EFFECT OF REGION OF INTEREST SELECTION AND UPTAKE MEASUREMENT ON GLOMERULAR FILTRATION RATE MEASURED BY 99mTc-DTPA SCINTIGRAPHY IN DOGS

Determinations of different methods of measurement of uptake of 99mTc-DTPA using scintigraphy of glomerular filtration rate (GFR) were made from 29 studies on 10 healthy beagle dogs. GFR was measured by calculating the percentage dose uptake (integral method) and rate of uptake (slope method) of 99mTc-DTPA using manual kidney regions of interest (ROI) and automatic kidney and background ROIs at different time periods of the uptake phase. These results were compared using linear regression analysis to the GFR obtained from 99mTc-DTPA plasma clearance using multiple blood samples. The best correlation coefficient between percentage DTPA uptake and GFR by DTPA clearance (r = 0.84, P < 0.001) was derived from time intervals between 30s-120s with a perirenal background ROI at 1 or 2 pixels out from the kidney ROI using automatic kidney ROI at 20% threshold. With the slope method, the best correlation coefficient (r = 0.85, P < 0.001) was obtained from time intervals between 30s-peak with the background ROI at 2 pixels out from the kidney ROI using automatic ROI at 35% threshold. The offset was higher, and the correlation varied more with different ROIs and the method was unreliable at time intervals extending beyond the peak radioactivity. Manual kidney ROIs with automatic background ROIs had slightly lower correlations. With DTPA renography both integral and slope uptake method with automatic kidney and background ROIs are accurate methods to estimate the GFR, but that the integral method is much more stable to variations in ROI size and the duration of the uptake phase of the renogram.     

Equine bone scintigraphic uptake patterns related to age, breed, and occupation.

It is well known that skeletal scintigraphy is an imaging modality with high sensitivity but low specificity. Sites of IRU provide good evidence of increased bone turnover but not its specific cause. Results of lameness workups, blocks, and other imaging techniques are required to determine specific causes. Overinterpretation of causes of IRU is tempting, especially in assigning diagnoses to EIBR--adaptive or non-adaptive. Nevertheless, a quarter of a century's experience with equine skeletal scintigraphy has shown that certain patterns and locations can be fairly predictive of certain pathologic findings. It behooves the equine scintigrapher to know those patterns and how they are affected by the patient's age, breed, and occupation so that he or she can indicate how to best focus other diagnostic procedures toward a definitive diagnosis. Those who are conducting research involving equine skeletal scintigraphy are challenged to help sharpen that focus, especially in evaluating the significance of relatively mild IRUs. Equine clinicians who use scintigraphy in their lameness workups are especially challenged. Working in concert with nuclear medicine imagers, they are in the best position to garner, collate, and analyze the information that is needed to correlate IRUs and the clinical picture. As difficult as they are to design and conduct, such studies are most productive if done prospectively and are most rewarding for those who carry them through.     

Evaluation of 99mTc-diethylenetriaminepentaacetic acid nuclear imaging for quantitative determination of the glomerular filtration rate of dogs

The suitability of 99mTc-diethylenetriaminepentaacetic acid (99mTc-DTPA) as an agent to assess glomerular filtration rate (GFR) in dogs was evaluated. Glomerular filtration rates of 12 healthy dogs were determined on the basis of creatinine and/or inulin clearance. Glomerular filtration rates also were determined in 7 dogs after induction of acute renal failure by administration of amphotericin B. The healthy dogs and the amphotericin B-treated dogs were given 99mTc-DTPA (1 to 2 mCi) IV. The percentage of the 99mTc-DTPA dose in the kidneys (percentage dose) was determined, with background activity subtracted from total activity at 15-s intervals 0 to 6 minutes after 99mTc-DTPA infusion. Linear regression analyses (LRA) were performed to determine whether the percentage dose at various time intervals after injection correlated with GFR calculated on the basis of creatinine and inulin clearance data. One to 3 minutes after 99mTc-DTPA administration appeared to be the best period for analysis of the data. The percentage dose of 99mTc-DTPA (corrected for kidney depth differences) was determined and LRA against GFR were performed. The percentage dose correlated better with inulin clearance (r = 0.94) than with endogenous creatinine clearance (r = 0.83). Only inulin clearance correlations improved with kidney depth correction. The LRA was used to derive an equation that could be used to calculate GFR on the basis of the percentage dose. The equation derived from inulin regression was: GFR (milliliter/minute/kilogram of body weight) = 0.194 (depth-corrected percentage dose)--0.37; the equation derived from the creatinine regression was: GFR (milliliter/minute/kilogram) = 0.171 (depth-corrected percentage dose)-0.15.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of a short-term saline diuresis protocol for the administration of cisplatin

