COMPARISON OF PER-RECTAL PORTAL SCINTIGRAPHY USING 99mTECHNETIUM PERTECHNETATE TO MESENTERIC INJECTION OF RADIOACTIVE MICROSPHERES FOR QUANTIFICATION OF PORTOSYSTEMIC SHUNTS IN AN EXPERIMENTAL DOG MODEL

Per-rectal portal scintigraphy using tech-netium-99m pertechnetate (^99mTcO₄^-) was performed in 8 normal dogs before and after surgical creation of a portacaval shunt. Shunt fractions were calculated by computer assisted analysis of dynamic images (IMG) and compared to shunt fractions determined by mesenteric venous injection of radioactive microspheres (MIC). The mean pre-operative shunt fraction was 1.59% using IMG and 3.00% using MCI. The mean postoperative shunt fraction was 64.56% using IMG and 69.56% using MIC. There was excellent correlation between both methods (r² 0.94). Per-rectal portal scintigraphy is an easily performed, inexpensive method to diagnose and quantify portosystemic shunts in dogs.     

TRANSSPLENIC PORTAL SCINTIGRAPHY USING 99MTC-MEBROFENIN IN NORMAL DOGS

Transsplenic portal scintigraphy using sodium pertechnetate is superior to per-rectal portal scintigraphy due to improved visualization of the portal vasculature with decreased patient and personnel exposure. The purpose of this study was to describe the use of 99mTc-mebrofenin, the radiopharmaceutical of choice for the evaluation of hepatic function, in place of pertechnetate for transsplenic portal scintigraphy in normal dogs. Sixteen juvenile dogs underwent transsplenic portal scintigraphy using 37-130 MBq 99mTc-mebrofenin in a 0.2-0.5 ml volume. After the initial dynamic acquisition obtained at 4 frames/s in right lateral recumbency, static right lateral, and ventral views were obtained at 5, 10, 15, 20, 25, 30, 40, 50, and 60 min. A nuclear angiogram of the splenic and portal veins was visible in all dogs, followed by rapid distribution of the radiopharmaceutical in the liver. Hepatic morphology was more easily defined than with pertechnetate. Transit time could not be calculated due to the high hepatic extraction of 99mTc-mebrofenin. Mean +/- SD shunt fraction was 0.8 +/- 0.8%. Time to peak liver activity was 3.1 +/- 1.1 min, and hepatic excretion T1/2 was 19.4 +/- 6.3 min. No visible blood pool and cardiac activity was seen after 5 min. The mean +/- SD time to visualization of defined biliary activity was 8.8 +/- 2.9 min. Absorption from the spleen was significantly higher than that reported for pertechnetate (87.9 +/- 8.2%, vs. 52.5 +/- 19.1%). 99mTc-mebrofenin can be used in place of pertechnetate for transsplenic portal scintigraphy, with the advantage of combining quantitative parameters of liver function with the already known advantage of transsplenic portal scintigraphy.     

QUANTITATIVE99mTc-PERTECHNETATE THYROID SCINTIGRAPHY IN NORMAL BEAGLES

This study was done to investigate the validity of published canine thyroid/salivary (TS) rations of approximately i in normal dogs and to detemine thyroid uptak of ^99mTc-pertechnetate (pertechnetate) measured as percent uptake of injected dose. These parameters were evaluated in 13 Beagle dogs over a 4 hour period. Mean ± standard deviation (SD) and median T/S ratios of 1.2 ± 0.3 and 1.1 were essentially the same at twenty minutes and 1 hour. T/S Values ranged from 0.9 to 2.2 at 20minutes and from 0.8 to 2.4 at 1 hour. T/S ratio values progressively declined over the subsequent time intervals with mean ± SD and median values of 0.6 ± 0.2 and 0.6, respectively, measured at 4 hour. The mean with a rang of 0.28% to 0.90%. The mean ± SD time interval from injection of pertechanetate to maximum uptake within the thyroid gland was 160 ± 55 minutes with a range 31–240 minutes. The data derived from this study of normal dogs may be useful in the evaluation of dogs with thyroidal diseases including hypthyroidism     

QUANTITATIVE HEPATOBILIARY SCINTIGRAPHY USING 99mTC-DISIDA IN THE DOG

Quantitative hepatobiliary scintigraphy using ^99mTc-2,6 diisopropylphenylcarbamoylmethyl iminodiacetic acid (DISIDA) was performed in normal dogs. ^99mTc-DISIDA is excreted by the hepatocyte into the biliary tract. Hepatic blood flow from arterial and portal venous sources was measured as the hepatic perfusion index. The hepatic clearance of the radiopharmaceutical was used to assess hepatocyte function and parenchymal biliary transport. Biliary ejection was evaluated using synthetic cholecystokinin infusion. The procedure should be useful in evaluating dogs with hepatic and biliary disease.     

