Inversion-Recovery-Prepared Oscillating Gradient Sequence Improves Diffusion-Time Dependency Measurements in the Human Brain

Abstract

Background: Oscillating gradient diffusion MRI (dMRI) enables measurements at a short diffusion-time (t_d ), but it is challenging for clinical systems. Particularly, the low b-value and low resolution may give rise to cerebrospinal fluid (CSF) contamination.

Purpose: To assess the effect of CSF partial volume on t_d -dMRI measurements and efficacy of inversion-recovery (IR) prepared oscillating and pulsed gradient dMRI sequence to improve t_d -dMRI measurements in the human brain.

Study type: Prospective.

Subjects: Ten normal volunteers and six glioma patients.

Field strength/sequence: A 3 T; three-dimensional (3D) IR-prepared oscillating gradient-prepared gradient spin-echo (GRASE) and two-dimensional (2D) IR-prepared oscillating gradient echo-planar imaging (EPI) sequences.

Assessment: We assessed the t_d -dependent patterns of apparent diffusion coefficient (ADC) in several gray and white matter structures, including the hippocampal subfields (head, body, and tail), cortical gray matter, thalamus, and posterior white matter in normal volunteers. Pulsed gradient (0 Hz) and oscillating gradients at frequencies of 20 Hz, 40 Hz, and 60 Hz dMRI were acquired with GRASE and EPI sequences with or without the IR module. We also tested the t_d -dependency patterns in glioma patients using the EPI sequence with or without the IR module.

Statistical tests: The differences in ADC across the different t_d s were compared by one-way ANOVA followed by post hoc pairwise t-tests with Bonferroni correction.

Results: In the healthy subjects, brain regions that were possibly contaminated by CSF signals, such as the hippocampus (head, body, and tail) and cortical gray matter, t_d -dependent ADC changes were only significant with the IR-prepared 2D and 3D sequences but not with the non-IR sequences. In brain glioblastomas patients, significantly higher t_d -dependence was observed in the tumor region with the IR module than that without IR (slope = 0.0196 μm² /msec² vs. 0.0034 μm² /msec² ).

Conclusion: The IR-prepared sequence effectively suppressed the CSF partial volume effect and significantly improved the t_d -dependent measurements in the human brain.

Evidence level: 1 TECHNICAL EFFICACY: Stage 1.

Keywords: 3D GRASE; CSF contamination; diffusion-time dependency; inversion-recovery; oscillating gradient diffusion MRI.