Magnetization Transfer Imaging Is Unaffected by Decreases in Renal Perfusion in Swine

Abstract

Objectives: Multiparametric renal magnetic resonance imaging (MRI), including diffusion-weighted imaging, magnetic resonance elastography, and magnetization transfer imaging (MTI), is valuable in the noninvasive assessment of renal fibrosis. However, hemodynamic changes in diseased kidneys may impede their ability to measure renal fibrosis. Because MTI assesses directly tissue content of macromolecules, we test the hypothesis that MTI would be insensitive to renal hemodynamic changes in swine kidneys with acute graded ischemia. Materials and Methods: Seven domestic pigs underwent placement of an inflatable silicone cuff around the right renal artery to induce graded renal ischemia. Multiparametric MRI was performed at baseline, 50%, 75%, and 100% renal artery stenosis as well as reperfusion. Measurements included regional perfusion, R 2 *, apparent diffusion coefficient (ADC), stiffness, and magnetization transfer ratio (MTR) using arterial spin-labeled MRI, blood oxygenation-dependent MRI, diffusion-weighted imaging, magnetic resonance elastography, and MTI, respectively. Histology was performed to rule out renal fibrosis. Results: During graded ischemia, decreases in renal perfusion were accompanied with elevated R 2 *, decreased ADC, and stiffness, whereas no statistically significant changes were observed in the MTR. No fibrosis was detected by histology. After release of the obstruction, renal perfusion showed only partial recovery, associated with return of kidney R 2 *, ADC, and stiffness to baseline levels, whereas cortical MTR decreased slightly. Conclusions: Renal MTI is insensitive to decreases in renal perfusion and may offer reliable assessment of renal structural changes.

Quantitative Magnetization Transfer Detects Renal Fibrosis in Murine Kidneys With Renal Artery Stenosis

“…Therefore, a robust imaging biomarker that is less affected by confounding factors is needed for more reliable assessment of renal fibrosis. In contrast, MT‐MRI evaluates the macromolecule content, which is less affected by coexisting hemodynamic factors 7 . This supports the possible usefulness of MT‐MRI, which directly quantifies the macromolecule content, in assessing the elevated collagen deposition in renal fibrosis.…”

“…Therefore, a simple measurement of the MT contrast, namely, magnetization transfer ratio (MTR), reflects the macromolecular content in tissue, providing a powerful tool for assessment of renal fibrosis. Indeed, it has been previously demonstrated that MTI is insusceptible to a sudden drop in renal perfusion relative to other MRI techniques 7 . Previous studies have demonstrated the feasibility of using MTR to detect microstructural disruptions in the brain, 8 spinal cord injuries, 9 and fibrosis 10 .…”

“…Indeed, it has been previously demonstrated that MTI is insusceptible to a sudden drop in renal perfusion relative to other MRI techniques. 7 Previous studies have demonstrated the feasibility of using MTR to detect microstructural disruptions in the brain, 8 spinal cord injuries, 9 and fibrosis. 10 Recently, the utility of MTR in measuring renal fibrosis in mouse [11][12][13] and swine 14 models of kidney diseases has been demonstrated.…”

Clinical and experimental approaches for imaging of acute kidney injury

“…Importantly, changes in physiological conditions and hemodynamics can affect measurements on DWI and BOLD imaging, even in the absence of fibrosis. However, MT measures remain the same during functional changes in kidneys [ 137 ].…”

Mesenchymal Stem/Stromal Cells and their Extracellular Vesicle Progeny Decrease Injury in Poststenotic Swine Kidney Through Different Mechanisms

“…T2*weighed images were acquired using a multiecho gradient echo sequence with the following parameters: repetition time (TR) = 100 ms, echo time (TE) = 2.1-27 ms, Flip angle = 40°, field-of-view (FOV) = 32 cm, Slice thickness = 7 mm, and Matrix = 256 • 256. The renal hypoxia index R2* was quantified by an exponential fitting of the signal intensity and echo times [16,17], after which the renal cortical and medullary R2* values were measured [18].…”