TRANS-SPLENIC PORTAL SCINTIGRAPHY IN NORMAL DOGS

The purpose of this study was to (1) establish a technique for ultrasound-guided trans-splenic portal scintigraphy (TSPS) using 99mTcO4(-), (2) evaluate portal vein morphology, (3) compare the radiation exposures for TSPS vs. per-rectal portal scintigraphy (PRPS), and (4) compare the quality of numerical data from the TSPS vs. PRPS. Eight juvenile dogs underwent PRPS and TSPS (minimum of 48h between studies) after initial screening tests. PRPS was done according to established protocol using 425 +/- 36MBq (mean +/- SD) of 99mTcO4(-). TSPS was done with the dogs in right lateral recumbency over the gamma camera. 99mTcO4(-) (57 +/- 13.9 MBq) was injected into the spleen 1-2s following initiation of the dynamic acquisition. The frame rate was 4 frames/s for 5 min. There was significantly lower radioactivity of 99mTcO4(-) given and significantly higher total counts recorded in the liver and heart during the TSPS compared with PRPS. The total counts for the TSPS and PRPS were 7120 +/- 4386 and 830 +/- 523, respectively. Percent absorption from the spleen was 52.5 +/- 19.1% compared with 9.2 +/- 5.7% for the colon. Calculated transit time for the TSPS studies was 7 +/- 2.3s. In TSPS studies, the splenic and portal veins were clearly identified. Radiation exposure levels of the dogs were significantly lower following TSPS than after PRPS. TSPS appears superior to PRPS as a method to image the portal venous system representing a valid alternative diagnostic test for animals with suspected portosystemic shunts.     

EVALUATION OF LYMPHOMA IN A CAT USING 99mTc-SESTAMIBI

This report describes the evaluation of cutaneous lymphoma in a cat using 99mTc-sestamibi. A mass in the left pes with extension to the left popliteal lymph node was diagnosed as B-cell lymphoma. Thoracic and abdominal radiography and abdominal ultrasound were unremarkable. Scintigraphy using 99mTc-sestamibi confirmed the lesion was confined to the left hind leg, and the leg was amputated. The cat made a full recovery.     

CLINICAL USE OF 99mTC-MDP SCINTIGRAPHY IN THE EQUINE MANDIBLE AND MAXILLA

^99mTc-methylene diphosphonate (MDP) radionuclide imaging examinations were done in four horses having clinical evidence of skull trauma or infection. Radiographs were made of each horse prior to scintigraphy. Four case histories are presented. In each instance, scintigraphy provided complementary information to that obtainable through radiography, which aided in accurately localizing and characterizing the site and extent of abnormalities, and which proved particularly valuable as an aid for therapeutic planning.     

DIURETIC RENAL SCINTIGRAPHY IN NORMAL CATS

The purpose of this study was to develop a protocol for diuretic renal scintigraphy (renography) in cats and describe normal findings. ^99mTc‐DTPA renal scintigraphy was performed twice in 10 healthy cats. Furosemide or saline were injected 4.5 min after radiopharmaceutical administration for the diuretic or control scan, respectively. A dynamic acquisition was performed for 8 min. The following parameters were evaluated: (1) global and individual glomerular filtration rate (GFR); (2) shape of the time–activity curve (TAC); (3) time of peak (TOP); (4) individual kidney excretion half‐time (T_1/2) of the radiopharmaceutical; (5) percentage of maximum activity measured at the end of the study. Global GFR in the control studies (2.79±0.83 ml/min/kg, mean±SD) did not differ significantly from the diuretic scans (2.34±0.51 ml/min/kg). The shape of most (16/20) TAC of diuretic renograms was similar to those of control renograms. The TOP of the diuretic renogram curves was 3.06±0.58 min, and did not differ from that of the control scans (3.01±0.61 min). T_1/2 of the diuretic renograms was significantly shorter (5.15±0.83 min) than that of the control renograms (6.31±1.50 min). A significantly lower percentage of maximum activity was present at the end of the study in diuretic renograms (median: 47.25%; range: 33.60–59.60%) compared with control renograms (63.40%; 30.00–69.40%). Diuretic renal scintigraphy is a noninvasive and fast procedure to perform in cats. The applicability of this technique needs to be investigated in patients with significantly impaired renal function and obstructive uropathies.     

