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Myocardial leukocyte infiltration is one hallmark of acute myocardial infarction. In order to detect noninvasively this inflammatory response associated with acute myocardial infarction, we produced coronary occlusion in eight dogs, intravenously administered autologously labeled indium-111 (111In) leukocytes and scintigraphically monitored accumulation of radionuclide in myocardium. Seventy-two hours after coronary occlusion, 111In-labeled white cells accumulated in regions corresponding to myocardial infarcts, and positive images with 111In-labeled leukocytes correlated well with images obtained with technetium-99m pyrophosphate and computer-reconstructed tomograms obtained with nitrogen-13-labeled ammonia. In contrast, two control dogs subjected to sham operation did not exhibit positive 111In-leukocyte images. Scintigraphic results with 111In-labeled leukocytes were verified in vitro by analysis of radioactivity in normal myocardium and in infarcts. Thus, leukocytic infiltration associated with acute myocardial infarction can be detected noninvasively in vivo.

The value of rest and exercise radionuclide angiography (RNA) for predicting specific events including death, recurrent acute myocardial infarction (AMI), coronary care unit readmission for unstable chest pain, and medically refractory angina after AMI was studied in 106 consecutive survivors of AMI. Analysis of the RNA variables using the Cox proportional hazards regression model yielded significant associations of the time to death with ejection fraction at rest and during exercise (X2 = 11.1 and 14.0, respectively). Both variables added significant prognostic information to the clinical assessment (X2 = 4.3 and 5.7, respectively). The change in ejection fraction from rest to exercise predicted the time to coronary artery bypass grafting for medically refractory angina before (X2 = 21.0) and after (X2 = 13.2) adjustment for the clinical descriptors, but did not predict death or other non-fatal events. Significant correlations were found between RNA variables and a variety of clinical descriptors previously reported to have prognostic significance. Clinical and RNA variables that are measures of left ventricular function were predictive of subsequent mortality, whereas those that reflect residual potentially ischemic myocardium were predictive of subsequent nonfatal ischemic events. Rest and exercise RNA after AMI provides significant prognostic information regarding specific events during follow-up independent of that provided by clinical assessment.

Mononuclear phagocytes (monocytes and macrophages) are widely disttibuted throughout the body. Indium-111 ( 111 In) oxine has been a useful radioactive label in studies of in vivo cellular kinetics and distribution. In preparation for in vivo monocyte investigations in humans, this study was designed to determine the effects of labeling human blood monocytes with 111 In on their function in vitro. The monocytes labeled with an efficiency of 57.9 ± 14.2% (range of 47–95%). The 111 In eluted from the cells at a rate of 0.25%/h over 48 h in vitro. The labeled monocytes had a slight, but statistically significant, reduction in their ability to phagocytize or mediate antibody-dependent cellular cytotoxicity of antibody- coated sheep erythrocytes. The labeled cells were not different than control monocytes with respect to viability (trypan blue exclusion and lactate dehydrogenase release), adherence to plastic, hydrogen peroxide production, chemotaxis to N -formyl methionylleucylphenylalanine, and antibody-dependent lysis of the tumor cells U937 and HeLa. 111 In-labeled human monocytes should be useful for in vivo studies of mononuclear phagocyte kinetics and distribution in normal and diseased subjects.

To study rest and exercise pulmonary capillary blood flow (Qc) and diffusing capacity (DLexh) assessed by the rapid analysis of methane, acetylene, and carbon monoxide during a single, slow exhalation, we evaluated 36 subjects during first-pass radionuclide angiography (RNA). At rest (N = 36) and at exercise (N = 21) there was no difference in the respective measurements of cardiac output (Qc = 6.0 +/- 1.7 and CORNA = 6.9 +/- 2.5 at rest; Qc = 13.7 +/- 3.2 and CORNA = 14.5 +/- 4.1 at exercise, L/min, mean +/- SD, r = .80). Mild maldistribution of ventilation, as manifested by an increased phase 3 alveolar slope for methane (CH4 slope), did not significantly influence the results. CH4 slope and DLexh did increase significantly with exercise, while total lung capacity remained unchanged (CH4 slope: 6.2 +/- 5.0 vs 12.5 +/- 6.8% delta CH4/L, mean +/- SD, p less than 0.001; Dsb: 27.7 +/- 9.2 vs 42.0 +/- 17.9 ml/min/mm Hg, mean +/- SD, p less than 0.001; TLC: 5.47 +/- .20 vs 5.96 +/- 1.20 L, mean +/- SD). DLexh was related to CORNA (r = .68) and RNA stroke volume (r = .50). Qc was significantly less than CORNA in the subset of studies with valvular regurgitation (VHD) (N = 7). On the other hand, Qc was significantly greater than CORNA in the setting of coronary artery disease (CAD) and severe wall motion abnormalities (N = 7). These differences may be attributed to regurgitant fractions in VHD, and the influence of wall motion abnormalities on the estimation of left ventricular volume by the area-length method in CAD. These two noninvasive methods compare well at rest and exercise in clinical subjects and may provide complementary information in certain cardiopulmonary diseases.

