Rationale for lung ventilation imaging

In a recent article Nimmo et al (1985) compared the economics of 127Xe, 133Xe and 81Krm for routine lung ventilation imaging. They concluded that 127Xe is the radiopharmaceutical of choice. The criteria for use of 123Xe and 133Xe were quite different, and we would like to comment on the rationale behind the use of radioactive gases for ventilation imaging. They state that, when using 133Xe, it is essential to perform the ventilation scan before the 99Tcm macroaggregated albumin perfusion study.