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Biomedical subjects

M Schwaiger

Publications and source records attributed to M Schwaiger.

At least 19 recordsLinked to original sources
PubMed1995

Noninvasive quantification of regional myocardial flow reserve in patients with coronary atherosclerosis using nitrogen-13 ammonia positron emission tomography. Determination of extent of altered vascular reactivity.

OBJECTIVES: The aim of this study was to evaluate patients with coronary artery disease to 1) determine the relation between flow reserve measured by nitrogen-13 (N-13) ammonia kinetic modeling and stenosis severity assessed by quantitative angiography, and 2) examine whether flow reserve is impaired in regions supplied by vessels without significant angiographic disease. BACKGROUND: With the advent of new therapeutic approaches for coronary disease, an accurate noninvasive approach for absolute quantification of flow and flow reserve is needed to evaluate functional severity and extent of atherosclerosis. Nitrogen-13 ammonia kinetic modeling may permit such evaluation. METHODS: Twenty-seven subjects were classified into three groups: group 1 = 5 young volunteers: group 2 = 7 middle-aged volunteers; and group 3 = 15 patients with coronary artery disease. Dynamic N-13 ammonia positron emission tomographic imaging was performed at rest and during adenosine infusion. A three-compartment model was fit to regional N-13 ammonia kinetic data to determine myocardial flow. Group 3 patients underwent quantitative coronary angiography. RESULTS: The regional blood flow results in patients with coronary disease were classified into four subgroups: no significant detectable disease and mild (50% to 69.9% area stenosis), moderate (70% to 94.9% area stenosis) or severe (95% to 100% area stenosis) coronary disease. Flow reserve was 2.95 +/- 0.65; 2.09 +/- 0.47; 2.02 +/- 0.51; 1.3 +/- 0.32, respectively (p < or = 0.01 except mild vs. moderate). Flow reserve was correlated with percent area stenosis (r = -0.56) and minimal lumen diameter (r = 0.75). In volunteers (groups 1 and 2), flow reserves were greater than in segments without detectable disease in group 3 patients (4.10 +/- 0.71 and 3.79 +/- 0.42, respectively, vs. 2.88 +/- 0.56, p < or = 0.02). CONCLUSIONS: The functional severity of coronary disease measured by N-13 ammonia positron emission tomography varied for a given stenosis but was significantly related to angiographic severity. Among patients with coronary disease, myocardial regions without significant angiographic stenoses displayed reduced flow reserve than did regions in control subjects, indicating that vascular reactivity was more diffusely impaired in group 3 than was suggested by angiography. Noninvasive quantification of myocardial flow reserve using dynamic N-13 ammonia positron emission tomography yields important functional data that permit definition of the extent of disease even when disease is not apparent by angiography.

Adenosine↗
PubMed1995

Heterogeneity of ventricular function and myocardial oxidative metabolism in nonischemic dilated cardiomyopathy.

OBJECTIVES: This study was performed to test the hypothesis that regional variation in ventricular function in patients with nonischemic dilated cardiomyopathy is related to regional variation in oxidative metabolism. BACKGROUND: Heterogeneity in regional left ventricular function has long been noted in patients with nonischemic dilated cardiomyopathy. Regional variation in wall stress has been proposed as the pathophysiologic mechanism. By correlating regional function with oxidative metabolism, one can test the hypothesis that heterogeneity in wall stress is responsible for heterogeneity in function. We hypothesized that preserved function as a result of more favorable loading conditions would be associated with regional oxidative metabolism that is equal to or lower than that in other regions. METHODS: Fifteen patients with nonischemic dilated cardiomyopathy (mean [+/- SD] ejection fraction 20.7 +/- 4.0%) were studied. Regional ventricular function was determined using short-axis chordal shortening on two-dimensional echocardiography. Regional oxidative metabolism was assessed by carbon-11 acetate clearance kinetics on dynamic positron emission tomography. An eight-segment model of the left ventricle was used. Segmental function and oxidative metabolism were defined as increased if they varied at least 1 SD from the respective mean value for that patient. RESULTS: Thirteen (87%) of 15 patients exhibited segments with increased function. In 7 (54%) of 13 patients, regional function was increased in the proximal lateral wall. Multivariate linear regression analysis showed a direct relation between regional function and oxidative metabolism (p = 0.02). The average concordance between increased function and increased oxidative metabolism among patients was 0.87 +/- 0.11 (95% confidence interval 0.70 to 1.00). CONCLUSIONS: Patients with nonischemic dilated cardiomyopathy display heterogeneity in regional ventricular function. Relative preservation is observed most frequently in the proximal lateral wall. Relative preservation of function is associated with higher regional oxidative metabolism, suggesting that mechanisms other than or in addition to local loading conditions may be responsible for heterogeneity in function.

