E. M. Stokely

A New Method for Radionuclide Imaging of Acute Myocardial Infarction in Humans

A new method of visualizing acute myocardial infarction in humans following intravenous injection of 15 mCi-5 mg of 99mTc stannous pyrophosphate in 23 patients is reported. Fifteen patients had histories suggestive of acute myocardial infarction and subsequently developed electrocardiogram and enzyme changes that confirmed the clinical diagnosis. Eleven of the 15 patients were scanned 3-5 days postinfarction, and all had positive scintigrams. The four remaining patients were scanned 7-10 days after their myocardial infarction; two had positive scintigrams. In those 8 patients with chest pain but without ECG and enzyme changes suggestive of myocardial infarction, scintigrams were negative. Positive scintigrams in the patients with myocardial infarction are thought to be due to incorporation of pyrophosphate into the crystalline structure of the hydroxyapatite found within the mitochondria of irreversibly damaged myocardial cells. The location of the acute myocardial infarction by scintigram correlated well with ECG localization in the 13 patients with positive scintigrams. This imaging method shows promise in 1) identifying the presence of acute myocardial infarction in patients with chest pain, 2) determining the location of acute myocardial infarction with a high degree of accuracy, 3) detecting the extension of the infarction, and 4) the possibility of determining the size of acute myocardial infarctions.

A new method for radionuclide imaging of myocardial infarcts.

Lesions such as ischemia, which result in myocardial cell death, are accompanied by cellular influx of calcium ions which localize within the mitochondria in the crystalline structure hydroxy-apatite. Using 99mTc-stannous pyrophosphate, an agent which labels hydoxyapatite for bone scanning, the authors have produced scintillation camera images of experimental myocardial infarcts in dogs. Tracer localization disappears with time, suggesting application of this method to fresh infarcts.

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.

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.

Orientation of 3-D structures in medical images

A tensor-based moment function method and a principal-axes method were investigated for registering 3-D test images to a standard image using translation, scale, and orientation. These methods were applied at two image resolutions to test discretization effects. At the higher resolution, both methods were found to perform well in cases where the test image could be described as an affine transform of the standard. At low resolutions, however, and when the test image was not an affine transform of the standard, only the principal-axes-based method performed adequately. The problem of quantifying the left ventricular function from gated blood pool single-photo emission computed tomographic images is considered. >

A model-based four-dimensional left ventricular surface detector

The authors have developed a general model-based surface detector for finding the four-dimensional (three spatial dimensions plus time) endocardial and epicardial left ventricular boundaries. The model encoded left ventricular (LV) shape, smoothness, and connectivity into the compatibility coefficients of a relaxation labeling algorithm. This surface detection method was applied to gated single photon emission computed tomography (SPECT) perfusion images, tomographic radionuclide ventriculograms, and cardiac rotation magnetic resonance images. Its accuracy was investigated using actual patient data. Global left ventricular volumes correlated well, with a maximum correlation coefficient of 0.98 for magnetic resonance imaging (MRI) endocardial surfaces and a minimum of 0.88 for SPECT epicardial surfaces. The average absolute errors of edge detection were 6.4, 5.6. and 4.6 mm for tomographic radionuclide ventriculograms, gated perfusion SPECT, and magnetic resonance images, respectively.

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.

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

SUMMARY 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 diag- nostic 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 responsible for increased myocardial uptake of 99mTc-PYP with a resultant positive 99mTc-PYP myocardial scintigram.

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.

Attenuation Correction for SPECT: An Evaluation of Hybrid Approaches

Most methods that have been proposed for attenuation compensation in single-photon emission computed tomography (SPECT) either rely on simplifying assumptions, or use slow iteration to achieve accuracy. Recently, hybrid methods which combine iteration with simple multiplicative correction have been proposed by Chang and by Moore et al. In this study we evaluated these methods using both simulated and real phantom data from a rotating gamma camera. Of special concern were the effects of assuming constant attenuation distributions for correction and of using only 180° of projection data in the reconstructions. Results were compared by means of image contrast, %RMS error, and a ¿2 error statistic. Simulations showed the hybrid methods to converge after 1-2 iterations when 360° data were used, less rapidly for 180° data. The Moore method was more accurate than our modified Chang method for 180° data. Phantom data indicated the importance of using an accurate attenuation map for both methods. The speed of convergence of the hybrid algorithms compared to traditional iterative techniques, and their accuracy in reconstructing photon activity, even with 180° data, makes them attractive for use in quantitative analysis of SPECT reconstructions.