Delivering high contrast diagnostic CT images while minimizing patient radiation dose has been the center of majority of all CT-related research. In this regard, improvement in the detector technology (alongside with automatic exposure control and improved reconstruction algorithms) may have the greatest impact. Current X- ray CT detectors operating in integration mode are not able to provide spectral information and also introduce large electronic noise in the acquired images. Current photon counting detectors (as alternative for integrating CT detectors) are based on direct conversion of the x-rays to electrica signal which relies on utilizing semiconductor materials (mainly Si, CdTe, CZT). For X-ray energies in medical imaging applications, Si becomes almost transparent resulting in a very low sensitivity and high patient dose. CdTe and CZT have been used for these energy ranges, however imposing technical challenges and performance issues such as charge sharing, pulse pileup and count rate capability, relatively low effective Z and low density compared with the current CT detector materials. Furthermore, limited availability of high purity materials (e.g. CZT can make a large area detector for clinical applications prohibitively expensive. While scintillation-based detectors are used in clinical nuclear imaging systems they cannot satisfy all the stringent requirements for clinical CT system at high flux mainly due to the lack of high light output scintillators with fast decay time as well as lack of reliable scintillator pixelation technologies to fabricate pixels smaller than 0.5x0.5 mm2. Our goal is to study the feasibility of a scintillator-based photon counting detector using pixelated high Z scintillator coupled with a dedicated ASIC where each ASIC pixel has a built-in photodiode, a charge sensitive preamplifier, a shaping amplifier with programmable peaking time, 3-4 energy windows and their associated counters. The significance of this research is that by using our scintillator pixelation technology, development of high-resolution photon counting CT detectors is achievable in a cost effective manner. The proposed detector will categorize the incident X-rays based on their energy and will handle the incident X-ray flux up to 108 photon/mm2/second as needed in clinical CT imaging.
The focus of this research proposal is to study the feasibility of a novel high-performance and cost-effective photon counting detector for clinical CT imaging. The goal is to develop pixelated scintillator arrays with 0.2 mm pixels while maintaining greater than 90% sensitivity for X-ray energies up to 140 keV.
| Sabet, H; Bläckberg, L; Uzun-Ozsahin, D et al. (2016) Novel laser-processed CsI:Tl detector for SPECT. Med Phys 43:2630 |
