CRYSTALLINE MICROCOLUMNAR CsI:Tl FILMS FOR USE IN GAMMA-RAY IMAGING WITH DEPTH-OF-INTERACTION SENSITIVITY

Columnar, amorphous CsI:Tl scintillators are attractive for biomedical imaging applications because they allow high spatial resolution with EMCCD detectors and BazookaSPECT. But these scintillators have a serious practical limitation, they are not useful in thickness larger than 0.5 mm, because of attenuation; this means that detection efficiencies are very poor for >= 100 keV gamma rays. The development of a new crystalline microcolumnar scintillator (CMS) of CsI:Tl is described. CMS CsI:Tl has high density and greatly improved light transmission properties. CMS films were prepared in three thicknesses (0.5 mm, 1.0 mm and 4.0 mm), and test results for these films are described. The light yield and energy resolution for 0.5 mm, CMS CsI:Tl films was equivalent to that of conventional bulk CsI:Tl scintillators; while some light attenuation was seen in 4 mm-thick CMS CsI:Tl samples, useable photopeaks were obtained at 122 keV. The spatial resolution measured for the 0.5 mm and 1.0 mm films in a BazookaSPECT system was excellent, 150-200 mu m. Imaging tests with the 4 mm-thick CMS CsI:Tl films in a BazookaSPECT system with 662 keV gamma rays showed progressive broadening of the signal clusters on the CCD camera with depth of interaction (DOI), indicating that DOI determination should be possible with these detectors, i.e. 3D detector operation. Future planned investigations are described.