Theoretical error in radionuclide ejection fraction study due to photon attenuation.

The ejection fractions measured with the radionuclide method are usually lower than those measured with the X-ray contrast method in our hospitals. One of the reasons for this may be that the photon attenuation by the cardiac blood pool and soft tissue is greater for the larger end-diastolic ventricle than that for the end-systolic ventricle. Mathematically, the error due to photon attenuation in radionuclide ejection fraction study is calculated to be about 5 percentage points. Clinically, if 5 percentage points are added to the ejection fractions measured by the radionuclide method, the results would correlate better with the studies by the X-ray contrast method. The correction factors for photon attenuation may also be applied in calculation of the residual urinary bladder volume.