Efficiency comparison between 99m Tc-tetrofosmin and 99m Tc-sestamibi myocardial perfusion studies.

The purpose of this investigation was to compare the efficiency of two different imaging protocols using two different clinically available 99mTc labelled myocardial perfusion tracers. One thousand one hundred and thirty-four imaging studies were performed prospectively, using either 99mTc-tetrofosmin or 99mTc-sestamibi, alternating the use of each tracer for a total period of 8 months. 99mTc-tetrofosmin rest studies were performed with injections of 259MBq-370MBq and imaging 30 min later. Exercise studies were performed with injections of 777MBq-1.11GBq and imaging 20 min later. 99mTc-sestamibi studies used doses similar to those in the 99mTc-tetrofosmin studies. Imaging followed a standard procedure, at 60 min after rest injection, and 30 min after exercise. For patients undergoing pharmacological stress testing99mTc-sestamibi was imaged 45 min after injection and 99mTc-tetrofosmin was imaged 30 min after injection. Variables analysed were (1) injection-to-imaging time for the procedure, and (2) the number of repeated scans because of extra cardiac activity. The completion time for the rest study was significantly shorter for 99mTc-tetrofosmin compared to 99mTc-sestamibi (47.7+/-21.7 min vs 74.3+/-25.8 min P<0.0001). Likewise, the total study time was shorter for 99mTc-tetrofosmin compared to 99mTc-sestamibi (90+/-32.7 min vs 124+/-37 min, P<0.0001). More importantly, the number of repeated scans was higher with 99mTc-sestamibi compared to 99mTc-tetrofosmin, 21.4% vs 10%, P=0.001 for rest studies and 16.4% vs 7.9% P=0.001 [corrected] for rest and stress. It was concluded that, using a same day rest/stress protocol, 99mTc-tetrofosmin provided higher patient throughput with fewer repeat scans. These factors may be considered for efficiency improvement in nuclear cardiology laboratories using 99mTc perfusion tracers.

Poststress measurements of left ventricular function with gated perfusion SPECT: comparison with resting measurements by using a same-day perfusion-function protocol.

PURPOSE: To investigate the relationship between the development of ischemia during stress testing and the changes in left ventricular ejection fraction (LVEF) measurements obtained after stress and at rest with a same-day perfusion-function imaging protocol. MATERIALS AND METHODS: One hundred twenty-six patients underwent a same-day rest-stress (61%) or stress-rest (39%) protocol and gated single photon emission computed tomography (SPECT). Perfusion analysis was performed with a 12-segment model. Defects were scored (0 = no defect, 1 = mild defect, 2 = moderate defect, and 3 = severe defect); differences between the summed stress and resting scores of greater than three indicated substantial ischemia. RESULTS: Resting and poststress LVEFs correlated significantly (r = 0.97, P <.001); however, patients with and patients without ischemia had significant differences in poststress versus resting LVEFs (-4.0 vs 1.0, respectively; P <.01). In patients with ischemia versus patients without ischemia, subgroup analysis stress-rest (-2.5 vs 1.0, P =.047) and rest-stress (-4.0 vs 1.0, P =.006) protocols yielded similar results. CONCLUSION: In patients with clinically important stress-induced perfusion abnormalities, the LVEF after stress was significantly lower than the LVEF at rest with same-day rest-stress and stress-rest imaging protocols. In the clinical setting, poststress LVEFs may be lower than true resting measurements, particularly in patients with moderate to severe stress-induced ischemia.

Ventilation-perfusion lung scintigraphy as a guide for pulmonary angiography in the localization of pulmonary emboli.

