QUANTITATIVE HEPATOBILIARY SCINTIGRAPHY WITH DECONVOLUTIONAL ANALYSIS FOR THE MEASUREMETN OF HEPATIC FUNCTION IN DOGS

A nuclear medicine procedure that has been used for quantification of hepatocyte function in man is applied and validated in the dog. This procedure employs deconvolutional analysis of liver and heart time activity curves obtained following peripheral intravenous injection of hepatobiliary radiopharmaceutical. The deconvolutional analysis simulates a bolus injection of the radiopharmaceutical into the afferent blood supple of the liver which permits the calculation of the hepatic extraction fraction. Hepatic extraction fraction is a measure of hepatocyte function. In this report, the deconvolutional analysis via fast Fourier transformations and subsequent calculation of hepatic extraction fraction is validated by direct afferent intravascular ijection of ^99mTc-mebrofenin. The hepatic extraction fraction determined via deconvolutional analysis was found to be the same as the first pass hepatic extraction fraction determined via deconvolutional analysis was found to be the same as the first pass hepatic extraction fraction determined by direct mesenteric (portal) vein injection. The same results can be obtained in a sedated animal, making the technique clinically applicable. Thus hepatic extraction fraction, obtained from a perlpheral intravenous injection of ^99mTc-mebrofenin, can provide a quatitative measure of hepatocyte function from a non-invasive procedure. The quantitative ability to measure hepatocyte function has potential in many clinical and research situations.     

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.     

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).     

IN VITRO EVALUATION OF CANINE GRANULOCYTES LABELED WITH 99mTC-HEXAMETHYLPROPYLENEAMINE OXIME:

Technetium-99m hexamethylpropyleneamine oxine (^99mTc-HMPAO) and Indium-111 oxine (¹¹¹In-oxine) labeled canine gramulocytes were evaluated in vitro over a six hour period. Labeling efficiency for ^99mTC-HMPAO and ¹¹¹In-oxine labeled granulocytes was 39.6%± 8.0% and 60.6%± 17.6% (mean ± SD) respectively. The mean in vitro elution of the radiolabel ranged from 8.7-14.0% for the ^99mTc-HMPAO grannulocytes and from 6.1-9.0% for the ¹¹¹In-oxine granulocytes. Mean cell viability, for the ^99mTc-HMPAO, ¹¹¹In-oxine and non-radiolabeled control granulocytes ranged from 97.8-99.4%, 96.4-98.5% and 98.2-99.0%, respectively. The phagocytic ability of the ^99mTc-HMPAO, ¹¹¹In-oxine and control granulocytes ranged from 47.5-54.1%, 38.9-56.2% and 46.6-57.8% respectively over the six hour study period. Although labeling efficiency using ¹¹¹In-oxine was significantly (P=0.05) better than ^99mTc-HMPAO, there was no significant difference in label retention of the two radiolabels. There was no significant difference in viability or phagocytic function during the six hour study period. Considering the potential cost advantage and the superior imaging qualities of Technetium-99m relative to Indium-111, ^99mTc-HMPAO appears to be a good alternative to ¹¹¹In-oxine as a granulocyte label.     

THE INSENSITIVITY OF 99mTc PERTECHNETATE FOR DETECTING METASTASES OF A FUNCTIONAL THYROID CARCINOMA IN A DOG

This report describes the use of ^99mtechnetium pertechnetate (^99mTcO₄⁻) and ¹³¹[for imaging of a metastatic thyroid carcinoma in a dog. The ¹³¹] imaging showed metastatic lesions undetected by the ^99mTcO₄⁻ imaging on 2 separate occasions. The possible mechanisms for the discrepancies between ¹³¹I and ^99mTcO₄⁻ imaging of thyroid carcinomas are discussed. The use of ¹³¹I for the imaging of functional thyroid carcinomas in the dog is recommended.     

