Evaluation of the attenuation correction on myocardial perfusion imaging: a phantom study

Myocardial perfusion imaging (MPI) with singlephoton emission computed tomography (SPECT) is important for risk stratification of coronary artery disease. MPI quantification obtained from available images may not be accurate due to several potential sources of error, being photon attenuation, especially in overweight patients, a significant problem. Attenuation maps derived from X-ray computed tomography (CT) may be used to correct for photon attenuation. The aim of this study was to evaluate the effects of non-attenuation correction (NAC) and attenuation correction (AC) in MPI SPECT imaging using anthropomorphic phantoms simulating patients with different attenuation profiles. Forty-nine SPECT and CT studies of Heart/Thorax phantoms with different attenuation layers were acquired. All SPECT imaging data were reconstructed with and without AC. Quantification of the myocardial signal (uptake) was performed in four regions of interest: septum, anterior wall, inferior wall and apex. This was done both in NAC and AC SPECT images. Qualitative evaluation was performed by a nuclear medicine physician also in NAC and AC SPECT images. The results demonstrated, as expected, statistically lower counts when the thickness of the phantom attenuating material increased and attenuation correction was lacking. On the other hand, when attenuation correction was applied, there were no statistically significant count differences whatever the thickness of the phantom attenuating material. In the qualitative evaluation, the nuclear medicine physician observed small variations in the anterior wall uptake according to the various conditions under test. However, the changes were not statistically significant. In conclusion, there is no evidence that the effects of attenuation in overweight patients are not properly corrected when the MPI SPECT images are reconstructed with CT-based AC. In terms of qualitative visual assessment, there is no significant variation in the classification of myocardial walls uptake with and without AC when the evaluation is done by an experienced physician.