PURPOSE: To assess the appropriateness of ventilation-perfusion (V-P) scintigraphic abnormalities as a guide to pulmonary angiography for the diagnosis of pulmonary embolism (PE). MATERIALS AND METHODS: V-P scintigrams and pulmonary angiograms of 104 patients with angiographically proved PE were reviewed by two nuclear medicine physicians and two interventional radiologists. For V-P scintigrams, the lung with the larger amount of perfusion abnormality was determined followed by identification of specific lobes. Pulmonary angiograms were similarly evaluated for lateralization and lobar distribution of PE. Conclusions were initially reached independently and subsequently by consensus. RESULTS: Interobserver agreement for lateralization was 88% (kappa = 0.75) for V-P scintigraphy and 98% (kappa = 0.96) for pulmonary angiography. In 72 patients, V-P scintigrams predicted unilateral embolus; 64 patients underwent pulmonary angiography of the suspected side. Eight patients underwent contralateral angiography only. Of the 64 patients, 61 (95%) had PE on the predicted side at angiography. V-P scintigrams predicted lobar distribution in 55 patients. Of these, PE was found in the predicted lobe in 42 (76%). CONCLUSION: Localization of perfusion abnormalities at V-P scintigraphy provides useful information for the interventional radiologist and serves as an accurate guide for determining the initial approach for pulmonary angiography.

Correlation of hippocampal neuronal density and FDG-PET in mesial temporal lobe epilepsy.

PURPOSE: Interictal [18F]fluorodeoxyglucose (FDG) positron emission tomography (PET) reveals regional hypometabolism in 60-80% of patients with mesial temporal lobe epilepsy (MTLE). The extent of hypometabolism generally extends beyond the epileptogenic zone. The pathophysiology underlying this widespread change is unknown. This study evaluated the relation between hippocampal neuronal loss and hypometabolism in patients with MTLE. METHODS: Forty-three patients with MTLE after anterior temporal lobectomy were included. Pathology demonstrated mesial temporal sclerosis (n = 41) or endfolium sclerosis (n = 2). Interictal FDG-PET scans were graded by visual analysis on a scale ranging from normal (grade 1) to severe (grade 5) hypometabolism. Neuronal counting was performed in the subiculum, hippocampal subfields, and dentate granular cell layer (DG). Neuronal density of patients was compared with that of seven autopsy controls. Data were compared by using Student's t tests and Kruskal-Wallis one-way analysis of variance (ANOVA). RESULTS: Significant neuronal loss in CA1 through CA4 and DG was found in patients compared with controls. Neuronal density in the subiculum, CA1, CA4, and DG did not correlate with severity of hypometabolism. However, patients with abnormal FDG-PET had higher neuronal density in CA2 and CA3 versus patients with normal studies. CONCLUSIONS: This study supports a previous observation that degree of FDG-PET hypometabolism does not parallel severity of hippocampal neuronal loss in MTLE.

Combined Tc-99m sestamibi first-pass radionuclide angiography and cardiac SPECT imaging during arbutamine infusion delivered by a computerized closed-loop system.

PURPOSE: This study evaluated the feasibility, hemodynamic responses, and relation of combined Tc-99m sestamibi SPECT imaging and first-pass radionuclide angiography during the infusion of a new beta agonist arbutamine. METHODS: Arbutamine was administered to 15 patients and constantly adjusted by a closed-loop computerized system. Rest and arbutamine Tc-99m sestamibi radionuclide angiography was performed with a multicrystal gamma camera followed by SPECT imaging with a rotating triple-head, single-crystal gamma camera. RESULTS: The mean differences (paired t-test) between rest and arbutamine studies for heart rate (HR), end-diastolic volume (EDV), stroke volume (SV), cardiac output (CO), and ejection fraction (EF) were as follows: 55 bpm for HR (P < 0.001), 5 ml for EDV (P=ns), 7.5 ml for SV (P=0.04), 4.4 l/min for CO (P < 0.001), and 6.4% for EF (P < 0.001), respectively. The results of SPECT studies were abnormal in six patients and normal in nine. Findings of radionuclide angiography were normal in 12 patients and abnormal in three. Interpretation of the perfusion and functional studies were concordant in 10 and discordant in five patients. CONCLUSIONS: Simultaneous cardiac radionuclide angiography and SPECT imaging are feasible during arbutamine infusion. This potent beta agonist increases cardiac output through a chronotropic effect with no significant changes in EDV. The discordance in SPECT and radionuclide angiography results may represent incremental diagnostic and prognostic information provided by both studies.

Locally increased uptake of fluorine-18-fluorodeoxyglucose after intracavitary administration of iodine-131-labeled antibody for primary brain tumors.

