Improvement of brain perfusion SPET using iterative reconstruction with scatter and non-uniform attenuation correction

Filtered back-projection (FBP) is generally used as the reconstruction meth od for single-photon emission tomography although it produces noisy images with apparent streak artefacts. It is possible to improve the image quality by using an algorithm with iterative correction steps. The iterative recon struction technique also has an additional benefit in that computation of a ttenuation correction can be included in the process. A commonly used itera tive method, maximum-likelihood expectation maximisation (ML-EM), can be ac celerated using ordered subsets (OS-EM). We have applied to the OS-EM algor ithm a Bayesian one-step late correction method utilising median root prior (MRP). Methodological comparison was per formed by means of measurements o btained with a brain perfusion phantom and using patient data. The aim of t his work was to quantitate the accuracy of iterative reconstruction with sc atter and non-uniform attenuation corrections and post-filtering in SPET br ain perfusion imaging. SPET imaging was performed using a triple-head gamma camera with fan-beam collimators, Transmission and emission scans were acq uired simultaneously. The brain phantom used was a high-resolution three-di mensional anthropomorphic JB003 phantom. Patient studies were performed in ten chronic pain syndrome patients. The images were reconstructed using con ventional FBP and iterative OS-EM and MRP techniques including scatter and nonuniform attenuation corrections. Iterative reconstructions were individu ally post-filtered. The quantitative results obtained with the brain perfus ion phantom were compared with the known actual contrast ratios. The calcul ated difference from the true values was largest with the FBP method; itera tively reconstructed images proved closer to the reality. Similar findings were obtained in the patient studies. The plain OS-FM method improved the c ontrast whereas in the case of the MRP technique the improvement in contras t was not so evident with post-filtering.