University of Wisconsin–Madison

Determining the Reproducibility of Functional MRI of the Kidney

September 2005 to April 2008

This research focuses on determining the reproducibility and natural variability of MR perfusion, blood oxygen level dependent (BOLD), and single kidney (SK) filtration rate sequences. Repetitive measurements of MR perfusion, BOLD MRI, and skGFR will be performed on adult volunteers in order to determine the reproducibility and accuracy of the methods. The goal of this research is to create a robust set of non-invasive imaging techniques to evaluate kidney function, specifically in the transplant population. These techniques will then be applied in a different research study to evaluate allograft dysfunction in the early post-transplantation period.

More than 400,000 individuals require dialysis or transplantation in the United States. This population has many co-morbidity factors, including a higher risk of cardiovascular disease. Although kidney transplantation can replace failed kidney function and offset some of these complications, in many instances, this is only a temporizing measure as allografts usually do not last a lifetime. Therefore, early diagnosis of kidney dysfunction, in both the native and transplanted kidneys, is of utmost importance to slow the rate of progressive loss of function and limit potential co-morbidities.

Various invasive and non-invasive exams are utilized to piece together a picture of renal health in the surveillance of kidney disease. Magnetic Resonance Imaging (MRI) can simultaneously assess both renal anatomy and physiology. We have developed MRI methods that are capable of providing information regarding renal perfusion, oxygen bioavailability, and single kidney glomerular filtration rate (skGFR) during a single non-invasive exam. To our knowledge, these methods have not yet been used to evaluate the transplanted kidney and we believe MRI is ideally suited for assessing transplanted kidney anatomy and function. MRI uses a non-nephrotoxic contrast agent, has excellent spatial resolution, and provides unprecedented image contrast for evaluating the different anatomical regions of the kidney separately.

A goal of this research is to evaluate current MR techniques for measuring intrarenal perfusion (T2*-weighted EPI), oxygen bioavailability (BOLD MRI), and skGFR, and to determine the accuracy and reproducibility of these measures in a group of kidneys with normal estimated glomerular filtration rate (eGFR > 80 ml/min) and in a group with a diminished estimated glomerular filtration rate (eGFR < 60 ml/min).

The specific aims of this study are: 1) Optimize current MR perfusion sequences, and determine their reproducibility and accuracy for measuring cortical and medullary blood flow and tubular dynamics. 2) Determine the reproducibility of calculated R2* values from blood oxygen level dependent (BOLD) MRI data and determine their correlation with levels of serum and urinary biomarkers of oxidative stress. 3) Determine the reproducibility and accuracy of MR derived skGFR.

The following scans will be performed: 1) Two T2* scans for blood oxygen-level dependent (BOLD) measurements, 2) two diffusion weighted imaging (DWI) scans, 3) a glomerular filtration rate (Look-Locker T1) measurement, 4) two perfusion measurements, 5) an MRA of the renal arteries with contrast enhancement, 6) a gradient echo scan post contrast for renal volume measurements, 7) a cardiac-gated phase contrast scan for renal blood flow measurements, and 8) another glomerular filtration rate measurement.

This project led by: Thomas M Grist MD, FACR