UNLABELLED: After the intracavitary administration of 131I-labeled monoclonal antibody for treatment of primary brain tumors after surgical resection, a persistent rim of 18F-fluorodeoxyglucose (FDG) accumulation surrounding the cavity can be observed on PET. This rim, although it accumulates more FDG than adjacent normal brain tissue, is not necessarily associated with tumor. In our study, we examine the characteristics of the rim that indicate persistent tumor and tumor progression. METHODS: Sequential PET studies obtained after treatment in 10 patients were reviewed and the results correlated with dosimetry and post-treatment histologic diagnoses. RESULTS: The rim of FDG accumulation was seen on the first post-treatment scan obtained 1-3 mo after therapy and persisted unchanged over the 2-26 mo follow-up period. Pathologically, the nonmalignant rim was associated with marked increase of macrophage infiltrates. Nodularity of the rim was associated with tumor. CONCLUSION: Our study demonstrates that a rim of FDG accumulation is seen after intracavitary administration of 131I-labeled monoclonal antibody therapy independent of the presence of malignant disease. Malignant recurrence is suggested by the development of new nodularity in the rim of FDG accumulation.

Iodine-131-metaiodobenzylguanidine uptake in metastatic carcinoid tumor to the orbit.

Metastatic tumor is one of several etiologies of space-occupying masses in the orbit that accounts for 1%-13% of all orbital masses (1). In the adult patient population, breast cancer is the most common tumor to metastasize to the orbit followed by metastases from the lung, prostate and gastrointestinal tract (2). It is rare for carcinoid tumors to metastasize to the eye or to the orbit. Carcinoid tumors arise from Kulchitsky cells that originate in the neural crest. Histologically, these tumors resemble, but are not as aggressive as, adenocarcinomas. Most carcinoids arise in the gastrointestinal tract or the lung. The most common site for carcinoid metastases is the liver. On anatomical imaging studies, such as CT and magnetic resonance imaging, metastatic orbital carcinoid tumors appear as nonspecific tumor masses. Carcinoid tumors have an affinity for uptake of the radiopharmaceutical 131I-metaiodobenzylguanidine (MIBG) (3). We report a case of a patient with a known carcinoid tumor who developed a left orbital mass that demonstrated abnormal uptake of 131I-MIBG indicative of metastatic carcinoid tumor to the orbit.

Analysis of cardiac arrhythmias during dobutamine pharmacologic stress testing in nuclear cardiology as related to the presence or absence of baseline arrhythmias.

BACKGROUND: Intravenous dobutamine is an acceptable pharmacologic stress agent for evaluation of myocardial ischemia, but it has the undesirable side effect of precipitating cardiac arrhythmias. All patients are susceptible to the arrhythmogenic potential of dobutamine. However, the presence of a baseline arrhythmia creates additional concern about proceeding with a pharmacologic dobutamine stress test. The purpose of this study was to evaluate cardiac arrhythmias during dobutamine stress as they relate to the presence or absence of baseline arrhythmias in patients undergoing radionuclide myocardial perfusion imaging. METHODS AND RESULTS: Data from 486 consecutive dobutamine stress tests in nuclear cardiology were reviewed retrospectively. Baseline and stress electrocardiographic monitoring and 12-lead electrocardiograms were used for classification of arrhythmias. For patients without baseline arrhythmias, the estimated probability of having nonsustained ventricular tachycardia with dobutamine stress was 4.0% (16 of 403), as compared with 15.7% (13 of 83) for patients with baseline arrhythmias (p < 0.001). Three of the 403 patients (0.7%) and 2 of the 83 patients (2.4%) had their study terminated because of ventricular tachycardia (p > 0.05). CONCLUSIONS: The probability of having nonsustained ventricular tachycardia with dobutamine stress testing was significantly greater in patients who had baseline arrhythmias than in those who had no arrhythmias at baseline. Although termination of the study because of ventricular tachycardia was not statistically significant between these two groups, patients with baseline cardiac arrhythmias should be considered at higher risk for the development of nonsustained ventricular tachycardia during dobutamine stress testing than patients who have no baseline arrhythmia.

Role of right ventricular and pulmonary functional abnormalities in limiting exercise capacity in adults with congenital heart disease.

