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Smart dosimetry by pattern recognition using a single photon counting detector system in time over threshold mode
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
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2012 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 7, no 1, p. Art. no. C01027-Article in journal (Refereed) Published
Abstract [en]

The function of a dosimeter is to determine the absorbed dose of radiation, for those cases in which, generally, the particular type of radiation is already known. Lately, a number of applications have emerged in which all kinds of radiation are absorbed and are sorted by pattern recognition, such as the Medipix2 application in [1]. This form of smart dosimetry enables measurements where not only the total dosage is measured, but also the contributions of different types of radiation impacting upon the detector surface. Furthermore, the use of a photon counting system, where the energy deposition can be measured in each individual pixel, ensures measurements with a high degree of accuracy in relation to the pattern recognition. In this article a Timepix [2] detector system has been used in the creation of a smart dosimeter for Alpha, Beta and Gamma radiation. When a radioactive particle hits the detector surface it generates charge clusters and those impacting upon the detector surface are read out and image processing algorithms are then used to classify each charge cluster. The individual clusters are calculated and as a result, the dosage for each type of radiation is given. In some cases, several particles can impact in roughly the same place, forming overlapping clusters. In order to handle this problem, a cluster separation method has been added to the pattern recognition algorithm. When the clusters have been separated, they are classified by shape and sorted into the correct type of radiation. The algorithms and methods used in this dosimeter have been developed so as to be simple and computationally effective, in order to enable implementation on a portable device. © 2012 IOP Publishing Ltd and SISSA.

Place, publisher, year, edition, pages
2012. Vol. 7, no 1, p. Art. no. C01027-
Keywords [en]
Dosimetry, Pattern Recognitionm, Single Photon Counting Detector, Time over Threshold Mode
National Category
Radiology, Nuclear Medicine and Medical Imaging Medical Image Processing Accelerator Physics and Instrumentation
Identifiers
URN: urn:nbn:se:miun:diva-15495DOI: 10.1088/1748-0221/7/01/C01027ISI: 000303806200027Scopus ID: 2-s2.0-84856994290Local ID: STCOAI: oai:DiVA.org:miun-15495DiVA, id: diva2:468017
Conference
13th International Workshop on Radiation Imaging Detectors (IWORID)
Available from: 2011-12-20 Created: 2011-12-20 Last updated: 2017-12-08Bibliographically approved
In thesis
1. A Hybrid Pixel Detector ASIC with Energy Binning for Real-Time, Spectroscopic Dose Measurements
Open this publication in new window or tab >>A Hybrid Pixel Detector ASIC with Energy Binning for Real-Time, Spectroscopic Dose Measurements
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Hybrid pixel detectors have been demonstrated to provide excellent quality detection of ionising photon radiation, particularly in X-ray imaging. Recently, there has been interest in developing a hybrid pixel detector specifically for photon dosimetry. This thesis is on the design, implementation, and preliminary characterisation of the Dosepix readout chip.

Dosepix has 256 square pixels of 220 mm side-length, constituting 12.4 mm2 of photo-sensitive area per detector. The combination of multiple pixels provides many parallel processors with limited input flux, resulting in a radiation dose monitor which can continuously record data and provide a real-time report on personal dose equivalent. Energy measurements are obtained by measuring the time over threshold of each photon and a state machine in the pixel sorts the detected photon event into appropriate energy bins. Each pixel contains 16 digital thresholds with 16 registers to store the associated energy bins. Preliminary measurements of Dosepix chips bump bonded to silicon sensors show very promising results. The pixel has a frontend noise of 120 e-. In low power mode, each chip consumes 15 mW, permitting its use in a portable, battery-powered system. Direct time over threshold output from the hybrid pixel detector assembly reveal distinctive photo-peaks correctly identifying the nature of incident photons, and verification measurements indicate that the pixel binning state machines accurately categorise charge spectra. Personal dose equivalent reconstruction using this data has a flat response for a large range of photon energies and personal dose equivalent rates.

Place, publisher, year, edition, pages
Mid Sweden University, 2012. p. 238
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 128
Keywords
Hybrid pixel detector, low power readout chip, photon counting, time over threshold (ToT), energy binning, active personal dosimeter (APD)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-16171 (URN)978-91-87103-20-9 (ISBN)
Public defence
2012-05-30, O102, Mittuniversitetet, Campus Sundsvall, Sundsvall, 13:00 (English)
Opponent
Supervisors
Available from: 2012-06-07 Created: 2012-05-03 Last updated: 2012-08-01Bibliographically approved

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Reza, SalimWong, WinnieFröjdh, ErikNorlin, BörjeFröjdh, ChristerThungstörm, GöranThim, Jan

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