The use of planar bone scintigraphy and HiSPECT for diagnosis of primary and concomitant flexor enthesopathy in the canine elbow.

OBJECTIVE: 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.

The use of the HiSPECT bone scan in canine flexor enthesopathy and coronoid pathology.

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 (P<0.0001) and increased uptake in the medial coronoid (P<0.0001) and the medial condylar area (P<0.013) 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.

High-resolution micro-SPECT to evaluate the regional brain perfusion in the adult Beagle dog.

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.

Effects of medetomidine and ketamine on the regional cerebral blood flow in cats: a SPECT study.

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.

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 (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.

Recognition of anatomical predilection sites in canine elbow pathology on bone scans using micro-single photon emission tomography.

The limited resolution of planar bone scintigraphy precludes exact anatomical localisation within a joint. Micro-single photon emission tomography (µ-SPECT) has a much higher resolution, and in this study the use of µ-SPECT in the evaluation of the canine elbow joint and fusion with structural imaging data were tested. Twelve elbows of seven normal dogs were included. µ-SPECT was performed with a conventional triple head gamma camera adapted with three multi-pinhole collimators (HiSPECT). Radiographs, computed tomography (CT) and magnetic resonance imaging (MRI) were performed on all elbows and data from CT and MRI were fused to the HiSPECT data using dedicated software. Different important anatomical regions could be recognised on the HiSPECT images. The improved resolution of the HiSPECT system allowed better differentiation of the anatomical areas in the elbow joint. Two case studies were included to demonstrate the potential of this methodology. Fusion software facilitated the use of combined structural and functional information.

Effect of recombinant human TSH on the uptake of radioactive iodine ((123)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 ((131)I) 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 ((123)I), 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 (123)I for a baseline RAIU; 1 group received 100 µg of rhTSH IV 24 h before (123)I, and 1 group received 100 µg of rhTSH IV 48 h before (123)I. All dogs received 37 MBq of radioactive (123)I 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.

The potential value of a pictorial atlas for aid in the visual diagnosis of 123I FP-CIT SPECT scans.

The aim of our study was to evaluate the value of a pictorial atlas of 123I FP-CIT SPECT images for aid in the visual diagnosis. PATIENTS, MATERIALS, METHODS: Sixty patients, of whom 20 were clinically diagnosed as 'non-parkinsonian' and 40 as having Parkinson's disease or any related disorder, were included in the study. An atlas consisting of 12 123I FP-CIT SPECT images was constructed first. Validity of the atlas was investigated by performing a receiver operating characteristic (ROC) analysis with the clinical diagnosis as the gold standard. The remaining 48 SPECT images were visually assessed twice by 5 observers, first with and secondly without consulting the atlas, or vice versa. The added value of the atlas was investigated by comparing the diagnostic accuracy and the interobserver variability for both methods. RESULTS: ROC analysis performed on the atlas yielded an area under the curve of 1 for a threshold discriminating between clinically non-parkinsonian and parkinsonian patients that was situated between image 4 and 5 of the atlas. For the diagnostic accuracy, we found that the area under the ROC curve was systematically higher if observers had access to the atlas compared to when they had not (Wilcoxon's test, p<0.05). Also, the interobserver variability was significantly lower when observers used the atlas when compared to when they did not (p = 0.05). CONCLUSION: Diagnostic accuracy was significantly higher and interobserver variability significantly lower if observers had access to the atlas compared to when they had not. Hence, having a pictorial atlas available may facilitate the visual assessment of 123I FP-CIT SPECT scans.

Recombinant human thyrotropin administration enhances thyroid uptake of radioactive iodine in hyperthyroid cats.