This study evaluates right ventricular (RV) and pulmonary function during exercise in adults with congenital heart disease (CHD). Thirty-one patients with CHD involving the right side of the heart underwent symptom-limited bicycle exercise testing with simultaneous expired gas analysis and measurement of RV ejection fraction (EF). Twenty-one age-matched normal controls underwent the identical exercise protocol. Maximal oxygen consumption was lower in the CHD than in normal controls (19.5 +/- 6.4 vs 30.5 +/- 0.8 ml/kg/min, p = 0.0001 patients vs controls). Both heart rate (156 +/- 25 vs 171 +/- 13 beats/min, p = 0.01) and oxygen pulse (9.3 +/- 3.7 vs 12.3 +/- 3.7 ml/beat, p = 0.01), an indirect measure of stroke volume, were found to be lower in the CHD group at peak exercise. Pulmonary dysfunction was evidenced in the CHD group by decreased forced expiratory volume, forced vital capacity and maximum voluntary ventilation, and by a higher ventilation/expired carbon dioxide ratio at peak exercise (37.2 +/- 6.9 vs 33.0 +/- 5.4, p = 0.02), suggesting an increase in dead space ventilation. Maximal oxygen consumption was lower in patients whose RVEF decreased with exercise (17.6 +/- 5.4 vs 22.8 +/- 6.4 ml/kg/min, p = 0.03 "decrease RVEF" group vs "increase RVEF" group). Maximal oxygen consumption correlated with the change in RVEF only in the group whose RVEF decreased with exercise (r = 0.5, p = 0.03). In the group that had increased RVEF with exercise, maximal oxygen consumption correlated with forced expiratory volume (r = 0.7, p = 0.02). Thus, adults with CHD have a reduced functional capacity compared with normal controls. This phenomenon appears to be associated with both RV and pulmonary abnormalities.

Prediction of severe coronary artery disease by combined rest and exercise radionuclide angiocardiography and tomographic perfusion imaging with technetium 99m-labeled sestamibi: a comparison with clinical and electrocardiographic data.

BACKGROUND: The purpose of this study was to compare the incremental value of clinical information, electrocardiographic data, myocardial perfusion imaging, and radionuclide angiography for predicting severe coronary artery disease at a single testing interval. Clinical information, treadmill exercise studies, radionuclide angiography, and myocardial perfusion imaging are important predictors of severe coronary artery disease. However, the relative and absolute diagnostic importance of each of these methods has not been addressed at a single testing interval. METHODS AND RESULTS: A same-day rest/treadmill exercise perfusion and function study was performed in 167 patients within 90 days of coronary angiography. A multivariable regression model was used to assess the independent informational content of these predictors. Clinical and electrocardiographic data were related strongly to the presence of severe coronary artery disease (chi2 = 12.2 and p < 0.001; chi2 = 11.8 and p < 0.001, respectively). Combined perfusion and functional studies contributed 31% of the diagnostic information beyond that provided by clinical and electrocardiographic data alone (p < 0.05). CONCLUSIONS: These data demonstrate that combined studies of myocardial perfusion and left ventricular function are able to improve prediction of the extent of coronary artery disease, even when clinical and electrocardiographic data are also available.

Estimation of myocardial blood flow for longitudinal studies with 13N-labeled ammonia and positron emission tomography.

BACKGROUND: Although several modeling strategies have been developed and validated for quantification of myocardial blood flow (MBF) from 13N-labeled ammonia positron emission tomographic data, a comparison of noise characteristics of the various techniques in serial studies is lacking. METHODS AND RESULTS: Dynamic 13N-labeled ammonia positron emission tomographic imaging was performed at baseline and after pharmacologic stress in (1) single studies of four dogs with concomitant measurement of microsphere blood flow and (2) initial and follow-up studies of eight normal volunteers. Data were obtained from short-axis images for the blood pool and myocardial regions corresponding to the three arterial vascular territories. Indexes of MBF were obtained by four distinct techniques: (1) University of California, Los Angeles, two-compartment model, (2) Michigan two-compartment model, and (3) a one-compartment model with variable blood volume term. Coronary flow reserve (CFR) was measured as the ratio of stress/rest MBF. The estimated standard deviation of the measurement error for the relative change between studies of rest and stress MBF and CFR was determined for each technique. Estimates of MBF from all techniques showed good correlation with microsphere blood flow (r = 0.95 to 0.96) in canine myocardium. In human studies, similar mean estimates of MBF were found with all techniques. Techniques 1 and 3 showed the smallest interstudy variability in MBF and CFR. The estimated standard deviations for these techniques were approximately 20%, 30%, and 27% for rest MBF, stress MBF, and CFR, respectively. CONCLUSION: Noninvasive quantification of MBF and CFR from dynamic 13N-labeled ammonia positron emission tomography is most reproducible with technique 1 or 3. The ability to account for differences in myocardial partial volume gives preference to technique 3. However, substantial interstudy variability in regional MBF remains, suggesting the importance of procedural factors or real temporal fluctuations in MBF.

