MAGNETIC-RESONANCE PERFUSION DIFFUSION IMAGING OF THE EXCISED DOG KIDNEY

RATIONALE AND OBJECTIVES. The authors developed a model of tissue capi llary beds applicable to perfusion/diffusion imaging with magnetic res onance imaging (MRI). The model consists of a formalin-fixed excised d og kidney attached to a variable speed pump. With this system, it is p ossible to perfuse the kidney at selected rates. METHODS. Using the in travoxel incoherent motion model (IVIM), the apparent diffusion coeffi cient (ADC), diffusion coefficient (D), and perfusion fraction (f) wer e computed for a region of interest (ROI) in the renal cortex and in t he medulla of seven kidneys, one of which was injected with a vasodila tor before fixation. ADC and D values were computed for both cortex an d medulla. These values were normalized to zero flow and plotted again st renal perfusion. The perfusion fraction f was expressed in percent and was not normalized to zero flow. RESULTS. Normalized ADC and f wer e correlated with tissue perfusion rates using the Spearman rank-sum t est (n = 18, r(s) > 0.5, P less-than-or-equal-to .02 for the standard preparation in both cortex and medulla), whereas normalized D (r(s) << 0.5) was uncorrelated for both preparations in cortex and medulla. CO NCLUSIONS. The isolated perfused dog kidney is a useful model of tissu e capillary beds for perfusion imaging technique development. The perf usion/diffusion-related parameters ADC and f increase as flow increase s in the tissues, whereas D does not.