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Biomedical subjects

E M Stokely

Publications and source records attributed to E M Stokely.

At least 37 records · Page 2Linked to original sources
PubMed1977

Myocardial infarct imaging with technetium-99m phosphates.

Technetium-99m-phosphate imaging is particularly valuable in detecting (1) small transmural infarcts (3 g and larger in size); (2) new acute transmural infarcts in or near regions of old infarction; (3) acute subendocardial infarcts (larger than 3 g in size); (4) acute infarction in patients with left bundle branch block; and (5) perioperative myocardial infarction. Localization of inferior and posterior myocardial infarction is improved with imaging. Sizing of acute anterior and lateral infarcts has been accurately done in dogs and should prove helpful in patients. Extensive evaluation in both experimental animals and in patients has shown 99mTc-phosphate myocardial imaging to be a useful clinical tool, and it may be one of the most sensitive noninvasive ways presently available to identify acute myocardial necrosis. It is important to understand that 99mTc-phosphate imaging has a different pathophysiology basis from EKG's or serum enzymes. These tests do not compete but instead should complement one another.

Acute Disease↗
PubMed1977

Sizing acute myocardial infarcts: present limitations and potential approaches.

It is now possible by scintigraphic imaging to identify the presence of acute transmural or nontransmural myocardial infarcts by noninvasive techniques and to localize acute transmural infarcts. Radionuclide blood-pool scintigraphy allows assessment of the impact of old and new myocardial damage on left ventricular function.

Heart↗
PubMed1977

Infarct sizing with technetium-99m stannous pyrophosphate scintigraphy in dogs and man; relationship between scintigraphic and praecordial mapping estimates of infarct size in patients.

The present study was performed in order to evaluate the ability of technetium-99m stannous pyrophosphate (99mTc-PYP) myocardial scintigrams to size infarcts in experimental animals and man. In 10 dogs with proximal left anterior descending coronary artery occlusion and acute anterior myocardial infarcts, there was a significant correlation between scintigraphic infarct size and histological infarct weight (P less than 0.01). In 25 patients with acute anterior or anterolateral myocardial infarcts, there was a significant correlation between relatively large infarct size determined scintigraphically and the acute development of left ventricular failure. There was some overlap, however, in 99mTc-PYP scintigraphic infarct size between patients who did and did not develop left ventricular failure with infarction. Presumably this is explained by some patients having had earlier myocardial damage and thus developing left ventricular failure with relatively small new infarcts. There was also a statistically significant, but weak, correlation in patients between scintigraphic infarct size and precordial ST segment mapping including peak ST segment elevation (P less than 0.05) and the number of praecordial sites with ST segment elevation equal to or greater than 2 mm (P less than 0.01). The data suggest that 99mTc-PYP scintigrams and praecordial mapping measure some similar but some dissimilar aspects of infarct size in patients, and that 99mTc-PYP scintigraphy does size acute anterior and anterolateral infarcts in experimental animals and patients.

Animals↗
PubMed1977

Computed tomography: in vitro evaluation of myocardial infarction.

An in vitro study of computed tomographic (CT) scanning of experimental myocardial infarction (MI) was performed by studying isolated canine hearts 18 to 48 yrs. post-infarction. CT scanning does not detect histologically present calcification in the area of an MI, but can be used to identify wall thickness changes in these areas. Decreased attenuation coefficients are found infarcted myocardium where thinning is present. The potential CT scanning to detect areas of MI is confirmed.

Animals↗
PubMed1977

Effect of kilovoltage on detectability of pulmonary nodules in a chest phantom.

A partial chest phantom was constructed to examine the effect of kilovoltage on the detectability of pulmonary nodules. Four different energies were studied: 100, 150, 200, and 300 kVp. Nodule detectability improved with increasing energies up to 200 kVp, but improvement was relatively small and was accompanied by an almost equal rise in the number of false positive readings. Patient exposures were least at 200 kVp. There seems to be no advantage in a 300 kVp technique, since nodule detectability decreased and patient exposures increased at this energy.

