Phantom study of breast tissue attenuation in myocardial imaging

The attenuation of photons by the breasts and other soft tissue overlying the chest may decrease the diagnostic accuracy of SPECT myocardial imaging. In this experiment, we measured the attenuation distortion of myocardial polar maps using a thorax phantom with a cardiac insert and added breast tissue. The distortion was measured using a regional semiquantitative analysis. Attenuation compensation was performed using a conebeam radionuclide CT attenuation map. Breast tissue attenuation created apparent "defects" in the polar map, where the intensity was reduced by up to 35% relative to the most intense region. However, the size, location and severity of the reduction depended on cardiac insert orientation and breast placement. For the geometries studied, apparent "defects" were observed in the anterior wall, the apex, the inferior wall and basal regions. These results suggest that attenuation artifacts may occur in almost any location. However, the attenuation compensation nearly eliminated the apparent defects and improved polar map symmetry. After compensation, the variations between regions were generally 5% or less. Therefore, we expect that attenuation compensation will improve diagnostic accuracy in myocardial imaging in female patients and in males with excessive musculature or soft tissue. Without such compensation, diagnosis may be compromised.