A modeling analysis of rest-stress and stress-rest injection sequences in performing thallium-201 myocardial...

A new thallium-201 stress testing protocol is proposed in which rest images are obtained prior to stress images. The advantages of the new protocol are that it saves time and requires no special diet or activity restriction between imaging sets. A potential problem from reversing the standard imaging sequence is decreased sensitivity to stress perfusion defects owing to background counts from the rest image. Using a cardiac phantom, 74 sets of stress and rest images were simulated under the new protocol and the standard stress-redistribution-reinjection protocol. Seven observers were asked to classify the images as normal or abnormal and to distinguish ischemic from fixed defects. Differences in observer performances between the two protocols were compared. With the new protocol, observers had sensitivities of 75%-90% and specificities of 100% in identifying a perfusion defect on the stress study. Accuracy was improved if the image counts from the rest study contributed less than 40% of the final counts of the stress study. Detection of ischemic and fixed defects was as good as or better than with standard protocols. Based on the phantom model, rest followed immediately by stress imaging sequence is an advantageous alternative for thallium-201 stress testing. Clinical trials are necessary to further evaluate this new protocol.