Search

Dogs can be used as research models in order to contribute to a better understanding of human neuropsychiatric disorders and to explore treatment options. In general, smaller laboratory animals, most often mice and rats, have been extensively used. Nevertheless, the implementation of larger animal (e.g. dogs) models has several important advantages. Their larger brain size omits the need for dedicated equipment (micro-PET or micro-SPECT), and the larger portion of the frontal cortex (crucial to behaviour regulation) in particular allows superior investigation of this area. They can further be used to investigate normal physiology and interaction of several neurotransmitter systems and the effects of drugs on brain function and chemistry. In this regard, they can also be used to obtain information on the pharmacokinetics and pharmacodynamics of newly developed drugs and the dosage at which maximal response and least side effects occur. Finally, natural animal behavioural models of disorders can be used to enlighten the biological base of several human neuropsychiatric disorders. In this chapter, an overview will be provided on the use of functional brain imaging in dogs suffering from impulsive aggression.

BackgroundCurrently, [18F] altanserin is the most frequently used PET-radioligand for serotonin2A(5-HT2A) receptor imaging in the human brain but has never been validated in dogs. In vivo imaging of this receptor in the canine brain could improve diagnosis and therapy of several behavioural disorders in dogs. Furthermore, since dogs are considered as a valuable animal model for human psychiatric disorders, the ability to image this receptor in dogs could help to increase our understanding of the pathophysiology of these diseases. Therefore, five healthy laboratory beagles underwent a 90-min dynamic PET scan with arterial blood sampling after [18F] altanserin bolus injection. Compartmental modelling using metabolite corrected arterial input functions was compared with reference tissue modelling with the cerebellum as reference region.ResultsThe distribution of [18F] altanserin in the canine brain corresponded well to the distribution of 5-HT2Areceptors in human and rodent studies. The kinetics could be best described by a 2-Tissue compartment (2-TC) model. All reference tissue models were highly correlated with the 2-TC model, indicating compartmental modelling can be replaced by reference tissue models to avoid arterial blood sampling.ConclusionsThis study demonstrates that [18F] altanserin PET is a reliable tool to visualize and quantify the 5-HT2Areceptor in the canine brain.

Numerous studies have shown that the serotonin(1A) (5-HT1A) receptor is implicated in the pathophysiology and treatment of several psychiatric and neurological disorders. Furthermore, functional imaging studies in a variety of species have demonstrated that 4-(2'-Methoxyphenyl)-1-[2'-(N-2 ''-pyridinyl)-p-[F-18]fluorobenzamidoethylpiperazine ([F-18]MPPF) is a valid and useful PET tracer to visualize the 5HT(1A) receptor. However, to our knowledge, [F-18] MPPF has never been demonstrated in the canine brain. The ability to image the 5HT(1A) receptor with PET in dogs could improve diagnosis and therapy in both canine and human behavioural and neuropsychiatric disorders. To examine the potential use of [F-18]MPPF in dogs, five healthy adult laboratory beagles underwent a 60-minutes dynamic PET scan with [F-18]MPPF while arterial blood samples were taken. For each region of interest, total distribution volume (V-T) and corresponding binding potential (BPND) were calculated using the 1-tissue compartment model (1-TC), 2-Tissue compartment model (2-TC) and Logan plot. The preferred model was chosen based on the goodness-of-fit, calculated with the Akaike information criterium (AIC). Subsequently, the BPND values of the preferred compartment model were compared with the estimated BPND values using three reference tissue models (RTMs): the 2-step simplified reference tissue model (SRTM2), the 2-parameter multilinear reference tissue model (MRTM2) and the Logan reference tissue model. According to the lower AIC values of the 2-TC model compared to the 1-TC in all ROIs, the 2-TC model showed a better fit. Calculating BPND using reference tissue modelling demonstrated high correlation with the BPND obtained by metabolite corrected plasma input 2-TC. This first-indog study indicates the results of a bolus injection with [F-18] MPPF in dogs are consistent with the observations presented in the literature for other animal species and humans. Furthermore, for future experiments, compartmental modelling using invasive blood sampling could be replaced by RTMs, using the cerebellum as reference region.

Radioiodine therapy is commonly used in hyperthyroid cats and has a high success rate, ranging from 85–95%. As in humans, thyroid volume has been reported to influence radioiodine therapy outcome in hyperthyroid cats. The purpose of this study was to relate total thyroid volume, calculated by a newly constructed formula for feline patients (0.438 × length × width²), to the outcome of radioiodine therapy. To search for a correlation between total thyroid volume and therapy outcome, 167 hyperthyroid cats were included. Patients were categorised according to the administered radioiodine dose and therapy outcome. Our analysis did not show a significant relationship between an increasing total thyroid volume and the odds for a final low total thyroxine concentration (TT4; P = 0.3930) or a final hyperthyroid outcome ( P = 0.0901). A significant relationship was found for an increase in the odds for a final low TT4 outcome with an increase in the number of foci detected on the pertechnetate thyroid scan ( P = 0.0238). This was not true for a final hyperthyroid outcome ( P = 0.7435). The number of detected foci was also significantly associated with the total thyroid volume ( P = 0.0006). Findings indicated that the presence of multiple affected foci influences therapy outcome towards a low TT4 outcome. Bilateral hyperthyroidism and its potential effect on a final low TT4 outcome should therefore be addressed when informing owners of the possible outcomes of radioiodine therapy for their cat.

