The value of registration correction in the attenuation correction of myocardial SPECT studies using low resolution computed tomography images.

Background: Artifacts caused by tissue attenuation create problems in the interpretation of myocardial perfusion studies. In a previous study we evaluated attenuation correction using 'Hawkeye' and noted that the incidence of anterior/apical defects increased after attenuation correction. This increased incidence appeared to be associated with mis-registration between emission and transmission images. The main aim of this study was to determine whether correction of mis-registration between emission and transmission scans reduced the incidence of these anterior/apical defects.

Methods: Ninety-four patients (64 men, 30 women) underwent stress/rest myocardial perfusion imaging using (99m)Tc-tetrofosmin (188 studies). Bull's-eye perfusion plots were created using proprietary software (QPS).

Results: The marked reduction in defect size, particularly obvious in male patients, in the inferior wall after attenuation correction was not significantly changed by the addition of registration correction. In the anterior and apical walls attenuation correction produced a confusing pattern particularly in females with an overall tendency to increase the defect size. After registration correction fewer anterior/apical defects were created.

Conclusion: Attenuation correction using 'Hawkeye' reduces the incidence of inferior myocardial perfusion defects but can create anterior and/or apical artifacts. It is essential to evaluate registration carefully in three dimensions before reporting the images. Correction of mis-registration reduces the incidence of anterior/apical defects and can restore the appearance of the anterior/apical area to pre-correction levels.