Myocardial Tracer Uptake Research Articles

Automated assessment of myocardial SPECT perfusion scintigraphy: A comparison of different approaches of case-based reasoning

This study compared the diagnostic accuracy of different approaches of case-based reasoning (CBR) for the assessment of coronary artery disease (CAD) using thallium-201 myocardial perfusion scintigraphy in comparison with coronary angiography. For each scintigraphic image set, regional myocardial tracer uptake was obtained by polar map analysis. CBR algorithms based on a similarity measure were employed to identify similar scintigraphic images within the case library, where each case contained the scintigraphic data together with results of coronary angiography. The angiographic data of retrieved cases were then used to determine whether significant CAD was present in one of the major coronary arteries. Three different approaches of CBR were compared: (1) case retrieval based on a global comparison of polar map data (GLOB), (2) case retrieval based on a territorial comparison of polar map data (TER), and (3) case retrieval based on a comparison of a given case with eight sub-libraries classified according to the involvement of the three major coronary vessels using a group similarity measure (GROUP). Two matching algorithms the best-match approach and an adapted retrieving approach were combined with all three case retrieval methods and their influence on the diagnostic accuracy were investigated. For overall detection of significant CAD, the best-match approach of both TER and GROUP retrieval methods showed a higher diagnostic accuracy than the GLOB retrieval method (75% and 77% versus 70%, respectively). ROC analysis for the adapted retrieving approach showed a similar diagnostic accuracy for all three methods with an area under the curve of 0.79, 0.8, and 0.8 for GLOB, TER, and GROUP, respectively. The observed improvement in the diagnostic accuracy by the new approaches may lead to further improvements of CBR systems, which have the potential to offer valuable decision support for human readers, especially for less experienced investigators.

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Direct comparison of adenosine and adenosine 5′-triphosphate as pharmacologic stress agents in conjunction with Tl-201 SPECT: Hemodynamic response, myocardial tracer uptake, and size of perfusion defects in the same subjects

Adenosine 5'-triphosphate (ATP), a potent and inexpensive coronary vasodilator, was introduced as a pharmacologic stress agent for thallium 201 single photon emission computed tomography (SPECT). However, there has been no direct comparison of ATP and adenosine as myocardial stressors in the same subjects. Thirty-six patients underwent consecutive Tl-201 SPECT imaging with adenosine and ATP in a randomly assigned order. There were no changes in clinical status and no invasive procedures were performed between the two tests. The hemodynamic response and side effects were monitored, and myocardial tracer uptake was assessed by use of a visual grading system and quantitative analysis via a CEqual map. The hemodynamic changes and adverse effects did not differ significantly between the two groups. There were no changes in the detection of any perfusion defect on a per-subject basis, except in one. The exact agreement rate for the visual grading of the myocardial tracer uptake was 84.8%. However, the average extent of the perfusion defect and the severity score were higher with adenosine. The hemodynamic changes and the degree of myocardial uptake were similar between the adenosine and ATP infusion. However, quantitative analysis by use of a CEqual map revealed smaller perfusion defects and lower severity scores in subjects undergoing Tl-201 SPECT with ATP.

Arterial concentration of 99mTc‐sestamibi at rest, during peak exercise and after dipyridamole infusion

Tracers for myocardial perfusion imaging during stress should not only have high cardiac uptake but they should also have a fast blood clearance to prevent myocardial tracer uptake after the ischaemic stimulus. The present study characterize the early phase of the arterial (99m)Tc-sestamibi (MIBI) time-activity curve after venous bolus injection at rest, during peak exercise and after dipyridamole infusion. We included 11 patients undergoing angioplasty for one-vessel disease (rest study) and 20 patients evaluated for the detection of haemodynamic significant coronary stenoses by (99m)Tc-sestamibi single photon emission computed tomography (SPECT) using either bicycle exercise testing (10 patients) or standard dipyridamole testing (10 patients). Arterial blood samples of 1 ml were taken from the left femoral artery (rest study) or the right radial artery (exercise and dipyridamole studies) every 5 s during the first 5 min postinjection. In the exercise and the dipyridamole studies blood sampling were extended to include blood samples every 5 min 5-30 min postinjection. Peak MIBI concentration was lower and decrease in concentration slower after tracer injection during exercise than during dipyridamole stress testing. This may cause an underestimation of perfusion defects during exercise because of MIBI uptake after the ischaemic stimulus. The implications of the study not only refer to the choice of stress modality when using MIBI. This study also underlines the importance of considering early blood clearance in addition to regional myocardial tracerkinetic aspects such as myocardial extraction fraction when new tracers are introduced.

