An Investigation of Reconstruction Strategies for Mediastinal Lesion Detection Using Hybrid Ga-67 SPECT Images

Ga-67 SPECT studies are especially useful in the pretreatment staging and post-treatment follow-up of patients with Hodgkin's and non-Hodgkin's lymphoma. Ga-67 is however a particularly challenging radionuclide for imaging. Patient specific background variability, which manifests itself as structured noise, can further impact lesion detection accuracy. A number of MCAT phantom studies with simulated lesions and idealized source distributions have been done to study the impact of compensation strategies on lesion detection accuracy. However, to more accurately assess the impact of various correction strategies on lesion detection a study employing actual clinical images with true clinical distributions is of interest. The approach we chose for conducting such an investigation was performing LROC studies employing hybrid images. Hybrid images are normal Ga-67 studies with their projection data modified by the addition of Monte Carlo simulated lesions. Our datasets consist of clinically normal Ga-67 SPECT/CT acquisitions obtained using the GE-VG dual detector SPECT/CT camera. After determining a target image contrast using human observers, we conducted pilot LROC studies to determine the optimal parameters for the reconstruction methods using human observers. Herein we report on the optimization for the forthcoming comparison of attenuation compensation, scatter compensation, and detector resolution compensation strategies used with the RBI reconstruction method and FBP reconstruction.