Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Detector Considerations for Time-of-Flight in Positron Emission Tomography
Stockholm University, Faculty of Science, Department of Physics. (System and instrumentation physics)
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.
Keyword [en]
Positron Emission Tomography, Time of Flight, Depth of Interaction, LSO
National Category
Radiology, Nuclear Medicine and Medical Imaging
Research subject
Medical Radiation Physics
Identifiers
URN: urn:nbn:se:su:diva-31587ISBN: 978-91-7155-979-1 (print)OAI: oai:DiVA.org:su-31587DiVA: diva2:278549
Public defence
2010-01-08, FB52, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
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
List of papers
1. Current and Future Use of LSO:Ce Scintillators in PET
Open this publication in new window or tab >>Current and Future Use of LSO:Ce Scintillators in PET
Show others...
2006 (English)In: Radiation detectors for medical applications / [ed] Stefaan Tavernier, Dordrecht: Springer , 2006, , 243-257 p.243-257 p.Conference paper, Published paper (Refereed)
Abstract [en]

Single crystal scintillators of Lu2SiO5:Ce (LSO:Ce) were first developed about 15 years ago and have been in commercial use in positron emission tomography systems for more than five years. Annual production now exceeds 10,000 kg. We review the development of LSO:Ce and its implementation in PET, and summarize the current understanding of the scintillation characteristics and mechanisms. In addition, we present the evolution of LSO:Ce detector design and consider the potential performance of future imaging systems. In particular, coincidence timing measurements are presented and time-of-flight systems that take better advantage of the timing characteristics of LSO:Ce are discussed.

Place, publisher, year, edition, pages
Dordrecht: Springer, 2006. 243-257 p.
Series
NATO security through science series. Series B, Physics and biophysics
Identifiers
urn:nbn:se:su:diva-31785 (URN)978-1-4020-5091-6 (ISBN)
Conference
NATO Advanced Research Workshop on Radiation Detectors for Medical Applications
Available from: 2009-11-26 Created: 2009-11-26 Last updated: 2009-12-22Bibliographically approved
2. Timing performance of Hi-Rez detector for time-of-flight (TOF) PET
Open this publication in new window or tab >>Timing performance of Hi-Rez detector for time-of-flight (TOF) PET
Show others...
2006 (English)In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 53, no 3, 1084-1089 p.Article in journal (Refereed) Published
Abstract [en]

Positron emission tomography (PET)-based on time-of-flight (TOF) is desired to enhance the image quality by improving the noise variance in the reconstruction. This benchtop study evaluates the timing performance of the current Hi-Rez detector which is based on a 13/spl times/13 LSO array of 4 mm/spl times/4 mm/spl times/20 mm crystals and not optimized for TOF PET applications. A Hamamatsu R9779, fast, 51-mm-diameter PMT was used for some experiments in this study as a reference PMT and its time resolution was measured to be 160 ps with a plastic scintillator. The average crystal time resolution of two Hi-Rez detectors, coupled to a 2/spl times/2 array of Hamamatsu 25-mm-diameter R8619 PMTs at +1050 V, in coincidence was measured to be 733 ps. The average crystal energy resolutions for two detectors were measured 13.1% and 13.2%. The average crystal time resolution of two Hi-Rez detectors improved from 733 ps to 642 ps when the PMT voltage was increased to +1300 V. The Hi-Rez detector was originally optimized for good energy resolution to reduce scatter and high packing fraction to obtain high sensitivity and improved spatial resolution for clinical PET.

Identifiers
urn:nbn:se:su:diva-31657 (URN)
Available from: 2009-11-26 Created: 2009-11-23 Last updated: 2017-12-12Bibliographically approved
3. Performance Study of the New Hamamatsu R9779 and Photonis XP20D0 Fast 2" Photomultipliers
Open this publication in new window or tab >>Performance Study of the New Hamamatsu R9779 and Photonis XP20D0 Fast 2" Photomultipliers
Show others...
2007 (English)In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 54, no 3, 422-426 p.Article in journal (Refereed) Published
Abstract [en]

The focus of this paper is the evaluation of the new fast 51 mm-diameter, 8-stage Hamamatsu R9779 photomultipliers (PMTs) with an acceleration-ring at the front-end and the Photonis XP20D0 PMTs with a screening grid in front of the anode. The following performance characteristics are presented: Timing resolution, anode-scan-uniformity and transit-time spread. The unfolded timing resolution for two R9779 was 192 ps and 210 ps using plastic scintillators. The individual timing resolutions for two XP20D0 using plastic scintillators are 181 ps and 154 ps, respectively. The variation in time resolution across the windows of the two R9779 ranged between 117 ps and 171 ps, and 79 ps and 73 ps for the two XP20D0 PMTs.