PET-CT Evaluation of 2-Deoxy-2-[ 18F]Fluoro-D-Glucose Myocardial Uptake: Effect of Respiratory Motion

PURPOSE: Using combined positron emission tomography (PET) and computerized tomography (CT) instrumentation, PET measurements of myocardial tracer uptake performed with CT attenuation correction may differ from estimates using 68Germanium transmission correction due to differences in respiratory motion during acquisition. The purpose of this study is to evaluate the effects of respiratory motion on the CT acquisition and emission corrected images, and to evaluate the correlation of diaphragm position with regional differences in myocardial 2-deoxy-2-[ 18F]fluoro-D-glucose (FDG) uptake in clinical studies. METHODS: A canine myocardial FDG-PET study was performed with controlled ventilation. Attenuation correction was performed with CT scans acquired at end expiration and end inspiration, and throughout multiple respiratory cycles with conventional 68Germanium transmission scan. The mean myocardial FDG activity was evaluated in multiple short axis regions of interest (n = 40) using each of these three AC maps. Differences in emission during CT acquisitions were identified and expressed as bias (%) compared to 68Germanium corrected data. Ten patient studies with high myocardial FDG uptake were retrospectively selected from a clinical population referred for whole body oncology studies. All subjects had both CT and 68Germanium AC. After analysis for diaphragm misregistration defined by imaging and diaphragm position, subjects were divided into two groups: Group A controls (n = 5) with no or mild misregistration, and Group B (n = 5) with moderate or severe diaphragm misregistration. Regional emission bias (n = 400 regions) from CT correction was defined by using the 68Germanium attenuation corrected emission as the standard. RESULTS: The canine study using end-expiration CT for attenuation correction showed regional overestimation of activity (1.8%±0.7% for inferior; 2.0%±0.5% for inferolateral) compared to the 68Germanium corrected images. Conversely, the study using end-inspiration CT attenuation correction showed underestimation (−3.9%±0.5% for inferior; −4.0%±0.6% for inferolateral) of myocardial activity compared to 68Germanium corrected images. In subjects, Group B showed significant relative underestimation of FDG myocardial activity compared to Group A in the regions adjacent to the diaphragm including the inferior ( P = 0.0003), inferoseptal ( P = 0.008), and inferolateral ( P<0.0001) regions. CONCLUSIONS: In canine myocardium, differences in respiration influenced CT attenuation maps and subsequent CT attenuation corrected PET images in the inferolateral and lateral regions. In clinical PET-CT studies, diaphragm misregistration is associated with relative decreased emission activity in inferior, inferoseptal, and inferolateral walls. Nonuniformity of bias in the emission data can affect quantitative accuracy, and therefore, the interpretation of myocardial viability. Further studies are required to determine if the frequency of these findings warrants the use of 68Germanium transmission attenuation correction in myocardial FDG-PET. The quantitative differences between these techniques were typically modest.

Electromechanical mapping versus positron emission tomography and single photon emission computed tomography for the detection of myocardial viability in patients with ischemic cardiomyopathy

ObjectivesWe compared catheter-based electromechanical mapping (NOGA system, Biosense-Webster, Haifa, Israel) with positron emission tomography (PET) and single photon emission computed tomography (SPECT) for prediction of reversibly dysfunctional myocardium (RDM) and irreversibly dysfunctional myocardium (IDM) in patients with severe left ventricular dysfunction. Furthermore, we established the optimal discriminatory value of NOGA measurements for distinction between RDM and IDM. BackgroundThe NOGA system can detect viable myocardium but has not been used for prediction of post-revascularization contractile function in patients with ischemic cardiomyopathy. MethodsTwenty patients (19 males, age [mean ± SD] 60 ± 16 years, ejection fraction [EF] 29 ± 6%) underwent viability testing with NOGA and PET or SPECT before revascularization. Left ventricular function was studied at baseline and six months after revascularization. ResultsThe EF increased to 34 ± 13% at six months (p < 0.05 vs. baseline). The 58 RDM and 57 IDM regions differed with regard to unipolar voltage amplitude (UVA) (9.2 ± 3.9 mV vs. 7.6 ± 4.0 mV, p < 0.05), normalized UVA (106 ± 54% vs. 75 ± 39%, p < 0.05), and tracer uptake (76 ± 17% vs. 60 ± 20%, p < 0.05). The NOGA local shortening did not distinguish between RDM and IDM (6.4 ± 5.8% vs. 5.4 ± 6.6%). By receiver operating characteristic curve analysis, myocardial tracer uptake had better diagnostic performance than UVA (area under curve [AUC] ± SE: 0.82 ± 0.04 vs. 0.63 ± 0.05, p < 0.05) and normalized UVA (AUC ± SE: 0.70 ± 0.05, p < 0.05). Optimal threshold was defined as the value yielding sensitivity = specificity for prediction of RDM. Sensitivity and specificity were 59% at a UVA of 8.4 mV, 65% at a normalized UVA of 83%, and 78% at a tracer uptake of 69%. ConclusionsThe NOGA system may discriminate RDM from IDM with optimal discriminatory values for UVA and normalized UVA of 8.4 mV and 83%, respectively. However, the diagnostic performance does not reach the level obtained by PET and SPECT in patients with severe heart failure.

