Proceedings Article | 14 March 2009
Proc. SPIE. 7258, Medical Imaging 2009: Physics of Medical Imaging
KEYWORDS: X-ray computed tomography, Imaging systems, Cameras, Sensors, X-rays, Scintillators, Electron multiplying charge coupled devices, High speed imaging, Spatial resolution, X-ray imaging
The limitations of current CCD-based microCT X-ray imaging systems arise from two important factors. First, readout
speeds are curtailed in order to minimize system read noise, which increases significantly with increasing readout rates.
Second, the afterglow associated with commercial scintillator films can introduce image lag, leading to substantial
artifacts in reconstructed images, especially when the detector is operated at several hundred frames/second (fps). For
high speed imaging systems, high-speed readout electronics and fast scintillator films are required. This paper presents
an approach to developing a high-speed CT detector based on a novel, back-thinned electron-multiplying CCD
(EMCCD) coupled to various bright, high resolution, low afterglow films. The EMCCD camera, when operated in its
binned mode, is capable of acquiring data at up to 300 fps with reduced imaging area. CsI:Tl,Eu and ZnSe:Te films,
recently fabricated at RMD, apart from being bright, showed very good afterglow properties, favorable for high-speed
imaging. Since ZnSe:Te films were brighter than CsI:Tl,Eu films, for preliminary experiments a ZnSe:Te film was
coupled to an EMCCD camera at UC Davis Medical Center. A high-throughput tungsten anode X-ray generator was
used, as the X-ray fluence from a mini- or micro-focus source would be insufficient to achieve high-speed imaging. A
euthanized mouse held in a glass tube was rotated 360 degrees in less than 3 seconds, while radiographic images were
recorded at various readout rates (up to 300 fps); images were reconstructed using a conventional Feldkamp cone-beam
reconstruction algorithm. We have found that this system allows volumetric CT imaging of small animals in
approximately two seconds at ~110 to 190 μm resolution, compared to several minutes at 160 μm resolution needed for
the best current systems.
