Evaluation of collimator-detector response compensation in tumor SPECT using medium- and high-energy collimators

The goal of the study is to evaluate collimator-detector response (CDR) compensation methods that apply to tumor SPECT imaging using medium-energy (ME) and high-energy (HE) collimators. The compensation method involves accurate models of the geometric, penetration and scatter components of ME and HE collimators based on Monte Carlo simulations verified by experimental measurements. The models were used in iterative OS-EM reconstruction methods for CDR compensation. In experimental studies, a cylindrical phantom consisting of spheres with different sizes and filled with Ga-67, In-111 or I-131 was used. Projection data were acquired using ME and HE collimators designed for use with the radionuclides. Patient data included those from Ga-67 citrate, In-111 octreotide, and I-131 tumor studies. The FBP without compensation and the iterative OS-EM with different models of the CDR were used in image reconstruction. Results from phantom studies showed asymptotic decrease of the reconstructed sphere sizes as a function of iteration number. The full CDR model that included the geometric, penetration and scatter components provided the best results. Drastic improvements in clinical image quality were found using the full CDR model. It is concluded that full CDR compensation provides substantial improvements in image quality and quantitative accuracy in tumor SPECT