The accurate measurement of cardiac chamber volume is of major importance in assessing cardiac performance. Accurate equilibrium radionuclide volume estimations are difficult to obtain, due to the geometry of the chambers, and the physical characteristics of the imaging system. The purpose of this study was to examine the effects of imaging projections on relative cardiac chamber volumes, indexes, and stroke volume ratios. Twenty-two male patients, free of clinical evidence of disease, were studied. A series of four 2-minute acquisitions were made with the patient successively imaged in the anterior, 30° left anterior oblique (LAO), 45° LAO, and 60° LAO projections with 15° of caudal inclination. Filtered stroke volume and original images were used by the operator to assign right ventricular (RV), left ventricular (LV), and a combined right and left ventricular (TOT) regions-of-interest. From the data we determined end-diastolic counts (EDC), endsystolic counts (ESC), stroke counts (SC), ejection fractions (EF), and R/L stroke count ratios. The following changes were observed as the projection was moved from the anterior to 60° LAO: 1) all RV parameters decreased in value, including, RVEDC (P<.001), RVESC (P<.01), RVESC (P<.01) and RVEF (P<.001); 2) LVEDC and LVESC (both P <.01) increased while LVEF decreased (P<.004); and 3) the R/L stroke count ratio decreased (P<.001). Variability could be explained by 1) chamber overlap and geometry; 2) patient variability; and 3) intrachamber, interchamber and chest wall photon attenuation and scatter. We suggest that close attention to detail, with computer assistance, to optimally position the patient may reduce the effect of inherent limitations in radionuclide volumetric measurements, thus improving the reliability and usefulness of existing studies.
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