Humans↗
PubMed1977

Effects of noise on the determination of ejection fraction from left ventricular time-activity curves.

The effects of Poisson noise on three estimates of ejection fraction made from left-ventricular time-activity curves have been investigated. All three methods are based on a sinusoidal model of left-ventricular volume changes. The first, developed by Schelbert et al., overestimates the ejection fraction for low-activity levels and low ejection fractions. The second estimate, which is merely a first-order correction for the contribution of Poisson noise to the first estimate, appears to be more accurate when both estimators are applied to simulated time-activity curves, and the resulting ejection fractions are compared. A third, "maximum likelihood" estimator, when applied to the same data, is apparently more accurate than the first two.

Heart Function Tests↗
PubMed1977

Comparison of different noninvasive methods of infarct sizing during experimental myocardial infarction.

This study evaluated the accuracy of several noninvasive infarct-sizing techniques in 12 awake, unsedated dogs with multivessel coronary obstructions and acute anterior myocardial infarcts. Estimations of infarct size by scintigraphy with technetium-99m Sn pyrophosphate (Tc-PP), serum creatine phosphokinase (CPK) release, peak serum myoglobin levels by radioimmunoassay, and precordial ECG mapping were compared and correlated with histologic measurements of infarct size. The comparisons indicate that precordial ST segments mapping, serum CPK release measurements and peak serum CPK, peak serum myoglobin, and Tc-PPi myocardial scintigraphy all provide approximate estimates of infarct size in this model. Each technique also has certain important limitations, however, including: (A) precordial mapping is relatively insensitive in the identification of small anterior infarcts, (B) serial serum CPK release measurements when obtained for only 24 hr after infarction tend to underestimate large anterior infarct size, and (C) Tc-PPi myocardial scintigrams may fail to recognize anterior infarcts less than 3 gm in size and may overestimate the size of small predominantly subendocardial infarcts. The findings also show that the closest estimate of histologic infarct size in this model was provided by combining two of the noninvasive techniques (precordial mapping to identify sites with 2 or more millimeters of ST segments elevation and Tc-PPi myocardial scintigrams) rather than by relying exclusively on any one technique alone.

Animals↗
PubMed1976

Gated blood pool imaging following 99mTc stannous pyrophosphate imaging.

Cardiac patients who have undergone 99mTc-stannous pyrophosphate (99mTc-PYP) myocardial imaging can be injected 24 hours later with 99mTc-pertechnetate (99mTc04) to assess left ventricular function. Reduction of 99mTc04 by tin remaining in the blood following the stannous pyrophosphate injection causes labeling of the red cells by 99mTc04 and the creation of a vascular tracer suitable for electrocardiographically gated imaging.

Animals↗
PubMed1976

Cardioversion and "false positive" technetium-99m stannous pyrophosphate myocardial scintigrams.

The present studies performed in experimental animals demonstrate that electrical direct current cardioversion can produce skeletal muscle damage and increased technetium-99m stannous pyrophosphate (99mTc-PYP) uptake; in experimental animals the electrically damaged skeletal muscle shows necrosis with extensive calcium deposition. In addition, the frequent administration of high energy cardioversion produces myocardial necrosis with calcium deposition, increased 99mTc-PYP myocardial uptake and a positive 99mTc-PYP myocardial scintigram. The data indicate that, if diagnostic 99mTc-PYP myocardial scintigraphy is contemplated after cardioversion, paddle placement should be slightly removed from the anteroposterior projection of the heart on the external chest wall to avoid possible subsequent confusion between increased myocardial and skeletal muscle uptake of 99mTc-PYP. If multiple high energy cardioversion episodes are necessary, myocardial necrosis resulting from electrical injury may occur and be responisble for increased myocardial uptake of 99mTc-PYP with a resultant positive 99mTc-PYP myocardial scintigram.

Animals↗
PubMed1976

Pathophysiology of technetium-99m stannous pyrophosphate and thallium-201 scintigraphy of acute anterior myocardial infarcts in dogs.

