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 μm. 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.