Acetates↗
PubMed1995

Comparison of fluorine-18-fluorodeoxyglucose PET, MRI and endoscopy for staging head and neck squamous-cell carcinomas.

UNLABELLED: Accurate, preoperative assessment of tumor extent and lymph node involvement is mandatory for individualized therapy in patients with squamous-cell carcinomas (SCCs) of the head and neck region. Metabolic imaging, [18F]fluorodeoxyglucose (FDG) PET and MRI were compared with postoperative, histologic tissue characterization. METHODS: Dynamic and static PET with 370 MBq [18F]FDG up to 60 min postinjection and MRI were compared prospectively in 22 patients with head and neck SCCs. PET results with and without attenuation correction were compared with postoperative T and N stages based on pathologic findings. RESULTS: Kinetic characteristics and tracer uptake intensity were similar in primary tumors and lymph node metastases. In both, FDG uptake did not reach a plateau phase 60 min postinjection. There was no statistically significant correlation of FDG uptake with plasma glucose level or histologic grading. All primary tumors were clearly demonstrated by PET, which tended to overestimate tumor size. The sensitivity and specificity for detecting individual lymph node involvement were 90% and 96%, respectively, for PET and, thus, significantly higher for MRI (78% and 71%, respectively; p < 0.05). N stages were correctly identified by MRI in only 4 patients; PET correctly staged lymph nodes in 15 of 17 patients. Based on "neck sides", the sensitivity and specificity were higher for PET, 89% and 100%, respectively, compared with MRI values of 72% and 56%, respectively. CONCLUSION: FDG-PET may be helpful in detecting occult primary tumors with positive lymph nodes.

Adult↗
PubMed1995

Carbon-11-acetate PET imaging in renal disease.

UNLABELLED: The purpose of this study was to investigate the use of [1-11C]acetate as a metabolic tracer for renal imaging in human subjects. METHODS: Eighteen patients underwent dynamic PET imaging of the kidneys after intravenous bolus injection of 10-20 mCi [1-11C]acetate. Time-activity curves of renal parenchyma tracer activity were fitted to a two-compartment model using direct arterial blood sampling for the arterial input function. RESULTS: Renal uptake of [1-11C]acetate is prompt and high target-to-background ratios are achieved even in the presence of markedly reduced renal function. Carbon-11-acetate is cleared from the renal parenchyma without any urinary excretion and the rate of clearance is comparable to myocardial clearance rates. Among normal subjects, K1, ranged from 0.653 to 1.37 ml/min-g, and was reduced to as low as 0.363 ml/min-g in severe renal disease (serum creatinine greater than 5 mg/dl), while k2 ranged from 0.114 to 0.166 min-1 among normal subjects and was reduced to as low as 0.053 min-1 in severe renal disease. Kinetic parameters K1 and k2 were both reduced in the presence of intrinsic renal disease or significant renal artery stenosis. Renal cell carcinoma demonstrated similar uptake of [1-11C]acetate, but substantially reduced the rate of clearance compared to normal and diseased non-neoplastic renal tissue, allowing for ready differentiation of renal cell carcinoma from non-neoplastic renal tissue on images acquired beyond 10 min of tracer administration. CONCLUSION: Carbon-11-acetate is a promising physiologic tracer for the study of renal disease.

Acetates↗
PubMed1995

Changes in myocardial oxygen consumption and efficiency with heart failure therapy measured by 11C acetate PET.

