Functional Magnetic Resonance Imaging of the Kidneys—With and Without Gadolinium-Based Contrast

Abstract

Assessment of renal function with magnetic resonance imaging (MRI) has been actively explored in the past decade. In this review, we introduce the principle of MRI, and review recent progress of MRI methods (contrast-enhanced and non-contrast) in assessing renal function. Contrast-enhanced MRI using ultra-low dose of gadolinium-based agent has been validated for measuring single-kidney glomerular filtration rate (GFR) and renal plasma flow (RPF) accurately. For routine functional test, contrast-enhanced MRI may not replace the simple serum-creatinine method. However, for patients with renal diseases, it is often worthy to perform MRI to accurately monitor renal function, particularly for the diseased kidney. As contrast-enhanced MRI is already an established clinical tool for characterizing renal structural abnormalities, including renal mass and ureteral obstruction, it is possible to adapt the clinical MRI protocol to measure single-kidney GFR and RPF, as demonstrated by recent studies. What makes MRI unique is the promise of its non-contrast methods. These methods include arterial spin labeling (ASL) for tissue perfusion, blood oxygen level dependent (BOLD) for blood and tissue oxygenation, and diffusion weighted imaging (DWI) for water diffusion. For each method, we reviewed recent findings, and summarized challenges.

Renal MRI: From Nephron to NMR Signal

“…A rapid series of T 1 ‐weighted images is collected, before and during the passage of a contrast agent bolus. The signal‐time‐curve (STC) reflects the passage of the contrast through the kidney tissue 91 . Analysis of DCE‐MRI data comprises kidney segmentation, delineation of the arterial input function (AIF) from the aorta, calculation of T 1 maps to convert voxel‐wise STCs to concentration time curves, before model‐based quantification of renal perfusion (in mL/100 mL/min) and glomerular filtration rate (in mL/min).…”

Functional magnetic resonance imaging of kidneys

“…Pri BOLD MRI koriste se različita magnetna svojstva oksihemoglobina i deoksihemoglobina kako bi se dobile informacije o stepenu iskorišćavanja kiseonika u tkivima koje se nalazi uz krvne sudove. Istraživanja pokazuju abnormalan odnos između bubrežnog metabolizma i tubularnog transporta natrijuma kod pacijenata sa hroničnom bolešću bubrega i hipertenzijom [19][20][21][22] [8,10,11]. DCE MRI se može koristiti za mjerenje perfuzije bubrega i glomerulske filtracije.…”

“…U fazi izlučivanja, intenzitet MRI signala u parenhimu bubrega se smanjuje zbog izlučivanja kontrastnog medija u ekskretorni sistem (MRI urografija). Na taj način mogu se otkriti i procijeniti prepreke oticanja urina kao alternativa scintigrafiji/CT urografiji kod pedijatrijskih pacijenata sa anomalijama urinarnog trakta [8,10,11].…”

“…Funkcionalna MRI bubrega može da se izvodi bez primjene MRI kontrastnih sredstava kao i njihovom primjenom, a omogućava da se analiziraju funkcije samo jednog bubrega, ali i samo jednog njegovog dijela (compartment analysis) [8][9][10][11].…”