Myocardial indium-111-antimyosin uptake in essential hypertension

Evaluation of myocardial uptake of (111)In-anti-myosin antibodies in patients with essential hypertension for the verification of our hypothesis that it may increase in stage 1 in the left ventricle as a result of myocardial damage. Twelve men (mean age: 59+/-2.4 years) suffering from angina like symptoms and essential hypertension in clinical stage 1 according to the JNC-VI criteria were included into the study. These patients showed normal perfusion as revealed by thallium-201 myocardial study and coronary angiography. Left ventricular mass index was determined in echocardiography. Planar antimyosin images were obtained 48 h after the intravenous injection of the tracer. Heart to lung ratios were calculated as a parameter of myocardial tracer uptake using appropriate region of interests; values>1.52 were considered as abnormal. We observed increased anti-myosin uptake (mean: 1.71+/-0.12) consistent with myocardial damage in 11 of 12 patients. Nine of 12 patients had a left ventricular hypertrophy with left ventricular mass index values (mean: 131 g/m(2)+/-9.48) above 115 g/m(2). Heart to lung ratio was correlated significantly to left ventricular mass index (r = 0.902, p<0.001) and duration of hypertension (r = 0.948, p<0.001). Our results suggest that (111)In-antimyosin imaging may indicate myocyte damage in early phases of hypertensive heart disease.

Quantification of limited augmentation of myocardial (99m)Tc-tetrofosmin uptake at exercise in stable coronary artery disease.

We evaluated the diagnostic accuracy of a new method for quantitative analysis of myocardial perfusion at exercise using (99m)Tc-tetrofosmin tomographic imaging. (99m)Tc-tetrofosmin imaging of an exercise-rest sequence was performed in 30 patients with coronary artery disease (CAD) and eight age-matched control subjects. The exercise-induced myocardial count increase was calculated as the relative value (per cent increase ratio, %IR) to that at rest by correcting for physical decay for (99m)Tc and injected doses and by a subtraction technique. Exercise and rest (99m)Tc-tetrofosmin images were assessed visually and quantitatively using the per cent peak count and %IR of the myocardial count at exercise. Segments with significant coronary stenosis (diameter stenosis=75% or more) showed a significantly lower %IR than did those without significant coronary stenosis in the CAD patients (37+/-19% vs 63+/-21%, P<0.05). The diagnostic efficacy of visual analysis for detecting coronary stenosis was as follows: sensitivity, 58.1% and specificity, 81.4%. When %IR=37% was used for detecting significant coronary stenosis, sensitivity and specificity increased to 74.2% and 93.2%, respectively. Furthermore, the quantitative analysis significantly (P=0.04) improved the overall diagnostic accuracy from 73.3% to 86.7% compared to that of visual assessment. Thus, augmentation of myocardial (99m)Tc-tetrofosmin uptake at exercise is blunted in the myocardium with significant coronary stenosis. The calculation of myocardial count increase at exercise relative to that at rest can improve the diagnostic value of (99m)Tc-tetrofosmin SPECT imaging and may contribute to more accurate quantification of myocardial ischaemia and impaired tracer uptake in coronary artery disease.

Can serum carnitine levels distinguish hypertrophic cardiomyopathy from hypertensive hearts?

