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G W Hamilton

Publications and source records attributed to G W Hamilton.

At least 19 recordsLinked to original sources
PubMed1986

Thallium-201 myocardial imaging during coronary vasodilation induced by oral dipyridamole.

Myocardial perfusion imaging of 201TI injected during maximum exercise has been an important diagnostic tool for coronary artery disease. Pharmacologic coronary vasodilation by i.v. infusion of dipyridamole may be used in lieu of exercise stress for purposes of diagnostic perfusion imaging. However, i.v. dipyridamole is not currently available from commercial sources for widespread routine use. Accordingly, this study was carried out in order to determine whether high dose, oral dipyridamole would be useful as a coronary vasodilator for purposes of diagnostic perfusion imaging. Fifty-eight patients undergoing diagnostic coronary arteriography also had myocardial perfusion imaging with 201TI under conditions of rest, maximum exercise stress, and high dose oral dipyridamole. Of those patients who had a defect on exercise thallium images, 75% also had a perfusion defect on thallium images after high dose oral dipyridamole. These results indicate that oral dipyridamole causes sufficient coronary arteriolar vasodilation and increase of coronary flow in nonstenotic arteries to identify perfusion defects comparable to those seen on maximum exercise stress in at least 75% of cases. In 25% of patients with exercise defects, no perfusion defect was seen after oral dipyridamole. Thus, oral dipyridamole is a potent coronary vasodilator, comparable to exercise stress in most cases, but in a minority of patients may not be comparable to exercise stress.

Administration, Oral↗
PubMed1982

111In-oxine platelet imaging in hemodialysis patients: detection of platelet deposition at vascular access sites.

The value of 111In-oxine platelet imaging to assess abnormal platelet deposition at different vascular access sites was studied in 19 hemodialysis patients. Platelets were labelled immediately following dialysis and imaging was performed 2 and 48 h later; abnormal platelet deposition was defined as a localized increase in activity over time when compared to the opposite, control extremity. 10 patients had bovine grafts, 4 had arteriovenous fistulae, and 5 had Gore-Tex grafts. 111In-oxine platelet imaging demonstrated abnormal platelet deposition in 13 out of 19 patients. Positive images were obtained in some patients with each type of vascular access. Preliminary evaluation showed no clear relationship between image positivity and the history of prior graft occlusion. The imaging method provided in vivo evidence of the efficacy of treatment with the antiplatelet agent sulfinpyrazone in half of the treated patients. Following 1 week of sulfinpyrazone, 200 mg t.i.d., in 6 patients, 3 showed a definite decrease in platelet deposition, 2 showed a probable decrease, and 1 showed no change following therapy. We conclude that platelet imaging may provide organ-specific, in vivo evidence for abnormal platelet deposition in several types of vascular access sites, and may be useful in assessing the thrombogenicity of prosthetic materials and the efficacy of antithrombotic drugs.

Adult↗
PubMed1982

Regional distribution of myocardial blood flow measured by single-photon emission tomography: comparison with in vitro counting.

An emission computed tomography system (SPECT), which uses a single large-field-of-view gamma camera, was evaluated for its ability to measure the relative distribution of myocardial blood flow and to assess the effect of attenuation, scatter, and cardiac motion on the tomographic images. Normalized regional myocardial counts from the SPECT images of the living dogs correlated closely with those from the anatomic slices and the samples counted at necropsy except for an over-estimate of tracer in the perfusion defect (SPECT) 57.7 compared to tissue count 32.1; p less than 0.05. The differences were less for the other imaging conditions. Heart and thorax motion, attenuation, and scatter contributed less than 25% to the over-estimate of defect counts. We conclude that the SPECT system accurately reflects regional distribution of myocardial blood flow except for overestimation of flow in regions of perfusion defects. Small perfusion defects might therefore be missed, but no artifactual defects are created.

Animals↗
PubMed1981

Detection of left ventricular thrombi with radionuclide angiography.

