Pixelated photon counting semiconductor X-ray detectors like the Medipix feature adjustable energy thresholds allowing selective counting of photons of a specified energy. This development permits ...for energy selective X-ray imaging with advanced material information. Furthermore the photon counting function principle of these detectors allows X-ray imaging with reduced noise, providing contrast improvement in low contrast objects. The aim of this study is to analyze the behavior of the new Medipix3 detector, especially regarding flatfield correction for X-ray imaging applications. First high resolution low contrast X-ray images and energy selective X-ray images acquired with the Medipix3 detector are presented as well in this paper.
In this work we present the design of a chip which provides the readout of a highly segmented diode array, in which signals induced by individual X-ray photons are processed discretely. There are ...several benefits to this approach, including the ability to achieve a high signal to noise ratio due to the inherently low sensor capacitance, and the suppression of background noise (
e.g. dark current) using an analogue threshold. The segmentation also ensures a linear behaviour even at very high dose rates. A time over threshold (ToT
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ToT: Time over threshold. ASIC: Application-specific integrated circuit. APS: Active pixel sensor. DAC: Digital to analogue convertor. CSA: Charge sensitive preamplifier. ENC: Equivalent noise charge.
) energy measurement technique provides an immediate digital value corresponding to the energy deposited onto the diode by each individual photon. Deadtime-free operation is achieved by reading out a subset of the detector segments at a time while the rest of the detector continues to process signals. This paper describes the application-specific integrated circuit (ASIC) chip which was designed to provide pre-processing of photo-induced signals in the detector and readout of the processed digital data.
► We have designed the ASIC of a hybrid pixel detector for photon dosimetry. ► The pulse processing circuits measure the time over threshold of discrete photons. ► Each pixel automatically sorts ToT measurements into 16 digital energy bins. ► The binned data is used to reconstruct the charge spectrum and dose in real time.
Low noise, high resolution, and high dose efficiency are the common requirements for most X-ray imaging applications. The dose efficiency is especially important for medical imaging systems. We ...present the imaging performance of the Medipix2 readout chip bump bonded to a 300 mum thick Si detector as a function of the detection threshold, a free parameter not available in conventional charge integrating imaging systems. Spatial resolution has been measured using the modulation transfer function (MTF) and it varies between 8.2 line-pairs/mm and 11.0 line pairs/mm at an MTF value of 70%. An associated measurement of noise power spectrum (NPS) permits us to derive the detective quantum efficiency (DQE) which can be as a high as 25.5% for a broadband incoming spectrum. The influence of charge diffusion in the sensor together with threshold variation in the readout chip is discussed. Although the Medipix2 system is used in photon counting mode with a single threshold in energy, the system is also capable of counting within a given energy window as narrow as ~1.4 keV. First measurements and images using this feature reveal capabilities that allow identifying fluorescence and other sources of disturbance
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