The application of 11C acetate kinetics determined by positron emission tomography (PET) imaging has been proposed as a noninvasive means to measure myocardial oxygen consumption in order to determine myocardial efficiency. Such an approach considers the balance of the effect of ventricular performance and myocardial oxygen consumption (MVO2), which may be important in the assessment of heart failure but is not usually evaluated by current methods. In this paper, the authors review their previously published series of studies, in which the aim was to: first, apply the 11C acetate PET approach in patients with dilated cardiomyopathy in order to determine myocardial oxidative metabolism and estimate myocardial efficiency; second, verify a correlation between 11C acetate kinetics and directly measured MVO2; and third, evaluate the effects of dobutamine and nitroprusside on MVO2 and efficiency in dilated cardiomyopathy. In these previous studies, 13 patients with severe dilated cardiomyopathy were studied, via echocardiography, hemodynamic and PET studies, at baseline and during drug infusion. Seven patients were given dobutamine and six were given nitroprusside. A two-compartment kinetic model approach was applied to 11C time activity curves obtained from dynamic 11C acetate PET imaging to determine the clearance rate constant, k2. Myocardial efficiency was estimated from a work metabolic index, defined as (stroke work index multiplied by heart rate) divided by k2. The k2 significantly increased with dobutamine (P < or = 0.05), consistent with increased MVO2, and tended to decrease with nitroprusside. The work metabolic index derived from hemodynamic parameters increased significantly with both drug regimens (P < or = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetates↗
PubMed1995

Simultaneous transmission-emission thallium-201 cardiac SPECT: effect of attenuation correction on myocardial tracer distribution.

UNLABELLED: This study evaluates the effect of attenuation correction on regional myocardial tracer distributions defined by 201TI cardiac perfusion SPECT images obtained from healthy volunteers and patients with coronary heart disease. METHODS: A three-detector SPECT system equipped with an 241Am line source and a fanbeam collimator was used for simultaneous transmission/emission (201TI) tomography on 40 patients and 10 normal volunteers. Uncorrected emission images were reconstructed using filtered backprojection (FBP), whereas the attenuation corrected images were iteratively reconstructed with a regularized, least-squares algorithm utilizing the attenuation map computed from the transmission data. Both sets of images were reoriented into short-axis and vertical long-axis slices. Circumferential profile analysis was applied to both datasets of short-axis slices. RESULTS: The normal volunteers demonstrated improved homogeneity in tracer distribution. For a basal short-axis slice, the lateral-to-posterior activity ratio improved from 1.17 +/- 0.12 for FBP to 1.01 +/- 0.07. Basal attenuation appeared properly compensated as the peak basal-to-apical slice activity gradient along the posterior-inferior wall changed from 1.15 +/- 0.12 for FBP to 1.01 +/- 0.09. The apex of the attenuation corrected images showed a significant decrease in activity relative to the base which appeared consistent with anatomic wall thinning. For the inferior and basal septal regions, the defect severity was slightly less in the attenuation corrected images, but the defects were more sharply defined compared to the FBP image defects. CONCLUSION: These results indicate that attenuation correction is clinically feasible and accurately corrects for photon attenuation. Clinical validation, however, is necessary to define the diagnostic benefits.

Coronary Disease↗
PubMed1994

Comparison of thallium-201 SPECT redistribution patterns and rubidium-82 PET rest-stress myocardial blood flow imaging.

To compare regional thallium-201 SPECT redistribution patterns with rubidium-82 PET, we studied 81 patients with both imaging modalities. Sixty patients had significant coronary artery disease. All patients underwent PET imaging after dipyridamole infusion, while SPECT imaging was performed after exercise stress (38 patients) and dipyridamole (43 patients). Sixty-eight percent of patients with prior infarct had fixed defects on SPECT, compared to 39% with PET. Sixty-one percent of patients with prior infarct had PET perfusion defects which exhibited 'reflow' or normal rubidium-82 tracer uptake (p < 0.05 vs. SPECT). Similar results were seen in patients without prior infarct (26% fixed defects on SPECT vs. 12% for PET, p < 0.05). Regional analysis showed that 57% of fixed SPECT defects corresponded to PET defects with reflow or normal rubidium-82 uptake, while 78% of 'fixed' PET defects corresponded to fixed SPECT defects. PET reflow and normal rubidium-82 uptake in sites of fixed thallium-201 SPECT perfusion defects suggest that imaging modalities employing separate tracer injections at rest and after stress, such as rubidium-82 PET, may be more specific in the assessment of myocardial viability, especially in patients with prior myocardial infarction.

Aged↗
PubMed1994

Metabolic tissue characterization in the failing heart by positron emission tomography.

