Imaging characteristics comparison of compact pixellated detectors for scintimammography

Although scintimammography is routinely used in the hospitals it had not the expected large diffusion. The low specificity of SESTAMIBI ^99mTc and the geometrical restrictions of prone scintimammography further contributed in limiting the clinical sensitivity for sub centimeter lesions. Researchers aware that to overcome intrinsic limitation of radio-pharmaceutical, they are optimized compact imager able to detect small amount of radioactivity emitted from 5 mm or less tumors. To investigate the overall imaging characteristics of scintillation imagers for scintimammography, a number of small gamma camera prototypes were assembled, based on PSPMT of first and last generation. They were coupled to a number of NaI(Tl) and CsI(Tl) scintillation both planar and pixellated, with different pixel size. Measurements were performed by line and circular source as well as by 3 mm to 10 mm diameter tumor phantoms. Spatial resolution seems the dominant factor, in detection of 5 mm and 3 mm tumor size. The best results were obtained from the scintillation crystals arrays coupled to Hamamatsu flat panel PMT. Decreasing crystal pixel size, contrast mean values slightly changed but their accuracy increases, demonstrating the influence of digitization on image quality. MTF curve obtained by planar NaI(Tl) integral assembly shows an improvement with a response at the highest frequency equal to one obtained from collimator parallel hole Monte Carlo simulation.