Investigation of physical properties of compact scintillation cameras for dedicated imaging applications

Two compact scintillation cameras, one based on a continuous NaI(Tl) scintillation crystal coupled to a single PSPMT, and another based on a pixilated array of NaI(Tl) scintillation crystals coupled to an array of PSPMTs, were investigated for use in dedicated applications such as breast and small animal imaging. They were designed to be portable, and were optimized for high resolution imaging in small field of view, shallow depth of field applications.; As part of their development for breast imaging, the performances of two dedicated cameras were compared with a standard clinical gamma camera. The dedicated cameras showed improved shallow depth of field spatial resolution, contrast, and signal to noise ratio when imaging hot tumors in a compressed breast phantom. This, with the additional advantage of being easily positioned close to the breast, suggests that dedicated cameras will play a strong role in breast cancer diagnosis and management.; The use of Retro-Reflective tape was investigated as a substitute for other reflective materials used with scintillation crystals. Coupled to the radiation incident side of the crystal, Retro-Reflective tape was found to improve spatial resolution in large continuous crystal gamma cameras relative to that seen with Teflon tape, without a reduction in signal amplitude or energy resolution. Improvements in spatial resolution were greater with thinner crystals and with higher energy gamma rays. This technique could profoundly impact the performance of continuous crystal scintillation cameras.; The use of dedicated scintillation cameras for in vivo small animal SPECT imaging was also investigated. Using pinhole collimation to image distributions of radiolabeled tracers, sub-millimeter spatial resolution can be achieved in small field of view applications in three dimensions. The dedicated cameras were modified for pinhole imaging, and their performance was evaluated for use with 99mTc and 125I. The evaluation included measurements of reconstructed axial spatial resolution, sensitivity, and the effect of object size on the quantitative assessment of isotope distributions. SPECT phantom images, and SPECT images of living mice obtained at sub-millimeter spatial resolution, illustrated the image quality achievable with the system. In addition, the challenges of imaging the low energy emissions from 125I were investigated. A thin NaI(Tl) scintillation crystal and 100 mum and 250 mum diameter pinholes were used to acquire sub-millimeter spatial resolution, 125I images of a mouse thyroid in vivo. The results of this study validate the emergence of dedicated pinhole SPECT for evaluating biodistributions of radiolabeled tracers in small animals in vivo.