[Evaluation of myocardial ischemia by (RAO) long-axial myocardial imaging using slant-hole collimator]

Myocardial perfusion imaging with thallium chloride has been found to be effective in the clinical evaluation of patients with myocardial infarction. However, conventional myocardial perfusion imaging of the myocardium showing the postero-septal and antero-lateral wall cannot be obtained clearly by the conventional collimator due to the inevitable distance between the collimator and the heart. In contrast, 30, 60-degree RAO images were obtained clearly using slant-hole collimator with the collimator closely contact with the heart, which enables us to observe the postero-septal and antero-lateral walls of the myocardium. As a result, we obtained myocardial perfusion images every 30-degrees in a radial direction. By dividing RAO images into 12 segments, we compared perfusion defect in the myocardial scintigram with akinesis detected by echocardiography and contrast left ventriculography segmentally and referred to the character and accuracy of these three examinations. As a result, these three methods well agreed in cases with myocardial infarction of single vessel disease, but did not always agree in cases with triple vessel disease. The character of each method was as follows: 1) Left ventriculography, which gives direct information concerning wall motion of the left ventricle, was most sensitive to detect ischemic lesions, but had a tendency to overestimate hypokinesis of wall motion due to its invasive nature. 2) In myocardial scintigraphy, when hypoperfusion is associated with perfusion defect, we occasionally diagnose mistakenly the hypoperfusion area as normal because the scintigraphic evaluation is based on the relative distribution of perfusion. To avoid such underestimation, exercise myocardial scintigraphy should be performed and myocardial ischemia should be evaluated by comparing exercise images with redistribution images. Moreover, we studied extension of perfusion defect in the anterior and infero-posterior infarction groups. In anterior myocardial infarction, perfusion defect extended beyond the apex and reached the point one-third away from the apex to the base. In infero-posterior myocardial infarction, perfusion defect extended into the apex but did not exceed the apex. It seemed that the most suitable point to make the boundary between apical and infero-posterior areas was the point one-third away from the apex to the base along the inferior half of the RAO image of the myocardium.