Objective—To image the spatial distribution of pulmonary blood flow by means of scintigraphy, evaluate ventilation-perfusion (VA/Q) matching and pulmonary blood shunting (Qs/Qt) by means of the multiple inert gas elimination technique (MIGET), and measure arterial oxygenation and plasma endothelin-1 concentrations before, during, and after pulse-delivered inhaled nitric oxide (PiNO) administration to isoflurane-anesthetized horses in dorsal recumbency. Animals—3 healthy adult Standardbreds. Procedures—Nitric oxide was pulsed into the inspired gases in dorsally recumbent isoflurane-anesthetized horses. Assessment of VA/Q matching, Qs/Qt, and Pao2 content was performed by use of the MIGET, and spatial distribution of pulmonary blood flow was measured by perfusion scintigraphy following IV injection of technetium Tc 99m–labeled macroaggregated human albumin before, during, and 30 minutes after cessation of PiNO administration. Results—During PiNO administration, significant redistribution of blood flow from the dependent regions to the nondependent regions of the lungs was found and was reflected by improvements in VA/Q matching, decreases in Qs/Qt, and increases in Pao2 content, all of which reverted to baseline values at 30 minutes after PiNO administration. Conclusions and Clinical Relevance—Administration of PiNO in anesthetized dorsally recumbent horses resulted in redistribution of pulmonary blood flow from dependent atelectatic lung regions to nondependent aerated lung regions. Because hypoxemia is commonly the result of atelectasis in anesthetized dorsally recumbent horses, the addition of nitric oxide to inhaled gases could be used clinically to alleviate hypoxemia in horses during anesthesia.

Objective: To determine whether the reported drug-drug interaction between the flea medication spinosad and ivermectin is attributable to inhibition of P-glycoprotein by spinosad. Animals: 6 healthy adult dogs with the ABCB1 wildtype genotype. Procedures: The study was conducted as a prospective, masked, randomized crossover design. Six dogs were allocated to 2 groups; each dog served as its own control animal. Dogs in one of the groups received spinosad at the manufacturer's recommended dose; the other group received no treatment. Forty-eight hours later, scintigraphic imaging of the head and abdomen were performed with the radiolabeled P-glycoprotein substrate methoxy-isobutyl-isonitrile (sestamibi) in both groups of dogs. After a washout period of 60 days, the dogs in each group received the alternate treatment, and scintigraphic imaging again was performed 48 hours later. Gallbladder-to-liver and brain-to-neck musculature ratios of technetium Tc 99m sestamibi were calculated for each dog and compared between treatments. Results: No significant differences in gallbladder-to-liver or brain-to-neck musculature ratios were found between treatments. Conclusions and Clinical Relevance: Results provided evidence that spinosad did not inhibit P-glycoprotein function 48 hours after spinosad was administered at the manufacturer's recommended dose. Further investigations will be necessary to elucidate the mechanism of the reported toxic interaction between spinosad and ivermectin.

Objective: To determine the effects of exercise on the distribution and pharmacokinetics of technetium Tc 99m medronate (99mTc-MDP) following intra-articular (IA) injection in horses. Animals: 5 horses. Procedures: 1 antebrachiocarpal joint (ACJ)/horse was assigned to the exercised group (n = 5), and the contralateral ACJ was evaluated in the nonexercised group (5) after a minimum washout period of 7 days. Following IA injection of 99mTc-MDP (148 MBq), blood and scintigraphic images of the carpus were obtained at 5, 10, 15, 20, 25, 30, 45, 60, 90, 120, 240, 360, 480, 600, 720, and 1,440 minutes. Plasma and scintigraphic radioactivity were determined over time, and pharmacokinetic parameters were generated via noncompartmental and compartmental analyses. Each horse was monitored via physical and lameness examination and ACJ synovial fluid analysis before injection and at days 1, 2, 3, and 7. Results: Lameness was not observed. Mean ± SD synovial fluid WBC count increased at day 1 (exercised, 721 ± 234 cells/μL; nonexercised, 948 ± 223 cells/μL), but returned to baseline at days 3 and 7 Mean time to maximum plasma radioactivity was earlier in the exercised group (16.00 ± 2.35 minutes) than the nonexercised group (43.75 ± 3.64 minutes). Linear regression of the scintigraphic radioactivity-time curves revealed a greater negative slope in the exercised group within the first 25 minutes. There was no difference in absorption or elimination rate constants in a 2-compartment model. Conclusions and Clinical Relevance: IA injection of 99mTc-MDP was safe and effective for evaluating synovial solute distribution. Exercise significantly increased early transfer of 99mTc-MDP from the ACJ into plasma, although absorption and elimination rate constants were not affected. Exercise may affect synovial clearance and withdrawal times of medications administered IA.