BACKGROUND: Hyperthyroidism is the most diagnosed endocrine disorder in cats and radioiodine (131I) is the treatment of choice. The dose emission rate and radioactivity in urine, saliva, and on hair and paws are determined by the dose of administered 131I. A dose reduction of therapeutic 131I could possibly be achieved after recombinant human thyrotropin (rhTSH) administration as in humans with nodular goiter. HYPOTHESIS: rhTSH will increase radioiodine uptake in hyperthyroid cats. ANIMALS: Five hyperthyroid cats. METHODS: Twenty-five micrograms rhTSH (day 1) or 2 mL 0.9% sodium chloride (NaCl) (day 9) was injected IV. One hour later, 11.4 +/- 4.1 (mean +/- SD) MBq 123I was injected IV. Radioactive iodine uptake (RAIU) was measured 6, 12, and 24 hours after rhTSH (RAIU-rhTSH) or NaCl (RAIU-blanco) injection. Blood samples for measurement of TT4 were taken before injection of rhTSH or NaCl (TT4(0)) and at the time of imaging. RESULTS: Percentages of RAIU-rhTSH (and RAIU-blanco) at 6, 12, and 24 hours after administration of rhTSH were 34 +/- 18 (31 +/- 21), 46 +/- 20 (38 +/- 18), and 47 +/- 15 (36 +/- 14). There was a statistically significant effect of rhTSH administration on RAIU (P = .043) but not on serum TT4 concentration. Baseline serum TT4(0) concentration influenced RAIU-rhTSH significantly at 6 hours (P = .037). CONCLUSION AND CLINICAL IMPORTANCE: The increased RAIU observed after rhTSH administration in hyperthyroid cats could lead to a lower therapeutic dose of 131I after rhTSH administration in hyperthyroid cats and decreased risk of environmental and owner contamination during and after hospitalization.

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

Serotonin transporter and dopamine transporter imaging in the canine brain.

The serotonergic and dopaminergic systems are involved in a wide range of emotional and behavioral aspects of animals and humans and are involved in many neuropsychiatric disorders. Selective serotonin (5-HT) reuptake inhibitors (SSRIs) are designed to block the 5-HT transporter (SERT), thereby increasing the available 5-HT in the brain. Functional imaging with specific SERT and dopamine transporter (DAT) ligands contributes to the study of the SSRI-transporter interaction. First, we evaluated the feasibility of a canine model in the study of the SERT and DAT with the radioligands [123I]-beta-CIT and [123I]-FP-CIT as well as single-photon emission computed tomography imaging. Second, we studied the effect of SSRIs (sertraline, citalopram and escitalopram) on the SERT and DAT in two dogs. The position of the canine model in the study of the SERT and DAT is discussed and compared with other animal models.

Prediction of functional outcome by quantification of sestamibi and BMIPP after acute myocardial infarction.

Iodine-123 15-(p-iodophenyl)-3-R,S-methylpentadecanoic acid (BMIPP) can be used to image myocardial fatty acid regional distribution and utilisation with single-photon emission tomography (SPET). By visual analysis, a mismatching with regional uptake of BMIPP less than that of a perfusion tracer has been shown to predict myocardial viability and functional improvement after restoration of flow in patients with myocardial infarction. The current study aimed to evaluate a newly developed quantitative method of analysis of sestamibi and BMIPP uptake for the prediction of functional recovery after revascularization in patients with acute infarction. BMIPP and gated sestamibi SPET studies at rest were obtained before and >3 months after revascularization in 18 patients with recent infarction. A colour-coded polar map was generated from the comparison of sestamibi and BMIPP uptake. Depending on the relative distribution of the two tracers, different patterns of uptake were identified and their extent expressed as percentages of the surface of the whole left ventricle and of the three main coronary artery territories. At follow-up, recovery was defined as a > or =5% increase in ejection fraction compared with baseline. Receiver-operating characteristic curve analysis was performed to analyse the data. At baseline, significant correlations were found between ejection fraction and the % surface with decreased sestamibi or BMIPP uptake (r=-0.68, P= 0.001, and r=-0.72, P<0.0001, respectively). When combining both tracers, ejection fraction was significantly associated with the extent of myocardium showing decreased sestamibi uptake with lower BMIPP uptake (mismatching; r=-0.68, P=0.001). At follow-up, significant functional recovery was found in 13/18 patients. By ROC curve analysis, the optimal pattern of distribution predicting recovery was a mismatching with uptake of sestamibi <70% and uptake of BMIPP at least 10% lower. For this parameter, optimal cut-off of extent was 10% of the whole left ventricle surface (sensitivity 69%, specificity 80%, accuracy 72%) and 25% of the infarct-related arterial territory (sensitivity 77%, specificity 80%, accuracy 78%). The areas under the curve were 79% for the left ventricle surface and 72% for the individual arterial territories. These results suggest that in patients with acute infarction, quantitative analysis of sestamibi and BMIPP could offer an objective and reproducible method for estimating the severity of cardiac dysfunction and predicting the evolution of ejection fraction after revascularization.

