Image formation in diffusion MRI: A review of recent technical developments

Abstract

Diffusion magnetic resonance imaging (MRI) is a standard imaging tool in clinical neurology, and is becoming increasingly important for neuroscience studies due to its ability to depict complex neuroanatomy (eg, white matter connectivity). Single‐shot echo‐planar imaging is currently the predominant formation method for diffusion MRI, but suffers from blurring, distortion, and low spatial resolution. A number of methods have been proposed to address these limitations and improve diffusion MRI acquisition. Here, the recent technical developments for image formation in diffusion MRI are reviewed. We discuss three areas of advance in diffusion MRI: improving image fidelity, accelerating acquisition, and increasing the signal‐to‐noise ratio. Level of Evidence: 5 Technical Efficacy: Stage 1J. MAGN. RESON. IMAGING 2017;46:646–662

Renal Functional MRI and Its Application

“…This geometry allows the application of DWI and diffusion tensor imaging (DTI). Numerous studies have validated the value of fMRI in kidney imaging in the context of various disease models . The aim of this review is to summarize the progressions and challenges of renal fMRI, with regard to dynamic contrast‐enhanced MRI (DCE‐MRI), BOLD MRI, DWI, DTI, ASL, and other techniques.…”

“…SSH‐EPI also yields limited acquired slices. Applying parallel imaging in this sequences still fails to resolve its deficiency . In the clinic, the absence of a standard protocol for DWI MRI and the dependency on b values remain obstacles to its clinical application.…”

SMS MUSSELS: A navigator‐free reconstruction for simultaneous multi‐slice‐accelerated multi‐shot diffusion weighted imaging

“…However, for high spatial resolution applications, this calls for high acceleration factors that results in significant signal‐to‐ratio (SNR) loss. Furthermore, the SNR benefits of the ultra‐high field scanners also cannot be fully harnessed to achieve spatial resolution using ss‐EPI techniques; the amplified decay induced blurring and induced geometric distortion significantly degrade the image quality at low acceleration factors . These factors have constrained the imaging resolution of DWIs to approximately 2 mm isotropic, which impose significant limitations on diffusion‐based microstructure studies where partial volume effects obscure the characterization of tissue microstructure in the brain.…”

“…Phase calibration using navigator‐based approaches require additional data acquisition to capture the shot‐to‐shot phase variations. While these methods can support high acceleration factors, navigators increases the effective TR, increase the specific absorption rate (SAR) and may not accurately capture phase variations in the presence of bulk motion . Navigator‐free phase calibration using parallel imaging is time efficient.…”

Improved MUSSELS reconstruction for high‐resolution multi‐shot diffusion weighted imaging

“…On standard clinical gradients (33 mT/m gradient strength, 120 T/m/s slew rate), ssEPI readouts contribute to a minimum TE of approximately 75‐120 ms for a 128 × 128 imaging matrix for typical b‐values of 1000‐3000 . Pushing the spatial resolution of DWIs beyond the 128 × 128 matrix size results in (a) increased geometric distortions along the phase‐encoding direction, (b) reduced signal‐to‐noise ratio (SNR) due to the long read out time involved in sampling the center‐of‐k‐space, and (c) increased blurring in the images due to the signal decay that accompanies the long readout duration . Thus, despite not being the ideal resolution to study the micro‐level tissue structural properties, the characteristic resolution of standard DWI studies has largely remained at approximately 2 mm isotropic.…”