Objective-To quantitatively assess distraction-induced bone formation in a crural lengthening model in dogs by use of delayed-image bone scintigraphy. Animals-12 mature Labrador Retrievers. Procedure-Dogs were randomly allocated to 1 of 3 groups. A circular external skeletal fixation system was mounted on the right crus of each dog. Osteotomy of the distal portion of the tibia and fibula was performed in groups 1 and 2 and was followed by a lengthening procedure of 10 mm in the first group only. The third group served as sham-operated controls. Delayed-image bone scintigraphy with technetium-99m hydroxy methylene diphosphonate was performed 2, 4, and 6 weeks after surgery. Delayed-image-to-region-of-interest, delayed-image-to-crural, and delayed-image-to-femoral scintigraphic activity ratios were calculated. New bone formation was quantified by use of densitometric image analysis, and values for the scintigraphic ratios were compared. Results-In the distraction and osteotomy groups, delayed-image-to-region-of-interest and delayed-image-to-crural ratios increased significantly. Although densitometric image analysis revealed increased bone formation after distraction, the region-of-interest ratios and crural ratios were similar in both groups. All dogs had increased delayed-image-to-femoral ratios. Conclusions and Clinical Relevance-Delayed-image bone scintigraphy ratios were not effective at differentiating between the amounts of distraction-induced bone and osteotomy-induced bone. Metabolic bone activity in the adjacent femur was increased as a consequence of circular external skeletal fixator placement. Delayed-image bone scintigraphy was not adequately sensitive to quantitatively monitor bone formation but may be useful as an early predictor of bone healing.

Objective-To determine tracheal mucociliary clearance rate (TMCCR) by use of a standard protocol in healthy anesthetized cats and to determine the effect of theophylline on TMCCR in healthy anesthetized cats. Animals-6 healthy cats. Procedure-Cats were anesthetized with propofol, and a droplet of the radiopharmaceutical technetium Tc 99m macroaggregated albumin was placed endoscopically at the carina. Dynamic acquisition scintigraphic imaging was performed, using the larynx as the end point. The TMCCR was determined by measuring the distance the droplet traveled by frame rate. Each cat was imaged 6 times as follows: 3 times following placebo administration and 3 times following the administration of sustained release theophylline (25 mg/kg, PO). Serum theophylline concentrations were assessed during imaging to ensure therapeutic concentrations. Results-The TMCCR in healthy adult cats anesthetized with propofol was 22.2 +/- 2.8 mm/min. Tracheal mucociliary clearance rate in cats receiving theophylline was 21.8 +/- 3.5 mm/min. Theophylline administration did not significantly alter TMCCR. Conclusion and Clinical Relevance-Theophylline has been shown to increase TMCCR in humans and dogs. In our study, we determined TMCCR in healthy anesthetized cats and found that it was not accelerated by the administration of theophylline.

To measure tracheal mucociliary transport rate (TMTR) in awake dogs, restrained in dorsal recumbency, 99mtechnetium-labeled macroaggregated albumin was administered by tracheal injection, and the cephalic movement of boluses containing the radiopharmaceutical was detected by a gamma camera positioned lateral to the dog's head and neck. The distance traveled by each bolus was measured, relative to external markers placed a known distance apart. Tracheal mucociliary transport rates were calculated by dividing the measured distance of radiopharmaceutical movement by elapsed time. The technique was efficient and well tolerated. Mean (+/- SD) TMTR was 35.3 +/- 15.9 mm/min. Significant (P = 0.029) difference in TMTR was found between males and females, but significant difference attributable to age of the dog was not detected. This method of measuring TMTR in awake dogs has potential for evaluation of clinical animal patients with suspected tracheal mucociliary abnormalities.

