Renal MRI: from Niche Application to New Tool in Nephrology

Abstract

Around 10% of the general population suffers from some form of chronic kidney damage. Yet, treatment options for chronic kidney diseases are limited. Current therapies can only slow down progression of chronic kidney disease. Early detection therefore is crucial to initiate treatment in an early stage and to prevent progression to end-stage renal disease. Existing diagnostic tests only detect damage in a later stage and do not provide insight in the underlying structural and functional problems. In this thesis, we show that MRI potentially addresses those problems and can proof to be a valuable diagnostic tool for nephrologists. In chapter 2 a multiparametric MRI protocol designed specifically for renal imaging is tested in terms of repeatability. Nineteen healthy volunteers are scanned twice with an interval of about a week. The results of both examinations are compared. In the multiparametric MRI examination multiple techniques are combined, yielding a comprehensive image of renal microstructure and function. Based on the results of this study, we can conclude that repeatability of most measurements is comparable to clinical tests for renal function like eGFR and inulin clearance. In chapter 3 an important problem in renal imaging is addressed: respiratory motion. In DCE MRI, for several minutes quick images of the kidney are continuously acquired, but due to respiratory motion those images are misaligned. We propose a solution for this problem by using slightly different images, simplifying automated motion correction. Chapter 4 describes remaining contrast agent in the kidneys one week after administration, a chance finding from the repeatability study. The current study once again shows that the mechanism of excretion of MR contrast agents is not fully understood. Further research is therefore indicated. In chapter 5 and 6 BOLD MRI is used to assess renal oxygenation in patients with hypertension. A correlation between activity of the renin-angiotensin-aldosterone system and renal hypoxia is found, but an intervention hypothesized to decrease activity of this system (renal denervation) did not improve renal oxygenation. Chapter 7 describes a case of a patient with end-stage failure of her transplant kidney. Since the transplant kidney was explanted, we were able to compare whole-kidney histology with the results of the multiparametric MRI. The MR measures correlated well with histological findings. Chapter 8 explores the possibilities of renal MRI at ultra-high field. Switching to 7 T creates new possibilities, but imposes additional challenges as well. This review article describes which techniques are expected to profit from 7 T MRI, what the challenges are and where to look for solutions. Finally, chapter 9 places these results in context. How should renal MRI be used in clinical practice to aid patients and doctors in early detection of renal damage and prevention of progression to end-stage renal disease? New technical developments can bridge the gap between research and clinical use. And we will touch upon the question how to employ MRI, a technique associated with both significant environmental as well as financial costs, in a sustainable way.