Although the favourable characteristics of escitalopram as being the most selective serotonin reuptake inhibitor and having an increased therapeutic efficacy via binding on an additional allosteric binding site of the serotonin transporter, its dosing regimen has not yet been optimized for its use in dogs. This study aimed to estimate the optimal dosing frequency and the required dose for achieving 80% occupancy of the serotonin transporters in the basal ganglia. The dosing frequency was investigated by determining the elimination half-life after a four day oral pre-treatment period with 0.83 mg/kg escitalopram (3 administrations/day) and a subsequent i. v. injection 0.83 mg/ kg. Blood samples were taken up to 12 hours after i. v. injection and the concentration of escitalopram in plasma was analysed via LC-MSMS. The dose-occupancy relationship was then determined by performing two PET scans in five adult beagles: a baseline PET scan and a second scan after steady state conditions were achieved following oral treatment with a specific dose of escitalopram ranging from 0.5 to 2.5 mg/kg/day. As the elimination half-life was determined to be 6.7 hours a dosing frequency of three administrations a day was proposed for the second part of the study. Further it was opted for a treatment period of four days, which well exceeded the minimum period to achieve steady state conditions. The optimal dosing regimen to achieve 80% occupancy in the basal ganglia and elicit a therapeutic effect, was calculated to be 1.85 mg/kg/day, divided over three administrations. Under several circumstances, such as insufficient response to other SSRIs, concurrent drug intake or in research studies focused on SERT, the use of escitalopram can be preferred over the use of the already for veterinary use registered fluoxetine, however, in case of long-term treatment with escitalopram, regularly cardiac screening is recommended.

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, 99m technetium-ethyl cysteinate dimer ( 99m Tc-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 99m Tc-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 99m Tc-ECD SPECT can be used in cats for studying the rCBF and that the clearance of 99m Tc-ECD in the feline brain is region dependent. As a result, the acquisition should be started between 40 and 60 minutes after tracer injection.

Conventional Single Photon Emission Computed Tomography (SPECT) precludes a detailed evaluation of the subcortical region. Micro-SPECT (μ-SPECT) has a higher resolution, but has not been used to evaluate the dog’s brain until now. In this study, μ-SPECT of the brain was evaluated in 10 Beagle dogs. Magnetic Resonance Imaging (MRI) of the brain was used to draw a new region map containing 19 volumes of interest (VOIs). Semi-quantitative analysis of the μ-SPECT data was performed and the regional cerebral perfusion was represented by the perfusion indices (PIs). The highest perfusion was found in the parietal cortex and the lowest in the piriform cortex. An asymmetry toward the left hemisphere in general and a regional asymmetry in the frontal, temporal and parietal cortex were found. This study shows that functional imaging of the canine brain is possible using μ-SPECT and it describes the normal regional brain perfusion in the adult Beagle dog.

Functional imaging provides important insights into canine brain pathologies such as behavioral problems. Two (99m) Tc-labeled single photon emission computed tomography (SPECT) cerebral blood flow tracers-ethylcysteinate dimer (ECD) and hexamethylpropylene amine oxime (HMPAO)-are commonly used in human medicine and have been used previously in dogs but intrasubject comparison of both tracers in dogs is lacking. Therefore, this study investigated whether regional distribution differences between both tracers occur in dogs as is reported in humans. Eight beagles underwent two SPECT examinations first with (99m) Tc-ECD and followed by (99m) Tc-HMPAO. SPECT scanning was performed with a triple head gamma camera equipped with ultrahigh resolution parallel hole collimators. Images were reconstructed using filtered backprojection with a Butterworth filter. Emission data were fitted to a template permitting semiquantification using predefined regions or volumes of interest (VOIs). For each VOI, perfusion indices were calculated by normalizing the regional counts per voxel to total brain counts per voxel. The obtained perfusion indices for each region for both tracers were compared with a paired Student's T-test. Significant (P < 0.05) regional differences were seen in the subcortical region and the cerebellum. Both tracers can be used to visualize regional cerebral blood flow in dogs, however, due to the observed regional differences, they are not entirely interchangeable.

This first-in-dog study evaluates the use of the PET-radioligand [C-11] DASB to image the density and availability of the serotonin transporter (SERT) in the canine brain. Imaging the serotonergic system could improve diagnosis and therapy of multiple canine behavioural disorders. Furthermore, as many similarities are reported between several human neuropsychiatric conditions and naturally occurring canine behavioural disorders, making this tracer available for use in dogs also provide researchers an interesting non-primate animal model to investigate human disorders. Five adult beagles underwent a 90 minutes dynamic PET scan and arterial whole blood was sampled throughout the scan. For each ROI, the distribution volume (V-T), obtained via the one-and two-tissue compartment model (1-TC, 2-TC) and the Logan Plot, was calculated and the goodness-of-fit was evaluated by the Akaike Information Criterion (AIC). For the preferred compartmental model BPND values were estimated and compared with those derived by four reference tissue models: 4-parameter RTM, SRTM2, MRTM2 and the Logan reference tissue model. The 2-TC model indicated in 61% of the ROIs a better fit compared to the 1-TC model. The Logan plot produced almost identical VT values and can be used as an alternative. Compared with the 2-TC model, all investigated reference tissue models showed high correlations but small underestimations of the BPND-parameter. The highest correlation was achieved with the Logan reference tissue model (Y = 0.9266 x + 0.0257; R-2 = 0.9722). Therefore, this model can be put forward as a non-invasive standard model for future PET-experiments with [C-11] DASB in dogs.

Contrast-enhanced ultrasound (CEUS) is an emerging technique to evaluate tissue perfusion. Promising results have been obtained in the evaluation of renal perfusion in health and disease, both in human and veterinary medicine. Renal scintigraphy using Tc-99m-Mercaptoacetyltriglycine (MAG(3)) is another non-invasive technique that can be used to evaluate renal perfusion. However, no data are available on the ability of CEUS or Tc-99m-MAG(3) scintigraphy to detect small changes in renal perfusion in cats. Therefore, both techniques were applied in a normal feline population to evaluate detection possibilities of perfusion changes by angiotensin II (AT II). Contrast-enhanced ultrasound using a bolus injection of commercially available contrast agent and renal scintigraphy using Tc-99m-MAG(3) were performed in 11 healthy cats after infusion of 0,9% NaCl (control) and AT II. Angiotensin II induced changes were noticed on several CEUS parameters. Mean peak enhancement, wash-in perfusion index and wash-out rate for the entire kidney decreased significantly after AT II infusion. Moreover, a tendency towards a lower wash-in area-under-the curve was present. Renal scintigraphy could not detect perfusion changes induced by AT II. This study shows that CEUS is able to detect changes in feline renal perfusion induced by AT II infusion.

