Fredrik Edling

Calculation of the modulation transfer function for the X-ray imaging detector DIXI using Monte Carlo simulation data

Abstract The imaging detector DIXI is a solid state hybrid pixel detector for 2D real-time imaging. A prototype detector has been constructed at the Uppsala University. Image quality parameters have been assessed by means of simulations in order to estimate the imaging capabilities of the detector. The MC simulations concern the sensor responses to mono-energetic and poly-energetic X-ray sources in terms of the charge carrier distribution and modulation transfer function. Different sensor materials and pixel sizes are included into the model and compared.

Performance of a pixel readout chip with two counters for X-ray imaging

A pixel readout chip for X-ray imaging has been developed and tested. It will he used in a hybrid pixel detector, where it is flip-chip bonded to a sensor. The sensor material can be silicon or a compound semiconductor, such as CdZnTe. A novel feature of the chip is the implementation of two counters inside each pixel cell. The chip consists of 992 pixels arranged in 31 columns and 32 rows. Each pixel size is 270 micrometer square and it consists of a preamplifier, shaper, discriminator and two counters. The circuit design with two integrated counters in each pixel cell makes it possible to acquire two images very close in time with practically no dead time in between. An externally adjustable threshold permits the discrimination of a portion of the X-ray spectrum. The detector is primarily aimed for dynamic medical X-ray imaging up to 100 frames per second. A characterization of the performance of the chip is presented and discussed.

Tuning tool for image quality optimization of a hybrid semiconductor pixel detector

Linear systems theory is used for the numerical assessment of the detective quantum efficiency (DQE) of the hybrid semiconductor pixel detector DIXI. The Monte Carlo based code GEANT is used to simulate the photon transport in the sensor, charge transport modeling is treated analytically and the readout chip is simulated using PSPICE. The DQE for two differently shaped X-ray spectra of the same quality and for different operational conditions of the readout chip regarding the discrimination level are computed in order to validate the model. The model described in this paper can be adopted for optimizing the detector.

A hybrid pixel detector with two counters for x-ray imaging

A semiconductor hybrid pixel detector for dynamic X-ray imaging is being developed. The detector consists of a 500 /spl mu/m thick silicon sensor and a pixel readout chip. The two parts are interconnected by means of anisotropic conductive film. The basic building block of the detector is approximately one square centimeter large and consists of 992 pixel cells arranged in 31 columns and 32 rows. Each pixel has an area of 270 micrometer square and the readout chip contains amplifier, discriminator and two 12 bit counters. An externally adjustable threshold level can be changed within one microsecond from one image to another in order to select different parts of the X-ray spectrum. The chip can be tuned to assign different weighting functions to photons with energies exceeding the threshold. It is possible to either operate the detector as a photon counter or as an energy integrator.