EFFECTS OF ACEPROMAZINE ON THREE-PHASE 99mTc-MDP BONE IMAGING IN 11 HORSES

Horses undergoing skeletal scintigraphy can have decreased radiopharmaceutical bone uptake in the limbs. This reduces the diagnostic value of the scan. The aim of the present study was to measure the changes in count density caused by vasodilatation and increased blood flow associated with intravenous injection of acepromazine during bone scintigraphy in normal horses. A three-phase bone scan was performed twice in 11 adult horses to study the effects of acepromazine on the count density of the resultant scintigrams. With acepromazine, there was a statistically significant mean difference of 12 s for initial blood flow and 21 s for peak flow. The time to initial blood flow and time to peak flow occurred earlier for the scans in which acepromazine was used. There were no significant differences in the bone to soft tissue ratios during the soft tissue and bone phases of the scan between procedures. Intravenous administration of acepromazine increases peripheral blood flow causing an earlier onset of the vascular phase during the three-phase bone scan. Acepromazine did not increase the count density of the bone phase scintigrams. As expected, the vasodilatation and increased blood flow associated with intravenous injection of acepromazine affected the count density of the vascular phase of the bone scan.     

ULTRASONOGRAPHIC EXAMINATION OF THE THYROID GLAND OF HYPERTHYROID CATS: COMPARISON TO 99mTcO−4 SCINTIGRAPHY

High-resolution ultrasonography was evaluated as an alternative to ^99mTcO^-₄ scintigraphy for examining size and appearance of thyroid glands in hyperthyroid cats. Thyroid ultrasound examinations were performed on 6 normal cats and 14 cats with hyperthyroidism. Thyroid lobe volume was estimated from ultrasound images using the equation for a prolate ellipsoid, π/6 (length * height * width). Total thyroid volume was estimated by adding the volume estimations of the left and right lobes. Thyroid lobes of hyperthyroid cats were considered abnormal if estimated volume exceeded the 99% confidence interval for normal thyroid volume determined from the control group. Scintigraphic examinations performed on hyperthyroid cats were evaluated for unilateral versus bilateral disease and for the presence of ectopic activity. Mean thyroid lobe volume and total thyroid volume for normal cats was 85 and 169 mm³, respectively. Mean thyroid lobe volume and total thyroid volume for hyperthyroid cats was 578 and 889 mm³. There was a significant difference in mean estimated total thyroid volume of normal and hyperthyroid cats. Thyroid lobes with greater than normal TcO^-₄ uptake on scintigraphy were larger and had variable homogeneity, echogenicity, and margination on ultrasound examination. There also was an 85.7% agreement of scintigraphy and ultrasonography in differentiating normal from abnormal thyroid lobes. A fair correlation between estimated total thyroid volume of hyperthyroid cats and most recent pretherapy serum thyroxine values were also found. This preliminary study indicates that thyroid ultrasound examination may provide information that is useful for diagnosis and treatment of feline hyperthyroidism. Although ultrasound provides accurate evaluation of the thyroid glands, it cannot replace ^99mTcO^-₄ scintigraphy for screening of metastatic lesions and ectopic glands.     

