| 1. |
- Brahme, A., et al.
(författare)
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Evaluation of a GEM and CAT-based detector for radiation therapy beam monitoring
- 2000
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 454, s. 136-141
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Tidskriftsartikel (refereegranskat)abstract
- We are developing a radiation therapy beam monitor for the Karolinska Institute. This monitor will consist of two consecutive detectors confined in one gas chamber: a keV-photon detector, which will allow diagnostic quality visualization of the patient, and a MeV-photon detector, that will measure the absolute intensity of the therapy beam and its position with respect to the patient. Both detectors are based on highly radiation resistant gas and solid photon to electron converters, combined with GEMs and a CAT as amplification structures. We have performed systematic studies of the high-rate characteristics of the GEM and the CAT, as well as tested the electron transfer through these electron multipliers and various types of converters. The tests show that the GEM and the CAT satisfy all requirements for the beam monitoring system. As a result of these studies we successfully developed and tested a full section of the beam monitor equipped with a MeV-photon converter placed between the GEM and the CAT.
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| 2. |
- Bäck, Torbjörn, et al.
(författare)
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A TOF-PET system for educational purposes
- 2002
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576. ; 477, s. 82-82
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Tidskriftsartikel (refereegranskat)abstract
- A TOF-PET system has been designed and constructed for educational purposes. The aim of this system is to demonstrate the possibilities of positron emission tomography in general and the time-of-flight method in particular to the students of various courses at the Royal Institute of Technology, Stockholm, Sweden. The set-up consists of 48 small BaF2 crystals coupled to fast photomultipliers placed in a ring geometry. The signals of the photomultipliers are fed into fast constant fraction discriminators (CFD). The outputs of these are directed to a specially designed logic VME unit. which combines the CFD signals of 6 neighbouring channels to one signal by adding a different delay to each channel. The logic circuitry produces a prompt pulse for each event that serves as the start pulse for the 8-channel fast TDC. The delayed pulses act as the stop pulses for the TDC. In a computer. the measured times are converted into information about which the photomultipliers fired with the difference in the time of flight. The set-up is described and the results are presented.
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| 3. |
- Bäck, Torbjörn, et al.
(författare)
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An educational tool for demonstrating the TOF-PET technique
- 2001
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : AMERICAN PHYSICAL SOC. - 0168-9002 .- 1872-9576. ; 471:1-2, s. 200-204
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Tidskriftsartikel (refereegranskat)abstract
- A detector system for positron emission tomography with time-of-flight capability has been built to serve as an educational tool for undergraduate students. The set-up consists of 48 BaF2 scintillator crystals, each coupled to a fast photo-multiplier tube, mounted in a circular geometry. The analogue detector pulses are handled by fast constant fraction discriminators. A dedicated unit reduces the 48 channels to eight channels via delay-fine encoding, and the signals are then fed to an eight channel fast time-to-digital converter. A VME processor sorts the events and sends them to a workstation where the coincident events are extracted. The time resolution of the detectors together with fast VME based electronics allows for time-of-flight measurements to improve on the signal-to-noise ratio in the, reconstructed images. The system can be used for different types of exercises for the students, varying from the fundamentals of scintillator detectors to advanced image reconstruction. The set-up is described and some results are presented. (C) 2001 Elsevier Science B.V. All rights reserved.
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| 4. |
- Carlson, P., et al.
(författare)
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Beyond the RICH : innovative photosensitive gaseous detectors for new fields of applications
- 2003
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 502:1, s. 189-194
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Tidskriftsartikel (refereegranskat)abstract
- We have developed and successfully used several innovative designs of detectors with solid photocathodes. The main advantage of these detectors is that rather high gains (> 10(4)) can be achieved in a single multiplication step. This is possible by, for instance, exploiting the secondary electron multiplication and limiting the energy of the steamers by distributed resistivity. The single step approach also allows a very good position resolution to be achieved in some devices: 50 mum on line without applying any treatment method (like center of gravity). The main focus of our report is new fields of applications for these detectors and the optimization of their designs for such purposes.
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| 5. |
- Fröjdh, Christer, 1952-, et al.
(författare)
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New sensors for dental X-ray imaging
- 1999
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 434:1, s. 24-29
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Tidskriftsartikel (refereegranskat)
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| 6. |
- Qatarneh, Sharif M., et al.
(författare)
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A whole body atlas for segmentation and delineation of organs for radiation therapy planning
- 2001
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - Berlin, Heidelberg : Springer. - 0168-9002 .- 1872-9576. ; 471, s. 160-164, s. 1168-1169
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Tidskriftsartikel (refereegranskat)abstract
- A semi-automatic procedure for delineation of organs, to be used as the basis of a whole body atlas database for radiation therapy planning was developed. The Visible Human Male Computed Tomography (CT)-data set was used as a standard man reference. The organ of interest was outlined manually and then transformed by a polynomial warping algorithm onto a clinical patient CT. This provided an initial contour, which was then adjusted and refined by the semi-automatic active contour model to find the final organ outline. The liver was used as a test organ for evaluating the performance of the procedure. Liver outlines obtained by the segmentation algorithm on six patients were compared to those manually drawn by, a radiologist. The combination of warping and semi-automatic active contour model generally provided satisfactory segmentation results, but the procedure has to be extended to three dimensions.