With the use of perfusion tracers, in vivo examination of the regional cerebral blood flow in cats can be performed with single photon emission computed tomography (SPECT). Reliable perfusion data of normal, healthy cats are necessary for future clinical studies or other research use. Therefore, this dataset of the regional perfusion pattern of the normal feline brain was created. Twelve cats were used in this study. Technetium-99m-ethyl cysteinate dimer (99mTc-ECD) was injected intravenously and the acquisition, using a triple head gamma camera equipped with three multi-pinhole collimators (pinhole SPECT), was started 40 mins after tracer administration under general anaesthesia. Nineteen regions of interest were defined using 7T magnetic resonance images of the feline brain and a topographical atlas. Regional counts were normalised to the counts of two reference regions: the total brain and the cerebellum. The highest tracer uptake was noticed in the subcortical structures, and the lowest in the frontal cortex and the cerebellum. Also left–right asymmetry in the temporal cortex and a rostrocaudal gradient of 5% were observed.

Brain perfusion can be investigated using single photon emission computed tomography (SPECT) and the intravenous injection of (99m)technetium ethyl cysteinate dimer ((99m)Tc-ECD). However, sedation using medetomidine, an α(2)-agonist, or anaesthesia using medetomidine and ketamine, an N-methyl-d-aspartate-(NMDA)-antagonist, may be required for SPECT studies in cats but can affect the regional cerebral blood flow (rCBF). The effects of medetomidine, with or without ketamine, on regional brain perfusion were therefore investigated in six cats under three conditions. Injection of tracer occurred before sedation or anaesthesia (condition A), following intramuscular (IM) sedation with medetomidine (condition M) or after IM anaesthesia with medetomidine and ketamine (condition MK). Medetomidine and medetomidine with ketamine caused a significantly higher total tracer uptake in all brain regions. Semi-quantification of brain perfusion gave lower perfusion indices in several sub-cortical regions in conditions M and MK, compared to A. Left-right differences were observed in the temporal cortex (A), the temporal, parietal cortex and the thalamus (M) and the frontal cortex (MK). A significantly higher perfusion index in the sub-cortical regions, compared to the whole cortex, was only present in condition A. This study showed that caution is needed when quantifying brain perfusion indices when using sedative or anaesthetic agents that may affect rCBF.

Background Currently, the underlying neurobiological mechanism as to how repetitive transcranial magnetic stimulation (rTMS) can alter depressive states remains unclear. Animal data suggest that its influence could occur at the neurotransmitter level, such as modulation of the serotonin system. Methods Twenty-one antidepressant-free medication-resistant unipolar depressed patients, and 21 age- and gender-matched healthy subjects were studied. We examined the neurobiologic impact of 10 high-frequent (HF)-rTMS sessions applied to the left dorsolateral prefrontal cortex (DLPFC) on postsynaptic 5-HT 2A receptor binding indices (BI) measured with 123 I-5-I-R91150 single photon emission computed tomography (SPECT) only in patients. Results Compared with the control group, patients displayed significantly less bilateral dorsolateral prefrontal cortical and significantly higher left hippocampal baseline 5-HT 2A receptor BI. Successful HF-rTMS treatment correlated positively with 5-HT 2A receptor BI in the DLPFC bilaterally and correlated negatively with right hippocampal 5-HT 2A receptor uptake values. Conclusions Our results indicate that HF-rTMS treatment affect the serotonergic system. Our data also suggest that this kind of treatment affects 5-HT 2A receptor BI in the DLPFC and in the hippocampus in different ways.

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

A 30-month-old female Cavalier King Charles dog was presented with a history of worsening compulsive behavior (shadow chasing). In vivo brain imaging using single-photon emission computed tomography and the dopamine transporter (DAT)-specific radiopharmaceutical 123 I-FP-CIT revealed a significantly higher DAT striatal-to-brain ratio. Treatment was started with the tricyclic antidepressant clomipramine 2.5 mg/kg PO, q. 12 hours. After 2 months of medication that resulted in clinical improvement, the DAT binding regained normal values.

canine frontal cortex. A. Adriaens, S. Vermeire, T. Waelbers, L. Duchateau, S. Sys, S. Van Dorpe, J. Eersels, A.Dobbeleir, B. De Spiegeleer, K. Audenaert, I. Polis, K. Peremans Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium; Drug Quality & Registration (DruQuaR) group, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium; Nuclear Medicine and PET research, VU University Medical Center, Amsterdam, The Netherlands; Faculty of Medicine, Ghent University, Gent, Belgium

Estimation of the glomerular filtration rate (GFR) is a useful tool in the evaluation of kidney function in feline medicine. GFR can be determined by measuring the rate of tracer disappearance from the blood, and although these measurements are generally performed by multi-sampling techniques, simplified methods are more convenient in clinical practice. The optimal times for a simplified sampling strategy with two blood samples (2BS) for GFR measurement in cats using plasma 51chromium ethylene diamine tetra-acetic acid (51Cr-EDTA) clearance were investigated. After intravenous administration of 51Cr-EDTA, seven blood samples were obtained in 46 cats (19 euthyroid and 27 hyperthyroid cats, none with previously diagnosed chronic kidney disease (CKD)). The plasma clearance was then calculated from the seven point blood kinetics (7BS) and used for comparison to define the optimal sampling strategy by correlating different pairs of time points to the reference method. Mean GFR estimation for the reference method was 3.7±2.5 ml/min/kg (mean±standard deviation (SD)). Several pairs of sampling times were highly correlated with this reference method ( r2≥0.980), with the best results when the first sample was taken 30 min after tracer injection and the second sample between 198 and 222 min after injection; or with the first sample at 36 min and the second at 234 or 240 min ( r2 for both combinations=0.984). Because of the similarity of GFR values obtained with the 2BS method in comparison to the values obtained with the 7BS reference method, the simplified method may offer an alternative for GFR estimation. Although a wide range of GFR values was found in the included group of cats, the applicability should be confirmed in cats suspected of renal disease and with confirmed CKD. Furthermore, although no indications of age-related effect were found in this study, a possible influence of age should be included in future studies.

