Energy-resolved Photon Counting Research Articles

Preliminary evaluation of a novel energy-resolved photon-counting gamma ray detector

In this paper, we present the design and preliminary performance evaluation of a novel energy-resolved photon-counting (ERPC) detector for gamma ray imaging applications. The prototype ERPC detector has an active area of 4.4 cm×4.4 cm, which is pixelated into 128×128 square pixels with a pitch size of 350 μm×350 μm. The current detector consists of multiple detector hybrids, each with a CdTe crystal of 1.1 cm×2.2 cm×1 mm, bump-bonded onto a custom-designed application-specific integrated circuit (ASIC). The ERPC ASIC has 2048 readout channels arranged in a 32×64 array. Each channel is equipped with pre- and shaping-amplifiers, a discriminator, peak/hold circuitry and an analog-to-digital converter (ADC) for digitizing the signal amplitude. In order to compensate for the pixel-to-pixel variation, two 8-bit digital-to-analog converters (DACs) are implemented into each channel for tuning the gain and offset. The ERPC detector is designed to offer a high spatial resolution, a wide dynamic range of 12–200 keV and a good energy resolution of 3–4 keV. The hybrid detector configuration provides a flexible detection area that can be easily tailored for different imaging applications. The intrinsic performance of a prototype ERPC detector was evaluated with various gamma ray sources, and the results are presented.

SU‐GG‐I‐133: Low Dose Dual Energy Breast Imaging with An Energy Resolving Photon Counting Detector

Purpose: To investigate the feasibility of low dose dual energy imaging with an energy resolving photon counting detector using a single exposure / single kVp technique for the measurement of breast density (the percentage of glandular breast tissue) in mammography. Method and Materials: An analytical simulation model was developed to determine the mean glandular dose required to quantify breast density with a novel energy resolving photon counting detector to within an accuracy of 1%. The detector was modeled as a 3 mm thick layer of CdZnTe. All detected photons above 15 keV were counted and separated into either a low or high energy bin as determined by a user defined threshold. Only stochastic x‐ray noise sources were considered. The breast was modeled as a semicircle 10 cm in radius with homogenous equal thicknesses of adipose and glandular tissues, corresponding to a density of 50%. Polyenergetic spectra from a tungsten target anode x‐ray tube were simulated from 20 – 150 kVp. Tube filtration was 1.0 mm Be and 0.5 mm Al. At each kVp, the threshold energy was varied to determine the optimal dual energy SNR in the breast density image. Results: For a 4.2 cm breast, the optimal beam energy determined from simulation was determined to be 95 kVp with a threshold separating low and high energy beam spectra at 30 keV. The predicted required minimal mean glandular dose for the dual energy image was low (< 1 μGy), and the corresponding incident photon fluence was approximately 10,000 photons per square millimeter. Conclusion: The results suggest that breast density, a quantity strongly associated with the risk of breast cancer, can be accurately measured at low dose, with an energy counting photon counting detector.

Responsivity of Ta-based STJ's to visible light as a function of Al trapping layer thickness

Superconducting tunneling junction devices are being developed as energy resolving photon counting imagers. We have fabricated a series of Ta/Al/AlOx/Al/Ta devices with variable Al layer thickness, dAl, and measured their response to a weak visible photon source. Single photon sensitivity is observed. We model our system with a set of modified Rothwarf–Taylor equations including quasiparticle losses, trapping, (back)tunneling and calculate the charge responsivity as a function of dAl with one fitting parameter. The quasiparticle loss time for Al and Ta is found to be τl(Al)=35μs and τl(Ta)=0.14μs in our devices, respectively.

Master index volumes 341–360

Spectral CT based on energy-resolving photon counting detectors is expected to deliver additional diagnostic value at a lower dose than current state-of-the-art CT [1]. The capability of simultaneously providing a number of spectrally distinct measurements not only allows distinguishing between photo-electric and Compton interactions but also discriminating contrast agents that exhibit a K-edge discontinuity in the absorption spectrum, referred to as K-edge Imaging [2]. Such detectors are based on direct converting sensors (e.g. CdTe or CdZnTe) and high-rate photon counting electronics.To support the development of Spectral CT and show the feasibility of obtaining rates exceeding 10 Mcps/pixel (Poissonian observed count-rate), the ChromAIX ASIC has been previously reported showing 13.5 Mcps/pixel (150 Mcps/mm2 incident) [3]. The ChromAIX has been improved to offer the possibility of a large area coverage detector, and increased overall performance. The new ASIC is called ChromAIX2, and delivers count-rates exceeding 15 Mcps/pixel with an rms-noise performance of approximately 260 e-. It has an isotropic pixel pitch of 500 µm in an array of 22×32 pixels and is tile-able on three of its sides. The pixel topology consists of a two stage amplifier (CSA and Shaper) and a number of test features allowing to thoroughly characterize the ASIC without a sensor. A total of 5 independent thresholds are also available within each pixel, allowing to acquire 5 spectrally distinct measurements simultaneously. The ASIC also incorporates a baseline restorer to eliminate excess currents induced by the sensor (e.g. dark current and low frequency drifts) which would otherwise cause an energy estimation error.In this paper we report on the inherent electrical performance of the ChromAXI2 as well as measurements obtained with CZT (CdZnTe)/CdTe sensors and X-rays and radioactive sources.