PERFUSION QUANTITATION IN TRANSPLANTED RAT-KIDNEY BY MRI WITH ARTERIAL SPIN-LABELING

The purpose of this study was to determine the feasibility of using qu antitative magnetic resonance imaging (MRI) with non-invasive arterial spin labeling to assess perfusion of transplanted kidneys in rats. MR I studies were performed on five groups of rats: normal Fisher 344 rat s, Fisher 334 rats that had received a syngeneic kidney transplant eit her 3 or seven days prior to study, and Fisher 344 rats that had recei ved an allogeneic kidney (ACI rat as the donor) either three or seven days prior to study. The contralateral native kidney remained in place for comparison. Cortical perfusion was quantitated from a slice throu gh the center of each kidney in anesthetized rats at 4.7 Tesla with a fast gradient-echo MRI sequence following the arterial spin labeling. The spin-lattice relaxation time was measured within the cortex, and t he cross sectional area of the kidney was also determined within the s ame MRI plane. Immediately after the perfusion imaging measurement, tr ansplanted kidneys were removed and scored for rejection using the Ban ff histological criteria. Renal cortical perfusion in normal kidneys w as 7.5 +/- 0.8 ml/g/min (N = 12 rats, 24 kidneys). At the third day po st-transplantation, that is, before marked acute rejection, the renal cortical perfusion rate was similar in both syngeneic and allogeneic k idneys [3.3 +/- 1.7 (N = 6) and 3.0 +/- 2.4 ml/g/min (N = 6), respecti vely]. In contrast, at the seventh day post-transplantation, that is, during severe rejection, the renal cortical perfusion rate in allogene ic kidneys was very low (undetectable) compared to the value in syngen eic kidneys [that is, less than or equal to 0.3 (N = 6) versus 5.2 +/- 2.0 ml/g/min (N = 6), respectively]. Moreover, the renal cortical per fusion rate determined by MRI was significantly (P < 0.05, r = -0.82) correlated with histological rejection. We conclude that the quantitat ive measurement of renal cortical perfusion by MRI with arterial spin- labeling could provide a non-invasive diagnostic method for monitoring the status of renal transplants without requiring the administration of a contrast agent.