Although echocardiography is a useful diagnostic tool in hypertrophic cardiomyopathy (HCM), it is sometimes difficult to differentiate it from hypertensive heart disease (HHD): some patients with HCM show symmetrical hypertrophy, whereas patients with HHD sometimes show asymmetrical septal hypertrophy. We used a radioiodinated long-chain fatty acid tracer to visualize the altered myocardial fatty acid metabolism of HCM and HHD. Carnitine is the essential substance for the beta-oxidation of long-chain fatty acids. We recently reported that serum free carnitine levels in HCM were elevated and that they were significantly correlated with the severity of myocardial fatty acid metabolic disorder. Therefore, we investigated serum carnitine levels in patients with HCM and HHD, which can contribute to the differentiation of each other. We studied 56 patients with HCM and 20 patients with essential hypertension. Serum free carnitine levels were significantly higher in patients with HCM than those with HHD (HCM 52.5+/-9.5 nmol/mL, HHD 46.6+/-6.4 nmol/mL, P<0.01), but they showed no statistical difference between patients with HHD and normal subjects. Serum acylcarnitine levels were significantly lower in patients with HCM than those with HHD (HCM 10.1+/-4.0 nmol/mL, HHD 14.5+/-4.9 nmol/mL, P<0.0005), although they did not differ between patients with HHD and normal subjects. Scintigraphic analyses with a long-chain fatty acid analog revealed that myocardial tracer uptake was much reduced in patients with HCM compared with that in patients with HHD (quantitative analysis: HCM 2.11+/-0.12, HHD 2.22+/-0.17, P<0.05; semiquantitative analysis: HCM 13.6+/-6.3, HHD 2.0+/-1.5, P<0.0001). In conclusion, the differences in serum carnitine levels between HCM and HHD reflect altered myocardial fatty acid metabolic impairment, and the levels can help to distinguish these 2 diseases.

Influence of prolonged exercise on myocardial distribution of 123I-MIBG in long-distance runners

Background. A study was conducted to determine if prolonged exercise could provoke sympathetic neuronal alteration in an athlete's heart through assessment of myocardial distribution of 123I-metaiodobenzylguanidine (MIBG) in nine ultramarathon runners at baseline and after a 4-hour race. Methods and results. After injection of 370 MBq of 123I-MIBG, the athletes ran for 4 hours, covering 45 ± 8 km. Planar and single-photon emission computed tomography (SPECT) images of the thorax were acquired at the end of the race. Two weeks later, studies at baseline were performed. A heart:mediastinum ratio (HMR) was calculated to quantify MIBG uptake. Basal MIBG studies showed normal myocardial tracer uptake, on both planar and SPECT images, and the HMR was 1.84 ± 0.16. After the 4-hour race, MIBG studies showed decreased myocardial uptake in all athletes, and the HMR was 1.70 ± 0.18 ( p < 0.005). A positive correlation between the percentage of decrease of HMR after the race and the distance covered was observed ( r = .910, p < 0.001). Conclusions. Myocardial MIBG activity is decreased by prolonged exercise in long-distance runners. The degree of reduction of myocardial MIBG activity is related to the distance covered. Prolonged exercise, as sustained sympathetic stimulus, may alter myocardial distribution of MIBG.

Indium-111-antimyosin fab imaging to demonstrate myocardial involvement in systemic lupus erythematosus: A.J. Morguet, D. Sandrock, M. Stille-Siegener, H.R. Figulla. Department of Cardiology/ Pulmonology, Center of Internal Medicine, Georg August University, Gottingen, Germany. J Nucl Med 1995;36:1432–5

Indium-111-antimyosin Fab imaging has been used to indicate myocardial injury. This report describes antimyosin accumulation in two patients with myocardial involvement in systemic lupus erythematosus. Both patients complained of chest pain, and significant stenoses of extramural coronary arteries were ruled out by angiography. The first patient, a 64-yr-old woman, had immunopathologic findings suggestive of systemic lupus. Indium-111-antimyosin Fab imaging showed myocardial tracer uptake. This prompted endomyocardial biopsy providing evidence of systemic lupus. The patient improved under immunosuppressive therapy. The second patient, a 47-yr-old man, had systemic lupus diagnosed by immunopathologic findings and skin biopsy. He had evidence of pericarditis on electrocardiography and echocardiography. Indium-111-antimyosin Fab imaging demonstrated additional myocardial involvement, which supported the initiation of immunosuppressive therapy. Our results suggest that 111In-antimyosin Fab imaging may provide valuable diagnostic information and influence patient management in systemic lupus erythematosus with suspected myocardial involvement.

Ga-67 Citrate Myocardial Uptake in a Patient with AIDS, Toxoplasmosis, and Myocarditis

A 38-year-old man with AIDS presented with fever of unknown origin, splenomegaly, anemia, and thrombocytopenia. Admission laboratory data revealed a positive toxoplasmosis titer in the blood. The initial chest x-ray showed small bilateral pleural effusions, a normal cardiac silhouette, no infiltrates, and no interstitial edema. Ga-67 imaging revealed markedly abnormal uptake in the myocardium. A diagnosis of toxoplasmosis myocarditis was made based on laboratory and imaging data. The patient was treated for toxoplasmosis. No myocardial uptake of tracer was demonstrated on a follow-up Ga-67 scan, performed after completion of treatment for toxoplasmosis.