Alterations of regional brain activity in the prefrontal cortex and in limbic areas have been reported in humans with anxiety disorders. This animal study reports the results of brain perfusion imaging with single photon emission computed tomography (SPECT) in dogs with anxiety disorders. Based on the human literature, we hypothesized altered prefrontal and higher temporal brain perfusion. SPECT acquisitions were performed using the 99mTc-labelled tracer ethyl cysteinate dimer (ECD). Eighteen dogs with pathological anxiety were compared with 18 normally behaving reference dogs. We found, in the group of dogs with anxiety disorders, lower perfusion in the left frontal cortex (p = 0.003), in the subcortical region (p = 0.007) and increased perfusion in the right (p = 0.05) temporal cortex. Taken together, our rCBF findings are suggestive for a dysfunction of the prefrontal cortex and the limbic system in canine anxiety disorders.

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 (R2= 0.9414), giving the following converting equation: clearance = (0.0066 × DV48 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.

To verify the applicability of a recently described resolution-independent method for the semi-quantification of 123I-FP-CIT scans.Visual interpretation, 'conventional' and resolution-independent semi-quantification was performed on 60 123I-FP-CIT scans. Using ROC analysis, the results were compared to the final clinical diagnosis after a follow-up of at least 18 months. Sensitivity and specificity values were calculated and a cut-off value of the specific binding, which differentiated between normal and abnormal scans with high sensitivity and specificity, was given.Application of the resolution-independent method to a new set of 123I-FP-CIT SPECT data yielded a cut-off value of the specific striatal binding of 55 ml. Corresponding values of sensitivity and specificity were 95% and 72%, respectively. Further, based on the values of the area under the ROC curve and the 95% confidence interval of different semi-quantitative methods, the resolution-independent semi-quantification agreed best with the final clinical diagnosis.We found a similar value of the specific 123I-FP-CIT binding as the one previously described in the literature, which proved the validity of the resolution-independent method. Further, this method, among other 'conventional' semi-quantitative methods, agreed best with the final clinical diagnosis. For this reason we recommend its use to aid in the diagnostic process.

Apraxic agraphia follows disruption of skilled movement plans of writing and is characterized by distorted, hesitant, incomplete, and imprecise letter formation. The causative lesion is located in the superior parietal lobe (storage of graphomotor plans) or the dorsolateral and medial part of prefrontal cortex (conversion of graphomotor plans to motor commands).1 Recently, the condition was also reported after left dorsomedial thalamic infarction with reduced oxygen metabolism in left premotor areas.2 ### Case report. A 72-year-old right-handed engineer acutely developed postural instability and gait disturbances. Neurologic examination showed a pure cerebellar deficit with distinct midline cerebellar dysfunction and less pronounced right appendicular ataxia. Apart from implantation of a pacemaker for sick sinus syndrome, his medical history was unremarkable. CT scan of the brain disclosed a hemorrhagic lesion in the right cerebellar hemisphere involving cortex and the medullary core (figure 1A). No supratentorial lesions were detected by repeat CT at 3 and 6 months after onset. Figure 1 CT scan and quantified Tc-99m-ethyl cysteinate dimer SPECT studies CT scan of the brain disclosing a hemorrhage in the right cerebellar hemisphere involving cortex and the medullary core (A). Quantified Tc-99m-ethyl cysteinate dimer SPECT studies conducted …

Objective: When taking into account the Society of Nuclear Medicine (SNM) and European Association of Nuclear Medicine (EANM) guidelines on diuretic renography in children, we see important divergences in the preparation, acquisition, processing, and interpretation of the results. In this study, we estimated the quality of renal drainage according to these two guidelines. Patients and methods: Ninety kidneys with hydronephrosis or severe vesicorenal reflux were processed and analyzed according to the SNM (estimation of the T1/2 of the washout curve and conclusions about the possible existence of obstruction) and EANM guidelines (estimation of normalized residual activity or NORA, and output efficiency or OE on the late postmicturition images, without any conclusion about the possible existence of obstruction). Among the 90 kidneys, 39, 20, and 31 were considered to have normal, equivocal, or poor drainage (obstruction), respectively, when the SNM guidelines were used. Results: All 39 kidneys with good drainage according to SNM were also considered as normal using the EANM guidelines. Among the 20 equivocal cases based on T1/2, concordance between the two guidelines was obtained in only 35 and 0% when using NORA and OE (OE was considered normal in all 20 cases), respectively. Among the 31 cases defined as obstructed by SNM, only five were classified as 'poor drainage' using NORA and no single case was classified thus using OE. Conclusion: This limited study demonstrates that the use of different guidelines can lead to different interpretations of the results. This is unacceptable, and an agreement between both pediatric task groups of the SNM and EANM is urgently required.

Ketamine, a dissociative anesthetic frequently used in veterinary medicine, possesses rapid-acting antidepressant effects in humans possibly indicating an interaction with the cerebral perfusion or with the serotonergic system. In this single-photon emission computed tomography study, 7 healthy dogs were used to investigate the influence of ketamine on the regional cerebral blood flow using technetium-99m-ethyl cysteinate dimer and on the binding of the 5-hydroxytryptamine 2A receptor radioligand iodine-123 labeled R91150 in the canine brain. Ketamine increased the regional perfusion in the left frontal cortex and right parietal cortex. Significant changes in the distribution of iodine-123 labeled R91150 were not observed. This study demonstrated an acute effect of ketamine on the regional brain perfusion but not on the 5-hydroxytryptamine 2A receptors in the canine brain in the dose used in this study.