IN-VIVO TESTING OF TECHNETIUM-99m-LABELED MONOCLONAL ANTIBODIES SPECIFIC FOR DIROFILARIA IMMITIS

Monoclonal antibodies specific for Dirofilaria immitis were labeled with technetium-99m (^99mTc) and tested in vivo in five heartworm positive and five heartworm negative dogs. Diethlyenetriaminepentaactic acid (DTPA) was used to label the ^99mTc to the antibody. Radiochemical purity of the ^99mTc-labeled antibodies (^99mTc-MoAb) was determined by gel filtration and by instant thin-layer chromatography. The uptake percentages in the blood, heart, lung, liver, and kidneys were determined from tissues obtained at necropsy and by computer analysis of images obtained at two and 24 hours. The percent uptake in the heart region of interest (ROI) at two hours was significantly higher in the heartworm-positive dogs. There was significant correlation between the uptake in the heart at two hours to the number and activity of the worms at necropsy.     

Biliary excretion of technetium-99m-sestamibi in wild-type dogs and in dogs with intrinsic (ABCB1-1Δ mutation) and extrinsic (ketoconazole treated) P-glycoprotein deficiency

P-glycoprotein (P-gp), the product of ABCB1 gene, is thought to play a role in the biliary excretion of a variety of drugs, but specific studies in dogs have not been performed. Because a number of endogenous (ABCB1 polymorphisms) and exogenous (pharmacological P-gp inhibition) factors can interfere with normal P-gp function, a better understanding of P-gp's role in biliary drug excretion is crucial in preventing adverse drug reactions and drug–drug interactions in dogs. The objectives of this study were to compare biliary excretion of technetium-99m-sestamibi (^99mTc-MIBI), a radio-labelled P-gp substrate, in wild-type dogs (ABCB1 wild/wild), and dogs with intrinsic and extrinsic deficiencies in P-gp function. Dogs with intrinsic P-gp deficiency included ABCB1 mut/mut dogs, and dogs with presumed intermediate P-gp phenotype (ABCB1 mut/wild). Dogs with extrinsic P-gp deficiency were considered to be ABCB1 wild/wild dogs treated with the P-gp inhibitor ketoconazole (5 mg/kg PO q12h × 9 doses). Results from this study indicate that ABCB1 mut/mut dogs have significantly decreased biliary excretion of ^99mTc-MIBI compared with ABCB1 wild/wild dogs. Treatment with ketoconazole significantly decreased biliary excretion of ^99mTc-MIBI in ABCB1 wild/wild dogs. P-gp appears to play an important role in the biliary excretion of ^99mTc-MIBI in dogs. It is likely that concurrent administration of a P-gp inhibitor such as ketoconazole will decrease P-gp-mediated biliary excretion of other substrate drugs as well.     

COMPARISON BETWEEN THE SCINTIGRAPHIC UPTAKE AND PLASMA CLEARANCE OF 99mTc-DIETHYLENETRIAMINEPENTACETIC ACID (DTPA) FOR THE EVALUATION OF THE GLOMERULAR FILTRATION RATE IN DOGS

The scintigraphically measured percentage dose uptake of ^99mTc-DTPA by the kidneys and the plasma clearance of ^99mTc-DTPA have been reported to correlate well with inulin clearance. These two parameters were evaluated in seven dogs with known or suspected naturally occurring renal disease and compared to simultaneously measured renal inulin clearance. Correlation between inulin clearance and the ^99mTc-DTPA plasma clearance was better ( p =.0016) than the correlation between the percentage DTPA uptake by the kidney. It was concluded that measurement of ^99mTc-DTPA plasma clearance is a more accurate method to estimate global glomerular filtration rate (GFR) than the percentage kidney uptake.     

EVALUATION OF HEART TIME-ACTIVITY CURVES AS A PREDICTOR OF HEPATIC EXTRACTION OF 99mTc-MEBROFENIN IN DOGS

In this study, heart time-activity curve, created following intravenous injection of 99mTc-mebrofenin were used to quantify hepatic function in normal dogs and dogs with induced hepatic parenchymal cell damage. The results were compared to a direct measurement of hepatic extraction following mesenteric venous injection of 99mTc-mebrofenin. The heart time-activity curves were normalized and the area under the curve from 0-30 minutes and 0-60 minutes were determined. In addition, the half-time clearance rate of the heart time-activity curve was analyzed using a two-compartment model. Linear regression analysis was used to describe the relationship between the area under the normalized heart time-activity curve and hepatic extraction. There was good correlation between the area under the normalized heart time-activity curve and hepatic extraction. The best correlation was obtained from the 0-30 minute data (r2 = 0.92). A formula for calculating hepatic extraction was derived using linear regression analysis: Hepatic extraction = 1.092 - (0.0000308 x AUC0-30 minutes). There was good correlation between the half-time clearance rates from the heart time-activity curve and hepatic extraction. The best correlation was between the fast phase half-time clearance and hepatic extraction (r2 = 0.88). The area under a normalized heart time-activity curve can be used as a simple alternative to deconvolutional analysis for the determination of hepatic extraction as a measure of hepatic parenchymal cell function in the dog.     