Left ventricular function was evaluated by first-pass radionuclide angiocardiography in 42 patients at 3 and 8 weeks following acute myocardial infarction. Left ventricular ejection fraction, diastolic volume, and wall motion were measured at rest and submaximal exercise at 3 weeks and at rest, submaximal and maximal exercise at 8 weeks. The mean ejection fraction, end-diastolic volume, and wall motion index did not change between 3 and 8 weeks in any group either at rest or during submaximal exercise. Ventricular function was decreased at rest in patients with previous and anterior myocardial infarction, but not in patients with inferior and subendocardial myocardial infarctions. During maximal exercise at 8 weeks, nine patients (21%) had ST segment depression, whereas 25 patients (60%) had a decrease in ejection fraction or a deterioration in wall motion. These abnormalities of ventricular function during exercise occurred equally among the infarct groups. Radionuclide angiography in patients with recent myocardial infarction demonstrated highly variable ventricular function at rest and/or during exercise in each infarct subgroup.

The effects of scatter and attenuation on single photon emission computed tomography (SPECT) images can be analyzed with the aid of sophisticated Monte Carlo simulation. Correction procedures can be evaluated by comparing corrected images with images absent of scatter and attenuation. The simulation enables control of components which govern the emission and transport of radiation through the source and attenuating medium. The basic calculation involves sampling the probability density functions (pdf) which govern the photon transport process. First, the origin of a photon is selected by sampling. Variance reduction is applied so that a detection is "forced" and weighted by the probability of an initial direction within the acceptance angle of the collimator multiplied by the probability that the photon is not attenuated. Second, the photon history is continued by sampling for a direction. The photon is forced to interact within the attenuating medium and an appropriate weight is calculated. Variance reduction is again applied with a weight determined by the product of the probability of interaction within the attenuating medium, the probability of scatter, the probability of scattering into the acceptance angle of the collimator, and the probability that the photon reaches the detector. Finally, a new direction and energy is selected. If the new energy is below the baseline energy, the history is terminated; otherwise, the second step is repeated. Presently, the collimator's geometric efficiency is considered without septal penetration.

We investigated the impact of direct jejunal delivery of various meals on gastric emptying, glucose tolerance, and insulin response in a chronic dog model following duodenojejunostomy. Ten beagle dogs underwent duodenal transection 2 cm distal to the pylorus and end-to-side duodenojejunostomy 20 cm distal to the ligament of Treitz. Three months after operation each dog underwent gastric emptying studies using radiolabeled normal saline, 20% glucose solution, and standardized mixed solid meal. Glucose tolerance tests with plasma insulin determinations were obtained using the glucose meal. After duodenojejunostomy both the rapid exponential pattern of emptying of normal saline and the slower linear pattern of glucose emptying seen in intact dogs were preserved. The linear gastric emptying of the solid meal which was slower than gastric emptying of either of the liquid meals was also preserved. Although integrated plasma glucose levels over 2 hr were 484.8 +/- 40.4 and 456.6 +/- 30.4 mg X hr/dl in intact and duodenojejunostomy dogs, respectively (P greater than 0.05), the initial rate of rise of plasma glucose was significantly delayed in the duodenojejunostomy dogs. But integrated plasma insulin levels over 2 hr differed significantly (P less than 0.05) between the intact (71.6 +/- 9.2 microU X hr/nl) and duodenojejunostomy (48.3 +/- 6.2 microU X hr/nl) dogs. We conclude that duodenojejunostomy (jejunal delivery) preserved the patterns of gastric emptying of saline, glucose, and mixed solid meals; retarded initial plasma glucose response to the glucose meal; and blunted plasma insulin response to the glucose load.

Platelets have been labeled with a lipid soluble complex of the radionuclide indium-111. The complex is formed with 8-hydroxyquinoline and extracted in chloroform which is then evaporated to dryness. The residue is dissolved in 50 μl of ethanol and diluted to 200 μl with normal saline. Platelets are separated by differential centrifugation, washed and suspended either in Tyrodes-albumin solution or in normal saline. The solution of 111 In-complex is added to separated platelets and more than 95% of the radioactivity is incorporated with the platelets. The function of the labeled platelets has been studied by their aggregability using adenosine diphosphate and collagen as the stimulating agents. No adverse effects have been observed. The survival of the indium-labeled platelets was similar to that observed with chromium-51 labeled platelets. Labeled canine platelets have been administered to dogs in whom venous thrombi had been induced by alteration of the intima by an electric current. The thrombi were detected by imaging 50 minutes after administration of the labeled platelets. Twenty-four hours later the thrombi were removed and had 20–50 times the radioactivity of an equal weight of blood. Accumulation of large amounts of radioactivity in surgical wounds has also been observed. Damage of the intima of carotid arteries in animals by a balloon catheter demonstrated 8 to 20 times more activity in the damaged artery than in the normal artery. Results indicate that In-111 labeled platelets have potential both for platelet survival studies and for evaluation of vascular damage.