Interpretation variability of 18FDG-positron emission tomography studies in dementia.

RATIONALE AND OBJECTIVES: Functional imaging studies such as 18F-fluoro-18-labeled-deoxyglucose-positron emission tomography (18FDG-PET) are being used increasingly in the evaluation of patients with dementia. The authors evaluate inter- and intraobserver interpretation agreement in a diverse group of patients with clinically diagnosed dementia and subjective memory complaints, as well as two healthy control subjects. METHODS: Ninety-six patients with clinical diagnoses of probable Alzheimer's disease (n = 18), possible Alzheimer's disease (n = 33), dementia (n = 26), and mild memory impairment (n = 17), as well as two healthy control subjects were studied using 18FDG-PET. Three observers graded all studies for regional 18FDG uptake in the temporal, parietal, and frontal regions bilaterally. The studies also were interpreted for the presence of bilateral temporoparietal hypometabolism, which typically is present in Alzheimer's disease. The kappa statistic was used to determine intra- and interobserver agreement for regional 18FDG uptake and bilateral temporoparietal hypometabolism. RESULTS: There was excellent intraobserver (kappa = .56, P < 0.0005) and interobserver (kappa = .51, P < 0.0005) interpretation agreement for bilateral temporoparietal hypometabolism. There also was excellent intraobserver (kappa = .61, P < 0.000) and interobserver (kappa = .55, P < 0.000) interpretation agreement of regional 18FDG uptake. Interobserver agreement was extremely high in those patients who were considered clinically to have possible (kappa = .42, P < 0.001) or probable (kappa = .42, P < 0.01) Alzheimer's disease. CONCLUSIONS: Results confirm that bilateral temporoparietal hypometabolism is the metabolic abnormality associated with the diagnosis of probable Alzheimer's disease. Furthermore, intra- and interobserver agreement of visual interpretation of 18FDG-PET images indicates that 18FDG-PET is acceptable as an imaging technique in the clinical evaluation of the dementia patient.

Association of physical fitness and transient myocardial ischemia in patients with coronary artery disease.

PURPOSE: To examine the relationship between physical fitness and transient myocardial ischemia (TMI) in the laboratory and during daily life, in a sample of coronary patients with a recent positive exercise test. METHODS: 47 patients with coronary disease (CAD) participated in laboratory mental and exercise stress testing and 48-hour outpatient Holter monitoring after being withdrawn from ant-ischemic medications. During laboratory testing, left ventricular performance was assessed by radionuclide ventriculography. Physical fitness was assessed by measurement of oxygen consumption during symptom-limited exercise treadmill testing. RESULTS: Higher physical fitness subjects were less likely to exhibit wall-motion abnormalities in response to mental stress (P < .05), and to exercise stress (P < .05) testing. They also had smaller decreases in left ventricular ejection fraction (LVEF) in response to mental stress than less fit subjects (P .056), and exhibited a mean increase in LVEF during exercise, compared to the less fit subjects who exhibited a decrease in LVEF (P < .02). Moreover, higher fit subjects exhibited fewer episodes of TMI (P < .04), for a shorter duration (P < .04), and less total ischemic burden (P < .04) during Holter monitoring. CONCLUSION: These findings suggest that within a population of CAD patients, higher levels of physical fitness are associated with less TMI assessed in the laboratory and during routine activities of daily living.

Relative importance of electrode placement over number of channels in transient myocardial ischemia detection by Holter monitoring.

