Single photon emission computed tomography(SPECT) is being widely used for thallium-201 myocardial perfusion imaging. The reoriented oblique slices provide three-dimentional information. Since the position and rotation of the heart varies considerably according to the person, we need to determine the angle of the left ventricular long-axis in original transverse slices manually, which may result in a probrem during reproducibility. We have, thereby, developed two methods for automatic determination of the angle of the left ventricular long-axis using processing programs. One is to detect the minimum countpoints in heart chamber at each y level and draw a regression line, and another is to detect points in septal and lateral ventricular wall at a transverse slice and locate the central line of heart chamber at half width of the pairs of their points. We have applied these methods to phantom as well as clinical studies. In the phantom studies, the angle of left ventricular long-axis obtained by each method matched the setting angle of the phantom. In addition, in the exercise myocardial perfusion studies, 18 of 23 patients showed good agreement using the second method with the standard data, which were manually determined by an experienced operator. Thus, the second method is considered to be useful for creating oblique slices automatically during myocardial perfusion imaging.
