Search PubMed⌕ Search

Biomedical subjects

G W Hamilton

Publications and source records attributed to G W Hamilton.

At least 37 records · Page 2Linked to original sources
PubMed1979

Myocardial imaging with thallium-201: the controversy over its clinical usefulness in ischemic heart disease.

Several uses of thallium myocardial imaging (assessment of questionable stenosis and detection of infarction) provide unique information and are useful adjuncts in the diagnostic workup and treatment of patients with coronary artery disease. Screening studies with thallium to detect the presence or absence of coronary artery disease have generated considerable controversy. Much of this conflict can be resolved by a careful analysis of the purpose of the screening study, the sensitivity and specificity of the imaging test, and the prevalence of disease in the subgroup under study. With the principles outlined, thallium imaging can be used to make patient-care decisions with a reasonable degree of confidence.

Bayes Theorem↗
PubMed1979

Thallium-201 myocardial imaging: a comparison of the redistribution and rest images.

Forty-one patients with chest pain and suspected coronary artery disease underwent thallium-201 myocardial imaging, performed immediately following maximal treadmill exercise, also at "redistribution" 4--5 hr after exercise, and at rest 1 wk later. All had coronary angiography. All images in seven patients without coronary artery disease were normal. Twenty-seven of the 34 (79%) patients with coronary artery disease had new, exercise-induced image defects. The redistribution and rest images were identical in 15/27 (56%) patients (complete redistribution). In 10/27 (37%) patients with exercise-induced defects, some redistribution occurred but defect size on the redistribution image was larger than that on the rest images (incomplete redistribution). In 2/27 (7%) of patients with exercise-induced defects, redistribution was absent. The presence of prior myocardial infarction, regional abnormalities of left-ventricular contraction or the severity of coronary stenoses did not correlate with the presence or absence of redistribution. Overall image quality between the two studies was similar, although image collection times for the redistribution study were prolonged. We conclude that some redistribution (complete or incomplete) occurs in most patients with exercise-induced image defects. When both fixed and reversible perfusion defects are present, defect size was often larger in the redistribution image and may thus overestimate the extent of prior myocardial infarction.

Adult↗
PubMed1978

Myocardial imaging with thallium-201: a multicenter study in patients with angina pectoris or acute myocardial infarction.

A multicenter study of rest and exercise thallium-201 myocardial imaging in 190 patients from five centers was performed. Exercise images were obtained after graded treadmill or bicycle stress with use of five different gamma camera models and were interpreted by the originating investigator without knowledge of other clinical data. Of 42 patients with less than 50 percent coronary stenosis, 4 (10 percent) had a resting image defect, 1 (2 percent) a new exercise defect and 5 (12 percent) either a resting or an exercise image defect, or both. Of 148 patients with coronary stenosis of 50 percent or greater, 64, (45 percent) had an image defect in the study at rest, 90 (61 percent) had new or increased defects after exercise, and 115 (78 percent) had resting or exercise defects, or both. New exercise image defects were more common than exercise S-T depression (90 of 148 [61 percent] versus 62 of 148[42 percent]; P less than 0.01). In a second group of 111 patients with acute myocardial infarction studied at three centers, 90 patients (81 percent) had image defects compared with 71 (64 percent) two had new electrocardiographic Q waves (P less than 0.01). Smaller infractions, as assessed with serum enzyme values, and diaphragmatic infarctions were less commonly detected than larger or anterior infarctions. These findings suggest that myocardial imaging complements the electrocardiographic identification of acute myocardial infarction of exericse-induced myocardial ischemia.

Acute Disease↗
PubMed1978

Myocardial imaging with 201thallium: an analysis of clinical usefulness based on Bayes' theorem.

Rest-exercise thallium-201 (201Tl) myocardial imaging and rest-exercise electrocardiography were performed in 137 patients with suspected coronary artery disease (CAD). The final diagnosis of coronary disease was made by arteriography. Sensitivity and specificity for the ECG and thallium studies alone or combined were then determined. Based on these data, the posttest probability of CAD with a normal or abnormal test was calculated using Bayes' theorem for disease prevalences ranging from 1%--99%. The difference between the probability of disease with a normal test and the probability of disease with an abnormal test was also calculated for each prevalence range. The results demonstrate that 201Tl imaging discriminates between disease absence or presence better than does the ECG. However, both the ECG and thallium studies provide rather poor discrimination between disease and no disease when the disease prevalence is low (less than 0.20) or high (greater than 0.70). Because of this characteristic, it is unlikely that screening tests for CAD will prove useful unless the disease prevalence in the group under study is in the moderate (0.20--0.70) range.