THE NON-CARDIAC DISTRIBUTION OF 99mTC-METHOXY-ISOBUTYL-ISONITRILE (SESTAMIBI) IN NORMAL BEAGLES

Technetium-99m methoxy-isobutyl-isonitrile (sestamibi) is a radiophartnaceutical used for the evaluation of myocardial perfusion. Increased uptake of sestamibi has also been documented in tumors. The objective of this study was to document the extracardiac biodistribution of ^99mTc sestamibi in the normal dog. Nine normal beagles were given 0.35 mCi/kg ^99mTc sestamibi intravenously, and 60 second images were made of the entire body at 1 hour post injection. A defined distribution pattern was recognized, with good visualization of the heart, liver, gallbladder, small intestine, kidneys, urinary bladder, popliteal lymph nodes, parotid salivary glands and zygomatic salivary glands. Splenic uptake was not seen.
Target to background ratios were calculated for all the regions listed, using background regions-of-interest with the smallest coefficient of variance for the denominator. The mean, range and standard deviation of these ratios are given.     

PRELIMINARY EVALUATION OF 99mTECHNETIUM DIETHYLENETRIAMINE PENTAACETIC ACID, 99mTECHNETIUM DIMERCAPTOSUCCINIC ACID, AND 99mTECHNETIUM MERCAPTOACETYLTRIGLYCINE FOR RENAL SCINTIGRAPHY IN CORN SNAKES (ELAPHE GUTTATA GUTTATA)

The efficacy of three radiopharmaceuticals, 99mTc-diethylenetriaminepentaacetic acid (99mTc-DTPA), 99mTc-dimercaptosuccinic acid (99mTc-DMSA), and 99mTc-mercaptoacetyltriglycine (99mTc-MAG3), for renal imaging was examined in 16 corn snakes (Elaphe guttata guttata). All snakes received the radiopharmaceutical via an intracardiac injection. The kidneys could not be visualized in the three snakes that received 99mTc-DTPA or in the three snakes that received 99mTc-DMSA, but were well delineated in all 10 snakes receiving 99mTc-MAG3. These snakes were anesthetized and a dynamic frame mode acquisition was obtained for 30 min immediately following injection. A 60 s single static frame mode image was then obtained with the snake in a curled position. Two of the 10 snakes that received 99mTc-MAG3 were removed from further analysis because of suspected pericardial injections. Of the remaining eight snakes, the mean (+/- SD) renal uptake was 25 +/- 9.8% or 24 +/- 9.7%, with or without correction for residual injection site activity, respectively. Correction for remaining radioactivity in the heart does not appear to be necessary if it is less than 10% of the total dose. 99mTc-MAG3 provided consistently high quality images of the kidneys and further studies are warranted to evaluate its sensitivity for detecting decreased function in snakes with renal disease.     

QUANTITATIVE HEPATOBILIARY SCINTIGRAPHY IN NORMAL CATS AND IN CATS WITH EXPERIMENTAL CHOLANGIOHEPATITIS

Quantitative hepatobiliary scintigraphy using 99mTc-mebrofenin was performed on eight normal cats and on the same cats after induction of experimental cholangiohepatitis by infection with the liver fluke Platynosomum concinnum. Hepatobiliary scintigraphy was performed 3 times at 10 weeks, 4 months and 6 months after infection. In addition, routine biochemical tests, hepatic ultrasound and ultrasound guided hepatic biopsy samples were obtained at the same time points, and the results compared with hepatobiliary scintigraphy. The normal hepatic extraction fraction was determined to be 85%, and the normal hepatic excretion half time (T 1/2) was 14 minutes. There was no significant change in scintigraphic parameters compared to pre-infection values at any time following infection with the liver fluke. No correlation between scintigraphic parameters and histologic scores was found; however, significant correlation was identified between parasite burden and histologic scores 6 months following infection. Despite the presence of severe multifocal histologic abnormalities, minimal clinical, biochemical and scintigraphic derangements were identified using this model of cholangiohepatitis. Based on this study, hepatobiliary scintigraphy appears to be an insensitive test for structural hepatobiliary abnormalities. The role of hepatobiliary scintigraphy in functional hepatobiliary abnormalities of the feline liver has not been determined.     

SCINTIGRAPHIC GASTROINTESTINAL BLEEDING LOCALIZATION WITH 99mTc-LABELED RED BLOOD CELLS

Ten scintigraphic gastrointestinal bleeding localization examinations were done in nine dogs. All dogs had clinical evidence of gastrointestinal bleeding prior to or on the day of the examination. Scintigraphy was done by in vivo labeling of red blood cells with ^99mTechnetium and imaging serially with a gamma camera over a 21-hour period. Of the nine dogs, four case history reports are presented. Three of these dogs had positive scintigraphic examinations. One dog had a negative scan but was later shown to have been ingesting material that mimicked the appearance of melena.     