Apparent filling defects compatible with left ventricular thrombus are occasionally noted in equilibrium radionuclide angiocardiograms. To define the usefulness of the radionuclide angiogram in detecting left ventricular thrombus, the anterior and left anterior oblique radionuclide angiograms of 39 patients with proved presence or absence of thrombus were blindly interpreted. The presence of thrombus was proved at autopsy in 5 patients, at cardiac operation in 2, or on indium-111 platelet imaging in 6; the absence of thrombus was proved at autopsy in 24 or at cardiac operation in 2. Overall, 13 radionuclide angiograms were interpreted as positive (n = 10) or equivocally positive (n = 3) for thrombus, and 26 studies were judged negative. The sensitivity of a positive or equivocally positive radionuclide angiogram for detection of thrombus was 77 percent (10 of 13 patients), the specificity 88 percent (23 of 26 patients), the positive predictive value 77 percent the negative predictive value 88 percent. If the three equivocal studies are instead considered negative for thrombus, the sensitivity was 62 percent, the specificity 92 percent, the positive predictive value 80 percent and the negative predictive value 93 percent. All thrombi were visualized in the anterior view in an area of akinetic or dyskinetic wall motion. A small group of 13 patients (8 with thrombus, 5 without) underwent two dimensional echocardiography, which was 100 percent sensitive and specific. The finding of a discrete filling defect or squared or cutoff ventricular apex in an area of abnormal wall motion in the anterior view of the radionuclide angiogram should suggest the diagnosis of ventricular thrombus, which may be confirmed by other noninvasive studies.

Autopsy↗
PubMed1981

Left ventricular thrombi: in vivo detection by indium-111 platelet imaging and two dimensional echocardiography.

Indium-111 platelet imaging, which can identify sites of active intravascular platelet deposition, and two dimensional echocardiography, which can identify intracardiac masses, can both be used to detect left ventricular thrombi noninvasively. We compared these techniques in 44 men at risk for thrombi from remote transmural myocardial infarction (31 patients) or cardiomyopathy (13 patients). All 44 patients underwent platelet imaging; 35 underwent echocardiography. On platelet imaging nine patients had thrombi and one had a possible thrombus. Of these 10 studies, none were positive at 2 hours, 5 were positive at 24 hours and all were positive 48 or 72 hours after platelet labeling. Nine of these patients underwent echocardiography, and all had an intraventricular mass. The findings on platelet scanning were negative in six patients who had positive (four patients) or equivocally positive (two patients) findings on echocardiography. All patients with thrombi detected by either noninvasive method had transmural anterior myocardial infarction with ventricular aneurysm. Of the seven patients who underwent cardiac surgery or autopsy, three had thrombi. Platelet imaging failed to identify one thrombus in a patient in whom imaging was performed only at 24 hours after labeling. There were no false positive platelet images in this group. Five of these seven patients (two with thrombi, three without) underwent echocardiography; in all cases the echocardiographic findings agreed with the pathologic findings. Both platelet imaging and echocardiography detect ventricular thrombi. Platelet imaging may detect only the most hematologically active thrombi. Both techniques may help define patients at risk of embolization and may be useful for in vivo assessment of antithrombotic drugs.

Aged↗
PubMed1981

Indium-111 platelet imaging for detection of platelet deposition in abdominal aneurysms and prosthetic arterial grafts.

