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Effect of Region of Interest Selection on First-Pass Radionuclide Cardiac Output Determination

Saint John's Hospital and Health Center, Santa Monica
Saint Agnes Medical Center and UCSF/Fresno Medical Education Program, Fresno
ADAC Laboratories, San Jose, California

Correspondence: For reprints contact: Edwin C. Glass, MD, Saint John's Hospital and Health Center, 1328 Twenty-Second St., Santa Monica, CA 90404.

ABSTRACT

In principle, region of interest (ROI) selection should not affect the measurement of cardiac output by the first-pass technique with a radioactive intravascular indicator. Clinical application of the method requires that this theoretical hypothesis be tested. Sixty-eight left anterior oblique first-pass studies were acquired with a scintillation camera and computer using red blood cells labeled in vitro with ^99mTc. Calculated mean cardiac output varied in the following order with respect to ROI: lung > right heart > left ventricle > whole heart (both ventricles) > aorta. Similar variations were observed in patients both with and without valvular regurgitation. Regions of interest over left ventricle or whole heart yielded the best correlations with cardiac output by thermodilution (r = 0.96, 0.95, respectively, n = 28) as well as the smallest interobserver variations (r = 0.994, 0.995, respectively, n = 33). First-pass studies with [^99mTc] red blood cells labeled in vitro can yield accurate, reproducible determinations of cardiac output provided that the effect of ROI selection is recognized and that regions are properly selected.