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Following 24-hour fasting and fluid deprivation, sequential changes in CT numbers of the canine kidney were determined in 4 dogs, each of whom received, at intervals, IV sodium diatrizoate, metrizamide, iopamidol, and sodium ioxaglate at a dose of 500 mgI/kg body weight. The urinary bladder was catheterized for baseline determination of urine osmolality and, subsequently, urine volume and CT number, CT number of the bladder urine from 0 to 10 minutes and from 10 to 20 minutes post-injection was obtained by scanning known dilutions of urine in vitro. Peak renal cortical enhancement occurred within 2 minutes of bolus injection and was not dependent on the chemical make-up of the contrast agent. Peak medullary enhancement occurred within 3 minutes of bolus injection. Peak medulla CT number following sodium diatrizoate was significantly less than that following metrizamide (P less than 0.025) or iopamidol (P less than 0.01). Peak medulla CT number was significantly less following sodium diatrizoate (P less than 0.01), metrizamide (P less than 0.01) and iopamidol (P less than 0.05) than following sodium ioxaglate. Urine iodine concentrations followed a similar pattern, with significant differences as follows: sodium diatrizoate less than metrizamide = iopamidol less than sodium ioxaglate. It was concluded that the investigational agents metrizamide, iopamidol, and sodium ioxaglate have theoretical advantage for excretory urography. Differences in renal handling of these agents are detectable, with CT scanning as differences in renal medullary enhancement and urine iodine concentration.

Using a 30-second computed tomography (CT) scanner, the sequential changes in CT numbers of the kidney were determined in three healthy dogs after intravenous administration of sodium and meglumine diatrizoate and iothalamate. For all contrast media, the mean CT number of the cortex was greatest within 2 minutes of rapid intravenous administration. At doses comparable to those used clinically, a linear relationship was demonstrated between the amount of iodine administered (in mg/kg body weight) and the corrected peak mean CT number of the cortex, such that doubling the amount of iodine caused the corrected peak mean CT number of the cortex to approximately double. Following the peak, the mean CT number of the cortex gradually declined. For all contrast media, the corrected mean CT number to corrected peak mean CT number ratios at 5, 10 and 20 minutes were 58 +/- 3%, 39 +/- 3%, and 28 +/- 5% respectively. Our data suggest that rapid-sequence CT may be a valuable tool for evaluating the physiology of renal contrast media excretion.

Following the intravenous administration of sodium and meglumine salts of both diatrizoate and iothalamate (at doses of 310-880 mg I/kg body weight) sequential changes in computed tomographic (CT) numbers of the inner medulla were determined in three dogs, using a 30-second CT scanner. Peak medullary enhancement was greater than, and usually occurred 1-2 minutes after, peak cortical enhancement. The CT number of the medulla increased linearly with increasingly large doses of the contrast agent. At peak enhancement, the meglumine salts produced a significantly lower (p less than 0.025) mean CT attenuation value of the medulla than did the sodium salts. The difference in mean attenuation values between the sodium salts and meglumine salts was maximum (50-60 HU)at peak enhancement. Our data indicate the known difference in renal handling of the meglumine and sodium salts is readily detectable by CT.