Objectives Compared with other non-invasive methods for diagnosing coronary artery disease (CAD), myocardial perfusion imaging (MPI) suffers from some lack of specificity, especially in patients with a small heart. Allowing the assessment of perfusion on end diastolic images instead of summed images, gated single photon emission computed tomography (SPECT) constitutes an attractive method for increasing the accuracy of MPI. Scatter correction, known to improve image contrast, might also be interesting. The present study aimed at comparing scatter corrected to uncorrected gated MPI for CAD diagnosis. Methods The results for 100 patients referred for gated 9 9 m Tc sestamibi SPECT were analysed. They were divided into two subgroups according to their end systolic volume (ESV) measured by QGS analysis (group A, ESV ≥ 30 ml, n=65; group B, ESV

To gain insights into the working mechanism of morphine, regional cerebral blood flow (rCBF) patterns after morphine administration were assessed in dogs. In a randomized cross-over experimental study, rCBF was estimated with Tc-99m-Ethylcysteinate Dimer single photon emission computed tomography in 8 dogs at baseline, at 30 minutes and at 120 minutes after a single bolus of morphine. Perfusion indices (PI) in the frontal, parietal, temporal and occipital cortex and in the subcortical and cerebellar region were calculated. PI was significantly decreased 30 min after morphine compared to baseline in the right frontal cortex. The left parietal cortex and subcortical region showed a significantly increased PI 30 min after morphine compared to baseline. No significant differences were noted for the other regions or at other time points. In conclusion, a single bolus of morphine generated a changing rCBF pattern at different time points.

Dogs can be used as research models in order to contribute to a better understanding of human neuropsychiatric disorders and to explore treatment options. In general, smaller laboratory animals, most often mice and rats, have been extensively used. Nevertheless, the implementation of larger animal (e.g. dogs) models has several important advantages. Their larger brain size omits the need for dedicated equipment (micro-PET or micro-SPECT) and the larger portion of the frontal cortex (crucial to behaviour regulation) in particular allows superior investigation of this area. They can further be used to investigate normal physiology and interaction of several neurotransmitter systems and the effects of drugs on brain function and chemistry. In this regard, they can also be used to obtain information on the pharmacokinetics and pharmacodynamics of newly developed drugs and the dosage at which maximal response and least side effects occur. Finally, natural animal behavioural models of disorders can be used to enlighten the biological base of several human neuropsychiatric disorders. In this chapter, an overview will be given on the use of functional brain imaging in dogs suffering from impulsive aggression.

According to the limited amount of literature available, there is no real difference in diagnostic accuracy between a DaT-SPECT scan and an 18F-FDOPA PET scan nor between an123I-IBZM SPECT and a 11C-raclopride PET. However, while DaT-SPECT and FDOPA PET have gained a role in the clinical evaluation of the parkinsonian patient, especially in the differential diagnosis with other pathologies such as essential tremor, less evidence has been presented for the use of IBZM SPECT in the differential diagnosis of Morbus Parkinson and parkinsonian syndromes. A promising role could be played by 18F-FDG PET or perfusion SPECT in this regard.

We evaluated the methodological issues underlying the assessment of normal confidence intervals, as used in clinically based region-of-interest (ROI) semi-quantification of 99 Tc m -HMPAO brain SPET. At two different centres equipped with high-resolution, triple-headed gamma cameras, HMPAO SPET scans were performed on two groups of 24 and 15 healthy volunteers respectively. Together with an operator-defined analysis (ODA), a semi-automated analysis (SAA) was conducted on the normal datasets in one centre. Tests of intra- and inter-observer variability were performed. Repeat scans were performed within 72 h after the first to analyse short-term regional inter-study variations. The overall regional uptake showed significant differences in most regions between both normal datasets. Intra-observer and inter-observer reproducibility were on average within 4% for the ODA, while for the SAA it was less than 1%. Inter-study variations were excellent for both centres, ranging from -4% to +3% for most regions studied. The variability in clinical brain perfusion studies largely depends on the reproducibility of the data analysis technique. A semi-automated approach shows clear advantages over an entirely operator-defined approach. Intra-subject repeat studies show enough stability for use as reliable baseline measurements in the construction of a normal database or to allow activation studies with high sensitivity.

Little is known about the usefulness of free fatty acid scintigraphy for assessing viability in chronic ischaemic heart disease. To investigate this, we quantified the uptake of 99 Tc m -sestamibi and 123 I-BMIPP at rest twice within 6 months in 20 patients with chronic ischaemic left ventricular dysfunction and infarction. Four patterns of the relative distribution of both tracers were observed and classified as normal, mismatched, matched and scar. The proportion of the left ventricular surface corresponding to each pattern was expressed as the percentage of the total surface using a polar map. Between the two studies, the patients either underwent revascularization or were treated conservatively. The quantitative results were compared with those of dobutamine stress echocardiography (DSE) in arterial territories with resting contractile dysfunction and correlated with the evolution of regional and global function at follow-up. At baseline, 25 arterial territories were analysed. Using sestamibi, on average one-third of their surface was considered to be normally perfused. No clear association was found between the percent normally perfused surface and the DSE findings. Adding BMIPP and using a value of >7% of the arterial surface with BMIPP lower than sestamibi (mismatch) as the cut-off for the significance of viability, 14 of 18 mismatched regions were considered viable by DSE, and six of seven with

The assessment of left ventricular ejection fraction is an important element in the evaluation of cardiac performance, and one of the most commonly performed tests in nuclear cardiology. The aim of this study was to evaluate the accuracy and reliability of ejection fraction values calculated from ECG-gated myocardial perfusion single photon emission tomography (GSPET) in comparison with standard scintigraphic methods. Eight-frame gated SPET was recorded 60-90 min after the injection of 99Tcm-sestamibi at rest. The ejection fraction was calculated using a semi-automatic edge-detection technique based upon a threshold-searching method and compared with values obtained from first-pass (FPRNA) or equilibrium radionuclide angiography (ERNA) in 60 and 40 patients respectively with a broad range of ejection fraction values. Very good reproducibility was noted, with an inter- and intra-observer variability of -0.2 +/- 3.5% (range -7.6 to 6.9%, r = 0.97) and -0.2 +/- 2.2% (range -5.9 to 3.5%, r = 0.99) respectively. Similarly, a high concordance was found between GSPET and FPRNA and between GSPET and ERNA over the range of ejection fraction values (13 to 77%), the mean (+/-S.D.) difference being 0.8 +/- 3.8% (r = 0.97, P = N.S.) and 0.03 +/- 5.3% (r = 0.94, P = N.S.) respectively. Applying the Bland-Altman plot, no systematic bias of one method related to the other was observed, even at extreme ejection fraction values. Gated myocardial perfusion SPET with a 99Tcm tracer thus offers a unique opportunity to quantify cardiac performance and perfusion simultaneously and non-invasively.