USE OF 99MTCO TRANS-SPLENIC PORTAL SCINTIGRAPHY FOR DIAGNOSIS OF PORTOSYSTEMIC SHUNTS IN 28 DOGS

Ultrasound-guided percutaneous trans-splenic portal scintigraphy (TSPS) using 99mTcO4(-) has been used to image the portal venous system in normal dogs. Compared with per-rectal portal scintigraphy, it provides higher count density, consistent nuclear venograms of the splenic and portal vein, and significantly decreased radiation exposures. This paper describes the use of TSPS for the diagnosis of portosystemic shunts in 28 dogs. TSPS was performed injecting 70 +/- 28 MBq of 99mTcO4(-) (mean +/- SD) into the splenic parenchyma with ultrasound guidance. A dynamic acquisition at a frame rate of four frames/s for 5 min was initiated after placement of the needle and approximately 2s prior to injection. All dogs had diagnoses confirmed via exploratory laparotomy or ultrasonographic identification of the shunting vessel(s). Three studies (10.7%) were nondiagnostic because of intraperitoneal rather than intrasplenic injection of the radionuclide. Three pathways were recognized on the scintigraphic images: (1) portoazygos shunts--the 99mTcO4(-) bolus traveled dorsally, running parallel to the spine and entering the heart craniodorsally; (2) single portocaval or splenocaval shunts--the 99mTcO4(-) bolus ran from the area of the portal vein/splenic vein junction in a linear fashion toward the caudal vena cava entering the heart caudally; (3) internal thoracic shunt-the 99mTcO4 bolus traveled ventrally along the thorax and abdomen entering the cranial aspect of the heart. Single and multiple shunts were easily distinguished. There were no distinguishing features between single intra and extrahepatic portocaval shunts.     

COMPARISON OF TRANSCOLONIC 123I-IODOAMPHETAMINE AND PORTAL VEIN INJECTION OF 99mTc-MACROAGGREGATED ALBUMIN SHUNT FRACTION CALCU-LATIONS IN EXPERIMENTAL DOGS WITH ACQUIRED POR-TOSYSTEMIC SHUNTS

Shunt fraction was determined using transcolonic ¹²³I-iodoamphetamine (IMP) and portal vein injection of ^99mTc-macroaggregated albumin (MAA) in a group of eight dogs with chronic cirrhosis and acquired portosystemic shunts subsequent to total common bile duct ligation. Hepatic parenchymal damage was confirmed by alterations in liver function tests and liver histology. Seven of the eight dogs developed portal hypertension and had angiographic evidence of hepatofugal portal blood flow with multiple peripheral portosystemic anastomoses. Shunt fractions determined in the seven dogs with shunts varied from 39 to 100 using IMP and 45 to 93 using MAA. The remaining dog had normal portal pressure, a normal portal angiogram, and normal IMP and MAA scintigraphic studies. There was an excellent correlation between the two methods of shunt fraction calculation (R²= 0.98) and the line of regression was not significantly different from unity (IMP = 1.09 × MAA - 0.03).     

RETROSPECTIVE ANALYSIS OF BRAIN SCINTIGRAPHY IN 116 DOGS AND CATS

We performed a retrospective study of 100 dogs and 16 cats with planar brain scintigraphy and histopathologically established diagnoses from a total of 485 studies performed from 1976 to 1992. Necropsy (112) or surgical biopsies (4) diagnoses were categorized in two ways: first as focal brain disease, diffuse brain disease or normal; second as either neoplastic, non-neoplastic or normal. A radiologist reviewed brain scintigrams and categorized the studies as focal areas of increased accumulation, diffuse or poorly localized areas of increased accumulation, or normal. We calculated for this population of 116 animals that focal brain scintigrams had 75% sensitivity and 90% specificity for any focal brain disease. The sensitivity and specificity of a focal scintigraphic lesion for a brain tumor was 72% and 82% respectively. The sensitivity and specificity of a diffuse or poorly localized scintigraphic lesion as a test for diffuse brain disease was 40% and 88% respectively.     