In contrast to young persons, normal elderly persons who undergo symptom-limited dynamic exercise demonstrate a decrease in left ventricular (LV) contractile performance characterized by a decrease in LV ejection fraction. To test the hypothesis that physical conditioning can be achieved in older persons and produces improvement in the exercise-induced decrease in LV ejection fraction observed during normal aging, we examined 24 normal elderly persons (mean age 72.0 years) before and after a 12-week program of physical training. The subjects had been screened for evidence of cardiovascular disease including rest and exercise stress electrocardiograms. All subjects underwent rest and exercise upright sitting radionuclide angiocardiography before and after the training program. The subjects achieved cardiovascular training effects as measured by increased functional capacity and decreased double product at one-half the maximum work load attained at the initial stress test. A significant increase occurred after training in the cardiac index response to exercise (p less than 0.02) and in the augmentation of the end-diastolic volume index produced by exercise (p less than 0.05). However, the exercise-induced decrease in LV ejection fraction and increase in LV end-systolic volume index remained unaltered by training. In conclusion, although older persons can achieve overall training effects from a program of physical conditioning, the age-associated differences in LV contractile performance remained unchanged. Our data suggest that deconditioning is not a significant contributor to the decline in LV contractile performance in the elderly.

Objectives Positron emission tomography has been demonstrated to improve the detection of distant metastases in patients with lung cancer. This study compares the efficacy of PET to mediastinoscopy in mediastinal staging of patients with non–small cell lung cancer. Methods Between May 1995 and May 2000, positron emission tomography was performed on 1988 patients with known or suspected non–small cell lung cancer at Duke University Medical Center. Cervical mediastinoscopy was subsequently performed in patients without demonstrable evidence of distant metastases. The efficacy of mediastinal staging was analyzed by comparing the prospective results of positron emission tomography with the histopathologic results of mediastinoscopy by nodal station. Results In this study 202 patients with non–small cell lung cancer (116 of whom were male) underwent mediastinoscopy after positron emission tomography. Of the 65 patients with positive results of positron emission tomography, only 29 patients had positive results of mediastinoscopy in the corresponding nodal station. Of the 137 patients with negative results of positron emission tomography, 16 patients were demonstrated to have N2 or N3 disease. The sensitivity, specificity, positive and negative predictive values, and accuracy for positron emission tomography were 64.4%, 77.1%, 44.6%, 88.3%, and 74.3%, respectively. Histologic findings in patients with non–small cell lung cancer and false-positive results of mediastinal positron emission tomography included granulomatous inflammation, sinus histiocytosis, and silicosis. Conclusions Positron emission tomography neither confirms nor excludes involvement of the mediastinum in patients with non–small cell lung cancer. Cervical mediastinoscopy with lymph node biopsy remains the criterion standard for mediastinal staging.

cl\ lglyccrol \\‘;Is tletected ill none of the amniotic Huid sarnplr\, although 11011e of the baby baboons born at term developed hyaline membrane disease. Compared 10 Iluman amniotic fluid. fluid from baboons had much Iightel lecithin spots on the chromatograms, suggesting low colicentrations of lecithin, even at ter-m. Of the eigllt surfactants purihed from amniotic fluid obtained at term, none contained detectable amounts of phosphatidvlgiyc.erol, yet six of’ seven surfactants purified from products of lung lavage did contain phosphatidylglycerol. These I./S ratio data al-c quite similar to those previousl~, reported in baboons.’ Compared to human>. baboons have low L/S ratios at term as well as a suggestion of lower overall concentrations of lecithins. The absence of phosphatidylglycerol at term, similar to that observed in sheep, is of great interest. Three explanations are possible: (I ) Baboon fetuses produce no phosphatidylgfycerol; (2) phosphatidylglyterol is prcsent in amniotic Huicl but its concentration is too low to be detected; (3) phosphatidylglycerol is present in the lungs but is not excreted into the amniotic, fluid. The absence of ~~~losphatidylglvcer-ol in concentrated hutfactants purified from am~‘lioric Huid and its present< in surktants purified f.rom lung lavagc point to thr third explanation. These data have two implications for perinatal care and research. First, absence of phosphatidylglycerol in amniotic Huid should not be assumed to imply absence of phosphatidylgl~cerol in alveolar fluid. Second, since phosphatidylglycerol appears to be necessary to maintain alveolar stability, surfactants purified from amniotic fiuid should be tested for phosphatidylglycerol prior to use in trials ofsurfactant replacement. Furthet research into the mechanism of lecithin excretion into amniotic fluid is needed.