In 17 dogs with acute myocardial infarcts produced by ligation of the proximal left anterior descending coronary artery, a comparative study was made of myocardial scintigrams obtained with technetium-99m stannous pyrophosphate (99mTc-PYP) and thallium-201 (201T1), tissue levels of 99mTc-PYP and 201T1 uptake, histopathologic alterations, and regional myocardial perfusion measured with radioactive microspheres. 9 of the 10 hearts examined histologically had transmural infarcts with outer peripheral, inner peripheral, and central zones characterized by distinctive histopathologic features. A progressive reduction in myocardial blood flow was demonstrated between normal myocardium and the centers of the infarcts, and correlated well with progressive reduction in 201T1 upatke in the same regions. Marked 99mTc-PYP concentration occurred in areas with partial to homogeneous myocardial necrosis and residual perfusion located in the outer peripheral regions of the infarcts. The latter areas also were characterized by the presence of muscle cell calcification. The patterns of distribution of 99mTc-PYP and 201T1 explained the filling defects on 201T1 myocardial scintigrams and the doughnut patterns on 99mTc-PYP myocardial scintigrams in dogs with transmural infarcts. One dog with a subendocardial infarct had a small homogeneous area of activity on the 99mTc-PYP myocardial scintigram, and showed marked uptake of 99mTc-PYP in subendocardial areas of extensive necrosis and calcification still receiving some coronary perfusion. Thus, the data indicate that the status of regional myocardial perfusion is a key determinant for the occurrence of distinctive patterns of myocardial necrosis and for the scintigraphic detection of acute myocardial infarcts with 99mTc-PYP and 201T1.

Acute Disease↗
PubMed1976

Measurement of acute myocardial infarcts in dogs with 99mTc-stannous pyrophosphate scintigrams.

Myocardial scintigrams using 99mTc-stannous pyrophosphate (99mTc-PYP) can be used to measure myocardial infarcts produced in dogs by proximal ligation of the left anterior descending coronary artery. Seven dogs had 99mTc-PYP myocardial scintigraphy performed 24--32 hr after ligation of the proximal left anterior artery. In each dog the scintigrams showed increased 99mTc-PYP uptake in the distribution of the artery. The scintigraphically visible areas of infarction, measured using interactive computer-aided techniques, were compared subsequently with independent histologic measurements of myocardial infarct size. Several methods for using the area measurements to estimate infarct size were tested. The most successful method (r = 0.92, p less than 0.01) assumed a linear relationship between the largest scintigraphic infarct area and the histologically determined infarct weight. The results suggest that 99mTc-PYP myocardial scintigrams provide a useful noninvasive method for measuring infarct size in dogs with proximal ligation of the left anterior descending coronary artery.

Animals↗
PubMed1976

Acute myocardial infarction imaged with 99mTc-stannous pyrophosphate and 201Tl: a clinical evaluation.

Twenty-six patients suspected of having acute myocardial infarction (AMI) underwent myocardial scintigraphy sequentially with 201Tl and 99mTc-stannous pyrophosphate (99mTc-PPi). Of the 26 patients, 24 had AMI documented by enzyme and electrocardiographic changes. Nineteen had transmural and five had subendocardial myocardial infarctions. The remaining two patients had "unstable angina pectoris." The mean time from onset to imaging was 4 days. Of the 24 patients with AMI, 22 had positive 99mTc-PPi scintigrams. In 20 the area of acute myocardial damage appeared to be the same by 99mTc-PPi scintigram as by ECG; in two, the location could not be precisely determined. The two patients with negative 99mTc-PPi scintigrams at the time of combined myocardial imaging had had positive 99mTc-PPi images previously. In all 24 patients, the 201Tl images were abnormal in at least the location suggested by the electrocardiogram. In seven patients, the area of decreased 201Tl activity was grossly equal to the positive area on the 99mTc-PPi images; in 15, the 201Tl defect was definitely larger; and in two, the 201Tl defect appeared slightly smaller. Although the 99mTc-PPi and 201Tl myocardial images provide different information, both are valuable in determining the overall integrity of the myocardium in patients with ischemic heart disease.

