Quantitative Renal Perfusion Measurements in a Rat Model of Acute Kidney Injury at 3T: Testing Inter- and Intramethodical Significance of ASL and DCE-MRI

Abstract

ObjectivesTo establish arterial spin labelling (ASL) for quantitative renal perfusion measurements in a rat model at 3 Tesla and to test the diagnostic significance of ASL and dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in a model of acute kidney injury (AKI).Material and MethodsASL and DCE-MRI were consecutively employed on six Lewis rats, five of which had a unilateral ischaemic AKI. All measurements in this study were performed on a 3 Tesla MR scanner using a FAIR True-FISP approach and a TWIST sequence for ASL and DCE-MRI, respectively. Perfusion maps were calculated for both methods and the cortical perfusion of healthy and diseased kidneys was inter- and intramethodically compared using a region-of-interest based analysis.Results/SignificanceBoth methods produce significantly different values for the healthy and the diseased kidneys (P<0.01). The mean difference was 147±47 ml/100 g/min and 141±46 ml/100 g/min for ASL and DCE-MRI, respectively. ASL measurements yielded a mean cortical perfusion of 416±124 ml/100 g/min for the healthy and 316±102 ml/100 g/min for the diseased kidneys. The DCE-MRI values were systematically higher and the mean cortical renal blood flow (RBF) was found to be 542±85 ml/100 g/min (healthy) and 407±119 ml/100 g/min (AKI).ConclusionBoth methods are equally able to detect abnormal perfusion in diseased (AKI) kidneys. This shows that ASL is a capable alternative to DCE-MRI regarding the detection of abnormal renal blood flow. Regarding absolute perfusion values, nontrivial differences and variations remain when comparing the two methods.

Fast imaging strategies for mouse kidney perfusion measurement with pseudocontinuous arterial spin labeling (pCASL) at ultra high magnetic field (11.75 tesla)

“…The short acquisition train length of sSE EPI (25 ms) allowed reducing the signal loss due to blood relaxation effects and venous outflow, which are particularly important sources of quantification errors in the context of high perfusion rate, as demonstrated by Wegener et al 27 On the contrary, nonsegmented TrueFISP with linear encoding and single-shot RARE, with respective acquisition train lengths of 130 ms and 180 ms, were more sensitive to these effects, thus resulting in ASL signal decay during the image acquisition. Consequently, and although in line with data referenced for rodents, [28][29][30] pCASL RARE and pCASL…”

“…Of interest, our results are different from the reports at clinical magnetic field on humans or on rats at a fairly modest spatial resolution in which the TrueFISP method demonstrates several advantages compared with single shot EPI and RARE. 4,13,17 As no gold standard measurement of perfusion was used in this study, it is difficult to draw any conclusion regarding the accuracy of any of the three techniques. However, systematic differences in DS/RBF were observed between techniques, and they can be directly related to the properties of sSE EPI, RARE, and TrueFISP readouts as used in this study.…”

“…S everal studies performed in humans [1][2][3][4][5][6][7][8] and in small animals [9][10][11][12][13] have demonstrated that Arterial Spin Labeling (ASL) MRI can be advantageously used for kidney perfusion studies as it allows quantitative analyses without the need of any exogenous tracer. If the high perfusion level in kidney is an asset for the intrinsically low-sensitive ASL techniques, magnetic field inhomogeneities encountered in the abdomen area along with motion related to respiration strongly challenge ASL measurement quality and robustness.…”

“…7T), thus resulting in long longitudinal relaxation time (T 1 ) and, therefore, enhanced the sensitivity of ASL techniques. Concerning the ASL scheme strategy, it has been recently demonstrated that, despite modest inversion efficiency, 9 the pCASL approach 2 provides several advantages compared with the widely used pulsed FAIR 14 technique 10,11,13 for mouse kidney perfusion measurement. For the readout strategy, several options are offered, among them EPI (echo planar imaging), RARE (rapid acquisition with relaxation enhancement), TrueFISP (true fast imaging with steady state precession), GRASE (gradient and spin echo), 15 UFLARE (ultra fast low angle rate) 16 or even spiral imaging.…”

“…Several kidney ASL perfusion studies have thus reported advantages of TrueFISP compared with single shot EPI and RARE for SNR and image quality concerns. 4,13,17 These experiments were, however, performed at clinical magnetic field strengths (1.5T/3T) either on humans (who present renal blood flow (RBF) values 2-2.5 times lower than that of rodents) or on rats at a fairly modest spatial resolution.…”