A pixel detector-based single photon-counting system as fast spectrometer for diagnostic x-ray beams

Abstract

Recent advances in semiconductor pixel detectors and read-out electronics allowed to build the first prototypes of single photon-counting imaging systems that represent the last frontier of digital radiography. Among the advantages with respect to commercially available digital imaging systems, there are direct conversion of photon energy into electrical charge and the effective rejection of electronic noise by means of a thresholding process. These features allow the photon-counting systems to achieve high imaging performances in terms of spatial and contrast resolution. Moreover, the now available deep integration techniques allow the reduction of the pixel size and the improvement of the functionality of the single cell and the read-out speed so as to cope with the high fluxes found in diagnostic radiology. In particular, the single photon-counting system presented in this paper is based on a 300-microm thick silicon pixel detector bump-bonded to the Medipix2 read-out chip to form an assembly of 256 x 256 square pixels at a pitch of 55 microm. Each cell comprises a low-noise preamplifier, two pulse height discriminators and a 14-bit counter. The maximum counting rate per pixel is 1 MHz. The chip can operate in two modalities: it records the events with energy above a threshold (single mode) or between two energy thresholds (window mode). Exploiting this latter feature, a possible application of such a system as a fast spectrometer is presented to study the energy spectrum of diagnostic beams produced by X-ray tubes.

Musculoskeletal imaging with a prototype photon-counting detector

“…Counting only events above a given energy threshold will minimise the contribution of detector and electronic noise, providing a higher detective quantum efficiency (DQE) compared to other direct radiography techniques [12]. Another possible application for such a system, as a fast spectrometer to study the energy spectrum of diagnostic beams produced by X-ray tubes, has been reported [13,14].…”

Detective quantum efficiency of photon‐counting x‐ray detectors

“…When equipped with multithresholding circuits, these systems enable energyresolving photon-counting (EPC) imaging where the deposited energy from each interacting x-ray photon is estimated. [1][2][3][4][5][6][7] It is anticipated that the resulting spectral distribution of energy-depositing events will lead to advanced spectroscopic procedures [8][9][10][11][12][13][14] and improve image quality by reducing image noise from random physical processes including Swank and electronic readout noise. 7,15 While photon-counting methods are receiving a great deal of interest, there remain many challenges to overcome.…”