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Eriksson, Lars
Publications (10 of 15) Show all publications
Conti, M., Eriksson, L., Rothfuss, H., Sjoeholm, T., Townsend, D., Rosenqvist, G. & Carlier, T. (2017). Characterization of Lu-176 background in LSO-based PET scanners. Physics in Medicine and Biology, 62(9), 3700-3711
Open this publication in new window or tab >>Characterization of Lu-176 background in LSO-based PET scanners
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2017 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 62, no 9, p. 3700-3711Article in journal (Refereed) Published
Abstract [en]

LSO and LYSO are today the most common scintillators used in positron emission tomography. Lutetium contains traces of Lu-176, a radioactive isotope that decays beta(-) with a cascade of. photons in coincidence. Therefore, Lutetium-based scintillators are characterized by a small natural radiation background. In this paper, we investigate and characterize the Lu-176 radiation background via experiments performed on LSO-based PET scanners. LSO background was measured at different energy windows and different time coincidence windows, and by using shields to alter the original spectrum. The effect of radiation background in particularly count-starved applications, such as Y-90 imaging, is analysed and discussed. Depending on the size of the PET scanner, between 500 and 1000 total random counts per second and between 3 and 5 total true coincidences per second were measured in standard coincidence mode. The LSO background counts in a Siemens mCT in the standard PET energy and time windows are in general negligible in terms of trues, and are comparable to that measured in a BGO scanner of similar size.

Keywords
LSO background, randoms, PET
National Category
Medical Engineering Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:su:diva-143445 (URN)10.1088/1361-6560/aa68ca (DOI)000399098700001 ()28333041 (PubMedID)2-s2.0-85017438938 (Scopus ID)
Available from: 2017-06-07 Created: 2017-06-07 Last updated: 2022-10-19Bibliographically approved
Conti, M. & Eriksson, L. (2016). Physics of pure and non-pure positron emitters for PET: a review and a discussion. EJNMMI Physics, 3(1), Article ID 8.
Open this publication in new window or tab >>Physics of pure and non-pure positron emitters for PET: a review and a discussion
2016 (English)In: EJNMMI Physics, ISSN 2197-7364, Vol. 3, no 1, article id 8Article, review/survey (Refereed) Published
Abstract [en]

With the increased interest in new PET tracers, gene-targeted therapy, immunoPET, and theranostics, other radioisotopes will be increasingly used in clinical PET scanners, in addition to F-18. Some of the most interesting radioisotopes with prospective use in the new fields are not pure short-range beta(+) emitters but can be associated with gamma emissions in coincidence with the annihilation radiation (prompt gamma), gamma-gamma cascades, intense Bremsstrahlung radiation, high-energy positrons that may escape out of the patient skin, and high-energy gamma rays that result in some e(+)/e(-) pair production. The high level of sophistication in data correction and excellent quantitative accuracy that has been reached for F-18 in recent years can be questioned by these effects. In this work, we review the physics and the scientific literature and evaluate the effect of these additional phenomena on the PET data for each of a series of radioisotopes: C-11, N-13, O-15, F-18, Cu-64, Ga-68, Br-76, Rb-82, Y-86, Zr-89, Y-90, and I-124. In particular, we discuss the present complications arising from the prompt gammas, and we review the scientific literature on prompt gamma correction. For some of the radioisotopes considered in this work, prompt gamma correction is definitely needed to assure acceptable image quality, and several approaches have been proposed in recent years. Bremsstrahlung photons and Lu-176 background were also evaluated.

Keywords
PET, Radioisotopes, Positron emitter, Prompt gamma, Non-conventional PET isotopes
National Category
Physical Sciences Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:su:diva-132506 (URN)10.1186/s40658-016-0144-5 (DOI)000379211600001 ()27271304 (PubMedID)
Available from: 2016-08-16 Created: 2016-08-15 Last updated: 2022-03-23Bibliographically approved
Eriksson, L. & Conti, M. (2015). Randoms and TOF gain revisited. Physics in Medicine and Biology, 60(4), 1613-1623
Open this publication in new window or tab >>Randoms and TOF gain revisited
2015 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 60, no 4, p. 1613-1623Article in journal (Refereed) Published
Abstract [en]

Time-of-flight (TOF) positron emission tomography (PET) typically reduces the variance in the images by a factor that is proportional to the size of the object to be scanned, and inversely proportional to the time resolution of the PET scanner. Attempts to better characterize this relationship and understand its limits have been published, showing that such gain also increases with random fraction. In this paper, new experimental and simulated data are analyzed and old results are incorporated in the study. The proportionality of TOF gain with time resolution is confirmed, the proportionality constant is measured, the effect of the randoms is validated, and the limit of the model for small objects is investigated.

