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Measurements and Ray-Tracing Simulations of Light Spread in LSO Crystals
Stockholm University, Faculty of Science, Department of Physics. (Siemens Molecular Imaging)
(Siemens Molecular Imaging)
(Siemens Molecular Imaging)
(Siemens Molecular Imaging)
2009 (English)In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, Vol. 56, no 5, 2566-2573 p.Article in journal (Refereed) Published
Abstract [en]

We report on measurements of the absolute light output from LSO crystals for irradiation with 511 keV gamma rays as a function of interaction position, reflector arrangement, detector coupling geometry and optical coupling to an adjacent crystal. The light output for this series of geometrical configurations is simulated with the ZEMAX ray-tracing software. By fine-tuning the optical parameters of the bulk and at the interfaces of the crystal, a model is obtained which yields good agreement with experimental data for all configurations. The resulting parameter set is applied to calculate the light distribution in a 12$,times,$ 12 crystal block detector. A comparison of measured and calculated block position profiles shows good agreement, demonstrating the potential of the simulation model to predict block detector performance data and provide guidelines for future array designs.

Place, publisher, year, edition, pages
2009. Vol. 56, no 5, 2566-2573 p.
URN: urn:nbn:se:su:diva-31661ISI: 000271100400002OAI: diva2:278542
Available from: 2009-11-26 Created: 2009-11-23 Last updated: 2009-12-22Bibliographically approved
In thesis
1. Detector Considerations for Time-of-Flight in Positron Emission Tomography
Open this publication in new window or tab >>Detector Considerations for Time-of-Flight in Positron Emission Tomography
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Positron-Emission-Tomography (PET) is a modern imaging technique in nuclear medicine providing quantitative 3D distribution of a radioactive tracer substance in the human body. The gamma-detector is the first link in the chain of components that constitutes a PET. It converts incoming radiation into optical light pulses, which are detected by photo multiplier tubes. Here the light is converted into electric pulses, to be further processed by the acquisition electronics. Improving detector sensitivity and resolution is of great value in research and in clinical practice.

The focus of this work is to improve the detector to give it time-of-flight (TOF) capabilities, in order to further improve sensitivity, which in turn leads to increased image quality, faster scan time and/or reduced dose exposure for the patient.

Image quality has improved over the years, but losses in image quality have been reported for heavy patients, due to increased attenuation, and more dispersed counts over a larger volume. Instrumentation limits are still significant in heavy patient images, but the incorporation of TOF information promises to alleviate some of the limitations.

In order to improve the timing resolution of the detector fast photo-multipliers and a novel scheme to extract the event timing trigger from a detector by using the summed dynode signal were investigated.

When designing new PET detectors, it is important to have detailed understanding and control of the light sharing mechanisms in the crystal arrays. Therefore it was necessary to perform optical simulations and single crystal light output measurements to derive a model for an LSO block detector.

Another way to improve the image quality is to use the depth-of-interaction (DOI) of the gamma ray within the detector. It is shown that a multi-layer phoswich detector comprised of LSO with different decay times and TOF capability, combines the benefits of TOF and DOI in one detector, maximizing the effective sensitivity gain.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2009. 78 p.
Positron Emission Tomography, Time of Flight, Depth of Interaction, LSO
National Category
Radiology, Nuclear Medicine and Medical Imaging
Research subject
Medical Radiation Physics
urn:nbn:se:su:diva-31587 (URN)978-91-7155-979-1 (ISBN)
Public defence
2010-01-08, FB52, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 7: Submitted. Available from: 2009-12-03 Created: 2009-11-19 Last updated: 2009-12-22Bibliographically approved

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