RELATIONSHIP BETWEEN MRI AND MORPHOMETRIC KIDNEY MEASUREMENTS IN DIABETIC AND NONDIABETIC RATS

The aim of the present study was to determine the applicability of mag netic resonance imaging (MRI) as a non-invasive measure of kidney volu me in vivo in diabetic and non-diabetic rats. Magnetic resonance, T1 w eighted Spin Echo, images were obtained after injection of contrast in anesthetized control (N = 14). On MRI imaging the total kidney, corte x, medullary and pelvic volumes were calculated. Immediately after MRI measurements the left kidneys were removed before weighting either as a clamped kidney weight (that is, the kidney containing blood and uri ne) or as a wet kidney weight (the kidney drained of blood and urine), while the right kidneys were perfusion-fixed for morphometric measure ments. On thin kidney slices obtained from perfusion-fixed kidneys the cortex, medullary and pelvic fractions were measured and subsequently the cortex, medulla and pelvic volumes were calculated. The cortical volume was measured according to three different approaches. The corti comedullary boundary was defined either to the arcuate arteries, to a curved line following the glomeruli, or to a line at the top of the me dullary rays. Both in control and diabetic rats, MRI measured kidney v olumes were similar to the volume of perfusion-fixed kidneys, while th e clamped kidney weight, and in particular the wet kidney weights, wer e smaller than the MRI obtained volumes. Good agreement was found betw een the MRI measured cortex and medulla volumes when the cortex was de fined to the top of the medullary rays in the morphometric analysis. I n conclusion, the present study demonstrates that MRI allows a reliabl e non-invasive estimate of renal morphology at a macroscopic level in both diabetic and non-diabetic rats.