INDIRECT AND DIRECT DETERMINATION OF THE PORTAL VEIN PRESSURE IN NORMAL AND ABNORMAL DOGS AND NORMAL CATS1

Portal hypertension resulting in ascites and portosystemic shunts leading to hepatoencephalopathy are major clinical manifestations of hepatic circulatory disease. Diffuse liver disease impairing sinusoidal blood flow can induce portal hypertension, portosystemic shunts, or both. The liver may also be involved secondarily in posthepatic hypertension and become the site of ascitic fluid formation. Portosystemic shunts may or may not be associated with portal hypertension. Selective catheterization of the hepatic and portal veins permits one to record pressures and to outline gross and subgross vascular anomalies by injecting contrast medium. Sequential pressure recordings in the caudal vena cava, in a free and wedged hepatic vein position, in the splenic pulp, and directly in the portal vein are the bases for the differentiation of prehepatic, liver-induced, and posthepatic portal hypertension. In addition to localizing the disease process along the postcaval-portal vein axis, pressure measurements are a reliable basis for the prognosis and selection of the most appropriate therapy. In dogs with portacaval shunts, wedge hepatic vein pressure recordings assist in the detection of hepatic sinusoidal anomalies that limit blood flow and preclude surgical ablation of the shunts. The various technics and their suitability for direct and indirect portal vein pressure recording are described and evaluated. Normal portal vein pressure values in 11 dogs and two cats, using different technics, are provided. The clinical usefulness of the various technics of pressure recording and angiography was illustrated in ten dogs with ascites, hepatoencephalopathy, or both.     

LYMPH NODE UPTAKE OF 99MTc-MDP DURING BONE SCINTIGRAPHY IN DOGS

Localization of ^99mTc-MDP in lymph nodes was apparent on the three-hour bone-scan image in seven dogs. In six dogs injection or leakage of the radiopharmaceutical into the perivascular tissues was associated with subsequent uptake in an ipsilateral lymph node. In the remaining dog, ^99mTc-MDP localized in a lymph node infiltrated by metastatic osteosarcoma. This aided staging of the tumor. Possible mechanisms of ^99mTc-MDP localization in soft tissues are briefly reviewed.     

INVESTIGATION OF TWO METHODS FOR ASSESSING THYROID-LOBE ASYMMETRY DURING PERTECHNETATE SCINTIGRAPHY IN SUSPECTED HYPERTHYROID CATS

Our aim was to investigate thyroid:thyroid (T:T) ratio and visual inspection for assessing thyroid-lobe asymmetry in suspected hyperthyroid cats. Although thyroid-salivary asymmetry is a preferred test, inherent thyroid symmetry may assist image interpretation. Association was determined using a scatter plot and Spearman's rank correlation. Agreement was assessed using the kappa (K) statistic. Accuracy was assessed by sensitivity and specificity. Hyperthyroidism was diagnosed in 33/48 (69%) cats based on elevated serum total thyroxine level. Using two Wilcoxan rank-sum tests, a significant difference (P < 0.0001) was detected between cats with and without hyperthyroidism for both methods of assessing thyroid symmetry. For the 18 cats with T:T ratios < or = 1.5, there was poor correlation between the two methods (r(s) = 0.39). Using a cut-point of 1.5 for the T:T ratio, the test accurately predicted hyperthyroidism in 28/33 cats (sensitivity, 85%; 95% confidence interval (CI), 71-99%) and correctly predicted that hyperthyroidism was absent in 14/15 cats (specificity, 93%; CI, 77-100%). For visual inspection, agreement for diagnosing hyperthyroidism was excellent between methods (kappa = 0.82), within the same examiner (weighted kappa = 0.85) and between examiners (weighted kappa = 0.89). Considering cats with only definitely asymmetric thyroid lobes as positive, visual inspection accurately predicted hyperthyroidism in 28/33 cats (sensitivity, 85%; CI, 71-99%) and correctly predicted that hyperthyroidism was absent in 11/15 cats (specificity, 73%; CI, 48-99%). Thyroid-lobe asymmetry occurs more frequently in hyperthyroid than in euthyroid cats but caution should be exercised because some euthyroid cats have asymmetric thyroid glands.