A COMPARISON OF DIATRIZOATE* AND IOXAGLATE† FOR POSITIVE CONTRAST SHOULDER ARTHROGRAPHY IN DOGS

In six experimental dogs, arthrographic quality and synovial inflammatory response with shoulder arthrography comparing meglumine-sodium diatrizoate (Urovison) and the monoacidic dimer, meglumine-sodium ioxaglate (Hexabrix) was evaluated. In our study initial films were of equally high diagnostic quality for both contrast media, but delayed films significantly favored ioxaglate for diagnostic quality. The rise in white blood cells in synovial fluid samples collected 24 hours after the arthrographic procedure was significantly lower after the use of ioxaglate. Histologic examination performed 14 days after the intra-articular injection revealed no drug related lesions.     

Thyroid imaging in the dog: current status and future directions

This review describes the advantages and disadvantages of radiography, ultrasonography, and nuclear medicine in the 2 most frequent thyroid pathologies of the dog: acquired primary hypothyroidism and thyroid neoplasia. Ultrasonography and scintigraphy remain the 2 most indicated imaging modalities for these thyroid abnormalities. However, as in human medicine, computed tomography and magnetic resonance imaging also have potential indications. This is especially the case in the evaluation of the extent, local invasiveness, and local or distant metastases of thyroid neoplasia. Based on experience with different imaging modalities in people, we suggest future directions in the imaging of the canine thyroid gland.     

REGIONAL BINDING INDEX OF THE RADIOLABELED SELECTIVE 5-HT2A ANTAGONIST 123I-5-I-R91150 IN THE NORMAL CANINE BRAIN IMAGED WITH SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY

The pattern of the specific 5-HT2A (5-hydroxytryptamine 2A receptor) antagonist 123I-5-I-R91150 was measured in 10 healthy dogs without neurologic and behavior abnormalities. Eight cortical regions (left and right fronto-, temporo-, parieto-, and occipitocortical area), one global subcortical region (including the thalamic system) were compared with a reference region lacking receptors; that is, the cerebellum. The 123I labeled radioligand was injected intravenously 100-200 minutes before acquisition. Both transmission and emission data were obtained with a triple head gamma camera equipped with high-resolution fanbeam collimators. The emission data were corrected for scatter and attenuation. To delineate different cerebral regions more accurately, the regions of interest (ROI) defined in a former study on brain perfusion measured with 99mTc-ethyl cysteinate dimer (ECD) in the same dogs were used. The co-registration of the 99mTc-ECD and the 123I-5-I-R91150, obtained from each dog, was realized with the help of corresponding transmission maps. By normalizing each regional cerebral activity to the activity observed in the cerebellum, the regional radioactivity (binding index) could be relatively quantified. Highest brain uptake was noted in the frontocortical brain areas (right: 1.85, left: 1.89), followed by the temporocortical region (right: 1.58, left: 1.56). Least uptake was noted in the more caudal and middle brain regions [occipito- (right: 1.46, left: 1.41), parietocortical (right: 1.30, left: 1.26), and striatal region (1.19)]. No gender nor age influence was noted in this series. The 123I labeled serotonin-2A receptor ligand seems to have similar cortical binding in the normal canine brain, as shown in humans and other animal species. A frontocortical to occipitocortical (rostrocaudal) binding index gradient was identified within the dog, which has not been seen in imaging studies from humans and other animal species. The significance of these results will need further investigation. This normative data can be used to compare regional brain uptake of the 123I-radioligand to dogs with behavioral disorders related to the serotonergic system, in future studies.     

AN INFECTED HIP PROSTHESIS IN A DOG DIAGNOSED WITH A 99mTC-CIPROFLOXACIN (INFECTON) SCAN

This case report describes the use of the 99mTc-labeled radiopharmaceutical ciprofloxacin (Infecton) in a case of hip prosthesis loosening in a dog. Serial planar radiographs were not conclusive, and culture of the synovial fluid was negative. Antibiotic treatment did not result in improvement of the lameness. Scintigraphy was performed with 99-Tc-Infecton, a tracer claimed to be specific for infection. Antibiotic treatment was interrupted 6 weeks prior to the examination. Planar and tomographic images at 3 h and at 24 h postinjection showed increased activity along the acetabulum and the proximal femoral bone surrounding the femoral prosthesis, indicating focal infection. Bacteriology performed after removal of the implant revealed Pseudomonas aeruginosa.     