Identifiers
urn:nbn:se:su:diva-31660 (URN)000247391200002 ()
Available from: 2009-11-26 Created: 2009-11-23 Last updated: 2017-12-12Bibliographically approved
4. Dynode-Timing Method for PET Block Detectors
Open this publication in new window or tab >>Dynode-Timing Method for PET Block Detectors
Show others...
2008 (English)In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 55, no 1, 451-456 p.Article in journal (Refereed) Published
Abstract [en]

The focus of this paper is the investigation of a new dynode-timing technique optimized for PET block detectors. This method allows utilization of dynode signals from single but especially multiple photo-multiplier tubes (PMTs), operated with negative high-voltage. The technique will provide an event-timing trigger without deteriorating the anode signal. A printed circuit board has been developed and built for this investigation. Benchmark measurements have been performed, comparing timing of the anode signal with timing of the inverted last-dynode signal and timing of the dynode signal extracted via a newly developed LVPECL-logic based board. Timing measurements were performed with plastic as well as LSO scintillators. From single PMT measurements we find a 30 ps improvement with the dynode-timing method compared to the standard anode timing with two Photonis XP2020Q PMTs with LSO (10 mmtimes10 mmtimes10 mm). For a quad-PMT block detector, assembled of four Hamamatsu R9800 with a Hi-Rez block, the timing-resolution improves ~10%, by 43 ps compared to the standard anode timing.

Identifiers
urn:nbn:se:su:diva-31664 (URN)000253224800001 ()
Available from: 2009-11-26 Created: 2009-11-23 Last updated: 2017-12-12Bibliographically approved
5. Evaluation of a Micro-Channel Plate PMT in PET
Open this publication in new window or tab >>Evaluation of a Micro-Channel Plate PMT in PET
2006 (English)In: Nuclear Science Symposium Conference Record, 2006, IEEE, 2006, 2503-2505 p.Conference paper, Published paper (Refereed)
Abstract [en]

The focus of this paper is the evaluation of micro-channel plate PMTs for PET detectors. Several properties of MCPs make them interesting for PET applications, such as fast time response, high spatial resolution, compact size, low susceptibility to magnetic fields, high gain and low power consumption. The preliminary tests in this paper are performed with the 51 mm times 51 mm square Burle 85011-501 assembly with 64 anodes (8 times 8). A new version of this MCP will be examined for the full paper. Initial measurements have been performed with a pulsed LASER (Hamamatsu Picosecond Light Pulser PLP-10 with M8903 Laser diode head). The engineering sample of the 85011 exhibited a time resolution of 26 ps. Further measurements will be performed, such as transit time measurements and timing measurements with scintillators. Single-photon timing measurements were presented earlier in [Ref. 1], from the old version as well as the suitability of the device in Cherenkov detectors in [Ref. 2]. For the full paper it is also planned to develop a circuit which allows lossless splitting of the anode signal.

Identifiers
urn:nbn:se:su:diva-31662 (URN)1-4244-0560-2 (ISBN)
Conference
Nuclear Science Symposium Conference
Available from: 2009-11-26 Created: 2009-11-23 Last updated: 2009-12-22Bibliographically approved
6. Measurements and Ray-Tracing Simulations of Light Spread in LSO Crystals
Open this publication in new window or tab >>Measurements and Ray-Tracing Simulations of Light Spread in LSO Crystals
2009 (English)In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, 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.

Identifiers
urn:nbn:se:su:diva-31661 (URN)000271100400002 ()
Available from: 2009-11-26 Created: 2009-11-23 Last updated: 2017-12-12Bibliographically approved
7. Depth of interaction with a 3-dimensional checkerboard arrangement LSO-LSO block
Open this publication in new window or tab >>Depth of interaction with a 3-dimensional checkerboard arrangement LSO-LSO block
2010 (English)In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 57, no 3, 971-975 p.Article in journal (Refereed) Published
Abstract [en]

In order to improve image quality in Positron Emission Tomography (PET) different routes are being pursued such as fast timing resolution for time-of-flight PET, higher spatial resolution by the use of smaller scintillator pixels and the use of depth-of-interaction information. The detection of the depth-of-interaction (DOI) of a gamma ray within a detector, deploying pulse shape discrimination (PSD), has been used to increase sensitivity and spatial resolution, especially at the edge of the field of view (FOV). The DOI information is used to reduce the parallax error; thus improving spatial resolution. Commonly, different scintillator materials with different decay times and light output and other differentiating factors, such as density, emission spectra, etc. are used for DOI detectors. We present a multi-layer phoswich detector comprised of LSO with different decay times in the range from 30 ns to 47 ns. The difference in decay times is achieved by co-doping LSO:Ce with Ca, resulting in short decay times of ~ 30 ns [1]. The use of a cut light guide allows the use of regular Photomultiplier tubes, giving the opportunity of a potential DOI detector replacement for current detectors. We were able to identify each pixel in the different detector layers

Keyword
Block detector, depth of interaction, lutetium oxyorthosilicate (LSO), positron emission tomography (PET)
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-31658 (URN)10.1109/TNS.2010.2041070 (DOI)000278812100008 ()
Available from: 2009-11-26 Created: 2009-11-23 Last updated: 2017-12-12Bibliographically approved

Open Access in DiVA

fulltext(4043 kB)1465 downloads
File information
File name FULLTEXT01.pdfFile size 4043 kBChecksum SHA-512
bf315f2cf6e4ac0bab5336c353172ba56d7cc8737001b69790eb87e2e14d2260d37087d30d1e7e6a7769e58559f7052243f492730436bce97622e8155e9fba15
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Bauer, Florian
By organisation
Department of Physics
Radiology, Nuclear Medicine and Medical Imaging

Search outside of DiVA

GoogleGoogle Scholar
Total: 1465 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 491 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf