DIFFERENCE ANALYSIS OF ANTIFIBRIN IMAGES IN THE DETECTION OF DEEP VENOUS THROMBOSIS

This study was designed to test the hypothesis that the detecion of no n-blood-pool localization due to deep venous thrombosis uptake can be enhanced by computer processing. Methods: Immediate blood-pool and 90- min delay images from 25 patient studies obtained with Tc-99m T2G1s an tifibrin were paired into 125 image sets (5/pt, including A, P knees, A, P calves and A thighs). After spatially aligning the image pairs, t he blood-pool activity obtained from the immediate image was removed f rom the delayed image to produce a ''clot only'' image. Unprocessed da ta (UnP) and computer processed images (CmP) were presented to novice readers as part of a receiver operator characteristic (ROC) comparison study. The image interpreters were asked to provide independent diagn ostic assessment at 250 limb sites using both datasets. Image intensit y and color scale mappings were freely adjustable. Three readers were presented with images adjusted with optimal image contrast as judged b y an observer with knowledge of the correct response. Results: The are a under the ROC curve (Az), a measure of the method's accuracy, for th ese readers was 88.5% (UnP) and 88.8% (CmP) (p = ns), Four readers who se images were not optimized showed Az of 79.1% (UnP) and 90.7% (CmP) (p < 0.05). Average diagnostic decision time for all readers, per limb site, was 18.2 +/- 7.8 sec, m +/- s.e.m., (UnP) and 7.6 +/- 4.6 sec ( CmP). Conclusion: Novice reader accuracy is improved with computer pro cessed images when image intensity and contrast factors are important. Computer processing can provide ''clot'' images that minimize nonspec ific blood background activity and allow greater interpreter decision speed/confidence.