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.     

THE USE OF99mTc RADIOAEROSOL VENTILATION AND MACROAGGREGATED ALBUMIN PERFUSION IMAGING FOR THE DETECTION OF PULMONARY EMBOLI IN THE DOG

This study was undertaken to design protocol for use of radioaerosol of technetium-99m-labeled diethylenetriaminepentacetic acid (^99mTc-DTPA) for ventilation imaging as clinical tool in the dog and to evaluate imaging characteristics in both normal dogs and dogs with simulated pulmonary embolism. Clearance of the 99mTc-DTPA radioaerosol from the lung was also evaluated. Six normal dogs were used in two phases: (1) as their own controls and (2) during pulmonary artery occlusion using Swan-Ganz catheter. Radioaerosol ventilation images were obtained and rate of clearance from normal and occluded lungs determined. Perfusion studies using technetium-99m-macroaggregated albumin (^99mTc-MAA) immediately followed. Clearance half-times (T_1/2) were found to be significantly increased (p < 0.05) in acutely occluded lungs; however, the small magnitude of this change was visually difficult to detect on the ventilation images. Good quality initial ventilation and perfusion images were obtained and provided ready evaluation of ventilation (V), perfusion (Q), and induced V/Q mismatches. A clinical case of pulmonary thromboembolic disease was also evaluated with diagnostic result, indicating that this method of V/Q scintigraphy can provide useful information in those clinical cases in which pulmonary thromboembolism is suspected.     

Frequency of pulmonary mineralization and hypoxemia in 21 dogs with pituitary-dependent hyperadrenocorticism

The purpose of this study was to determine the frequency of hypoxemia and pulmonary mineralization using ^99mTc-methylene diphosphonate (^99mTc-MDP) in dogs with pituitary-dependent hyperadrenocorticism (PDH). Twenty-one dogs with PDH were pro-spectively evaluated using thoracic radiography, arterial blood gas analysis, and bone phase and pulmonary perfusion scintigraphy (using ^99mTc-macro-aggregated albumin [^99mTc-MAA]). The radiographs and bone and perfusion studies were evaluated subjectively. An averaged quantitative count density ratio was calculated between the thorax and cranial thoraco-lumbar vertebrae from lateral thoracic ^99mTc-MDP images. Thoracic: vertebral ratios were calculated using ^99mTc-MDP studies from 21 control dogs. The thoracic: vertebral ratios were compared between the 2 groups (PDH and control). The mean age (±SD) of the 21 PDH dogs was 10.2 (±3) years, whereas the mean age of the control group was 9.8 (±3) years. Seven of the 21 dogs with PDH were hypoxemic (denned as an arterial partial pressure of oxygen [PaO₂] <80 mm Hg) with an average PaO₂ (±SD) of 62 (±15) mm Hg. Of the 7 hypoxemic dogs, 2 were found to have pulmonary mineralization based on bone scintigraphic images. Pulmonary perfusion abnormalities were not identified using ^99mTc-MAA in any of the 21 PDH dogs. Six PDH dogs had an abnormal interstitial pulmonary pattern and 5 of these dogs were hypoxemic. The average quantitative thoracic: vertebral ratio was not significantly different between the PDH and control dogs (0.5 ± 0.4 versus 0.4 ± 0.1, P = .16). Causes of hypoxemia other than pulmonary thromboembolism should be considered in dogs with PDH. Pulmonary mineralization may contribute to hypoxemia in dogs with PDH.     