Evaluation of glomerular function is a useful part of the diagnostic approach in animals suspected of having renal disease. Time-interval and background region of interest (bg ROI) selection are determining factors when calculating the glomerular filtration ratio (GFR) based on percentage uptake of 99mtechnetium-labelled diethylene triamine penta-acetic acid (99mTc-DTPA). Therefore, three different time intervals (60–120 s, 120–180 s, 60–180 s) and three different bg ROIs (C-shape, caudolateral, cranial + caudal) were investigated. In addition, global GFRs based on percentage dose uptake of 99mTc-DTPA for the different time-intervals and bg ROIs were compared with the global GFR based on 51chromium-ethylene diaminic tetra-acetic acid (51Cr-EDTA) plasma clearance in nine healthy European domestic shorthair cats. Paired Student’s t-tests and linear regression analysis were used to analyse the data. Different time intervals seemed to cause significant variation ( P 99mTc-DTPA and 51Cr-EDTA, although a significant difference ( P

UNLABELLED: Subanesthetic doses of ketamine can be used as a rapid-acting antidepressant in patients with treatment-resistant depression. Therefore, the brain kinetics of (123)I-5-I-R91150 (4-amino-N-[1-[3-(4-fluorophenyl)propyl]-4-methylpiperidin-4-yl]-5-iodo-2-methoxybenzamide) and the influence of ketamine on the postsynaptic serotonin-2A receptor (5-hydroxytryptamine-2A, or 5-HT2A) status were investigated in cats using micro-SPECT. METHODS: This study was conducted on 6 cats using the radioligand (123)I-5-I-R91150, a 5-HT2A receptor antagonist, as the imaging probe. Anesthesia was induced and maintained with a continuous-rate infusion of propofol (8.4 ± 1.2 mg kg(-1) followed by 0.22 mg kg(-1) min(-1)) 75 min after tracer administration, and acquisition of the first image began 15 min after induction of anesthesia. After this first acquisition, propofol (0.22 mg kg(-1) min(-1)) was combined with ketamine (5 mg kg(-1) followed by 0.023 mg kg(-1) min(-1)), and the second acquisition began 15 min later. Semiquantification, with the cerebellum as a reference region, was performed to calculate the 5-HT2A receptor binding indices (parameter for available receptor density) in the frontal and temporal cortices. The binding indices were analyzed with Wilcoxon signed ranks statistics. RESULTS: The addition of ketamine to the propofol continuous-rate infusion resulted in decreased binding indices in the right frontal cortex (1.25 ± 0.22 vs. 1.45 ± 0.16; P = 0.028), left frontal cortex (1.34 ± 0.15 vs. 1.49 ± 0.10; P = 0.028), right temporal cortex (1.30 ± 0.17 vs. 1.45 ± 0.09; P = 0.046), and left temporal cortex (1.41 ± 0.20 vs. 1.52 ± 0.20; P = 0.046). CONCLUSION: This study showed that cats can be used as an animal model for studying alterations of the 5-HT2A receptor status with (123)I-5-I-R91150 micro-SPECT. Furthermore, an interaction between ketamine and the 5-HT2A receptors resulting in decreased binding of (123)I-5-I-R91150 in the frontal and temporal cortices was demonstrated. Whether the decreased radioligand binding resulted from a direct competition between ketamine and (123)I-5-I-R91150 or from a decreased affinity of the 5-HT2A receptor caused by ketamine remains to be elucidated.

Single photon emission tomographic imaging of myocardial perfusion with 99Tcm-labelled agents is usually performed with single-detector gamma camera systems and 180 degrees anterior data collection. With multi-detector systems, reconstruction over 180 degrees and 360 degrees has been reported. We used a data set of normal subjects to compare both reconstruction methods. In addition, we tested an alternative approach, reconstructing data from 240 degrees acquisitions, excluding the right posterior views, which provide little myocardial information and which are responsible for a reduced signal-to-noise ratio. On the transverse slices, the known apical distortion with the 180 degrees reconstruction was not noted with the 360 degrees or 240 degrees reconstructions. Using semi-quantitative analysis of apical, mid-ventricular and basal short-axis slices, almost complete overlap was observed between the 240 degrees and 360 degrees circumferential profiles of our 20 normal volunteers, except in the inferior wall where a reduction in activity was noted. However, this finding was less pronounced with the 240 degrees than with the 180 degrees reconstruction. The frequent reduction in activity in the anterior wall was more prominent with the 180 degrees than with the 240 degrees and 360 degrees reconstructions. A 240 degrees acquisition represents a useful compromise between 180 degrees and 360 degrees imaging protocols when a single-detector device is used, allowing more homogeneous tracer distribution and a reduction in the apical distortion without material change of contrast or doubling of the acquisition time.

Functional imaging provides important insights into canine brain pathologies such as behavioral problems. Two (99m) Tc-labeled single photon emission computed tomography (SPECT) cerebral blood flow tracers-ethylcysteinate dimer (ECD) and hexamethylpropylene amine oxime (HMPAO)-are commonly used in human medicine and have been used previously in dogs but intrasubject comparison of both tracers in dogs is lacking. Therefore, this study investigated whether regional distribution differences between both tracers occur in dogs as is reported in humans. Eight beagles underwent two SPECT examinations first with (99m) Tc-ECD and followed by (99m) Tc-HMPAO. SPECT scanning was performed with a triple head gamma camera equipped with ultrahigh resolution parallel hole collimators. Images were reconstructed using filtered backprojection with a Butterworth filter. Emission data were fitted to a template permitting semiquantification using predefined regions or volumes of interest (VOIs). For each VOI, perfusion indices were calculated by normalizing the regional counts per voxel to total brain counts per voxel. The obtained perfusion indices for each region for both tracers were compared with a paired Student's T-test. Significant (P0.05) regional differences were seen in the subcortical region and the cerebellum. Both tracers can be used to visualize regional cerebral blood flow in dogs, however, due to the observed regional differences, they are not entirely interchangeable.

