The influence of attenuation and scatter compensation on the apparent distribution of Tc-99m sestamibi in cardiac slices.

BACKGROUND

Our objective was to study the differences in relative count distributions in the left ventricular walls with attenuation compensation (AC) versus AC and triple-energy-window scatter compensation (SC), compared with standard filtered backprojection (FBP).

METHODS AND RESULTS

Two hundred patients identified as having normal cardiac perfusion with FBP after undergoing either pharmacologically or physiologically induced stress were included in this study. Projection data were reconstructed with FBP, 10 iterations of ordered-subset expectation-maximization (OSEM) with AC, and OSEM with AC+SC. A comparison was made of average percentage of maximum counts within each of 9 regions of CEqual (Marconi Medical Systems, Inc, Cleveland, Ohio) polar maps (ie, the apex, 4 midventricular regions, and 4 basal regions). Compared with OSEM(AC), a slight decrease at the apex exists when SC is included. The elevated inferior-to-anterior count ratio in the midventricular and basal regions noted with OSEM(AC) decreased to close to 1.0 with OSEM(AC+SC). The anterior-to-lateral ratio for both regions was closest to 1.0 for OSEM(AC+SC). In the midventricular region, the lateral-to-septal ratio decreased further below 1.0 with OSEM(AC+SC) than it did with OSEM(AC). This was the only basal ratio not to improve to close to 1.0 with OSEM(AC+SC). In a subset of patients identified at the time of clinical reading as having a possible attenuation-caused decrease in the inferior region, AC elevated the inferior-to-anterior ratio to above 1.0 for the midventricular region. AC+SC resulted in a ratio of near 1.0 for this region. In another subset of patients identified as having anterior attenuation artifacts, compensation methods (either AC or AC+SC) failed to show an improvement compared with FBP.

CONCLUSIONS

AC and SC improve the uniformity of the polar map, especially by bringing the inferior-to-anterior ratio closer to 1.0. Further investigation is necessary to determine the cause of the increased midventricular septal polar map count. In addition, the subset of patients identified as having breast-like attenuation artifacts causing a decreased polar map count in the anterior wall (relative to the inferior wall) also needs further attention.