Acute Disease↗
PubMed1975

Acute subendocardial myocardial infarction in patients. Its detection by Technetium 99-m stannous pyrophosphate myocardial scintigrams.

Eighty-eight patients admitted to a coronary care unit with chest pain of varying etiology but without ECG evidence of an acute transmural myocardial infarction had myocardial scintigrams using technetium-99m stannour pyrophosphate (99m-Tc-PYP). Seventeen of these patients had ECG and enzymatic evidence suggestive of acute subendocardial myocardial infarction. In each of these the scintigrams were postivie demonstrating increased 99m-Tc-PYP uptake either in a faintly but diffusely positive pattern or in a well-localized strongly positive one. The remaining 71 patients did not evolve ECG or enzymatic evidence of acute myocardial infarction. In each of these patients the myocardial scintigram was negative. Thus 99m-Tc-PYP myocardial scintigrams are capable of identifying the presence of acute subendocardial myocardial infarction in patients. The absolute frequency with shich subendocardial myocardial infarction can be recognized utilizing this technique will have to be established in a larger number of patients in the future.

Acute Disease↗
PubMed1975

Morphologic correlates of technetium-99m stannous pyrophosphate imaging of acute myocardial infarcts in dogs.

To obtain insight into the mechanism(s) responsible for the direct visualization of acute myocardial infarcts by myocardial scintigraphy with technetium-99m stannous pyrophosphate (99mTc-PYP), scintigraphic and morphologic studies were performed in 22 dogs subjected to occlusion of the proximal left anterior descending coronary artery (LAD). Grossly visible myocardial infarcts occurred in ten of 11 dogs with LAD occlusion for one day, five with LAD occlusion for two days, two with LAD occlusion for seven days and two with LAD occlusion for 13 days. Rare, microscopic foci of necrosis were observed in one dog with LAD occlusion for one day, and no lesions were present in two dogs subjected to temporary LAD occlusion for eight minutes and reflow for 24 hours. In the latter three dogs, 99mTc-PYP myocardial scintigrams were negative. In the 19 dogs with gross infarcts, 99mTc-PYP myocardial scintigrams were strongly positive at one and two days after LAD occlusion, much less positive at seven days and faintly positive at 13 days after occlusion. Positive myocardial scintigrams in most showed "doughnut" patterns, with marked peripheral concentration of radioactivity around central zones of much lower activity. On histologic examination, the one and two-day-old infarcts exhibited subendocardially located central zones and surrounding peripheral zones, both of which showed distinctive histopathological and histochemical features, including the selective occurrence in the peripheral zones of calcified muscle cells with ultrastructurally demonstrable apatite-like crystals in mitochondria. Selective occurrence of high tissue levels of 99mTc-PYP radioactivity also was demonstrated in the peripheral zones of four infarcts. Hearts with older infarcts (seven and 13 days) showed progressive replacement of necrotic myocardium by granulation tissue and progressive reduction in calcium deposits in the areas of damage. The data obtained in this study establish a temporal and topographical relationship between calcium accumulation in acute myocardial infarcts and 99mTc-PYP uptake responsible for scintigraphic detection of the lesions with this radionuclide in dogs subjected to proximal LAD occlusion.

Acute Disease↗
PubMed1975

Measurement of myocardial blood flow.

This paper represents a review of the recent literature on techniques to measure myocardial blood flow in man. A short discussion on flow meters in followed by a more detailed discussion of the radionuclide techniques used to measure myocardial blood flow. The radionuclide techniques are discussed in two groups: (1) qualitative measurement of blood flow using static images; and (2) quantitative measurements of blood flow using diffusible substances that actively enter the cell, radioactive labeled particles, and radioactive diffusible gases.

Absorptiometry, Photon↗