Thirty-four platelet imaging studies were performed in 23 patients to determine whether platelet deposition could be detected in patients with vascular aneurysms (18 patients) or in patients in whom Dacron prosthetic grafts had been place (5 patients). In patients in whom abnormal platelet deposition was detected, the effect of administration of platelet-active drugs on platelet deposition was examined. Of the 18 patients with an aneurysm, 12 had positive studies on initial imaging and 2 had equivocally positive images. Of five patients with Dacron arterial grafts in place, four had diffuse platelet deposition in the grafts; the fifth patient had platelet deposition only in a pseudoaneurysm. Eight patients with an abdominal aneurysm and positive or equivocally positive baseline images were restudied during platelet-active drug therapy either with aspirin plus dipyridamole (seven patients) or with sulfinpyrazone (four patients). No patient studied during treatment with aspirin plus dipyridamole had detectably decreased platelet deposition compared with baseline determinations. In contrast, two of four patients studied while receiving sulfinpyrazone showed decreased platelet deposition. Thus, platelet imaging may be of value for studying platelet physiology in vivo and for assessing platelet-active drugs and the thrombogenicity of prosthetic graft materials in human beings.

Abdomen↗
PubMed1981

Seven-pinhole emission tomography with thallium-201 in patients with prior myocardial infarction.

Thirty-six patients with prior myocardial infarction, and 14 patients without, had myocardial imaging at rest using both seven-pinhole emission tomography and planar imaging with thallium-201. The sensitivity and specificity of the two approaches for the detection of prior myocardial infarction were compared. Qualitatively, planar imaging yielded sensitivities of 69% (25 of 36) and 80% (29 of 36) with Polaroid and video display formats, respectively. A semiquantitative analysis gave a sensitivity of 75% (27 of 36). Specificities for these three planar approaches were, respectively, 100% (14 of 14), 93% (13 of 14), and 71% (10 of 14) for the Polaroid, video, and semiquantitative analyses. Seven-pinhole tomography had a sensitivity of 83% (30 of 36) by qualitative or visual inspection and 86% (31 of 36) by semiquantitative analysis. Specificities by these two techniques were 71% (10 of 14) and 57% (8 of 14). There were no statistically significant differences in either sensitivity or specificity between the planar and tomographic approaches. Repeat seven-pinhole images were identical in 95% (46 of 48) of patients, showing that reproducibility was satisfactory. We conclude that the seven-pinhole tomographic approach has no advantage over standard planar imaging in the detection of prior myocardial infarction.

Adult↗
PubMed1980

Anthracycline cardiotoxicity: clinical and pathologic outcomes assessed by radionuclide ejection fraction.

A clinical syndrome of severe cardiomyopathy often accompanies administration of high doses of anthracycline agents. We studied 36 patients serially with radionuclide angiography. At three weeks following drug administration, 8 of 36 patients showed depression of ejection fraction (EF). All had received at least 280 mg/m2 of the drug and 7 had received more than 380 mg/M2. Definite clinical syndromes of congestive cardiomyopathy developed only in patients showing EF depression and in some patients, EF depression developed without signs of congestive heart failure. Ejection fraction studies at 5 minutes, 1 hour, 4 hours, 24 hours, 72 hours, and one week following drug administration showed no changes when compared to immediate preg-drug EF. Seven patients who died during the study underwent histologic examination. Only the single patient with a depressed EF showed histologic evidence of athracycline cardiotoxicity, although all but 1 of these patients had received at least 400 mg/M2. We conclude that serial radionuclide EF just prior to anthracycline administration is a potentially useful predictor of cardiac toxicity, and that EF depression and/or preservation of a normal EF should be weighed in the decision for administering a drug of this type at high dosage levels.

Antibiotics, Antineoplastic↗
PubMed1980

In vivo simulation of thallium-201 myocardial scintigraphy by seven-pinhole emission tomography.

Seven-pinhole emission tomography has been studied under conditions that simulate clinical myocardial imaging with thallium-201, and is compared with planar imaging with a heart phantom. The seven-pinhole technique produces reconstructed images that offer a tomographic presentation of the object but do not quantitatively represent true cross sections of the object's activity distribution. Tomography produces significantly greater image contrast than planar imaging, even when maximal background subtraction is used to enhance the planar images. Two quantitative limitations of seven-pinhole tomography are noted for a simulated 24-g, 1.5-cm-thick complete transmural infarct: (a) the defect's activity concentration is not accurately reconstructed, and (b) it propagates longitudinally into some reconstructed planes that do not contain it. The imaging limitations of seven-pinhole tomography under the conditions studied are shown to be consistent on several camera/computer/software configurations.