Angiography↗
PubMed1978

Cardiac chamber imaging: a comparison of red blood cells labeled with Tc-99m in vitro and in vivo.

A detailed comparison was performed between the quality of cardiac images obtained using red blood cells labeled in vitro and in vivo. Both methods gave cardiac images of high quality. The in vitro method resulted in subjectively superior images, better intravascular retention of injected radioactivity, and a higher left-ventricle-to-background count ratio (p less than 0.05). The differences in image quality and left-ventricular blood-pool activity were not great, however, and the slight advantage of the in vitro method was offset by a somewhat more complicated preparative procedure. We believe that both agents are suitable for radionuclide imaging of the cardiac chambers.

Erythrocytes↗
PubMed1978

Implementation of a digital image superposition algorithm for radionuclide images: an assessment of its accuracy and reproducibility.

An operator-interactive algorithm to achieve superposition of organ images has been used with a dedicated nuclear medicine computer system. Its purpose is to achieve organ registration in 128 X 128 digitized images before a direct numerical comparison of the regional distribution of a deposited radiotracer is performed. The accuracy and reproducibility of the algorithm for myocardial images has been tested by four operators, using a set of 28 image pairs in which the relative position of the heart differed by more than 10 mm for each pair. Comparing their results with the known displacements on two occasions provided an assessment of these two important parameters. The accuracy and reproducibility for superposing myocardial images by this digital technique are found to be well within the spatial resolution (FWHM) of the imaging system of the Tl-201 tracer studied.

Computers↗
PubMed1978

Radionuclide angiography for the evaluation of anthracycline therapy.

A sensitive and reproducible method to noninvasively monitor cardiac function in patients receiving anthracycline therapy is badly needed. The radionuclide ejection fraction (EFrn) appears to be a suitable technique to provide this hemodynamic information. This paper describes the technique for determining the left ventricular EFrn with the use of technetium99m-labeled rbcs, a gamma scintillation camera, and a dedicated computer. The comparison of radionuclide and radiographic contrast EFrn showed a high correlation ( r = 0.84) in 30 patients.

Angiography↗
PubMed1978

Time- and dose-dependent changes in ejection fraction determined by radionuclide angiography after anthracycline therapy.

Twenty patients receiving anthracycline chemotherapy were studied by the technique of radionuclide ejection fraction (EFrn). This technique is capable of detecting noninvasively small changes in left ventricular function. Two patterns of anthracycline toxicity emerged: (a) an acute toxicity observable between 24 and 72 hours after administration of greater than 60 mg/m2 of anthracycline with some recovery noted by 72-96 hours (no changes were observed within the first 4 hours after administration of the drug), and (b) a chronic dose-dependent decrease in left ventricular function when studies were performed 3 weeks after the last dose of anthracycline. After anthracyclines were stopped, four of four patients showed significant recovery in left ventricular function. We concluded that the radionuclide EFrn is a sensitive noninvasive index of left ventricular function which can be used to serially study patients receiving anthracycline therapy and can potentially be used to evaluate pharmacologic means for preventing anthracycline cardiotoxicity.

Adult↗
PubMed1978

A field procedure for the quantitative assessment of nuclear imaging cameras.

Techniques developed for the quantitative assessment of gamma cameras are described. The performance parameters discussed include energy resolution, intransic line spread function, uniformity, and extrinsic line spread function. In addition to describing the equipment used and indicating methods used in analyzing data, some of the potential problems in interfacing multichannel analyzers to gamma cameras are discussed.

Electronics, Medical↗
PubMed1977

Myocardial imaging and radionuclide angiography in survivors of sudden cardiac death due to to ventricular fibrillation: preliminary report.

