Attenuation correction of myocardial SPECT studies using low resolution computed tomography images

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Abstract
Artefacts caused by tissue attenuation can create problems in the interpretation of myocardial perfusion studies. This study aimed to determine if attenuation correction using the ‘Hawkeye’ low-resolution X-ray computed tomography facility attached to a GE Millennium VG gamma camera reduced attenuation artefacts in our patient group. This technique offers potential advantages over isotope transmission methods of attenuation correction because of the lack of noise in the transmission images. Ninety-four patients (64 males, 30 females) underwent stress/rest myocardial perfusion imaging using 99mTc tetrofosmin (188 studies). Semi-quantitative analysis of the attenuation corrected and non-corrected perfusion images was carried out using proprietary software (Emory ECToolbox). No significant differences between attenuation corrected and non-corrected images were seen in the septal, lateral or apical segments. Attenuation correction produced a significant reduction in the defect scores in the inferior segment indicating the presence of attenuation artefacts. This was more marked in male patients. The incidence of attenuation artefacts in the inferior segment increased with weight although patients of normal weight also showed attenuation artefacts. The changes in the anterior segment were more difficult to interpret particularly in females, with attenuation correction increasing the defect score in some patients. Minor degrees of mal-registration (even of 1 pixel) between emission and transmission images increased the likelihood of creating a defect. Attenuation correction using Hawkeye is likely to improve diagnostic accuracy in men, but is less likely to be useful in women.