Myocardial perfusion imaging with technetium-99m-labeled agents

Thallium-201 (201Tl) is suboptimal as a single-photon emitting agent for myocardial perfusion imaging, in view of its low-energy photons and long half-life. To circumvent these limitations, two new myocardial perfusion imaging agents labeled with technetium-99m (99mTc) have been developed. They are Tc-sestamibi and Tc-teboroxime. Clinical trials of myocardial perfusion with both tracers have shown results similar to those obtained with 201Tl for detection of coronary artery disease. Results to date indicate that Tc-sestamibi accurately detects and locates myocardial infarction and can accurately assess both left and right ventricular ejection fractions by the first-pass technique. In addition, research has shown that rest-stress studies can be performed on the same day and that Tc-sestamibi can be used to assess the results of thrombolytic therapy. Tc-teboroxime has excellent myocardial tracer uptake characteristics but is cleared very rapidly from the myocardium. These features make Tc-teboroxime well suited to rapid serial studies. These new technetium myocardial perfusion agents have just become available for routine clinical use and are likely to replace 201Tl in many of its clinical applications.

Diagnosis of acute myocardial infarction by indium-111 antimyosin antibodies and correlation with the traditional techniques for the evaluation of extent and localization

This clinical study evaluated the accuracy of planar myocardial scintigraphy with antimyosin monoclonal antibodies radiolabeled with indium-111 (AMA-Fab) in the detection and localization of acute myocardial infarction (AMI). Fifty-seven patients admitted for suspected AMI were studied; 17 patients underwent thrombolytic therapy with intravenous streptokinase and 11 had clinical signs of reperfusion; 9 had had a previous myocardial infarction. Fifty of 57 patients were discharged from the coronary care unit with a confirmed diagnosis of AMI. The AMA-Fab study results were positive for AMI in 49 patients (98%) and negative in 1 (2%). Among the 7 patients without AMI, 5 had unstable angina, 1 had Prinzmetal's variant angina and 1 had acute pancreatitis. AMA-Fab results were negative in 6 of 7 patients (85%) and positive in 1 (15%). Therefore, the sensitivity and specificity of AMA-Fab scintigraphy were 0.98 and 0.85, respectively. To assess accuracy in defining the extent and location of AMI, AMA-Fab results were compared with those of the electrocardiogram, echocardiogram, technetium-99m pyrophosphate myocardial scintigraphy and coronary angiography and left ventriculography. AMA-Fab scintigraphy showed a good concordance with the traditional techniques in the topographic definition of the infarcted regions. No uptake of AMA-Fab was seen in the regions of previous old infarcts. Ten healthy volunteers also underwent AMA-Fab scintigraphy. No evidence of myocardial tracer uptake was noted in them. No adverse reactions or side effects were noted after injection of AMA-Fab in any patient. It is concluded that planar myocardial scintigraphy with AMA-Fab is a reliable method for AMI detection and location.

A Novel Surface Reconstruction and Display Method for Cardiac PET Imaging

Positron emission tomography (PET) allows the in vivo assessment of biochemical activity in humans. The newer PET cameras can create several imaging planes, or slices, through an organ inside the body. The interpretation of two-dimensional (2-D) slices of an organ is often difficult for the clinician since he or she has to form a three-dimensional (3-D) mental composite of the structure of interest. We have developed a set of algorithms to reconstruct a functional three-dimensional surface model of the cardiac left ventricle from a set of two-dimensional cross-sectional image slices generated by PET. The theoretical techniques for this reconstruction method are applicable to most organs provided that the appropriate models for the organs are considered. An automatic boundary detection algorithm outlines the surface of the left ventricle from the 2-D images and assigns intensity values to the surface points whose level is proportional to the local activity. A 3-D surface of the intensity levels, with pseudocolor enhancement, is then displayed with the long axis of the heart in a vertical position. Such a display allows the 3-D myocardial tracer uptake to be clearly visualized by the clinician for better diagnosis.

A quantitative approach to the analysis of the normal thallium-201 myocardial image.

The visual interpretation of Thallium-201 myocardial images is made more difficult by nonhomogeneity of myocardial tracer uptake in normal studies. To increase the objectivity of the study, the variation in count density in different myocardial areas has been calculated using a computer regions of interest technique in 14 healthy, young subjects following intravenous injection of the radionuclide at rest and in 10 after injection during maximal exercise. The "normal ranges" for regional Thallium-201 uptake so obtained are presented and discussed.