To compare interpretation of traditional planar ventilation–perfusion lung scan images with planar images reformatted from single photon emission computed tomography (SPECT) data using two different techniques.
Planar and SPECT ventilation–perfusion (V/Q) data were acquired from 50 patients referred with suspected pulmonary embolism. In addition to traditional six-view planar images, six-view planar images were also generated from SPECT data using two methodologies: an angular summing technique (angular summed planar images) and a forward projection technique (reprojected planar images). Three experienced nuclear medicine clinicians reviewed the images in a blinded, randomized fashion. Results were analysed by comparing the two reprojected techniques with the traditional true planar scans, examining for differences in the defects seen (number, type and confidence), and the impact on final clinical interpretation.
Compared with true planar scintigraphy, angular summed images demonstrated fewer mismatched defects (P<0.0001), while the reprojected planar images had more matched defects (P=0.013). In addition, there was a significant change in the clinical interpretation of the angular summed planar images resulting in clinicians perceiving a decreased likelihood of pulmonary embolism (P<0.016). No such difference in interpretation was observed for the reprojected planar images.
Angular summed planar images result in a perceived decreased likelihood of pulmonary embolism compared with true planar images. In contrast, while reprojected planar images result in an increased number of matched defects compared to true planar scans, there was no change in the clinical interpretation. Caution should be exercised when interpreting SPECT derived angular summed planar images in isolation.
Departments of aRespiratory Medicine
bNorthern Clinical School
cThe Woolcock Institute of Medical Research, Sydney, Australia
eSchools of Physics and Medical Radiation Science, University of Sydney
fBiomedical Engineering, Royal North Shore Hospital, St Leonards
Correspondence to Dr Benjamin Harris, Department of Respiratory Medicine, Royal North Shore Hospital, Pacific Highway, St Leonards 2065, Australia
Tel: +61 2 992 67111; fax: +61 2 990 66391;
Received 14 October 2007 Accepted 20 November 2007