Status of Direct Conversion Detectors for Medical Imaging With X-Rays

Abstract

Imaging detectors for medical X-ray and computed tomography (CT) applications have undergone many improvements and technology changes over time. But most (dynamic) detectors sold in this field still rely on indirect conversion, using scintillators and photodiodes to convert the X-ray quanta ultimately into electrical signals. Direct conversion detectors promise very high spatial resolution and high signal-to-noise ratios. Some direct conversion materials may allow for counting or even energy resolving detection of the X-ray quanta. Based on this, for example spectrally resolving CT systems are becoming an interesting option for the next decade. This contribution highlights the requirements of advanced medical X-ray and CT imaging and reviews examples of status and progress in the field. The emphasis is on the direct conversion sensors for pixelated detectors, but considerations on read-out concepts and on associated challenges such as interconnects will also be presented. Finally, the most burning issues, such as count rate limitations and polarization effects, will be discussed from an application point of view.

Design and optimization of collection efficiency and conversion gain of buried p-well SOI pixel X-ray detector

“…The direct imaging system directly converts the X-ray information into electrical signals by using an X-ray conversion film (i.e., X-ray photoconductor). Since the direct system does not need scintillators, energy absorption efficiency can be improved and the inherent deterioration of spatial resolution can be avoided [3,4].…”

Textured α-HgI2 ceramics for sensitive X-ray detection

“…Either X-rays (or other high energy beams) are first converted into visible light by a scintillating material and then into an electrical signal (scintillationbased detection) or X-rays are directly converted into photogenerated electrical charges in a photo-conducting material (direct conversion), these charges being then collected by applying an electric field. However, detection based on direct conversion of X-ray is claimed to be a more efficient alternative to scintillationbased detection [1,2]. Direct conversion requires an insulating material with good photoconduction properties.…”

Development of a compact radiation-hardened low-noise front-end readout ASIC for CZT-based hard X-ray imager

“…In these applications, semiconductor radiation detectors with front-end electronics are required. With well known good spatial and good energy resolution, CdZnTe (CZT) detectors show great potentialities as the candidate of X-ray detectors [5][6][7]. However, since CZT detectors suffer of low gain, low-noise front-end electronics is required to read out the weak current signals.…”