A study was undertaken to determine the toxic effects of cisplatin, an antineoplastic agent, on canine kidneys and bone marrow when administered during a 6-hour saline diuresis. Cisplatin (70 mg/m2 of body surface) was administered IV to 6 healthy dogs over a 20-minute period after 0.9% NaCl solution (saline) was administered IV for 4 hours at a rate of 18.3 ml/kg/hr. After cisplatin injection, saline diuresis was continued at the same rate for 2 hours. Each dog vomited within 8 hours after the drug was administered. Clinical status, weight gain, and food consumption were normal throughout the 27-day study. All measures of renal function remained unchanged and were within normal limits for 27 days after the drug was administered. Nadirs in the daily neutrophil count were observed on days 6 (3,240 +/- 404/microliters) and 15 (1,196 +/- 275/microliters). There were no important gross or histologic abnormalities referable to cisplatin administration when the dogs were necropsied at the conclusion of the study (day 27). We concluded that cisplatin can be administered safely at a dosage of 70 mg/m2 of body surface, using a short-term diuresis protocol, and that the drug induces a nadir in the neutrophil count on days 6 and 15.     

Comparison of left ventricular ejection fractions determined in healthy anesthetized dogs by echocardiography and gated equilibrium radionuclide ventriculography

Left ventricular ejection fractions (LVEF) of 8 pentobarbital-anesthetized dogs were calculated by gated equilibrium radionuclide ventriculography (RVG) and by M-mode and two-dimensional echocardiography (2-DE) prior to and during constant IV infusion of isoproterenol. Mean LVEF (+/- SD), determined with RVG by use of an automatic edge detection algorithm (RVG-auto) to define the left ventricular region of interest, increased from a resting value of 53.5% (+/- 4.9%) to 71.9% (+/- 6.8%) during isoproterenol infusion. Mean LVEF, determined with RVG by use of visual inspection (RVG-manual) to define the left ventricular region of interest increased from a resting value of 51.6% +/- 3.8% to 67.0% +/- 5.6% during isoproterenol infusion. Using 2-DE and the bullet formula to calculate left ventricular volume (LVV = 5/6 x cross-sectional area x length), mean LVEF increased from 52.3% (+/- 3.50) to 74.7% (+/- 5.0%). Using 2-DE area measurements and Teicholz formula, mean LVEF increased from 48.9% (+/- 5.1%) to 69.5% (+/- 6.0%). Using M-mode echocardiographic left ventricular diameter measurements and Teicholz formula, mean LVEF increased from 52.3 (+/- 9.0%) to 78.3% (+/- 8.1%). Before and during isoproterenol infusion, the mean LVEF values calculated by RVG agreed closely with mean LVEF values calculated from M-mode and 2-DE. Correlation coefficients determined from linear regression analysis of LVEF by echocardiography vs LVEF by radionuclide ventriculography ranged from 0.79 to 0.88. Correlation coefficients were higher and SEM were lower when LVEF was determined by RVG-manual, rather than by RVG-auto methods and when LVEF was calculated from 2-DE measurements, rather than from M-mode measurements.     

Nuclear imaging of the stomach of healthy dogs.

To evaluate the use of technetium pertechnetate (99mTcO4) as a means of estimating gastric mucosal integrity, nuclear images of the empty stomach were obtained from 6 dogs at 20, 40, 60, 120, 180, and 240 minutes after IV administration of the radiopharmaceutical. Blood and gastric secretion samples were collected during the same time intervals. The left lateral-view image of the stomach was used to calculate the relative fraction of the dose in the stomach and the count density ratio. Between 20 and 40 minutes and 40 and 60 minutes, significant differences (P less than 0.001) were apparent in the amount of 99mTcO4 in the stomach. Blood concentration of 99mTcO4 decreased significantly (P less than 0.001), whereas gastric secretion concentration increased significantly (P less than 0.001) over time. Qualitative assessment of the gastric nuclear scans and the statistical analytic results indicated that the optimal time for imaging the canine stomach was between 40 and 60 minutes after radiopharmaceutical administration. In a second study, the same dogs were pretreated with the H2-receptor antagonist cimetidine and the cholinergic antagonist glycopyrrolate to block gastric secretions. Over time, changes in the relative dose fraction in the stomach and the density ratio were the same as values obtained during the experiment performed without use of cimetidine and glycopyrrolate. Results of the study indicate that nuclear imaging with 99mTcO4 outlines normal canine gastric mucosa and that pretreatment with cimetidine and glycopyrrolate has no effect on the quality of the gastric image.     

Nuclear angiography in a dog with congestive cardiomyopathy

Nuclear angiography was used as a diagnostic aid and in monitoring the clinical course of a case of congestive cardiomyopathy in a dog. Serial examinations revealed progressively deteriorating values for left ventricular ejection fraction before the dog's death. This noninvasive technique can be an alternative to echocardiography for the evaluation of cardiac performance.