The goal of this paper was to investigate the benefits that could be realistically achieved on a microCT imaging system with an energy-resolved photon-counting x-ray detector. To this end, we built and evaluated a prototype microCT system based on such a detector. The detector is based on cadmium telluride (CdTe) radiation sensors and application-specific integrated circuit (ASIC) readouts. Each detector pixel can simultaneously count x-ray photons above six energy thresholds, providing the capability for energy-selective x-ray imaging. We tested the spectroscopic performance of the system using polychromatic x-ray radiation and various filtering materials with Kabsorption edges. Tomographic images were then acquired of a cylindrical PMMA phantom containing holes filled with various materials. Results were also compared with those acquired using an intensity-integrating x-ray detector and single-energy (i.e. non-energy-selective) CT. This paper describes the functionality and performance of the system, and presents preliminary spectroscopic and tomographic results. The spectroscopic experiments showed that the energy-resolved photon-counting detector was capable of measuring energy spectra from polychromatic sources like a standard x-ray tube, and resolving absorption edges present in the energy range used for imaging. However, the spectral quality was degraded by spectral distortions resulting from degrading factors, including finite energy resolution and charge sharing. We developed a simple charge-sharing model to reproduce these distortions. The tomographic experiments showed that the availability of multiple energy thresholds in the photon-counting detector allowed us to simultaneously measure target-to-background contrasts in different energy ranges. Compared with single-energy CT with an integrating detector, this feature was especially useful to improve differentiation of materials with different attenuation coefficient energy dependences.

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We have studied the radiation hardness of the VA1, a Viking-architecture preamplifier VLSI chip. Large-scale integrated (LSI) samples are fabricated in 0.8 and 0.35 m process technologies to improve the radiation hardness of the LSI for the Belle silicon vertex detector upgrade.We have observed significant improvement of the radiation hardness with 0.8-m technology compared to 1.2-m technology. Little degradation of noise and gain is observed up to a total dose of 20 Mrd for the VA1 fabricated in the 0.35-m technology. We find that the radiation hardness improves with a scaling of better than 6 ox ( ox : oxide thickness). Basic parameters of MOSFETs are also studied to understand the mechanism of radiation damage in the VA1.

A new low noise multi-channel application specific integrated circuit (ASIC) has been designed for use in nuclear medical imaging single photon emission computed tomography (SPECT), and prototypes have been produced and tested. The ASIC has 128 charge sensitive amplifiers (CSA) followed by shapers, threshold discriminators and sample-and-hold. The ASIC delivers analog signal amplitude and digital address from channels with signals above threshold, and optionally allows one to read signals from any channel using a random-access readout. The total power consumption is 358 mW. The ASIC parameters have been specified and measured as follows: each amplifier measures charge within a linear dynamic range from -40000 e to +40000 e. The pre-amplifier noise is 56 e+11.6 e/pF at 10 µs shaping time. The ASIC is ideally suited for readout of radiation sensors with a few pF capacitance and less than 100 pA dc input current. The ASIC has been tested with silicon diode pad sensors. The diode had a capacitance of ≈ 1 pF and a leakage current of 20 pA. We measure an equivalent noise charge of 85 e, and achieve a triggering threshold of 800 e. Energy spectra from radioactive isotopes have been measured with energy resolution of 823 eV FWHM for 5.9 keV x-rays.