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| 7. |
- Sipos, A., et al.
(författare)
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Visualization of neutron and proton induced particle production in a CMOS image sensor
- 2003
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 509:03-jan, s. 328-332
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Tidskriftsartikel (refereegranskat)abstract
- A commercially available off the shelf CMOS Image Sensor was irradiated with neutron and proton beams. The Image Sensor is equipped with standard video output. The data were collected on VHS videotapes and analyzed off-line after digitization. The camera chip with 110 000 pixels each having 12 x 12 mum(2) size, shows the nuclear reactions occurring in the sensitive layer as bright spots or tracks. Several applications are suggested based on the inexpensive CMOS Image Sensor.
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| 8. |
- Wallmark, M., et al.
(författare)
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Operating range of a gas electron multiplier for portal imaging
- 2001
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 471:02-jan, s. 151-155
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Tidskriftsartikel (refereegranskat)abstract
- At the Karolinska Institute in Stockholm, Sweden a new detector for portal imaging is under development, which could greatly improve the alignment of the radiation beam with respect to the tumor during radiation treatment. The detector is based on solid converters combined with gas electron multipliers (GEMs) as an amplification structure. The detector has a large area and will be operated in a very high rate environment in the presence of heavy ionizing particles. As was discovered recently high rates and alpha particles could cause discharges in GEM and discharge propagation from GEM to GEM and to the readout electronics. Since reliability is one of the main requirements for the portal imaging device, we performed systematic studies to find a safe operating range of the device, free from typical high rate problems, such as discharges.
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| 9. |
- Andreassen, Björn, 1975-, et al.
(författare)
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Development of an efficient scanning and purging magnet system for IMRT with narrow high energy photon beams
- 2009
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 612:1, s. 201-208
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Tidskriftsartikel (refereegranskat)abstract
- Due to the clinical advantages of Intensity Modulated Radiation Therapy (IMRT) high flexibility and accuracy in intensity modulated dose delivery is desirable to really maximize treatment outcome. Although it is possible to deliver IMRT by using broad beams in combination with dynamic multileaf collimation the process is rather time consuming and inefficient. By using narrow scanned high energy photon beams the treatment outcome can be improved, the treatment time reduced and accurate 3D in vivo dose delivery monitoring is possible by PET-CT based dose delivery imaging of photo nuclear reactions in human tissues. Narrow photon beams can be produced by directing a low emittance high energy electron beam on a thin target, and then cleaning the therapeutic photon beam from transmitted high energy electrons, and photon generated charged leptons, with a dedicated purging magnet placed directly downstream of the target. To have an effective scanning and purging magnet system the purging magnet should be placed immediately after the bremsstrahlung target to deflect the transmitted electrons to an efficient electron stopper. In the static electron stopper the electrons should be safely collected independent of the desired direction of the therapeutic scanned photon beam. The SID (Source to Isocentre Distance) should preferably be short while retaining the ability to scan over a large area on the patient and consequently there are severe requirements both on the strength and the geometry of the scanning and purging magnets. In the present study an efficient magnet configuration with a purging and scanning magnet assembly is developed for electron energies in the 50-75 MeV range and a SID of 75 cm. For a bremsstrahlung target of 3mm Be these electron energies produce a photon beam of 25-17 mm FWHM (Full Width Half Maximum) at a SID of 75 cm. The magnet system was examined both in terms of the efficiency in scanning the narrow bremsstrahlung beam and the deflection of transmitted and photon generated electrons. The simulations show that its is possible to have a scan area on the patient of up to 43 x 40 cm2 for an incident electron energy of 50 MeV and 28 x 40 cm2 at 75 MeV, while at the same time adequately deflecting the transmitted electron beam.
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| 10. |
- Danielsson, Mats, et al.
(författare)
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Novel gaseous detectors for medical imaging
- 2004
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 518:1-2, s. 406-410
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Tidskriftsartikel (refereegranskat)abstract
- We have developed and successfully tested prototypes of two new types of gaseous detectors for medical imaging purposes. The first one is called the Electronic Portal Imaging Device (EPID). It is oriented on monitoring and the precise alignment of the therapeutic cancer treatment beam (pulsed gamma radiation) with respect to the patient's tumor position. The latest will be determined from an X-ray image of the patient obtained in the time intervals between the gamma pulses. The detector is based on a sandwich of hole-type gaseous detectors (GEM and glass microcapillary plates) with metallic gamma and X-ray converters coated with CsI layers. The second detector is an X-ray image scanner oriented on mammography and other radiographic applications. It is based on specially developed by us high rate RPCs that are able to operate at rates of 10(5) HZ/mm(2) with a position resolution better than 50 mum at 1 atm. The quality of the images obtained with the latest version of this device were in most cases more superior than those obtained from commercially available detectors.
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