Quantification of 99Tcm-HMPAO brain SPET in two series of healthy volunteers using different triple-headed SPET configurations: normal databases and methodological considerations.

We evaluated the methodological issues underlying the assessment of normal confidence intervals, as used in clinically based region-of-interest (ROI) semi-quantification of 99Tcm-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.

Validation of the cerebellum as a reference region for SPECT quantification in patients suffering from dementia of the Alzheimer type.

In longitudinal brain studies of dementia of the Alzheimer type (DAT), the cerebellum is often used as a reference region for single photon emission computed tomography (SPECT) quantification, which assumes no significant regional influence of physiological fluctuations or pathology. With the use of absolute quantification in DAT patients, reproducibility of cerebellar uptake of technetium-99m-d,l-hexamethylpropyleneamine oxime (HMPAO) was tested and compared with the mean absolute cerebellar tracer uptake value in DAT patients and healthy control subjects. In 13 DAT patients SPECT studies were repeated within 2 weeks to assess reproducibility of cerebellar regional brain uptake (rBU). With calibrated point sources as scaling factors, cerebellar activity was expressed as rBU of HMPAO per cm3 brain tissue in percent of the injected lipophilic dose of 740 MBq (20 mCi). Also, mean cerebellar rBU in patients suffering from DAT was calculated and compared with a previously established database obtained in healthy volunteers. Repeated SPECT studies within a 2-week interval in clinically stable patients resulted in a mean rBU increase of 6.8 +/- 10.3% in the second SPECT study as compared with the first. A similar shift was previously reported in healthy volunteers. Mean cortical cerebellar rBU values in DAT patients and in the healthy reference population concurred, after cumulative corrections for body surface and for a mean brain volume of 1350 ml (obtained in healthy control subjects), showing respective mean values of 53.9 +/- 7.4 and of 52.0 +/- 7.3 x 10(-6) of the injected lipophilic dose 740 MBq (20 mCi) of HMPAO per cm3 of brain tissue. A unidirectional shift in mean absolute cerebellar uptake values occurs between repeat SPECT examinations in DAT patients similar to previous findings in a group of healthy volunteers. The origin of this phenomenon remains elusive but deserves further study with regard to SPECT (semi)quantification in DAT patients. Most interestingly, the presented findings suggest that with the use of HMPAO SPECT in DAT patients the cerebellum remains scintigraphically uninvolved.

BMIPP imaging to improve the value of sestamibi scintigraphy for predicting functional outcome in severe chronic ischemic left ventricular dysfunction.