99mTc-METHOXY-ISOBUTYL-ISONITRILE (SESTAMIBI) IMAGING OF MALIGNANT CANINE LYMPHOMA

Technetium-99m methoxy-isobutyl-isonitrile (sestamibi) imaging of malignant canine lymphoma was performed in thirteen dogs 1 hour after intravenous injection of ^99mTc-sestamibi at 13 MBq (0.35 mCi) per kilogram body weight. Abnormal tracer uptake was visualized in the liver, spleen, bone marrow, and mesenteric, inguinal, popliteal, sternal, cranial cervical and mandibular lymph nodes. Radiopharmaceutical uptake was also noted in a nasal mass. One large neoplastic renal mass did not have demonstrable sestamibi uptake. Other regions had no significant difference in the target:background ratios when compared with values from normal dogs ( P > 0.05). ^99mTc-sestamibi can be used to image malignant lymphoma, and has potential applications in the management of patients to document response to treatment and to stage of extent of disease.     

QUANTITATIVE THYROID SCINTIGRAPHY IN GREYHOUNDS SUSPECTED OF PRIMARY HYPOTHYROIDISM

The existence of hypothyroidism in greyhounds remains controversial and its investigation is complicated by the low circulating thyroid hormone concentrations typically found in healthy dogs of this breed. Quantitative measurement of thyroidal technetium-99m pertechnetate (^99mTcO₄⁻) uptake is known to be useful in assessing thyroid function in other breeds. The aim of this study was to evaluate thyroid scintigraphy as a method of assessing thyroid function in greyhounds suspected of primary hypothyroidism. Twenty greyhounds (eight females, 12 males) were studied. Thirteen had bald thigh syndrome and seven poor performance and low total T4. Total T4 concentrations were decreased in 18 (90%), and free T4 in two (10%) dogs. All canine thyroid stimulating hormone concentrations were within the reference interval. Thyroidal ^99mTcO₄⁻ uptake values (mean ± SD, 0.76 ± 0.26%) were within the reference limits published for euthyroid dogs (0.39–1.86%) making hypothyroidism highly unlikely. There were no significant differences ( P <0.05) when comparing data between dogs with bald thigh syndrome (13 dogs) and the remaining dogs (seven dogs). Seventeen (85%) dogs had higher uptake in the left thyroid gland than in the right that might reflect an anatomic feature of the greyhound breed. Calculation of percent thyroidal uptake of ^99mTcO₄⁻ is more accurate than thyroid:salivary gland ratios because of high variability in salivary gland uptake. Percent thyroidal uptake of ^99mTcO₄⁻ should be used when assessing thyroid function scintigraphically in the greyhound breed.     

TECHNETIUM-99M AND IODINE-131 THYROID SCINTIGRAPHY IN NORMAL AND RADIOTHYROIDECTOMIZED COCKATIELS (NYMPHICUS HOLLANDICUS)

Thyroid scintigraphy using sodium ^99mTechnetium pertechnetate (⁹⁹TcO₄-) was performed in normal and radiothyroidectomized cockatiels ( Nymphicus hollandicus ). ¹³¹I scintigraphy was performed in the course of ablating the thyroid glands. The thyroid glands in normal birds were clearly visualized, but were not individually resolvable. Thyroid glands were not visualized in thyroid-ablated birds. With ^99mTcO₄ scans, thyroid (or other region of interest)/body count density ratios were used for comparisons of normal and thyroid-ablated birds. Normal ^99mTcO₄- thyroid/body ratios (mean +/− SD) for the dorsal and lateral views were 1.83 +/− 0.31 and 1.70 +/− 0.34 respectively. Pertechnetate thyroid/body count density ratios decreased (to 0.93 -/−0.14 and 0.88 +/− 0.12 for dorsal and lateral views respectively) after thyroid ablation, while crop/body ratios increased. ^99mTcO₄- thyroid scintigraphy, therefore, was capable of detecting hypofunctional thyroid abnormalities in ¹³¹I radiothyroidectomized cockatiels.     

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.     

