Objectives: Decreases in the apical and apex activities, namely "apical thinning", are a well-known phenomenon in attenuation corrected (AC) myocardial perfusion. The aim of this study was to compare actual myocardial thickness derived from a multidetector-row computed tomography (MDCT) with AC myocardial perfusion count from a hybrid single-photon emission computed tomography (SPECT)/CT to investigate the cause of apical thinning.
Methods:We enrolled 21 subjects with low likelihood of coronary artery disease (mean age 65 ± 21 years, 13 male) from 185 consecutive patients and 11 healthy volunteers, who independently underwent Tc-99m sestamibi SPECT/CT and 64-slice MDCT scans. AC and non-AC myocardial perfusion counts and thickness were measured based on a 17-segment model and averaged at the apex, apical, mid and basal walls.Results: Myocardial thickness at the apex was significantly thinner than that at the apical and mid walls (5.1 ± 1.3, 7.3 ± 1.3, 9.9 ± 2.4 mm, respectively, p < 0.005). AC count at the apex was significantly lower than that at the apical and mid regions (76.0 ± 5.5, 82.8 ± 4.7, 85.6 ± 3.8, respectively, p < 0.002). Moderate relationship was observed between myocardial thickness and AC count (y = -10.5 + 0.22x, r = 0.54, p < 0.0001). No relationship was found between thickness and non-AC count (r = 0.16, p = 0.263).
Conclusions:The low apex and apical counts were caused by anatomical thinning of the myocardium in AC myocardial perfusion imaging. AC provided accurate relationship between myocardial count and thickness due to the partial volume effect.