UNLABELLED: Mismatching between beta-methyl-p-iodophenyl-pentadecanoic acid (BMIPP) and perfusion accurately predicts functional outcome after acute myocardial infarction. The current investigation was aimed at evaluating the value of this method to predict the evolution of global function according to the applied treatment in patients with chronic ischemic heart disease. METHODS: Twenty patients with infarction and chronic left ventricular dysfunction were studied (median infarction age 12 wk, range 2 wk-15 y). Radionuclide angiography, two-dimensional echocardiography and BMIPP and gated sestamibi scintigraphy were performed with the patient at rest before and >6 mo after treatment (revascularization in 13 patients and conservative therapy in 7 patients). In 7 patients, radionuclide angiography was repeated after 1 y. RESULTS: On a patient basis, mismatching with BMIPP less than sestamibi was noted in 15 patients at baseline. Of these 15 patients, 11 had significant functional improvement at follow-up versus only 1 of the 5 patients with a matched decreased uptake. Hence, the combined sestamibi/BMIPP was 73% positive and 80% negative in predicting functional outcome, with a global accuracy of 75%. On a segmental basis, using an optimal threshold of uptake defined by receiver operating characteristic curve analysis, sestamibi was only 63% accurate in predicting regional outcome. Adding BMIPP improved the accuracy to 80% (P = 0.001). At follow-up, significant mismatching was still noted in 7 patients in the revascularized group and 1 in the medically treated group. The mismatch was associated with a further increase in ejection fraction at 1-y follow-up in only the revascularized group. CONCLUSION: In patients with chronic left ventricular dysfunction after infarction, a mismatching with BMIPP less than sestamibi reliably identifies jeopardized but viable myocardium and predicts functional recovery with an accuracy similar to that reported in the acute and subacute phases of the infarction.

Quantification of 99Tcm-sestamibi and 123I-BMIPP uptake for predicting functional outcome in chronically ischaemic dysfunctional myocardium.

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 99Tcm-sestamibi and 123I-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 < 7% mismatched surface or matching were not. Fifteen patients were viable, of whom 13 were revascularized (16 territories). At follow-up, global function improved in 11 of the 15 viable patients, all in the revascularized group. Regional improvement was noted in 11 of 16 revascularized territories, and was associated with a significant increase in sestamibi and BMIPP uptake and in the percent normally perfused myocardial surface. In the five patients without significant viability, no functional deterioration or changes in the quantitative parameters were observed during treatment. The results suggest that quantitative analysis of the uptake of sestamibi and BMIPP is a reliable method to objectively assess the presence of myocardial viability in chronic ischaemic heart disease and to predict functional improvement after revascularization.

Influence of high-energy photons on the spectrum of iodine-123 with low- and medium-energy collimators: consequences for imaging with 123I-labelled compounds in clinical practice.

Using iodine-123 labelled radiotracers, the presence of 2.5% high-energy photons causes image deterioration due to increased scatter. To investigate the influence of these photons on image quality, we measured the spectrum of 123I with a medium-energy (ME), a low-energy all-purpose (LEAP) and a low-energy high-resolution (LEHR) collimator. Even in air, using low-energy collimators a high baseline activity was observed over the total energy detection range of the gamma camera. The 159-keV photopeak to scatter activity ratio fell from 5.9 for ME to 3.6 and 2.9 for LE collimators. Acquisition of images with LEHR collimators with energy windows set at 159 keV and 500 keV demonstrated that the 159-keV LEHR image is a combination of the ME image of the object and of the LEHR 500-keV image. Because of their important septal penetration and greater geometric detection efficiency compared with the 159-keV photons of 123I, the contribution of high-energy photons is dependent on the source-detector distance. For a small source placed in air, the scatter to photopeak activities varied from 17.4% at 80 cm to 37.8% at 5 cm distance from an LEHR collimator. Considering only the scatter problem, ME collimators are the best choice for 123I studies. When using LE collimators for high-resolution tomography with 123I-labelled compounds, scatter contribution from high-energy photons has to be corrected for quantitative analysis or when dual-isotope studies are performed, whether or not these studies are acquired simultaneously.

Influence of methodology on the presence and extent of mismatching between 99mTc-MIBI and 123I-BMIPP in myocardial viability studies.