Congestive heart failure represents an important clinical issue which can benefit from newer imaging approaches. Use of radiolabelled pharmaceuticals allow for functional tissue characterization in patients with impaired left ventricular function. Assessment of regional myocardial perfusion and metabolism with either SPECT or PET methods provide accurate detection of tissue viability. Several studies have indicated the utility of these imaging approaches for improved selection of patients for revascularization. The combination of functional measurements with echocardiography and metabolic tissue characterization with PET allows for the non-invasive measurement of cardiac efficiency. The effect of various therapeutic interventions can be objectively assessed by a work-metabolic index. Finally, autonomic innervation of the heart plays an important role in the modulation of the haemodynamic performance of the failing heart. New imaging approaches using radiolabelled catecholamine analogues or receptor antagonists have been used to identify the integrity of myocardiac pre- and post-synaptic sympathetic innervation. Imaging results in patients with dilated cardiomyopathy not only demonstrated a down-regulation of beta-receptor density, but also an abnormal pre-synaptic neuronal function, which may result into impaired regulation of extraneuronal catecholamine concentration. Thus, advanced scintigraphic imaging approaches may improve our diagnostic and prognostic workup in patients with congestive heart failure and may provide objective endpoints for the assessment of therapy.

Autonomic Nervous System↗
PubMed1994

Intravenous Fluosol in the treatment of acute myocardial infarction. Results of the Thrombolysis and Angioplasty in Myocardial Infarction 9 Trial. TAMI 9 Research Group.

BACKGROUND: This study was performed to determine the safety and potential efficacy of an intravenous perfluorochemical emulsion (Fluosol) as an adjunct reperfusion therapy aimed at preventing reperfusion injury for patients with acute myocardial infarction. METHODS AND RESULTS: Patients (430) were randomized in a prospective open-labeled study, 213 to receive Fluosol and 217 to receive no Fluosol, along with 100 mg of tissue-type plasminogen activator given over 3 hours. Major end points included global ejection fraction, regional wall motion analysis, infarct size as measured by tomographic thallium imaging, and a composite clinical outcome measure. Baseline patient and angiographic characteristics were similar in the two groups. No significant difference in global ejection fraction (52% without Fluosol, 51% with Fluosol) or regional wall motion (-2.4 SD/chord with Fluosol, -2.2 SD/chord without Fluosol) was demonstrated in patients receiving Fluosol versus those not receiving Fluosol, nor was there a significant difference in thallium infarct size. Although Fluosol-treated patients with anterior infarction had an insignificantly lower mean infarct size (18.7% of the left ventricle) compared with patients with anterior infarction not treated with Fluosol (21.2% of left ventricle), this trend was not evident in the median infarct size values (22% versus 17%), left ventricular ejection fraction values (46% without Fluosol, 47% with Fluosol), or regional wall motion (-2.5 SD/chord in both groups). Rates of death and stroke were no different in the two groups; however, patients who received Fluosol experienced less recurrent ischemia. Patients receiving intravenous Fluosol had more transient congestive heart failure and pulmonary edema, perhaps because of necessary fluid administration. There was no difference in hemorrhagic complications between the two study groups. CONCLUSIONS: When given with a thrombolytic agent, Fluosol was not associated with improvement in ventricular systolic function, reduction in thallium infarct size, or overall clinical outcome. Fluosol was, however, associated with a reduction in ischemic complications and with an increase in pulmonary edema and congestive heart failure.

Adolescent↗
PubMed1994

Early detection of abnormal coronary flow reserve in asymptomatic men at high risk for coronary artery disease using positron emission tomography.