To compare the efficacy of 3-channel ambulatory electrocardiographic monitoring (Holter monitoring) with 2-channel Holter monitoring in the detection of transient myocardial ischemia (TMI), channels CM2, CM5, and modified II were studied. Sixty patients with documented coronary artery disease underwent 48-hour Holter monitoring during their normal daily life, followed by exercise stress testing in the laboratory monitored by means of radionuclide ventriculography and standard 12-lead electrocardiography. Analysis revealed that 3-channel Holter monitoring identified 24 patients with a total of 205 TMI episodes and a total ischemic burden of 371.00 mV-min. By itself, CM2 would have detected only 3 patients (13% of the TMI population), 6 TMI episodes (3% of the total TMI episodes), and a 2.4 mV-min ischemic burden (0.7% of the total ischemic burden). Modified II alone would have identified 17 patients (71% of the TMI population), 160 TMI episodes (78% of the total TMI episodes), and 307.24 mV-min of the ischemic burden (82% of the total ischemic burden). The combination of CM5/modified II identified 23 patients (96% of the TMI population), 201 TMI episodes (98% of the total TMI episodes), and 370.44 mV-min of the ischemic burden (98% of the total ischemic burden). These findings suggest that the electrode placement is more important than the absolute number of channels in the detection of TMI by Holter monitoring.

18-Fluorodeoxyglucose positron emission tomography in children and adolescents with traumatic brain injury.

Twenty-two previously normal children and adolescents who suffered a severe, non-penetrating traumatic brain injury had PET during rehabilitation at a median of 1.5 months after the injury. Outcome was assessed at a median of 25 months after brain injury. 16 subjects had CT or MRI within 24 days of PET and 11 subjects had a second PET at the point of outcome (median 28 months after first PET). The PET score (obtained by adding the score of 15 brain regions: normal metabolism = 1; reduced = 0) was significantly associated with the clinical outcome measure. PET earlier than 12 weeks after head trauma correlated with outcome, but later PET did not. PET scores improved significantly between rehabilitation and outcome for the 11 subjects who had two PETs, but improvement was not associated with improvement in clinical condition. PET score did not add to the amount of variance explained in the last regression model for prediction of outcome when the results of contemporaneous CT/MRI and clinical condition were taken into account. The data suggest that routine PET during rehabilitation is no more useful than contemporaneous CT or MRI for prediction of outcome.

Neural correlates of dementia: regional brain metabolism (FDG-PET) and the CERAD neuropsychological battery.

The present Investigation examined the biological correlates of the cognitive deficits of Alzheimer's disease and related dementias using the neuropsychological assessment battery of the Consortium to Establish a Registry of Alzheimer's Disease (CERAD) and positron emission tomography (PET). Resting state cerebral glucose metabolism was measured using the labelled radiotracer, [18F] Fluoro-2-deoxyglucose (FDG), in a sample of patients with mild to moderate dementia (n = 66). Specific and predictable relationships were seen between regional brain metabolism (left and right, frontal, temporal, and parietal lobes) and the neuropsychological measures of verbal fluency, constructional praxis, and verbal list learning. On tests of naming and delayed verbal recall only diminished FDG uptake in the left frontal lobe and the left temporal lobe, respectively, approached significance. This study demonstrates the expected relationships between neuropsychological performance and regional cerebral metabolism, thereby providing support for the CERAD battery as a valid measure in the clinical evaluation of dementia and for the use of FDG-PET in brain-behavior studies of dementia.

Cerebral imaging of decompression injury patients with 18-F-2-fluoro-2-deoxyglucose positron emission tomography.

The objective assessment of the extent of cerebral insult and the effects of therapy in decompression injury patients has proven to be difficult by most imaging modalities. In this pilot study we evaluated the ability of 18-F-2-fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) to identify metabolic brain abnormalities in decompression injury patients. Twenty-two patients who were evaluated at our institution for decompression accidents were evaluated with FDG-PET. Four of the 22 patients had no neurologic symptoms and no neurologic findings on clinical exam at the time of the FDG-PET study. No statistically significant correlations were found between the presence of symptoms and the demonstration of abnormalities on the PET study and no statistically significant correlation was found between the location of the decompression injury and the demonstration of abnormalities on the PET study. We conclude that FDG-PET imaging of the brain cannot reliably identify cerebral abnormalities in patients with decompression injuries and would be of limited benefit for monitoring therapy in patients with decompression illness.