XE-127, A COMPARISON WITH XE-133 FOR VENTILATION STUDIES

Abstract

In 133Xe ventilation studies the 81-keV .gamma. photon emitted is a major disadvantage for imaging. Using a lung model with the same attenuation coefficient as inflated lung, 133Xe was compared with 127Xe to determine the smallest lesion that could be imaged at different places within the lung. With the lung lesion directly against the collimator, the lesion had to be 10 ml in volume in order to be seen with 127Xe, but with 133Xe the lesion had to be 30 ml. 127Xe gave better resolution, no matter where the lesion was placed within the lung. 127Xe was not better than 133Xe in resolving a lead bar phantom. When 133Xe was used with 99mTc in a model of pulmonary embolism, a ventilation defect was apparent even though the distribution of Xe was even throughout the model. This artifact was not seen when the 127Xe model was imaged.