Inverse Monte Carlo (IMOC) reconstruction for SPECT uses a Maximum Likelihood (EM) estimator with detection probabilities generated as Monte Carlo solutions to the photon transport equation (PTE). To evaluate the behavior of the iterative EM algorithm, reconstructions from experimental projection data for up to 1000 iterations were examined. Compensation for scatter and attenuation was achieved by including those effects in the PTE. For uniform activity distributions, noise increased monotonically with iteration. With line sources included, both noise and resolution improved between 1 and 30 iterations after which resolution was slightly improved at the expense of noise. Contrast (for a nonactive region surrounded by activity) improved from 0.32 at 5 iterations to 0.90 at 200 iterations, and 0.97 at 1000. Uncertainty in the measurement increased due to increased noise in the active region.

A simple method for the assessment of regional left ventricular (LV) function using gated radionuclide angiography is described. The method divides the LV region of interest in the left anterior oblique view into quadrants using a count-weighted center point and a transparent overlay. The regional ejection fraction (EF) was determined at rest and during upright bicycle exercise for each of 3 quadrants identified as posterior, septal and apical. The study group consisted of 50 patients with chest pain. Nine of these patients had normal coronary arteries and 41 had significant coronary artery disease (CAD). Regional EF measurements were highly reproducible at rest and exercise in all regions. Regional EF values at rest were compared with the subjective assessment of wall motion on the contrast ventriculogram and were significantly lower in regions with abnormal wall motion. Regional EF increased with exercise in all patients with normal coronary arteries. In patients with CAD and normal regional wall motion at rest, the regional exercise response was significantly more sensitive (p = 0.004) than global exercise response and marginally more sensitive (p = 0.06) than the subjective assessment of exercise wall motion on visual radionuclide images in the diagnosis of CAD. These results suggest that the measurement of regional LV function may be useful in the noninvasive diagnosis of CAD.

The effect of iodination level on the biological clearance of radioiodinated fibrinogen was investigated. Canine, human and rabbit fibrinogen were included in the study to also test for possible differences among various species. Iodination of fibrinogen with 3 to 9 iodine atoms/molecule resulted in essentially unchanged isotopic clottability as compared to preparations at the conventional level of 0.5 iodine atom/molecule. No changes in molecular size due to covalent aggregation were observed by SDS gel electrophoresis with radioiodinated human fibrinogen preparations. Canine and human fibrinogen iodinated with up to 4.5 iodine atoms/molecule exhibited little change in biological clearance behavior relative to the conventional iodination level. However, rabbit fibrinogen iodinated with 3.5 iodine atoms/molecule displayed a difference in clearance when compared to the 0.5 iodine atom/molecule preparations. Thus, canine and human fibrinogen can be iodinated with 4.5 iodine atoms/molecule without altering their biological clearance behavior while rabbit fibrinogen is more sensitive to this iodination level.

To determine the physiologic mechanisms of the decline in aerobic work performance with age, a cross-sectional study was performed. Twenty-four sedentary male volunteers, aged 20 to 50 years, underwent right-sided cardiac catheterization, arterial cannulation, radionuclide angiography and expired gas analysis for detailed evaluation of central and peripheral cardiovascular function during submaximal and maximal exercise. Habitual physical activity level varied but was well matched across the age range. Over the 3-decade age range studied, there was no detectable change in cardiovascular function at rest. When peak exercise variables were examined, an age-related 25% decrease in O2 consumption was noted (r = -0.43, p = 0.04); this was associated with a 25% decrease in peak cardiac index (r = -0.54, p = 0.01) and a 20% decrease in peak heart rate (r = -0.63, p = 0.002). In addition, there was an age-related increase in calculated systemic and pulmonary vascular resistances and an increase in left ventricular ejection time. No age relation was seen for exercise stroke volume index, end-diastolic volume index, end-systolic volume index, pulmonary artery wedge pressure, ejection fraction or arteriovenous O2 difference. These results indicate that the age-related decline in aerobic work performance among men aged 20 to 50 years results primarily from a reduced exercise heart rate in older subjects rather than from a reduction in stroke volume or peripheral O2 utilization.

