Diffusion-weighted Renal MRI at 9.4 Tesla Using RARE to Improve Anatomical Integrity

Abstract

Diffusion-weighted magnetic resonance imaging (DWI) is a non-invasive imaging technique sensitive to tissue water movement. By enabling a discrimination between tissue properties without the need of contrast agent administration, DWI is invaluable for probing tissue microstructure in kidney diseases. DWI studies commonly make use of single-shot Echo-Planar Imaging (ss-EPI) techniques that are prone to suffering from geometric distortion. The goal of the present study was to develop a robust DWI technique tailored for preclinical magnetic resonance imaging (MRI) studies that is free of distortion and sensitive to detect microstructural changes. Since fast spin-echo imaging techniques are less susceptible to B0 inhomogeneity related image distortions, we introduced a diffusion sensitization to a split-echo Rapid Acquisition with Relaxation Enhancement (RARE) technique for high field preclinical DWI at 9.4 T. Validation studies in standard liquids provided diffusion coefficients consistent with reported values from the literature. Split-echo RARE outperformed conventional ss-EPI, with ss-EPI showing a 3.5-times larger border displacement (2.60 vs. 0.75) and a 60% higher intra-subject variability (cortex = 74%, outer medulla = 62% and inner medulla = 44%). The anatomical integrity provided by the split-echo RARE DWI technique is an essential component of parametric imaging on the way towards robust renal tissue characterization, especially during kidney disease.

Diffusion‐weighted magnetic resonance imaging in rat kidney using two‐dimensional navigated, interleaved echo‐planar imaging at 7.0 T

“…Application of diffusion‐sensitizing gradients to RARE may face the issue that motion during the Stejskal–Tanner preparation experiment may violate the Carr–Purcell–Meiboom–Gill condition, 40 which may induce signal loss and errors in diffusion measurement. Split‐echo RARE 28 successfully addresses this problem and improves the anatomic integrity of renal DWI. The train of refocusing pulses results in an imaging speed and RF power deposition handicap over EPI 41 .…”

“…The evaluation of geometric distortion was performed following the approach reported by Periquito et al 28 First, the kidney outlines were manually segmented in T2W RARE images to define the distortion‐free reference. Subsequently, the reference contours were superimposed to nondiffusion‐sensitized images of ss‐EPI and four‐shot EPI acquisitions.…”

“…For this purpose, extra navigator echoes were implemented to correct intershot phase variations in interleaved ms‐EPI. The image quality of diffusion‐sensitized ms‐EPI of rat kidney was systematically evaluated using contrast‐to‐noise ratio (CNR) and distortion level 28 for benchmarking against single‐shot DWI‐EPI. Differences in MD and FA between renal cortex and medulla were compared for the DWI‐EPI variants employed.…”

Renal MRI Diffusion: Experimental Protocol

“…Other readouts apart from EPI can be use in DWI such as rapid acquisition with relaxation enhancement (RARE) (Fig. 3) which is less prone to suffering from geometric distortion specially at ultrahigh magnetic fields [6].…”

“…A RARE readout can be used to minimize the magnetic susceptibility artifacts which cause geometric distortions on DW-EPI. DW-RARE is not commercially available, pulse programming skills are needed to implement it[6]…”