s, p-value, r² derived from Pearson’s correlation).

Figure 5

Test-retest reliability of EPImix (T₁-w) tissue volume estimates. Reliability of voxel-wise volume estimates, and corresponding probability density plots, in grey matter (A, B), white matter (C, D) and CSF (E, F). Test-retest reliability was evaluated using the one-way random effects model for the consistency of single measurements (ICC(3,1)). Only voxels with at least 0.001 mm³ tissue volume in at least 95% of participants are shown.