ChromAIX: a high-rate energy-resolving photon-counting ASIC for spectal computed tomography

Roger Steadman; Christoph Herrmann; Oliver Mülhens; Dale G. Maeding; James Colley; Ted Firlit; Randy Luhta; Marc Chappo; Brian Harwood; Doug Kosty

doi:10.1117/12.844222

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22 March 2010 ChromAIX: a high-rate energy-resolving photon-counting ASIC for spectal computed tomography

Roger Steadman, Christoph Herrmann, Oliver Mülhens, Dale G. Maeding, James Colley, Ted Firlit, Randy Luhta, Marc Chappo, Brian Harwood, Doug Kosty

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Proceedings Volume 7622, Medical Imaging 2010: Physics of Medical Imaging; 762220 (2010) https://doi.org/10.1117/12.844222
Event: SPIE Medical Imaging, 2010, San Diego, California, United States

Abstract

In Computed Tomography applications a major opportunity has been identified in the exploitation of the spectral information inherently available due to the polychromatic emission of the X-ray tube. Current CT technology based on indirect-conversion and integrating-mode detection can be used to some extent to distinguish the two predominant physical causes of energy-dependent attenuation (photo-electric effect and Compton effect) by using dual-energy techniques, e.g. kVp switching, dual-source or detector stacking. Further improvements can be achieved by transitioning to direct-conversion technologies and counting-mode detection, which inherently exhibits a better signal-to-noise ratio. Further including energy discrimination, enables new applications, which are not feasible with dual-energy techniques, e.g. the possibility to discriminate K-edge features (contrast agents, e.g. Gadolinium) from the other contributions to the x-ray attenuation of a human body. The capability of providing energy-resolved information with more than two different measurements is referred to as Spectral CT. To study the feasibility of Spectral CT, an energy-resolving proprietary photon counting ASIC (ChromAIX) has been designed to provide high count-rate capabilities while offering energy discrimination. The ChromAIX ASIC consists of an arrangement of 4 by 16 pixels with an isotropic pitch of 300 μm. Each pixel contains a number of independent energy discriminators with their corresponding 12-bit counters with continuous read-out capability. Observed Poissonian count-rates exceeding 10 Mcps (corresponding to approximately 27 Mcps incident mean Poisson rate) have been experimentally validated through electrical characterization. The measured noise of 2.6 mV_RMS (4 keV FWHM) adheres to specifications. The ChromAIX ASIC has been specifically designed to support direct-converting materials CdZnTe and CdTe.

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Roger Steadman, Christoph Herrmann, Oliver Mülhens, Dale G. Maeding, James Colley, Ted Firlit, Randy Luhta, Marc Chappo, Brian Harwood, and Doug Kosty "ChromAIX: a high-rate energy-resolving photon-counting ASIC for spectal computed tomography", Proc. SPIE 7622, Medical Imaging 2010: Physics of Medical Imaging, 762220 (22 March 2010); https://doi.org/10.1117/12.844222

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