BACKGROUND: The objective of this study was to compare coronary flow reserve (CFR) as a measure of vascular integrity in asymptomatic middle-aged men with family history of coronary artery disease (CAD) and a high-risk lipid profile with men without risk factors for CAD using positron emission tomography (PET). Previous studies suggested that the assessment of CFR is a sensitive means to detect vascular abnormalities before angiographic appearance of CAD. N-13 ammonia PET scanning allows noninvasive evaluation of regional and global myocardial blood flow and thereby quantification of CFR. METHODS AND RESULTS: We used dynamic N-13 ammonia PET imaging in conjunction with intravenous adenosine to assess regional and global CFR in asymptomatic middle-aged men with high risk (group 1, n = 16) and men without any known risk factors (group 2, n = 11) for CAD. Group 1 patients were selected based on positive family history of CAD, one or more lipid abnormalities, and a normal stress test. No patient had history of diabetes or hypertension. A three-compartment tracer kinetic model developed and validated in our institution was used to calculate myocardial blood flow. Absolute myocardial blood flow (mL/100 g per minute) was calculated in five territories for each patient. CFR was defined as the ratio of blood flow during maximum pharmacological vasodilatation to blood flow at rest. Comparisons of CFR between the two groups of patients were performed. The mean age was similar between groups (group 1, 49.3 +/- 0.5 years; group 2, 48.1 +/- 8.7 years; P = NS). Group 1 had higher total cholesterol (mg/dL) (241 +/- 43 versus 173 +/- 34, P < .001), total cholesterol to high-density lipoprotein cholesterol ratio (6.4 +/- 1.6 versus 4.1 +/- 1.4, P < .001), and low-density lipoprotein cholesterol (mg/dL) (167 +/- 33 versus 107 +/- 32). No group 1 patient had evidence of ischemia by exercise ECG or exercise of pharmacological radionuclide perfusion studies. The mean global absolute myocardial blood flow at rest was not significantly different among groups (group 1, 76 +/- 18; group 2, 66 +/- 8; P = NS; (in mL/100 g per minute). However, blood flow after adenosine infusion was higher for group 2 (group 1, 217 +/- 56; group 2, 264 +/- 39; P < .001), which resulted in a larger CFR for group 2 (group 1, 2.93 +/- 0.86; group 2, 4.27 +/- 0.52; P < .001). Univariate linear regression analysis revealed significant negative correlation of CFR to total cholesterol (P < .05, r = -.41), low-density lipoprotein (P < .05, r = -.38), and total cholesterol to high-density lipoprotein cholesterol ratio (P < .05, r = -.47). CONCLUSIONS: Noninvasive quantification of absolute myocardial blood flow by N-13 ammonia PET allows the detection of abnormal vasodilatory response to intravenous adenosine in male patients with family history of CAD and high-risk lipid profiles. Early assessment of alterations of vascular reactivity to adenosine in relation to high-risk lipid profiles in asymptomatic men may allow early detection of preclinical atherosclerosis and may initiate modification and/or elimination of risk factors that may slow, retard, or even reverse the progression of CAD.

Adenosine↗
PubMed1994

Relation of regional function, perfusion, and metabolism in patients with advanced coronary artery disease undergoing surgical revascularization.

BACKGROUND: Imaging of myocardial glucose metabolism using [18F]fluorodeoxyglucose (FDG) with positron emission tomography (PET) has been proposed for identification of tissue viability in patients with advanced coronary artery disease. This study was designed to evaluate the predictive value of flow and metabolic imaging for functional recovery after revascularization in myocardial segments of varying degrees of dysfunction. METHODS AND RESULTS: Thirty-seven patients (mean age, 59 +/- 11 years) with coronary artery disease and impaired left ventricular function (ejection fraction, 34 +/- 10%) were studied with PET using FDG and [13N]ammonia before surgical coronary revascularization (3 +/- 1 grafts per patient). Tissue was scintigraphically characterized as normal, nonviable (concordant reduction of perfusion and FDG uptake), viable without discordance of perfusion and metabolism (mildly reduced perfusion and metabolism), or ischemically compromised (mismatch of reduced perfusion and maintained FDG uptake). Functional outcome was assessed by serial radionuclide ventriculography before and at 13 +/- 13 weeks (median interval of 8 weeks) after coronary revascularization. Preoperatively impaired regional wall motion improved significantly in ischemically compromised (mismatch) revascularized segments but not in nonviable myocardium or in viable myocardium without discordance of perfusion and metabolism. The negative predictive value of PET for functional recovery was 86%, whereas the positive predictive value in revascularized regions ranged from 48% to 86% depending on severity of baseline wall motion abnormalities. CONCLUSIONS: PET identifies metabolically active tissue, which benefits from revascularization. Although the negative predictive value of PET for recovery was high, functional improvement of viable but ischemically compromised tissue was less frequent than previously reported. The predictive value of PET was highest in left ventricular segments with severe dysfunction and a mismatch or reduced perfusion but preserved metabolism. Integration of PET, angiographic, and functional data is necessary for the optimal selection of patients with advanced coronary artery disease and impaired left ventricular function for revascularization.