SummaryObjective: To investigate the possibilities and limitations of planar bone scintigraphy and high resolution single photon emission computed tomography (HiSPECT) to diagnose flexor enthesopathy and to distinguish primary flexor enthesopathy from the concomitant form.Materials and methods: A prospective study of 46 dogs with primary flexor enthesopathy, concomitant flexor enthesopathy, medial coronoid disease, and normal elbows was performed. All dogs underwent planar bone scintigraphy and HiSPECT imaging. The obtained images were visually scored for increased radiopharmaceutical uptake in the medial humeral epicondylar and medial coronoid process region using a score from 1-3.Results: Planar bone scintigraphy demonstrated increased radiopharmaceutical uptake in all diseased elbow joints, except for one. HiSPECT demonstrated increased radiopharmaceutical uptake of the medial humeral epicondyle in nearly all clinically affected joints with primary and concomitant flexor enthesopathy. Additional uptake of the medial coronoid process was recorded in all clinically affected joints with concomitant flexor enthesopathy and in six out of 18 with primary flexor enthesopathy. No difference in intensity of the uptake was noticed.Clinical significance: Planar bone scintigraphy allows the attribution of lameness to the elbow joint in cases of primary flexor enthesopathy with minimal or even absent radiographic changes. The more detailed HiSPECT enables the localization of pathology within the elbow joint and is a sensitive technique to detect flexor enthesopathy. However HiSPECT is insufficient to distinguish primary from concomitant flexor enthesopathy.

Apraxic agraphia is a peripheral writing disorder caused by neurological damage. It induces a lack or loss of access to the motor engrams that plan and programme the graphomotor movements necessary to produce written output. The neural network subserving handwriting includes the superior parietal region, the dorsolateral and medial premotor cortex and the thalamus of the dominant hemisphere. Recent studies indicate that the cerebellum may be involved as well. To the best of our knowledge, apraxic agraphia has not been described on a developmental basis. This paper reports the clinical, neurocognitive and (functional) neuroimaging findings of a 15-year-old left-handed patient with an isolated, non-progressive developmental handwriting disorder consistent with a diagnosis of "apraxic dysgraphia". Gross motor coordination problems were objectified as well but no signs of cerebellar, sensorimotor or extrapyramidal dysfunction of the writing limb were found to explain the apraxic phenomena. Brain MRI revealed no supra- and infratentorial damage but quantified Tc-99m-ECD SPECT disclosed decreased perfusion in the anatomoclinically suspected prefrontal and cerebellar brain regions crucially involved in the planning and execution of skilled motor actions. This pattern of functional depression seems to support the hypothesis that "apraxic dysgraphia" might reflect incomplete maturation of the cerebello-cerebral network involved in handwriting. In addition, it is hypothesized that "apraxic dysgraphia" may have to be considered to represent a distinct nosological category within the group of the developmental dyspraxias following dysfunction of the cerebello-cerebral network involved in planned actions.

In this study the use of the high resolution Micro-Single Photon Emission Tomography (HiSPECT) system with a radioactive bonemarker, (99m)Tc-oxidronate, was evaluated in dogs with coronoid pathology and/or flexor enthesopathy. Sixty-five elbows of 34 dogs were included. CT and HiSPECT were performed on all elbows, arthroscopy on 59. Tracer uptake in 8 anatomical regions was graded according to two models. Increased activity in the medial epicondylar region was associated with flexor pathology on CT (P=0.0002) and arthroscopy (P0.0001) and increased uptake in the medial coronoid (P0.0001) and the medial condylar area (P0.013) with coronoid pathology. Uptake in the remaining areas was not associated with both pathologies. In conclusion, the improved resolution of the HiSPECT system allows identification of increased tracer uptake in the anatomical regions involved in coronoid pathology and flexor enthesopathy. This modality may improve the diagnostic potential of the bone scan in canine elbow disease.

The standardized added metabolic activity (SAM) is a new marker of total lesion glycolysis that avoids partial volume effect (PVE) and thresholding. SAM is calculated by drawing a volume of interest (VOI(1)) around the tumour and a larger VOI (VOI(2)) around VOI(1). Subtracting the background activity in VOI(2)-VOI(1) from VOI(1) yields SAM. If VOI(1) is set at a reasonable distance from the tumour, PVE are avoided. Phantom and initial clinical validation data are presented.Spheres of a Jaszczak phantom were filled with a 5.4, 3.64 and 2.0 times higher concentration relative to background activity and positron emission tomography (PET) data were acquired during 10 min. SAM of all spheres was expressed as a percentage of the expected value (the actual activity ratio minus 1). In 15 patients a 10-min list-mode acquisition PET study centred on their primary squamous cell carcinoma (PSCC) was performed and images of 1-10 min reconstructed. SAM1-9min values of PSCC were expressed as a percentage of SAM10min. Nineteen patients suffering from liver metastases treated with chemotherapy underwent PET/CT prior to (scan 1) and after 3-6 cycles of chemotherapy (scan 2). SAM and maximum standardized uptake values (SUV(max)) of the liver lesions on scan 1 (SAM1 and SUV(max)1) and the percentage reduction between both ΔSAM and ΔSUV(max) were related to Response Evaluation Criteria in Solid Tumors (RECIST) response.For the phantom acquisitions, the mean normalized SAM/sphere volume calculated was 94.9 % (SD 5.9 %) of the expected value. In the PSCC patients, the mean difference between SAM1min and SAM10min was only 4 % (SD 5 %). SUV(max)1min and SUV(max)10min proved to be not significantly different, but the variability was slightly larger than that of SAM (SD 6.4 %). SAM1 and ΔSAM values for responders versus non-responders were, respectively, 57 (SD 119) versus 297 (SD 625) for SAM1 (p = 0.2) and 99 % (SD 3 %) versus 32 % (SD 44 %) for ΔSAM (p = 0.001). SUV(max)1 and ΔSUV(max) values in responders versus non-responders were, respectively, 3.9 (SD 2.4) versus 6.3 (SD 3.1) for SUV(max)1 (p = 0.08) and 94 % (SD 17) versus 7 % (SD 40 %) for ΔSUV(max) (p = 0.0001). The AUC of ΔSAM and ΔSUV(max) were not significantly different on receiver-operating characteristic (ROC) analysis (AUC 1.0 and 0.99, respectively, p = 0.6).SAM is a promising parameter for tumour response assessment of liver metastases by means of (18)F-fluorodeoxyglucose PET.

