ATTENUATION CORRECTION BY SIMULTANEOUS EMISSION-TRANSMISSION MYOCARDIAL SINGLE-PHOTON EMISSION TOMOGRAPHY USING A TC-99M-LABELED RADIOTRACER - IMPACT ON DIAGNOSTIC-ACCURACY

Irregular photon attenuation may limit the diagnostic accuracy of myoc ardial single-photon emission tomography (SPET). The aim of this study was to quantify the potential benefit of attenuation correction by si multaneous emission and transmission imaging for the detection of coro nary artery disease (CAD) of vessels supplying the inferoposterior wal l segments. In 25 male patients with greater than or equal to 50% sten oses of the right coronary artery and/or circumflex artery but without significant narrowing of the left anterior descending artery, stress studies using technetium-99m tetrofosmin (400 MBq) were carried out wi th and without attenuation correction. A dual-head camera with L-shape d detector positioning was equipped with two scanning gadolinium-153 l ine sources. Tomograms were reconstructed and quantified using circumf erential count rate profiles of myocardial activity (two in each patie nt). The profiles were compared with the respective normal ranges obta ined from a database of 25 male patients with a <10% likelihood of CAD . In patients without CAD, the maximal differences in count density of different wall segments were reduced from 29.0% in non-corrected (NC) studies to 9.5% in attenuation-corrected (AC) studies. In particular, the inferoposterior and septal wall segments were represented by sign ificantly increased relative count densities after attenuation correct ion. The effects of attenuation correction proved independent of body mass. In patients with CAD, segmental count densities were abnormal in 84% of the NC studies and 100% of the AC studies. In single-vessel di sease the stenotic vessel was identified in 66% of cases by NC studies and in 100% by AC studies. In AC studies, the extent and depth of def ects exceeded those in NC studies. For the detection of CAD of the rig ht coronary artery, the receiver operating characteristic (ROC) curves relating to the AC studies demonstrated improved discrimination capac ity (P<0.05). ROC analysis of CAD detection yielded normalcy rates of 82% (NC) and 94% (AC) for the circumflex artery and 65% (NC) and 97% ( AC) for the right coronary artery area at a sensitivity level of 95%. It is concluded that attenuation correction using the above system may enhance the diagnostic accuracy of myocardial SPET when inferoposteri or wall segments are to be evaluated.