The effects of oral prazosin (PZ), 15 to 20 mg/day, on symptoms, exercise performance and left ventricular (LV) function were assessed in a 6-month, double-blind, placebo-controlled study of patients in New York Heart Association functional class III. Ejection fraction (EF) was measured at rest and during upright bicycle exercise by equilibrium radionuclide angiography; end-diastolic volume, stroke volume and cardiac output were derived from corresponding count measurements. Although there was no statistically significant difference between clinical responses in the prazosin and placebo groups, qualitative differences suggested a clinical response to prazosin. Of the 9 patients who received PZ, 5 improved to functional class II and 2 became asymptomatic; the 2 nonresponders deteriorated to functional class IV when PZ was stopped. Four of 9 patients who received placebo improved to functional class II and 2 deteriorated to class IV. Exercise time tended to increase in the prazosin group (from 541 ± 204 to 630 ±100 seconds at 6 months) and decrease in the placebo group (from 539 ± 141 to 435 ±148 seconds at 6 months), but neither change was significant. Prazosin effected a sustained decrease in mean blood pressure of approximately 10 mm Hg at rest, and a quantitatively similar but insignificant decrease during exercise. Radionuclide EF increased and LV end-diastolic counts decreased significantly at rest and during exercise in the prazosin group, but not in the placebo group. Because changes in EF and end-diastolic counts were similar, stroke counts and count output were unchanged. Thus, long-term oral PZ therapy caused sustained changes in blood pressure and LV function in most patients in functional class III, but these changes were not uniformly translated into clinical improvement or increased exercise tolerance. Prazosin does not appear to increase cardiac output during exercise in patients with heart failure.

Radioiodinated soluble fibrin, a derivative of radioiodinated fibrinogen, has been investigated for thrombus localization. Soluble fibrin can be labeled with 123 I as the radionuclide for imaging thrombi with a scintillation camera. Protein iodination grade 123 I is produced by a distillation and extraction procedure from the product of the 121 Sb ( α , 2 n ) 123 I reaction in the Washington University 54-in. cyclotron. Labeling with these 123 I preparation is effected by the iodine monochloride method. Induced 4–6-hr-old femoral vein thrombi in dogs can be visualized beginning 2 hr after injection of 1 mCi of 123 I-labeled soluble fibrin. This new radiopharmaceutical may be useful for imaging actively-propagating thrombi in patients, especially in areas of large blood pool. Its potential appears to be similar to that of 123 I-labeled highly iodinated fibrinogen, another new thrombus imaging agent.

The cardiovascular and behavioral adaptations associated with a 4-month program of aerobic exercise training were examined in 101 older men and women (mean age = 67 years). Subjects were randomly assigned to an Aerobic Exercise group, a Yoga and Flexibility control group, or a Waiting List control group. Prior to and following the 4-month program, subjects underwent comprehensive physiological and psychological evaluations. Physiological measures included measurement of blood pressure, lipids, bone density, and cardiorespiratory fitness including direct measurements of peak oxygen consumption (VO2) and anaerobic threshold. Psychological measures included measures of mood, psychiatric symptoms, and neuropsychological functioning. This study demonstrated that 4 months of aerobic exercise training produced an overall 11.6% improvement in peak VO2 and a 13% increase in anaerobic threshold. In contrast, the Yoga and Waiting List control groups experienced no change in cardiorespiratory fitness. Other favorable physiological changes observed among aerobic exercise participants included lower cholesterol levels, diastolic blood pressure levels, and for subjects at risk for bone fracture, a trend toward an increase in bone mineral content. Although few significant psychological changes could be attributed to aerobic exercise training, participants in the two active treatment groups perceived themselves as improving on a number of psychological and behavioral dimensions.

The conventional methods for the assess-ment of myocardial functional integrity, which rely on the external detection of an administered radiopharmaceutical, share the following crippling limitations. (1) The field of view of the radiation detector always encompasses the contribution of activity contained in tissues overlying and underlying the plane of interest. This contribution, which in general cannot be subtracted from the measured signal, contributes noise, and in general considerably depresses the contrast in the plane of interest between tissues containing different activities. (2) The attenuation of the gamma radiation originating from the activity in the myocardium is dependent upon the amount of tissue interposed between the myocardium and the radiation detector. This effect is difficult to compensate for. The combination of the above two defects seriously depresses contrast in myocardial nuclear imaging, and all but precludes the reliable quantitative assessment of the distribution of a radio-active label in the myocardium.© (1976) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Vascular competence in the upper extremities of 44 patients was evaluated by three-phase bone scans consisting of rapid sequence dynamic radionuclide imaging (DRI), an immediate postinjection "blood pool" image, and a 3- to 4-hour delayed image. Findings were correlated with definitive anatomy determined by arteriography, operative findings, or both, in 50 extremities. DRI provided the correct diagnosis in all but four extremities (92%). Limited resolution precluded precise anatomic definition of aneurysms in three limbs and of digital artery occlusion, with adequate collateral circulation in the fourth limb. The greatest value of DRI was its provision of quantitative information about relative blood flow and preferential perfusion in every instance. We believe DRI to be a useful adjunct to preoperative and postoperative assessment of arterial perfusion.