Twenty-one long-term survivors of out of hospital sudden cardiac death due to ventricular fibrillation underwent radionuclide angiography and myocardial imaging with thallium-201. In 13 patients images were obtained at rest and after maximal treadmill exercise; 11 of these 13 (85 percent) had an image defect in one or both studies. Eleven of the 21 patients (52 percent) had a defect in the image obtained at rest. The magnitude of myocardial image defects was typically great; some patients had an image abnormality without other clinical evidence (angina, S-T depression) of ischemia. The mean ejection fraction, assessed in 16 patients with radionuclide angiography, was 0.41 +/- 0.15 (standard deviation); in 5 of the 16 ejection fraction was normal (more than 0.50) and in 3 it was severely abnormal (less than 0.25). Thus, noninvasive radionuclide studies defined a broad spectrum of ischemic and ventriculographic abnormalities in survivors of sudden cardiac death. Further application of these noninvasive studies may identify those at high risk.

Adult↗
PubMed1977

Myocardial imaging with intravenously injected thallium-201 in patients with suspected coronary artery disease: analysis of technique and correlation with electrocardiographic, coronary anatomic and ventriculographic findings.

Myocardial imaging was performed after intravenous injection of thallium-201 at rest in 50 patients with suspected coronary artery disease and the results were compared with electrocardiographic, ventriculographic and coronary arteriographic findings. The thallium-201 myocardial images were of good quality and compared favorably with images previously obtained with intracoronary particle injection. Myocardial to background ratios averaged 2:1, a considerable improvement over ratios reported with potassium-43. There was complete intra- and interobserver agreement in the interpretation of images in 90 and 82 percent of cases, respectively. Major disagreement occurred in less than 5 percent of cases. Overall, 15 (30 percent) had an abnormal, 10 patients (20 percent) a borderline abnormal and 25 patients (50 percent) a normal myocardial image. Of patients with electrocardiographic Q waves, 91 percent had an image defect. Of 39 patients without Q waves, 13 percent had an image defect. All 30 patients with a normal or borderline abnormal thallium-201 image had a normal ventricular contraction pattern. All patients with a segmental ventriculographic abnormality had an image defect. In all cases, the area of electrocardiographic or ventriculographic abnormality corresponded to the area of the thallium-201 image defect. The systolic ejection fraction was depressed (0.49 +/- 0.18 [mean +/- standard deviation]) in patients with an image defect compared with that in patients with a normal image (0.64 +/- 0.06, P less than 0.005). Coronary arterial lesions were present and usually of high grade in all patients with an abnormal image; however, the presence of high grade coronary stenosis or occlusion as such correlated with image defects only to the extent that prior myocardial infraction was associated. Thus, satisfactory myocardial images at rest appear to be obtained with intravenously administered thallium-201 and electrocardiographic, ventriculographic and coronary arteriographic data suggest that image defects denote regions of prior myocardial infarction.

Coronary Angiography↗
PubMed1977

Myocardial imaging with thallium-201 at rest and during exercise. Comparison with coronary arteriography and resting and stress electrocardiography.

Myocardial imaging with intravenous thallium-201 (201Tl) was performed at rest and following maximal treadmill exercise in 101 patients with suspected coronary artery disease. Results were interpreted from Polaroid scintiphotos by three independent observers with complete interobserver agreement in 79%. Of 25 patients with no or insignificant coronary artery disease (less than 50% diameter stenosis), one (4%) had a resting 201Tl image defect, one (4%) had an exercise 201Tl defect, none had an ECG Q wave, and four (16%) had exercise ST-segment depression. Among 76 patients with coronary artery disease (greater than or equal to 50% diameter stenosis), 58 (76%) had a defect on either the rest or exercise 201Tl image. The proportion of patients with an exercise image defect (50/76, 66%) was greater than the proportion with exercise ST depression alone (34/76, 45%; P less than 0.02). Overall, 69 of the 76 (91%) patients with coronary artery disease had either a positive rest or exercise myocardial image and/or a positive rest (ECG Q waves) or exercise (ST depression) electrocardiogram. This exceeded the proportion with only rest or exercise electrocardiographic abnormalities (50/76, 65%; P less than 0.001). We conclude that rest and exercise myocardial imaging with 201Tl is easily accomplished with readily available imaging equipment. The image data enhanced the diagnostic sensitivity of stress electrocardiography, and provided spatial identification of the abnormal segment(s) of myocardium.

Adult↗