<title>Performance of a 4096-pixel photon counting chip</title>

Abstract

A 4096 pixel Photon Counting Chip (PCC) has been developed and tested. It is aimed primarily at medical imaging although it can be used for other applications involving particle counting. The readout chip consists of a matrix of 64 x 64 identical square pixels, whose side measures 170 Pm and is bump-bonded to a similar matrix of GaAs or Si pixel diodes covering a sensitive area of 1.18cm2 . The electronics in each cell comprises a preamplifier, a discriminator with variable threshold and a 3-bit threshold tune as well as a 15-bit counter. Each pixel can be individually addressed for electrical test or masked during acquisition. A shutter allows for switching between the counting and the readout modes and the use of a static logic in the counter enables long data taking periods. ABSTRACTA 4096 pixel Photon Counting Chip (PCC) has been developed and tested. It is aimed primarily at medical imaging although it can be used for other applications involving particle counting. The readout chip consists of a matrix of 64 x 64 identical square pixels, whose side measures 170 Pm and is bump-bonded to a similar matrix of GaAs or Si pixel diodes covering a sensitive area of 1.18 cm 2 . The electronics in each cell comprises a preamplifier, a discriminator with variable threshold and a 3-bit threshold tune as well as a 15-bit counter. Each pixel can be individually addressed for electrical test or masked during acquisition. A shutter allows for switching between the counting and readout modes and the use of static logic in the counter enables long data taking periods. Electrical tests of the chip have shown a maximum counting rate of up to 2 MHz in each pixel. The minimum reachable threshold is 1 400 e -with a variation of 350 e -rms that can be reduced to 80 e -rms after tuning with the 3-bit adjustment. Electrical noise at the input is 170 e -rms. Several read-out chips have been bump bonded to 200 Pm thick GaAs pixel detectors. Tests with J-ray and E -sources have been carried out. A number of objects have been imaged and a 260 Pm thick aluminium foil which represents a contrast to the surrounding air of only 1.9 % has been correctly imaged.

Experimental study of Compton scattering reduction in digital mammographic imaging

“…The detector is a 300-m thick silicon crystal with an array of 64 64 square pixels, 170 m on each side. The data readout is performed by a photon counting chip (PCC), which is a very large scale integration (VLSI)-integrated circuit, developed as part of the MEDIPIX collaboration [7]- [9]. The electronics chip is connected to the sensor by means of bump-bonding techniques.…”

Full-field images of mammographic phantoms obtained with a single photon counting system

“…The digital imaging system we are developing for mammography is based on a semiconductor pixel detector operating in single photon counting mode [7]. The X ray sensor element is a thin slab of crystalline semiconductor where an array of square contacts organized in 64 rows by 64 columns covers one side of the detector.…”

“…Pixel detectors have been originally developed for High Energy Physics experiments but soon their use has been extended to digital radiography. Nowadays several research institutes have built various dedicated devices [7][8] [9]. X rays sensing element is a semiconductor diode, reverse biased, coupled to an electronics read-out system which converts into a digital pulse the charge signal produced by the photon interaction in the detector.…”

Detective quantum efficiency of the Medipix pixel detector

“…The working of the chip is explained in more detail in references [2] and [3]. The chip performs single photon counting in each pixel cell.…”