MR Elastography for Evaluation of Kidney Fibrosis

Abstract

Renal fibrosis is a major hallmark of chronic kidney disease (CKD) that affects millions of people in the USA and many more around the world. CKD causes renal fibrosis and a gradual loss of kidney function leading to renal failure necessitating dialysis or kidney transplant. If untreated, CKD could even result in death. The current gold standard for diagnosing kidney fibrosis is biopsy, which is painful, invasive, and limited by sampling bias and inter- and intra-observer variability. In addition, biopsy poses risk of complications including significant bleeding. Hence, there is a need for non-invasive techniques to diagnose renal fibrosis reliably and accurately.

Magnetic Resonance Elastography (MRE) is a non-invasive, FDA-approved, and clinically useful technique that can be used to estimate the stiffness of soft tissues. Currently, MRE is an established clinical tool that is used worldwide for diagnosing and staging liver fibrosis and is being investigated for stiffness estimations in other organs. For MRE, external mechanical vibrations are applied to the organ of interest at a fixed frequency and images are acquired at different time points during the application of external vibration and the resulting motion within the tissue is encoded in the phase of MR images with the help of motion encoding gradients. These wave images are then processed using an inversion algorithm to obtain stiffness maps, for quantitative measurement of stiffness of the soft tissue of interest.

In this chapter, we review the physics of MRE as it relates to kidney and its recommended acquisition protocol, set-up, patient preparation, post-processing methods, interpretation, and potential clinical applications. We have divided the chapter into three sub-sections. Part 1 provides an introduction, describes MR elastography physics, and sets a foundation for clinical implementation of MR elastography of the kidney. We also provide details on how to post-process the acquired images and obtain mean stiffness measurements. In part 2, we provide a recommended kidney MRE acquisition protocol. Finally, in part 3, we discuss the potential clinical applications of kidney MRE along with relevant case examples from the published studies in the literature.