Keywords
PET, TOF PET, TOF gain, randoms, time resolution
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:su:diva-115674 (URN)10.1088/0031-9155/60/4/1613 (DOI)000349529100013 ()25615713 (PubMedID)2-s2.0-84922311230 (Scopus ID)
Note

AuthorCount:2;

Available from: 2015-04-01 Created: 2015-03-27 Last updated: 2022-10-14Bibliographically approved
Westerwoudt, V., Conti, M. & Eriksson, L. (2014). Advantages of Improved Time Resolution for TOF PET at Very Low Statistics. IEEE Transactions on Nuclear Science, 61(1), 126-133
Open this publication in new window or tab >>Advantages of Improved Time Resolution for TOF PET at Very Low Statistics
2014 (English)In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 61, no 1, p. 126-133Article in journal (Refereed) Published
Abstract [en]

In this paper, Monte Carlo generated data are used to simulate a time-of-flight (TOF) positron emission tomography (PET) scanner with improving time resolution, down to 200-ps time resolution. TOF and non-TOF ordered subsets expectation maximization (OSEM) reconstructions were compared in terms of contrast recovery and signal-to-noise ratio, with the purpose of characterizing the differences of TOF and non-TOF at very low counts. This study shows that there is a lower limit to the number of counts in a PET scan, in order to obtain a quantitative PET image. Below this limit, the reliability of the measurement is very poor. The use of TOF information has the beneficial effect of lowering this statistical limit, allowing for shorter reliable PET scans. Another interesting finding derives from the comparison with TOF filtered back projection (FBP) images: if time resolution can be improved, TOF FBP images become competitive with TOF MLEM and OSEM algorithms, not only in terms of contrast recovery but also in terms of reduced noise level.

Keywords
Low statistics, signal-to-noise ratio, time resolution, TOF PET
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-104006 (URN)10.1109/TNS.2013.2287175 (DOI)000334923000016 ()2-s2.0-84988329781 (Scopus ID)
Note

AuthorCount:3;

Available from: 2014-06-02 Created: 2014-05-27 Last updated: 2022-10-10Bibliographically approved
Conti, M., Eriksson, L. & Westerwoudt, V. (2013). Estimating Image Quality for Future Generations of TOF PET Scanners. IEEE Transactions on Nuclear Science, 60(1), 87-94
Open this publication in new window or tab >>Estimating Image Quality for Future Generations of TOF PET Scanners
2013 (English)In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 60, no 1, p. 87-94Article in journal (Refereed) Published
Abstract [en]

Images taken with time-of-flight (TOF) positron emission tomography (PET) scanners are of improved quality compared to equivalent non-TOF images. This improvement is dependent on the scanner time resolution. The present generation of commercial TOF scanners has a time resolution in the range of 500-600 ps full width half maximum. In this work we investigate how the image characteristics will improve for future generations of TOF PET. We performed a Geant4 simulation of a 30-cm uniform cylinder containing hot spheres, with time resolution ranging from 600 to 200 ps. Data were reconstructed using TOF filtered back projection (FBP) and TOF ordered subsets expectation maximization (OSEM), with nonTOF reconstruction as a reference. Images were compared in terms of contrast recovery and variance in the image. The TOF gain was evaluated for both reconstruction methods. The TOF gain was also evaluated vs. counts in the scan, in order to understand the behavior of such gain at very low statistics. Using TOF FBP, it was shown that the TOF gain can be used as a sensitivity amplifier, reducing (according to the expected TOF gain) the number of counts necessary to produce an image of the same characteristics. Some limitations in the TOF gain were observed at very low counts, particularly if using iterative methods.

