Abstract
The authors summarise the results of an assessment of the performance of a SPECT (single photon emission computed tomography) system, including phantom studies, which was carried out prior to the clinical series, to determine the feasibility of SPECT lung ventilation imaging with aerosols. The diagnosis of pulmonary embolism depends on the detection of a cold' defect on the perfusion image which is unmatched on the corresponding ventilation image. The larger the embolus the more certain can be the diagnosis. Thus a segmental perfusion defect with no matching ventilation defect would be highly significant whereas smaller unmatched defects would not be quite so certain diagnostically. The study considers the factors which determine if a 'cold' defect in the ventilation activity distribution can be imaged using SPECT, particularly in view of work (G. Muehllehner, 1985) which suggests that with current SPECT systems a small improvement in spatial resolution leads to an improvement in image quality which more than offsets the effect of a relatively large reduction in count density.