CANINE VENTRAL BODY WALL LYMPHOSCINTIGRAPHY

The scintigraphic characteristics of lymph nodes draining the ventral body wall were analyzed in 12 dogs as to their pattern of appearance and image contrast. Each dog was scanned using ^99mTc-antimony sulfide colloid and ^99mTc-dextran, and the imaging characteristics of these agents were compared. A large degree of variability exists in the number and pattern of lymph node appearance with either agent. No significant difference in average numbers of lymph nodes per dog was shown between agents. However, ^99mTc-antimony sulfide colloid provided a significantly (p<.05) better target-to-background ratio, which determines the contrast with which lymph nodes stand out from background activity. From these findings, it is suggested that too great a variability in lymph node appearance exists using this procedure to allow a high degree of confidence in the diagnosis of metastasis to lymph nodes of the ventral body wall. However, for other purposes, ^99mTc-antimony sulfide colloid is the lymphoscintigraphic agent of choice.     

SCINTIGRAPHIC MEASUREMENT OF UTERINE CLEARANCE IN MARES

Uterine clearance of technetium 99m-albumin colloid (^99mTc-μAA) was qualitatively and quantitatively measured in 5 reproductively normal mares and 5 mares susceptible to endometritis (infertile). The percentage of 370 MBq ^99mTc-μAA cleared from the uterine lumen within 2 hr of intrauterine infusion was measured in 10 mares on day 3 of estrus and 48 hr after ovulation. The procedure was repeated 3 times on day 3 of estrus in 6 mares to determine repeatability. Six mares were infused with 1110 MBq ^99mTc-μAA on day 3 of estrus to evaluate the effect of increasing the dose to reduce the imaging time. There was no statistically significant difference in the mean percentage of radiocolloid cleared from the uterus during day 3 of estrus or 48 hr after ovulation or in the percent cleared when the studies were repeated in individual mares. There was no statistically significant difference in uterine clearance between the 370 and 1110 MBq dose studies in each mare from 15 to 120 min. Reproductively normal mares cleared approximately 50% of the radiocolloid from the uterus by 120 min while susceptible mares cleared less than 15%.     

QUALITATIVE AND QUANTITATIVE THYROID IMAGING IN FELINE HYPERTHYROIDISM USING TECHNETIUM-99M AS PERTECHNETATE

Thyroid imaging using technetium-99m as pertechnetate (^99mTcO₄) was carried out in five healthy, euthyroid and 37 hyperthyroid cats using both pinhole and parallel-hole collimators. Images of greater resolution, necessary to distinguish bilateral lobe involvement, were obtained using the pinhole collimator. Per cent thyriod ^99mTcO₄ - uptake was calculated in each cat and was significanly (P < 0.001) higher in hyperthyroid compared with euthyroid cats. In the hyperthyroid cats, per cent thyroid uptake was significantly correlated with serum total thyroxine (T4) and triiodothyronine (T3) Concentrations. Per cent thyroid ^99mTcO₄ - uptake is increased in feline hyperthyrodism and may be calculated using a pinhole collimator alone at the time of qalitative assessment of the extent of thyroid tissue involvement.     

EVALUATION OF HEPATOBILIARY SCINTIGRAPHY AS AN INDICATOR OF HEPATIC FUNCTION IN DOMESTIC PIGEONS (COLUMBA LIVIA) BEFORE AND AFTER EXPOSURE TO ETHYLENE GLYCOL

This study investigated the use of quantitative hepatobiliary scintigraphy to assess liver function in 14 white Carneaux pigeons (Columba livia). Liver scintigraphy using 99mTc-mebrofenin was performed and liver function was quantified using deconvolutional analysis and the area under the normalized heart time-activity curve as previously described in the dog and horse. Liver biopsies were performed in all birds before and after toxin-induced liver damage with ethylene glycol. Before the induction of liver disease, all biopsy specimens showed varying degrees of granulomatous inflammation. After ethylene glycol administration, hepatic lesions were scored and compared with scintigraphic findings. Scintigraphic results showed a significant decrease (P = 0.04) in hepatic function using the area under the normalized time-activity curve. There was good correlation between the overall histologic score posttoxin exposure and scintigraphic measures of liver function (P < 0.03). Based upon these preliminary results, the area under the heart time-activity curve can determine hepatic extraction as a measure of hepatic parenchymal cell function. The results also showed that worsening hepatic cellular function correlated with increased histologic damage to the liver. The use of hepatobiliary scintigraphy using 99mTc-mebrofenin to determine liver function in pigeons has not been previously reported. Additional studies are warranted to evaluate the application of this technique in clinical patients and to establish the sensitivity of this technique.