The influence of the tracer injection–acquisition interval on the distribution of 99mTc-ECD in the brain of laboratory cats

Single-photon emission computed tomography (SPECT) can be used to study the regional distribution of the cerebral blood flow in the feline brain without interference of anesthetics. When the tracer, ^99mtechnetium-ethyl cysteinate dimer (^99mTc-ECD), is injected in the awake animal, the acquisition can be performed afterward under general anesthesia, whereas the tracer distribution still represents the regional cerebral blood flow (rCBF) in the awake animal. The aim of this study was to look at the in vivo stability of ^99mTc-ECD in the feline brain. For this purpose, 6 cats (n = 6) were used, and 3 serial acquisitions were performed starting at 40 (T40), 60 (T60), and 85 (T85) minutes after tracer injection. Total counts and perfusion indices (PIs), normalized to the total brain and to the cerebellum, were calculated. When T85 was compared with T40, total counts decreased, depending on the brain region, with 29% (left thalamus) to 51% (bulbus olfactorius). These regional differences in tracer clearance resulted in significantly altered PIs at T85 as compared with T40. This study shows that ^99mTc-ECD SPECT can be used in cats for studying the rCBF and that the clearance of ^99mTc-ECD in the feline brain is region dependent. As a result, the acquisition should be started between 40 and 60 minutes after tracer injection.     

A Single Sample Method for Evaluating 51Chromium-Ethylene Diaminic Tetraacetic Acid Clearance in Normal and Hyperthyroid Cats

Background: Chronic kidney failure is frequently seen in middle-aged and elderly cats. ⁵¹Chromium-ethylene diaminic tetraacetic acid (⁵¹Cr-EDTA) clearance and single blood sample (SBS) method are used in several species to estimate the glomerular filtration rate (GFR).
Hypothesis: The hypothesis of this study was that ⁵¹Cr-EDTA clearance could be determined using an SBS method in normal and hyperthyroid cats.
Animals: Forty-six cats were included in this study, with an average age of 9.5 years. Of these cats, 27 had hyperthyroidism; 19 were healthy.
Methods: After IV injection of ⁵¹Cr-EDTA (average dose: 4.25 MBq), 7 blood samples were obtained between 5 and 240 minutes. Reference clearance was calculated in mL/min and mL/min/kg body weight, using a 2-compartment model. Optimal time for clearance measurement with SBS was then determined by systematically comparing each individual plasma concentration to the reference multisample clearance.
Results: The average reference plasma clearance of ⁵¹Cr-EDTA for all cats was 14.9 mL/min (3.7 mL/min/kg). The clearance in hyperthyroid cats averaged 16.4 mL/min (4.3 mL/min/kg) and in normal cats averaged 10.3 mL/min (2.4 mL/min/kg).
The optimal time for the SBS was 48 minutes after injection of tracer ⁵¹Cr-EDTA ( R ²= 0.9414), giving the following converting equation: clearance = (0.0066 × DV_{48 minutes}) – 0.9277 (in mL/min).
Conclusions and Clinical Importance: In this study, the single sample ⁵¹Cr-EDTA clearance method was used to estimate the global GFR in cats. The method identified differences in clearance between normal and hyperthyroid cats. The optimal time for an SBS was 48 minutes.     

Effect of recombinant human TSH on the uptake of radioactive iodine (I) by the thyroid gland in healthy beagles

