C. Ronnqvist

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.

A new 2-dimensional high resolution Si detector for β- and γ-radiography

Abstract A double-sided silicon microstrip detector read out by a CMOS low noise self-triggering 128-channel chip has successfully been tested with low energy γ- and X-rays and β-emitting sources for imaging of simple patterns. The readout chip is described in detail, as well as the detector, the ancillary electronics and the data acquisition. Images of the size of 6.4 × 6.4 mm 2 are presented. The readout pitch is 50 μm in both the x - and the y -direction. The energy resolution for the 44.23 keV K α -line from Tb is measured to 0.86 keV (240 e − rms). For β-patterns with 35 S, the spatial spread shows a good correlation with the range of the particles (130 μm).

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.

Energy discrimination with an X-ray pixel detector — a Monte-Carlo simulation

Abstract Monte-Carlo simulations have been performed for the purpose of investigating the energy discriminating feature of a semiconductor hybrid pixel detector at diagnostic energies. Part of the evalution was performed using synthetic images obtained from the simulated data.

Development of a digital X-ray imaging detector

A fast high-resolution hybrid silicon pixel detector is being designed at Uppsala University as a part of on digital X-ray imaging (DIXI) project. The pixel size is 250/spl times/250 /spl mu/m/sup 2/ and the first design aims at an overall area of 128/spl times/128 mm/sup 2/ with a total of 262k pixels. The readout electronics will be connected to the sensor array via bump bonding. Each pixel contains implemented logic for preprocessing and registration. A prototype 0.5 mm thick Si sensor with 16/spl times/8 pixels is processed, a 1 mm version has been ordered, and a readout chip with 8/spl times/8 pixels is in production.

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.

Test results from a pixel readout chip for 2D dynamic x-ray imaging

A VLSI readout chip for a solid-state hybrid pixel detector for two-dimensional real-time imaging is part of a project with the goal to construct a large-area digital detector with good efficiency for X-rays in the energy range 20 - 70 keV. A new circuit concept with integrated analog counters in each cell makes the detector suitable for high-intensity dynamic imaging. The aim is to acquire 12-bit images with a speed of up to 100 frames per second. The detector concept also includes single-photon counting and an adjustable threshold. The size of the pixel is a trade-off between spatial resolution and amount of implemented logic, and is chosen to 270 micrometer X 270 micrometer. A 8 X 8-channel prototype readout chip, (ANGIE), with a pixel size of 250 micrometer X 250 micrometer, has been fabricated and tested. The results from functional tests are presented.