Adult↗
PubMed1994

[Jejunum pouch after total gastrectomy--clinical and scintigraphic studies of function and quality of life].

The formation of a pouch is a surgical procedure to restore the lost of reservoir function after resection of the stomach. After total gastrectomy the intestinal passage can be reconstructed by a jejunal pouch performing a Siewert/Peiper esophagojejunoplication. Regarding the postoperative quality of life we supposed that there is an advantage for this reconstruction method compared to simple esophagojejunostomy. The following study investigated whether the pouch reconstruction by jejunoplication can develop a reservoir function and therefore a better clinical course compared to jejunostomy. Without evidence of a local recurrence after total gastrectomy 18 patients with and 18 without pouch reconstruction were evaluated by alimentary scintigraphy for at least 6 months after operation. Only patients were included with a tumor stage not exceeding T2 (UICC). The results of the transit times with a solid radioactively labelled test meal were correlated with the complaints and nutritional status of the patients, evaluated with a standardized questionary for creating an individual score note. The transit in a jejunal pouch follows a linear decreasing function and is significantly slower compared to the exponential passage of the jejunostomy. Both patterns remain still significantly accelerated compared to the physiological ranges of gastric emptying. Patients with a pouch judge their postoperative individual state better than patients with simple jejunostomy indicated with an on average symptom related score note better than 3. As long as the tumor stage is associated with a beneficial prognosis and the tumor localisation allows the reconstruction by an esophagojejunoplication the formation of a pouch after total gastrectomy is recommended because of an improved transit pattern and clinical course.

Adult↗
PubMed1994

Compartmental analysis of technetium-99m-teboroxime kinetics employing fast dynamic SPECT at rest and stress.

UNLABELLED: We have examined the feasibility of compartmental analysis of 99mTc-teboroxime kinetics in measuring physiological changes in response to adenosine-induced coronary vasodilation. To evaluate the effect of tracer recirculation on 99mTc-teboroxime kinetics in the myocardium, we also compared compartmental analysis with washout analysis (monoexponential fitting), which does not account for this effect. METHODS: Eight healthy male volunteers were imaged using fast dynamic SPECT protocols (5 sec per tomographic image) at rest and during adenosine infusion. A two-compartment model was used and compartmental parameters K1 and k2 (characterizing the diffusion of 99mTc-teboroxime from the blood to the myocardium and from the myocardium to the blood, respectively) were fitted from myocardial time-activity curves and left ventricular input functions. RESULTS: Both K1 and washout estimates for the whole left ventricular myocardium changed significantly in response to coronary vasodilation. Mean stress-to-rest (S/R) ratios were almost two times higher for K1 (S/R = 2.7 +/- 1.1) than for washout estimates (S/R = 1.5 +/- 0.3). Estimation of K1 for all local regions, except the septal wall, is feasible because variations in K1 estimates for all local regions, except the septum during stress, are comparable with those for the global region. CONCLUSIONS: We conclude that quantitative compartmental analysis of 99mTc-teboroxime kinetics provides a sensitive indicator for changes in response to adenosine-induced coronary vasodilation.

Adenosine↗
PubMed1994

Modeling of carbon-11-acetate kinetics by simultaneously fitting data from multiple ROIs coupled by common parameters.

UNLABELLED: One of the unique aspects of PET is its ability to noninvasively quantify metabolic processes. Metabolic rate parameters are estimated by fitting the time-activity curves from regions of interest (ROIs) placed on dynamic PET images with a kinetic model. In many cases it is possible to couple these datasets with common parameters, such as the time delay between arrival of tracer in the ROIs and the sampling site. METHODS: Data from eight ROIs placed about images of the myocardium were coupled by the parameters describing the metabolite concentration in the blood. The method was evaluated by comparing estimates of k2 made using the coupled region method and the standard process of fitting data from each region separately. In addition, comparisons were made between estimates of k2 and measured myocardial oxygen consumption. RESULTS: Very little change in mean values of k2 was obtained. The variances, however, were reduced by an average of 37%, compared to the standard method, when the common parameters were not constrained. When the values of the common metabolite parameters were constrained to values previously measured, the average variance in estimates of k2 was reduced by 30%. CONCLUSION: We have demonstrated that the use of this technique can significantly increase the precision of estimates of myocardial oxygen consumption utilizing 11C-acetate PET images. More precise estimates of such quantities can facilitate detection of small regional and/or temporal physiological changes measured with PET. Furthermore, this method can be utilized whenever it is known a priori that one or more kinetic model parameters has the same value for every set of ROI data.

