Usefulness of the Chang attenuation correction method using CT-based μ map in SPECT-MPI

Objectives The attenuation correction (AC) is generally performed using a CT-based μ map by an ordered-subsets expectation-maximization (OS-EM) method built μ-value into the detection probability. On the other hands, the Chang AC method using CT μ map (Chang AC) has been established. The Chang method has the advantage of performing after either reconstruction of OS-EM method without AC and filtered back projection (FBP) method. The aim of this study was to evaluate the usefulness of Chang method for the single-photon emission computed tomography-myocardial perfusion imaging (SPECT-MPI) by phantom and clinical study.

Methods In the phantom study, a thoracic phantom with parts of myocardium, liver, spine and lungs is used. The myocardium, liver and lungs were filled with 99mTc water solution, respectively. Fifteen patients without myocardial ischemia were enrolled for the clinical study. The SPECT/CT imaging was performed with a two-head SPECT/CT system and the three images with AC were reconstructed. They were the reconstructed images iteratively corrected by OS-EM method (OS-EM Iterative AC), those performed Chang AC after the reconstruction with OS-EM method (OS-EM Chang AC) and those with FBP method (FBP Chang AC). In the phantom and clinical studies. The following indices were used for the evaluation; counts ratio between myocardial counts and left ventricular cavity counts (contrast ratio), counts uniformity in the myocardium (uniformity), left ventricular volume and myocardial radioactivity concentration.

Results The OS-EM Chang AC and the FBP Chang AC were superior to the OS-EM Iterative AC for contrast ratio and uniformity in the phantom and clinical studies. The FBP Chang AC was superior to the two OS-EM for left ventricular volume in the phantom and clinical studies and myocardial radioactivity concentration in the phantom study.

Conclusions The Chang AC methods have a potential to improve image quality and quantitative accuracy especially by using the FBP Chang AC.