Evaluating the image quality and brain microstructural exploration of mean apparent propagator-MRI–a pilot study

BACKGROUND: To investigate the impact of positivity constraints and Laplacian regularization on Mean Apparent Propagator (MAP)-MRI image quality and effectiveness in analyzing brain microstructural changes, validated using an Intermittent Exotropia (IXT) cohort. METHODS: A total of 31 patients with IXT (16 males, 15 females; mean age 10.94 ± 1.69 years) and 37 age- and sex-matched healthy controls (23 males, 14 females; mean age 11.14 ± 2.06 years) underwent MRI scans. Imaging protocols included simultaneous multi-slice echo planar imaging (SMS-EPI) for q-space sampling and 3D magnetization-prepared rapid acquisition gradient echo (MP-RAGE) sequences. Three MAP-MRI-based reconstruction algorithms were evaluated: MAPL (with Laplacian regularization), CMAP (positivity-constrained), and CMAPL (combining both constraints). Image quality was assessed objectively using wavelet-based signal-to-noise ratio (WSNR), and subjectively by two radiologists using a 5-point scale rating signal uniformity, contrast, noise level, and anatomical completeness. Statistical analyses included one-way ANOVA, Kruskal-Wallis tests, and Cohen's κ for inter-rater agreement. Diagnostic performance was evaluated using voxel-wise t-tests with Gaussian Random Field (GRF) correction at P = 0.01. RESULTS: MAPL outperformed CMAP and CMAPL in both objective and subjective image quality, particularly in RTOP, RTAP, MSD, and QIV maps (all P < 0.05). It also provided a more comprehensive visualization of changes in the bilateral dorsal visual pathways, including BA17, BA18, BA19, BA39, BA40, BA8, BA6, and the supplementary motor area (SMA). Moreover, MAPL demonstrated superior sensitivity in detecting alterations in brain regions associated with language, emotion, and decision-making (BA10, BA11, BA22, BA37, and BA47), which may reflect secondary changes induced by visual impairment. CONCLUSIONS: MAPL surpasses CMAP and CMAPL in both image quality and the ability to display brain microstructural changes, establishing it as the superior method for exploring brain structural alterations. CLINICAL TRIAL INFORMATION: It was registered on July 18, 2021 (ChiCTR2100048852) at www.chictr.org.cn and commenced on September 1, 2021.