Heart↗
PubMed1980

Performance characteristics of a commercial ECG gate.

A commercial ECG gate was tested to evaluate its ability to predict accurately the time of end-systole. The predicted times followed the manufacturer's specifications quite well. These times were compared with the actual times of end-systole as determined by computer-derived left-ventricular time-activity curves using Tc-99m-labeled red blood cells. Although there was moderate scatter, the predicted times of end-systole correlated well with the actual times (n = 59, r = 0.829). If the left-ventricular ejection fraction was calculated using the predicted time of end-systole, the error would be 0.03, or less, for 95% of the subjects.

Cardiac Output↗
PubMed1980

Radionuclide angiocardiography: a comparison of first transit and gated blood pool methods.

First-transit and gated blood-pool radionuclide angiocardiography are two fundamentally different methods for scintigraphic examination of the heart. Both are equally accurate methods of measuring left ventricular ejection fraction as shown by comparison with cineangiography (correlation coefficients range 0.84 t 0.95). Both methods demonstrate a high degree of reproducibility in the results obtained from repeated determinations of ejection fraction in the same patient (correlation coefficients range 0.93 to 0.95). Additionally, both methods enable assessment of segmental ventricular wall motion and volumes; while there is good agreement between scintigraphic and cineangiographic findings with respect to wall motion, quantification of volumes remains problematic. Shunt assessment and calculation of transit times can only be obtained with the first-transit method. Notable advantages of the blood-pool method are simplicity and the ability to obtain multiple repeated studies for several hours after a single injection of imaging agent. The major disadvantages of the blood pool method are the problem of chamber superimposition which substantially complicates the process of wall motion analysis and the temporal and spatial distortion of data inherent to the need for relatively long imaging times. The chief advantage of the first-transit method is temporal separation of right and left heart imaging. This allows easy and accurate assessment of ventricular wall motion from any view desired. Short acquisition time makes heart rate variation and patient motion less critical. The most notable disadvantages of the first-transit method are the necessity to inject at additional bolus of imaging agent for each study performed and the complexities of performing and processing the studies.

Angiocardiography↗
PubMed1979

R-wave synchronized blood-pool imaging.

Three methods for determining the left ventricular ejection fraction (EF) from R-wave synchronized blood-pool images were compared to contrast angiography; the reproducibility of these methods was established in 51 patients. The EF was systematically underestimated by the fixed region-of-interest (ROI) method compared to the two methods that used varying ROI's which track the left ventricular boundary. All methods correlated reasonably well with angiography and were highly reproducible. Use of varying ROI's resulted in EF values that were essentially identical to those determined by angiography. Resolution-recovery image processing appeared to improve reproducibility when varying ROI's were used.

Angiography↗
PubMed1979

Radioactive particle imaging of coronary blood flow distribution.

The intracoronary injection of radionuclide-labeled macroaggregated albumin particles has been shown to be safe and to provide excellent myocardial imaging. When performed in the resting state, it is more sensitive than either the ECG or ventriculogram in identifying areas of scarring and fibrosis due to previous myocardial infarction. Combined with contrast induced coronary hyperemia, intracoronary MAA particles are useful in identifying stenoses of moderate severity that do not alter resting coronary blood flow. Particle studies are likely more sensitive than the rest-exercise 210T1 myocardial scan in identifying patients with significant coronary artery disease. Resting perfusion abnormalities are more closely related to improved or unimproved left ventricular function after surgery than are the ECG or resting left ventriculogram. While the long-range clinical utility of the particle technique is uncertain, its most useful application currently is identification of significant stenoses undetected by 201T1 and of questionable significance by arteriography.

Albumins↗