Characteristics of single- and dual-photopeak energy window acquisitions with thallium-201 IQ-SPECT/CT system.

OBJECTIVES: Although dual-energy (DE) acquisition with conventional (201)Tl myocardial perfusion SPECT has several advantages such as improved attenuation of the inferior wall and increased acquisition counts, the characteristics of IQ-SPECT have not been fully evaluated. We evaluate the difference of characteristics between single-energy (SE) and dual-energy (DE) imaging using (201)Tl myocardial IQ-SPECT.

METHODS: Two myocardial phantoms were created simulating normal myocardium and infarction of the inferior wall. Energy windows were set at 70 keV ± 10% for SE, and an additional 167 keV ± 7.5% for DE. SPECT images were reconstructed using the ordered subset conjugates gradient minimizer (OSCGM) method. We visually and quantitatively compared short-axis images of correction for no (NC), for attenuation (AC) or for both AC and scatter (ACSC) images.

RESULTS: The average counts of SE and DE projection data were 17.5 and 20.3 counts/pixel, respectively. The DE data increased acquisition counts by approximately 16% compared with the SE data. The average visual score of normal myocardium did not differ significantly between the SE and DE images. However, the DE image of defective myocardium showed a significantly lower score in AC than SE images. The % uptake values of DE image with both NC and AC were significantly higher than those of SE images. The DE images of the inferior defective areas (segments 4 and 10) showed approximately 5-10% higher uptake compared with the SE images.

CONCLUSION: The DE image with NC improved attenuation of the inferior wall. However, DE image with AC showed low defect detectability. Thus, AC should be used with SE rather than DE. Furthermore, while the SE image with ACSC can be used to detect perfusion defects, it must be interpreted carefully including the possibility of artificial inhomogeneity even in the normal myocardium.