Restriction Spectrum Imaging: An evolving imaging biomarker in prostate magnetic resonance imaging

Restriction spectrum imaging (RSI) is a novel diffusion-weighted magnetic resonance imaging technique that utilizes the mathematically distinct behavior of water diffusion in separable microscopic tissue compartments to highlight key aspects of the tissue microarchitecture with high conspicuity. RSI can be acquired in less than 5 minutes on modern scanners utilizing a surface coil. Multiple field gradients and high b-values in combination with post-processing techniques allow the simultaneous resolution of length-scale and geometric information, as well as compartmental and nuclear volume fraction filtering. RSI also employs a distortion correction technique and can thus be fused to high resolution T2 weighted images for detailed localization, which improves delineation of disease extension into critical anatomic structures. In this review we discuss the acquisition, post-processing, and interpretation of RSI for prostate MRI. We also summarize existing data demonstrating the applicability of RSI for prostate cancer detection, in vivo characterization, localization, and targeting.