Glomerular filtration rate (GFR) was measured in 12 clinically normal horses, using the standard inulin clearance method, and values were compared with values for 2 methods, using a single rapid IV injection of (99m)Tc-labeled diethylenetriaminepentaacetic acid ((99m)Tc-DTPA). The first (99m)Tc-DTPA method used a 2-compartment model to calculate GFR blood clearance of the tracer. The second method used sequential digital gamma camera images of the kidneys to determine fractional accumulation of the total dose of the tracer in the kidneys (percentage of injected dose, gamma camera) from 0 to 10 minutes after radionuclide administration. Linear correlation among the 3 methods was determined. Mean (+/- SD) GFR, using the inulin clearance method, was 154.67 +/- 42.28 ml/min/100 kg of body weight. Mean GFR, using the 2-compartment blood clearance curve, was 146.92 +/- 27.49 ml/min/100 kg. Mean GFR, using percentage of injected dose (gamma camera method) was 154.7 +/- 22.00 ml/min/100 kg. The percentage of injected dose (gamma camera method) did not correlate significantly to the inulin clearance results. However, a significant (r = 0.666, P < 0.018) correlation was observed between the inulin method and the (99m)Tc-DTPA blood clearance method. Significant (P < 0.0001) difference also was observed in the split function of the equine kidneys, with GFR of the right kidney contributing 60.1 +/- 9.12% of the total function, as determined by (99m)Tc-DTPA gamma camera imaging. Because the (99m)Tc-DTPA blood clearance method does not require urine collection, it may be a more practical procedure to measure GFR in the horse.

A nuclear imaging technique of the stomach, using technetium pertechnetate (99mTcO4), was evaluated in healthy dogs. The stomach was first insufflated with room air, then filled with barium sulfate to induce mild distention, outlining the gastric wall. Six dogs were imaged twice: initially without use of drugs that might affect gastric secretion of 99mTcO4, then after pretreatment with cimetidine and glycopyrrolate. These scans established the appearance of the normal (control) stomach and compared the quality of the image in the same dogs not pretreated, then pretreated with cimetidine and glycopyrrolate before administration of 99mTcO4. Avascular defects were then surgically created on the greater curvature of the stomach of the same 6 dogs, and gastroscintigraphy was performed in similar manner. Significant (P < 0.05) quantitative differences were detected in the gastric images for scans of the avascular area, compared with various control scans. Qualitative assessment had overall accuracy of 90.28%. Results of the study reported here indicate that nuclear imaging can be a valuable diagnostic technique for detecting ischemic areas in the gastric wall of dogs.

In 25 dogs with spontaneous cholestatic disease, the hepatobiliary dynamics were evaluated by use of scintigraphy and a 99mTc-labeled iminodiacetate (IDA) derivative. Hyperbilirubinemia existed in all dogs, with serum total bilirubin concentration ranging from 6 to 262 micromole/L. An appropriate compartmental model was used to characterize the liver time-activity curves. Model-dependent variables for hepatic uptake and biliary excretion of radiolabeled IDA were found to reliably represent the underlying physiologic processes. Measurements directly derived from the liver time-activity curves of IDA, representing the moments of accumulation of 50 and 95% of the maximal hepatic activity did not accurately represent the hepatic uptake by being significantly influenced by biliary excretion and by competition of renal excretion. The time-interval between 95% and 50% of the maximal activity in the excretory phase proved to be a quantitative characteristic of bile flow in all instances. Compartmental analysis of 99mTc-IDA excretory scintigraphy characterized bile flow quantitatively in clinically normal dogs and in dogs with cholestasis. The method permitted the clinical evaluation of cholestasis based on quantitative, instead of the usual qualitative, and on functional, instead of phenomenologic, criteria.

Autologous canine neutrophils were labeled with technetium 99m and reinjected in 7 dogs with experimentally induced focal abscessess to determine the ability of scintigraphy to localize a focus of sepsis (abscess). Good localization of labeled cells in an abscess was achieved; however, a large portion of the technetium 99m eluted from the neutrophils.