UNLABELLED: Discordant uptake (mismatching) of 123I-labeled beta-methyl-piodophenyl-pentadecanoic acid (BMIPP) less than 99mTc-labeled methoxyisobutyl isonitrile (MIBI) is a good predictor of myocardial viability. However, methodological factors can influence assessment of the presence of mismatching because of differences in background activity between the tracers. In this study, we investigated the influence of methodological parameters on the mismatching between BMIPP and MIBI in patients with chronic ischemic heart disease. METHODS: Polar maps were created to quantify the extent of mismatched tissue measured in 10 patients with myocardial infarction according to three methods for data processing: no correction, subtraction of background activity measured in the left ventricle cavity and dual-window scatter correction. Mismatching was expressed as a percentage of the surface of the left ventricle globally as well as for each arterial territory using a BMIPP uptake of at least 10% less than MIBI as the threshold. The results of dobutamine stress echocardiography and the evolution of the regional contractility at 6-mo follow-up were used as references. RESULTS: Mean background activity in the ventricle cavity was 9.3% of the maximum activity for MIBI and 21.4% for BMIPP before, and 2.8% and 8.3% after scatter correction. Fourteen arterial vascular territories demonstrated baseline wall-motion abnormalities; 9 territories showed contractile reserve with dobutamine stress echocardiography. Significant mismatching was found in 5 of 14 regions without correction, 9 of 14 after scatter correction and 13 of 14 after background subtraction. Compared with the evolution of resting regional contractility at follow-up, optimal results were found when using the scatter-corrected data. Without correction, mismatching between BMIPP and MIBI was partially disguised because of the higher noise level in the iodine images. On the contrary, subtraction of background measured by means of a single region of interest overestimated the magnitude of mismatching due to the heterogeneous background distribution in the ventricular cavity. CONCLUSION: In quantifying the presence and extent of mismatching between MIBI and BMIPP in chronic ischemic heart disease, significant differences in the detection of viability are noted according to the acquisition and processing methods used. Scatter correction of the acquisition data is the most accurate and reliable method for identifying viable myocardium.

Abnormal BMIPP uptake in chronically dysfunctional myocardial segments: correlation with contractile response to low-dose dobutamine.

UNLABELLED: Discordance between 123I-15-(p-iodophenyl)-3-(R,S)-methyl pentadecanoic acid (BMIPP) and sestamibi uptake has been described as a good predictor of functional recovery in patients with a recent myocardial infarction. The current investigation aimed at evaluating BMIPP as a viability tracer in patients with chronic ischemic left ventricular dysfunction. METHODS: Thirty-one studies were obtained in 25 patients with severe left ventricular dysfunction postinfarction (median infarction age 3.6 mo; range 2 wk-15 yr). All patients underwent dobutamine stress echocardiography and a resting 99mTc-sestamibi/123I-BMIPP SPECT study in a 3-day interval. The relative uptake of the two tracers was compared to the evolution of wall motion during dobutamine infusion in 8 matched myocardial segments. RESULTS: Among the 130 segments with abnormal wall motion at rest, 70 improved under dobutamine. Using sestamibi, a normal uptake was 88% predictive of a positive response to dobutamine, and a decreased uptake of 63% predicted negative stress echocardiography response. In the segments with abnormal sestamibi uptake, adding BMIPP significantly increased the accuracy of scintigraphy to detect residual viability; 28 of 48 segments (58%) with a mismatched pattern demonstrating residual inotropic reserve under dobutamine infusion versus only 5 of 40 segments (13%) with a matched defect. Global agreement between the two approaches was 77%, and positive and negative predictive values for scintigraphy were 72% and 88%, respectively. CONCLUSION: In patients with chronic ischemic left ventricular dysfunction, the combined assessment of metabolism and perfusion with 123I-BMIPP and 99mTc-sestamibi correlates well with the response of wall motion to dobutamine during stress echocardiography and is more sensitive than sestamibi alone for differentiating viable from scar segments.