STIMULATE Kolloquium

Dosepix: a spectroscopic pixel detector for gamma dosimetry and x-ray imaging

Datum/Zeit

2. Dezember 2019, 14:00 Uhr 

Ort

Meeting room of the University Library (G30- 01)

Referent

Priv.-Doz. Dr. Thilo Michel, Group leader of the “Detector physics / Medical physics” – group at the chair of experimental particle- and astroparticle physics of Prof. Gisela Anton at the Institute of Physics of the Friedrich-Alexander University of Erlangen-Nuremberg

Abstract

Dosepix is a spectroscopic, photon counting semiconductor pixel detector dedicated to x- and gamma-ray dosimetry and energy resolved x-ray imaging. It has been developed in collaboration between CERN and the Erlangen Centre for Astroparticle Physics. In each of its 256 pixels, it features 16 energy channels, capable of counting the number of detected events above about 10 keV between 16 thresholds that can be adjusted freely. As the main application of Dosepix is dosimetry of ionising radiation, a new readout scheme was implemented: the rolling shutter principle which allows continuous recording of events. Dosepix features more operation modes, such as a photon counting mode with single threshold, an integration mode and single-event energy measurements. In order to cope with very low dose rates, 192 large pixels with a pixel pitch of 220 micrometers were realized. Additional 64 pixels with a much smaller pixel pitch of 55 micrometers allow dosimetry at very large dose rates. Due to the principle of dosimetry with such a spectroscopic detector, various dose quantities can be derived from the same measured data set such as deep dose, skin dose, air kerma. In a collaboration with the german metrology institute PTB in Braunschweig we were able to achieve excellent dosimetric performance between 15 keV and 1.3 MeV. We could show operation up to 700 Sv/h which is an extension of the dynamic range of several orders of magnitude compared to commercial active electronic dosimeters. In addition to that, the doses measured by Dosepix do not depend on pulse rate as the detector is operated in a camera like manner.

As the detector is a photon counting x-ray camera chip, energy-resolved x-ray images can be recorded. We were able to demonstrate that the signal-to-noise ratio in Talbot-Lag based phase-contrast and dark-field x-ray imaging can be improved by properly weighting the images obtained in different energy channels. This allows in principle for a reduction of the dose to be applied to a patient.

In this talk, we will present functionalities and properties of the Dosepix detector, the principle for determining the dose with photon counting pixel detectors, and show dose measurements obtained together with PTB. Furthermore we will present our results obtained in energy-resolved phase-contrast and dark-field imaging.