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Magnetic resonance perfusion/diffusion imaging of the excised dog kidney.

RATIONALE AND OBJECTIVES
The authors developed a model of tissue capillary beds applicable to perfusion/diffusion imaging with magnetic resonance imaging (MRI). The model consists of a formalin-fixed excised dog kidney attached to a variable speed pump. With this system, it is possible to perfuse the kidney at selected rates.


METHODS
Using the intravoxel incoherent motion model (IVIM), the apparent diffusion coefficient (ADC), diffusion coefficient (D), and perfusion fraction (f) were computed for a region of interest (ROI) in the renal cortex and in the medulla of seven kidneys, one of which was injected with a vasodilator before fixation. ADC and D values were computed for both cortex and medulla. These values were normalized to zero flow and plotted against renal perfusion. The perfusion fraction f was expressed in percent and was not normalized to zero flow.


RESULTS
Normalized ADC and f were correlated with tissue perfusion rates using the Spearman rank-sum test (n = 18, rs greater than 0.5, P less than or equal to .02 for the standard preparation in both cortex and medulla), whereas normalized D (rs much less than 0.5) was uncorrelated for both preparations in cortex and medulla.


CONCLUSIONS
The isolated perfused dog kidney is a useful model of tissue capillary beds for perfusion imaging technique development. The perfusion/diffusion-related parameters ADC and f increase as flow increases in the tissues, whereas D does not.