In human medicine, recombinant human thyroid-stimulating hormone (rhTSH) increases thyroid radioactive iodine uptake (RAIU), allowing radioiodine-131 (¹³¹I) dose reduction and greater efficacy in the treatment of differentiated thyroid cancer and multinodular goiter. The goal of this study was to evaluate the effect of rhTSH, administered 24 h and 48 h before radioiodine-123 (¹²³I), on the thyroid RAIU in healthy dogs. Seven healthy euthyroid beagles were randomly allocated to 3 groups (2 groups of 2 dogs and 1 group of 3 dogs) in a prospective, blinded, crossover study. At Week 1, 1 group received ¹²³I for a baseline RAIU; 1 group received 100 μg of rhTSH IV 24 h before ¹²³I, and 1 group received 100 μg of rhTSH IV 48 h before ¹²³I. All dogs received 37 MBq of radioactive ¹²³I IV, and thyroid RAIU was determined 8 h, 24 h, and 48 h thereafter. The study was designed in such a manner that each dog received the 3 treatments and a wash-out period of 3 wk was respected in between. Blood samples were taken for measurement of serum total thyroxine (TT4) and thyrotropin (TSH) concentrations at baseline and 6 h, 12 h, 24 h, and 48 h after rhTSH administration. Recombinant human TSH caused no significant change on thyroid RAIU. The overall mean thyroid RAIU significantly decreased during the study independent of the treatment. Recombinant human TSH significantly increased serum TT4 concentration, which peaked 6 h after rhTSH administration. Compared to baseline, serum TSH concentration remained higher at 6 h, 12 h, 24 h, and 48 h. However, a statistically significant difference was reached only at 6 h and 12 h after rhTSH administration. No adverse effects of rhTSH were observed during the study. Further studies are needed to determine the best timing and dosage of administration of rhTSH in healthy and thyroid carcinoma dogs.     

Neuro-imaging the serotonin 2A receptor as a valid biomarker for canine behavioural disorders

The serotonergic system is disturbed in different mood and affective disorders, with especially the serotonin (5-HT) 2A receptor involved in impulsive aggressiveness and anxiety. The aim of the study was to evaluate the involvement of the brain 5-HT 2A receptor in dogs with different behavioural disorders. Three groups of drug naive dogs were studied: 22 dogs showing impulsive aggressive behaviour, 22 showing normal behaviour, and 22 showing anxious behaviour. The serotonin 2A receptor was evaluated with Single Photon Emission Computed Tomography (SPECT) and the serotonin 2A receptor-selective radiopharmaceutical (123)I-R91150. A serotonin 2A receptor binding index (BI), proportional to the cortical receptor density, was calculated. A receiver operating characteristic (ROC) analysis was performed to determine cut-off values at which optimal sensitivity and specificity are achieved and to evaluate the general performance of the BI in reflecting the state of the dog, i.e., impulsive aggressive, normal or anxious. Significantly (P<0.0056) altered 5-HT 2A receptor binding indices were found in bilateral frontal, temporal and occipital cortical brain areas of the dogs behaving abnormally, with consistently increased BI in impulsive aggressive dogs and decreased BI in anxious dogs. These results provide clear evidence for a disturbed serotonergic balance in canine impulsive aggression and anxiety disorders. A right frontal cut-off value of ≥1.92 with 86.4% sensitivity and 2.3% (1-specificity) was obtained for the impulsive aggressive dogs. Differentiating the anxious dogs from the rest of the population was possible with a cut-off value of ≤1.73 with 86.4% sensitivity and 18.2% (1-specificity). We conclude that SPECT imaging with the radioligand (123)I-R91150 can be a helpful tool in evaluating the involvement of the serotonin 2A receptor in the complex mechanisms of impulsive aggressive and anxious behaviour. The 5HT-2A binding index of the right frontal cortex appears to be a valid biomarker in differentiating the studied canine behavioural disorders.     

The effect of medetomidine on the regional cerebral blood flow in dogs measured using Technetium-99m-Ethyl Cysteinate Dimer SPECT

Sedatives and anaesthetics are known to cause changes in the regional cerebral blood flow. In dogs intramuscular sedation with medetomidine, a potent sedative frequently used in veterinary medicine, is sometimes indicated prior to intravenous injection of ^99mTechnetium-Ethyl Cysteinate Dimer (^99mTc-ECD) in brain perfusion studies using Single Photon Emission Computed Tomography (SPECT). Based on the knowledge of the distribution of alpha₂-receptors in the brain, we hypothesized altered regional brain perfusion in dogs receiving medetomidine prior to ^99mTc-ECD. Two conditions were compared in 10 dogs; tracer injection before and after intramuscular sedation with medetomidine. In our study, medetomidine caused a significantly higher tracer uptake in all brain regions. Semi-quantification of brain perfusion rendered a lower perfusion index in the subcortical region and an imbalance between left and right cortical perfusion induced by medetomidine. This study shows that caution is needed when quantifying the brain perfusion indices under medetomidine sedation.