CLINICAL COMPARISON OF XE-127 AND XE-133 FOR VENTILATION STUDIES

Abstract

133Xe and 127Xe were compared by performing ventilation studies with both radionuclides in 19 patients with a variety of lung diseases. Assessment of the counting rate over the chest, relative to the radioactivity in the lungs, permitted the evaluation of each isotope in terms of usable photons detected by a scintillation camera with a large field of view and appropriate collimation. A greater proton yield was obtained with 127Xe. Markedly improved resolution was shown by measurement of a line phantom, but was not apparent on subjective appraisal of scintiphotos except in the washout phase. 127Xe appears to be preferable to 133Xe because of the higher counting rates, lower patient radiation dose and longer shelf life. In addition, a prior perfusion study using a 99mTc radiopharmaceutical does not affect the quality of a 127Xe ventilation study. The use of 127Xe permits the selection for ventilation studies of only those patients with suspected pulmonary embolism and eliminates unnecessary radiation exposure. A further improvement in image quality obtained with 127Xe should be possible with certain modifications of the scintillation camera that would permit use of the 375-keV photopeak along with the 172- and 203-keV .gamma. energies. Charcoal traps designed for 133Xe will require additional shielding and longer storage time when used for 127Xe. 127Xe might be used again after appropriate processing.