Acetates↗
PubMed1993

Blood flow-dependent uptake of indium-111 monoclonal antimyosin antibody in canine acute myocardial infarction.

OBJECTIVES: The relation of myocardial blood flow and indium-111 (111In) antimyosin antibody uptake was studied by inducing myocardial infarction in 18 dogs, 8 with closed chest left anterior descending artery balloon occlusion for 3 h followed by reperfusion (group A) and 10 dogs with open chest left anterior descending artery ligation (without reperfusion, group B). BACKGROUND: The relation of antimyosin uptake to myocardial injury has been documented. However, its relation to tracer delivery by myocardial blood flow has not been studied and has been assumed to be independent. METHODS: Indium-111 antimyosin antibody, 2 mCi, was injected 20 min after reperfusion and 3 h after coronary artery ligation in groups A and B, respectively. Regional blood flows were determined by radiolabeled microspheres during occlusion and 24 h later in both groups. On day 2, dogs were killed after risk zone delineation with gentian violet. The heart was excised and stained with triphenyltetrazolium chloride solution and graded for increasing severity of tissue injury based on extent of staining. Microsphere activity and 111In antimyosin activity were measured in control tissue (grade 1), noninfarct tissue at risk (grade 2), mixed tissue (grade 3), infarct tissue (grade 4) and hemorrhagic infarct tissue (grade 5, present only in group A dogs). Count activity was normalized to that of the mean value in control tissue (grade 1) and expressed as a ratio of activity. RESULTS: Indium-111 antimyosin activity was high in triphenyltetrazolium chloride grade 4 tissue in both groups but was attenuated in grade 4 tissue in group B dogs (10.6 +/- 5.1 vs. 5.0 +/- 4.5; p < 0.05 group A vs. group B), which had lower blood flow on day 2 (0.51 +/- 0.36 vs. 0.23 vs. 0.22; p < 0.01). Normalizing 111In antimyosin activity for blood flow on day 2 resulted in equivalent 111In antimyosin uptake for infarct tissue (32.6 +/- 21.6 vs. 36.6 +/- 29.8 for group A vs. group B; p = NS). CONCLUSIONS: Thus, 111In antimyosin uptake is a specific marker of necrotic tissue with a high signal ratio in reperfused tissue. However, its uptake is dependent on residual blood flow in the infarct territory. Indium-111 antimyosin could potentially serve as a suitable tracer for infarct sizing if myocardial blood flow in the same region were factored simultaneously.

Animals↗
PubMed1992

Comparison of technetium-99m sestamibi and thallium-201 retention characteristics in canine myocardium.

OBJECTIVES: The aim of this study was to compare the myocardial retention of technetium-99m (Tc-99m) sestamibi and thallium-201 over a wide range of blood flow at different time points after tracer injection. BACKGROUND: Technetium-99m sestamibi has been proposed as a new perfusion tracer with better physical characteristics than those of thallium-201 for scintigraphic imaging. However, no studies have simultaneously compared the ability of both tracers to assess myocardial blood flow during pharmacologic vasodilation. METHODS: The myocardial retention of Tc-99m sestamibi and thallium-201 were compared over a wide range of blood flow induced by regional coronary occlusion and dipyridamole infusion in an open chest dog model. Myocardial retention of both tracers was determined by in vitro tissue counting at 2, 5, and 20 min after tracer injection and was correlated with microsphere-determined blood flow. RESULTS: Thallium-201 demonstrated greater absolute tissue retention than did Tc-99m sestamibi. At 2 min after tracer injection, there was an almost linear relation between the retention of both tracers and myocardial blood flow over a wide flow range. However, this relation was not maintained over time. At 20 min after injection, the retention of both tracers underestimated myocardial blood flow at higher flow rates. At 2, 5 and 20 min after injection, increments of relative tracer retention between the different levels of flow were always greater for thallium-201 than for Tc-99m sestamibi. CONCLUSIONS: Thallium-201 displays more suitable physiologic characteristics as a flow tracer and may allow better differentiation of myocardial regions with different levels of coronary flow reserve. For both tracers, early cardiac imaging may minimize underestimation of blood flow at higher flow rates.

Animals↗