Neuro-imaging studies have shown altered, yet often inconsistent, serotonergic and dopaminergic neurotransmission in patients with obsessive–compulsive disorder (OCD). We investigated both serotonergic and dopaminergic neurotransmission in 9 drug-naive dogs with compulsive behaviour, as a potential model for human OCD. Single photon emission computed tomography was used with 123 I-R91150 and 123 I-FP-CIT, in combination with 99m Tc-ECD brain perfusion co-registration, to measure the serotonin (5-HT) 2A receptor, dopamine transporter (DAT) and serotonin transporter (SERT) availability. Fifteen normally behaving dogs were used as reference group. Significantly lower 5-HT2A receptor radioligand availability in frontal and temporal cortices (bilateral) was observed. Further, in 78% of the compulsive dogs abnormal DAT ratios in left and right striatum were demonstrated. Interestingly, both increased and decreased DAT ratios were observed. Finally, significantly lower subcortical perfusion and (hypo)thalamic SERT availability were observed in the compulsive dogs. This study provides evidence for imbalanced serotonergic and dopaminergic pathways in the pathophysiology of compulsions in dogs. The similarities with the altered neurotransmission in human OCD provide construct validity for this non-induced, natural canine model, suggesting its usefulness for future investigations of the pathophysiology of human OCD as well as the effectiveness of psychopharmacological interventions.

the right kidney can be determined both for the anterior and the posterior projection, allowing calculation of its geometric mean. The same can be done for the standard placed at the level of the left kidney using the first and the third acquisitions. As the same standard is used for the right and for the left kidney, if the attenuation is equal, the ratio of the geometric mean of the standard at these two locations is one. The ratio of the calculated geometric mean will differ from unity because of bone attenuation and differences in body thickness at the levels of the right and the left kidney. This calculated value can then be used to correct the geometric mean of the differential renal function calculated from the first data acquisition. The same approach can be used in renography to estimate renal split function in the presence of a pelvic kidney.

Until recently, renogram, performed in children with pelvi-ureteric junction stenosis detected antenatally, has not been able to predict the probability of function improvement after surgery or the risk of function deterioration in case of conservative attitude. Recently, Schlotmann et al. have suggested that cortical transit might have this predictive role. The aim of this study, focused on those kidneys with severely impaired cortical transit, was to verify this statement.All renograms performed in children during a 3-year period (n=729) were retrospectively reviewed and 19 pediatric patients were selected based on an antenatally detected unilateral pelvi-ureteric junction syndrome, the existence of at least two renograms during the follow-up and a severe cortical transit impairment, visually defined. Twenty-six pairs of data could be analyzed and allowed comparing preoperative and postoperative differential renal function (DRF), and the DRF changes during the conservative management.Among the 16 patients who underwent pyeloplasty, 10 showed a significant DRF improvement. Among the 10 patients with conservative follow-up, four showed a significant DRF deterioration.Severely impaired cortical transit seems to be a valuable marker of those patients who could benefit from a pyeloplasty, either because of the high probability of postoperative DRF improvement, or because of DRF deterioration in case of an conservative approach. However, a normal cortical transit, as defined in this study, does not exclude the risk of DRF deterioration. Alternatively, the design of this study does not allow excluding the fact that DRF might improve after pyeloplasty despite a normal cortical transit.

In this study we investigated the influence of technical factors (positioning, background (BG) correction and attenuation correction) on qualitative and quantitative (absolute (AU) and relative (RU) uptake) assessment of feline kidneys with 99mtechnetium labelled dimercaptosuccinic acid (99mTc-DMSA). Eleven healthy adult cats were included. Influence of BG and depth correction on quantitative assessment was evaluated. Depth correction was based on the geometric mean method (using dorsal and ventral images) and the use of two standards placed over each individual kidney. Visual evaluation showed superiority of dorsal and ventral over lateral positioning due to increased separation of the kidneys permitting region of interest (ROI) placement without overlap. No apparent influence of BG correction was found for RU. However, AU was systematically overestimated without BG correction. Depth correction did not seem to affect RU in most cases, however, in some cats the differences were not negligible. The values for AU without depth correction were lower compared to depth corrected values.

The objective of the study was to present a simple method for comparing clinical PET images to a set of increasing quality images. Those different quality images were obtained by varying the activity concentration and the acquisition time.Images of a Jaszczak phantom were acquired with scan times that were calculated with a spreadsheet application for a personal computer to obtain 500, 1000, 2000, 5000, 7000 and 9000 counts/4 mm(3) voxel. During a 10-h period, each scan was repeated with longer acquisition times to obtain the same number of counts in the reconstructed images, but with lower count rate. On the second day, the study was repeated, putting the phantom in a water bath to simulate larger patients.The quality of the images obtained with the phantom in water was worse than without, as expected. Phantom data demonstrated clearly the effect of higher counts on image quality. Good quality images were obtained with counts above 5000 counts/voxel. Patient data can be situated to the phantom image set by comparing the counts per voxel and the activity concentration. The counts per voxel in all the regions of interest on patient data, with the exception of the brain, were at sub-optimal level leading to decreased image quality. It is clear that better image quality can be achieved mainly by incrementing the scan time. Our PET system, however, allows doubling our standard injected activity to obtain more image counts without significant contrast loss.This simple test can be performed at any PET center to situate the quality of routine clinical PET images in comparison to the optimal possible for that system.

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 (99m)Technetium-Ethyl Cysteinate Dimer ((99m)Tc-ECD) in brain perfusion studies using Single Photon Emission Computed Tomography (SPECT). Based on the knowledge of the distribution of alpha(2)-receptors in the brain, we hypothesized altered regional brain perfusion in dogs receiving medetomidine prior to (99m)Tc-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.