The pheochromocytoma-scanning agent 131I-meta-iodobenzylguanadine (131I-MIGB) was concentrated in the platelets of ten subjects undergoing scans for suspected pheochromocytomas. In vitro studies also demonstrated that 131I-MIBG was concentrated in platelets. In contrast to serotonin, which had maximum in vitro platelet uptake of one hour, the peak in vitro platelet uptake of 131I-MIBG did not occur until six hours. In vitro platelet 131I-MIBG uptake was decreased by 79% to 98% following the neuronal-uptake-blocking agent imipramine. These studies suggest that pheochromocytomas take up 131I-MIBG by a neuronal-pump mechanism. Further studies to determine if 131I-MIBG is taken up by other tumors with a neuronal-pump mechanism, such as carcinoid tumors, will be valuable.

This study assessed the effects of partial reductions in exercise work load on radionuclide angiographic indexes of ischemia in patients with coronary artery disease. Left ventricular function was measured by first pass radionuclide angiography in 43 male patients at rest, during an ischemic response to symptom-limited exercise and immediately after a partial reduction in work load. To assess the sensitivity of exercise-induced left ventricular dysfunction to reductions in work load, the effects of moderate (50%; Group 1) and small (200 kilopond-meters/min; Group 2) reductions in work load were analyzed.In Group 1, ejection fraction decreased from 49 ± 18% (mean ± standard deviation) at rest to 43 ± 16% at symptom-limited exercise, and then increased to 52 ±21% during work load reduction (p < 0.001). In Group 2, ejection fraction decreased from 53 ± 18% at rest to 44 ± 16% at symptom-limited exercise, and then increased to 52 ± 19% during work load reduction (p < 0.001). If the ejection fraction response during work load reduction rather than during symptom-limited exercise was considered for diagnostic purposes, the sensitivity would have been reduced from 100 to 52% in Group 1 and to 70% in Group 2. The ejection fraction increased during work load reduction despite persistent ST segment depression in eight patients in Group 1 and in nine patients in Group 2. Increases in ejection fraction during work load reduction were associated with increases in the ratio of systolic blood pressure to end-systolic volume and lessening of regional wall motion abnormalities.In patients who develop ischemia during symptom-limited exercise, small decreases in work load which are accompanied by minor hemodynamic changes may result in a rebound increase in left ventricular function and significant reduction in the diagnostic sensitivity of the exercise radionuclide angiogram.

Sixty-eight indium-111-labeled leukocyte imaging studies were performed in 53 patients with suspected abdominal abscesses. Twenty-nine studies gave abnormal results. Nine wound infections were demonstrated, and 14 abscesses were correctly identified. Four studies demonstrated colonic accumulation, one of which remains unexplained, and two accessory spleens were identified. Indium-111 leukocyte imaging is a sensitive and specific study in evaluating patients with suspected abdominal abscess. Differentiation of abscess from other causes of inflammation has not been a problem. The exact role of leukocyte imaging compared with gallium-67 citrate imaging, ultrasound and computerized tomography remains to be determined.

The relative sensitivity and combined value of myocardial technetium-99m stannous pyrophosphate imaging and determinations of serum MB creatine phosphokinase (the "myocardial" CPK isoenzyme) in detecting acute myocardial infarction were evaluated in 41 patients with suspected infarction and 23 patients recovering from cardiac surgery. In the patients with suspected infarction, myocardial infarction was confirmed in 25 and was consistently associated with increased serum MB CPK. Abnormal radionuclide images were obtained in 23 of 25 patients (92 percent) with definite myocardial infarction and in 2 of 16 patients without confirmed infarction. Although the localization of infarction by imaging correlated well with the localization by electrocardiogram, infarct size estimated by imaging did not correlate well with estimates based on peak total serum CPK activity or serial changes in CPK activity. Serum MB CPK activity increased after cardiac surgery in 6 patients undergoing valve replacement and in 17 patients undergoing coronary arterial bypass surgery. However, no patient with valve replacement and only 1 of the 17 with bypass surgery had an abnormal radionuclide image. These results suggest that (1) abnormal radionuclide images in patients without infarction can be distinguished from abnormal images indicative of ischemic necrosis by consideration of MB CPK activity and (2) interpretation of elevated MB CPK activity, particularly in particularly in patients undergoing cardiac surgery, is facilitated by evaluation with imaging.

Improved SPECT reconstructions have been obtained by the use of an Inverse Monte Carlo (IMOC) reconstruction algorithm. Monte Carlo solution to the photon transport equation for SPECT generates an accurate system response model for use in an iterative Maximum Likelihood estimation (MLE) algorithm. Reconstruction from simulated projections demonstrate that the MLE algorithm continues to converge at 1000 iterations for noise free data. Reconstruction from experimentally acquired projections reveals superior RMS noise and resolution recovery when compared with filtered backprojection for simple phantoms. Compensation for scatter and attenuation is provided by including these effects in the Monte Carlo simulation.

Eight patients, aged 5 to 57 years, with uncontrolled symptomatic tachycardia for 2.5 to 41 years (mean 15) and significant left ventricular (LV) dysfunction in the absence of any other apparent underlying cardiac disease underwent evaluation. Incessant tachycardia was present for 0.5 to 6.0 years (mean 2.1) in 7 patients. One patient had an ectopic atrial tachycardia and 7 patients had an accessory atrioventricular pathway that participated in reciprocating tachycardia. Six patients underwent surgery; the ectopic focus was ablated in 1 patient and an accessory pathway was divided in 5 patients. One patient underwent open ablation of the His bundle and 1 patient underwent closed-chest ablation of the atrioventricular conduction system. Myocardial biopsy specimens were obtained from 5 patients, none of which yielded a specific diagnosis. Pretreatment radionuclide angiography demonstrated a mean ejection fraction (EF) of 19 +/- 9% (range 10 to 35%). Following tachycardia control a marked improvement in LV function was noted in 6 of 8 patients at rest and in 1 additional patient during exercise. The EF increased to 33 +/- 17% (range 16 to 56%) an average of 8 days after treatment and to 45 +/- 15% (range 22 to 67%) at late follow-up 3.5 +/- 40 months (mean 17) later (p less than 0.005). Seven patients remain asymptomatic 11 to 40 months (mean 22) after the corrective procedure and have resumed normal activities. These findings suggest that chronic uncontrolled tachycardia may result in significant LV dysfunction, which is reversible in some cases after control of the arrhythmia.

This investigation assesses prospectively the accuracy of rest and exercise radionuclide angiocardiography (RNA) in detecting coronary artery disease (CAD). By retrospective analysis of 496 patients, optimal RNA criteria were determined for the presence or absence of CAD. Multivariate analysis of patients with normal coronary arteries on catheterization provided a formula to predict normal exercise ejection fraction (EF) in a given patient. The presence of CAD was indicated by 1 or more of the following RNA measurements: (1) rest EF less than 0.50, (2) exercise EF at least 0.06 less than the predicted value, (3) exercise increase in end-systolic volume greater than 20 ml, (4) exercise-induced wall motion abnormality. The absence of CAD was indicated by the absence of all 4 criteria. After applying these criteria to 221 consecutive patients, the RNA determinations were compared with the catheterization, determinations. Significant CAD was present in 71% of the patients studied. The sensitivity of the test was 0.87 and the specificity 0.54. Thus, because of its high sensitivity, RNA is of value in screening patients under consideration for cardiac catheterization. No patient with significant left main coronary narrowing and only 4 of 65 patients with 3-vessel disease were misdiagnosed. The poor specificity of the test, however, limits its overall accuracy.

Reconstructed images for single photon emission computed tomography (SPECT) with quantitative compensation for scatter and attenuation are provided using Inverse Monte Carlo (IMOC): Maximum likelihood estimation with Monte Carlo modeling of the photon interaction and detection probabilities. Quantitative compensation was evaluated by comparing region of interest values for compensated images of line sources scanned in water with line sources scanned in air. Compensation was demonstrated for both 360° 180° acquisition. Lesion contrast was investigated for cold spheres in an active background.

Radionuclides in Cardiology have been used mainly for detection of myocardial infarction’ and assessment of left ventricular function.2 The need for improved detection of myocardial infarction is related to the lack of sensitivity and specificity of the ECG or plasma enzymes in certain clinical conditions.“, a Diagnosis of infarction after cardiac surgery is particularly troublesome since even creatine phosphokinase isoenzymes, specific for myocardial damage, are consistently elevated as a result of the iatrogenic injury., The recent interest in protection of ischemic myocardium6 requires measurement of infarct size and several studies suggest that quantification of infarct images may be possible,‘, 8 which has intensified the search for more appropriate radionuclidesg Four categories of radionuclides have been utilized to identify zones of h (2) metabolic substrates (labeled free fatty acids, 13NH,15; (3) inert gases (s5Kr, *%e)l6,1’; and (4) labeled microspheres or macroaggregates.18, I9 However, radionuclides which accumulate in areas of infarction (“hot

The relation between bicycle exercise performance and determinants of central and peripheral cardiovascular function was assessed in 17 patients with class II to III heart failure and in 9 normal subjects. Proportional changes in oxygen consumption (VO2) from rest (R) to maximal exercise (Ex), or Mets, were used as an objective measure of the exercise capacity or functional reserve of the cardiovascular system. Left ventricular ejection fraction (EF) and proportional changes in end-diastolic volume, stroke volume, and cardiac output were determined from appropriate count data by equilibrium radionuclide angiography. Proportional changes in arteriovenous oxygen difference (A-VO2) were derived from the equation Ex/R A-VO2 = Ex/R VO2 divided by Ex/R CO, where CO = count output. Each subject exercised to an anaerobic endpoint. Maximal VO2 was significantly lower in patients than in normal subjects. Because Ex/R A-VO2 was comparable in normal subjects and patients, the lower exercise performance in patients resulted from a reduced count output response. The reduced CO response in patients resulted from failure of the ejection fraction to increase or from an attenuated heart rate response, or both. Exercise performance was variable in both groups. Multivariable analysis in the patient group identified changes in heart rate, count output, and A-VO2 with exercise as important predictors of Mets, but found no relation between Mets and changes in ejection fraction or stroke counts during exercise. Similarly, multiple regression analyses between Mets and determinants of cardiovascular function demonstrated significant correlations with Ex/R heart rate, Ex/R count output, and Ex/R A-VO2 in both groups. In patients, EF at rest ranged from 0.09 to 0.36, but it did not correlate with Mets, nor did changes in ejection fraction, stroke counts, or end-diastolic counts during exercise. The variable exercise performance among patients with severe left ventricular dysfunction was determined predominantly by a variable heart rate and A-VO2 response and not by rest or exercise indexes of left ventricular function.

Camera-based single photon emission computed tomography (SPECT) provides increased information about the organ scanned by eliminating superpositioned radionuclidic activity in the reconstructed images. Current literature contains little detail regarding the potential of and the technical aspects involved in using this emerging imaging modality. A description of the instrumentation supplements a general, but practical, background for nuclear medicine personnel. Some of the considerations for successfully utilizing a SPECT system are described, along with a discussion of the basis for these procedures. Pitfalls are mentioned and clinical images from our SPECT imaging system are included.

A simple and economically practical method of improving the sensitivity of camera-based SPECT was developed using converging (cone-beam) collimation. This geometry is particularly advantageous for SPECT devices using large field-of-view cameras in imaging smaller, centrally located activity distributions. Geometric sensitivities, spatial resolutions, and fields-of-view of a cone-beam collimator having a focal length of 48 cm and a similarly designed parallel hole collimator were compared analytically. At 15 cm from the collimator surface the point-source sensitivity of the cone-beam collimator was 2.4 times the sensitivity of the parallel-hole collimator. SPECT projection data (simulated using Monte Carlo methodology) were reconstructed using a 3-D filtered backprojection algorithm. Cone-beam emission CT (CE-SPECT) seems potentially useful for animal investigations, pediatric studies, and for brain imaging.

We have evaluated the quantitative aspects of a whole-body SPECT system which consists of 2 large-field-of-view scintillation cameras mounted in a rotatable gantry and interfaced to a minicomputer. Data are continuously collected through a 360 degree rotation and result in 32 contiguous transverse images which can be reorganized into 16 frontal and 16 sagittal images. Pulmonary perfusion studies were performed in dogs to compare the information from SPECT with routine gamma camera images. Five plastic spheres ranging from 2 to 6 cm in diameter were placed in a 22 cm diameter cylinder with technetium-99m distributed in the spheres and cylinder in varying concentration ratios. A semi-automatic region of interest program was used to evaluate the multiple slices from the SPECT data, and the volumes were calculated by computing the total number of voxels within each region of interest. The SPECT measured volumes correlated very well with the actual volumes. To evaluate the ability of SPECT to determine radionuclide concentrations in an object, elliptical and cylindrical phantoms were uniformly filled with technetium-99m in concentrations from 0.05 to 1.5 μCi/ml. Using attenuation corrected data, the SPECT concentrations correlated very well with the actual concentrations over the entire range tested. We also evaluated the concentration ratios of the spheres to the cylinder using attenuation corrected SPECT images. The concentration ratios were derived from the measured SPECT image contrast by correcting for attenuation, scattered photons and image degradation resulting from finite system spatial resolution. Using this procedure, the SPECT measured concentration ratios correlated well with the actual concentration ratios. Perfusion defects from normal anatomic structures, as well as perfusion abnormalities secondary to occlusion of a bronchus or pulmonary artery are better defined on the SPECT images than the gamma camera images. Thus, SPECT gives additional information concerning pulmonary perfusion.

THE TENDENCY for gallium citrate Ga 67 to localize in inflammatory lesions can provide an extremely useful, noninvasive test in the septic patient.1-4As with any diagnostic test, associated conditions that can compromise the diagnostic value of67Ga scanning should be known. We recently had a patient with pseudomembranous colitis with a colonic accumulation of67Ga, which to our knowledge, has not been previously reported. Report of a Case A 71-year-old man was in good health until 24 hours prior to admission, when he first had abdominal pain and vomiting. There was no history of hematemesis, diarrhea, melena, or bright red blood originating from the rectum. On physical examination, the patient had a temperature of 38.5 C (101.3 F) and a distended abdomen with left lower quadrant rebound tenderness. Results of the rest of the examination were unremarkable. All laboratory values were within normal limits. An abdominal