Keywords
Filtered back projection (FBP), low statistics imaging, signal-to-noise ratio (SNR), time-of-flight (TOF) gain, TOF positron emission tomography (PET), time resolution
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:su:diva-88676 (URN)10.1109/TNS.2012.2233214 (DOI)000314972900012 ()2-s2.0-84988311558 (Scopus ID)
Note

AuthorCount:3;

Available from: 2013-03-26 Created: 2013-03-25 Last updated: 2022-10-06Bibliographically approved
Eriksson, L., Conti, M., Melcher, C. L., Zhuravleva, M., Eriksson, M. & Rothfuss, H. (2013). LuYAP/LSO Phoswich Detectors for High Resolution Positron Emission Tomography. IEEE Transactions on Nuclear Science, 60(1), 194-196
Open this publication in new window or tab >>LuYAP/LSO Phoswich Detectors for High Resolution Positron Emission Tomography
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2013 (English)In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 60, no 1, p. 194-196Article in journal (Refereed) Published
Abstract [en]

The spatial resolution in positron emission tomography (PET) can be improved by the addition of depth-of-interaction (DOI) information. This can be achieved by using the phoswich approach in which depth identification relies on differences in scintillation decay time and pulse shape discrimination techniques. In this paper we have looked at a special phoswich combination LuAP/LSO or LuYAP/LSO. This combination of scintillators is especially interesting since LuAP and LuYAP have emission in the excitation band of LSO, which may have an impact on the timing resolution of the detector. As will be shown in this paper, the phoswich concept based on these two scintillators can be utilized, however, with some limitations. This paper is an extension of our previous phoswich investigation [3].

Keywords
Phoswich detectors, positron emission tomography (PET), scintillators
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:su:diva-88675 (URN)10.1109/TNS.2012.2233217 (DOI)000314972900024 ()2-s2.0-84873653484 (Scopus ID)
Note

AuthorCount:6;

Available from: 2013-03-26 Created: 2013-03-25 Last updated: 2022-10-07Bibliographically approved
Watson, C. C., Eriksson, L. & Kolb, A. (2013). Physics and applications of positron beams in an integrated PET/MR. Physics in Medicine and Biology, 58(3), l1-L12
Open this publication in new window or tab >>Physics and applications of positron beams in an integrated PET/MR
2013 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 58, no 3, p. l1-L12Article in journal (Refereed) Published
Abstract [en]

In PET/MR systems having the PET component within the uniform magnetic field interior to the MR, positron beams can be injected into the PET field of view (FOV) from unshielded emission sources external to it, as a consequence of the action of the Lorentz force on the transverse components of the positron's velocity. Such beams may be as small as a few millimeters in diameter, but extend 50 cm or more axially without appreciable divergence. Larger beams form 'phantoms' of annihilations in air that can be easily imaged, and that are essentially free of gamma-ray attenuation and scatter effects, providing a unique tool for characterizing PET systems and reconstruction algorithms. Thin targets intersecting these beams can produce intense annihilation sources having the thickness of a sheet of paper, which are very useful for high resolution measurements, and difficult to achieve with conventional sources. Targeted beams can provide other point, line and surface sources for various applications, all without the need to have radioactivity within the FOV. In this paper we discuss the physical characteristics of positron beams in air and present examples of their applications.

National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:su:diva-88273 (URN)10.1088/0031-9155/58/3/L1 (DOI)000313564200001 ()23295197 (PubMedID)2-s2.0-84872723047 (Scopus ID)
Note

AuthorCount:3;

Available from: 2013-03-13 Created: 2013-03-12 Last updated: 2022-10-07Bibliographically approved
Eriksson, L., Melcher, C. L., Zhuravleva, M., Eriksson, M., Rothfuss, H. & Conti, M. (2011). Phoswich solutions for the PET DOI problem. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 648, S288-S292
Open this publication in new window or tab >>Phoswich solutions for the PET DOI problem
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2011 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 648, p. S288-S292Article in journal (Refereed) Published
Abstract [en]

A high spatial resolution in PET can be achieved by using small detector elements. To maintain good sensitivity these elements have to be quite long, thus introducing parallax error and making the spatial resolution non-uniform over the image volume. Uniformity of spatial resolution can be improved by utilizing depth-of-interaction (DOI) information to reduce the parallax error. In the present study we have focused on phoswich approaches based on interacting scintillators, that is, a phoswich combination in which one scintillator emits light in the excitation band of the other. We have looked at LaBr3:Ce and LaCl3:Ce and the interactions of those two scintillators with LSO:Ce, GSO:Ce and YSO:Ce. The reasons to use the two Lanthanum scintillators are twofold: light output is high and the two different emission wavelengths, 350 nm (LaCl3:Ce) and 380 nm (LaBr3:