Cause of apical thinning on attenuation-corrected myocardial perfusion SPECT

Abstract

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.

Nuclear myocardial perfusion imaging using thallium-201 with a novel multifocal collimator SPECT/CT: IQ-SPECT versus conventional protocols in normal subjects

“…Both low myocardial uptake with attenuation correction and myocardial thinning were recognized at the apex. Therefore, apical thinning on the attenuation-corrected images was caused by anatomical thinning of the myocardium as previously reported [24]. Attenuation-corrected images would provide an accurate relationship between myocardial count and thickness because of the apical volume effect.…”

Normal values and standardization of parameters in nuclear cardiology: Japanese Society of Nuclear Medicine working group database

“…These observations are common characteristics seen in attenuation-corrected SPECT images with parallel-hole collimation [ 37 , 38 ]. The decreased apical wall activity is partly due to the physiologically thin apical wall and larger apical wall movement [ 39 ]. Although attenuation correction was considered potentially useful and recommended [ 40 ], its use is still limited in Japan, because nuclear medicine physicians and cardiologists have become accustomed to using conventional imaging without attenuation correction and inconsistency of the effects of attenuation correction regarding camera systems and processing tools [ 41 ].…”

Improvements in Segmentation Using Scatter and Photopeak Window Data for Attenuation Correction in Myocardial SPECT

“…6). These decreases are a well-known phenomenon in attenuation corrected myocardial perfusion (20,21). "Apical thinning"on the SSPAC image may be caused by both low attenuation corrected myocardial uptake and myocardial thinning.…”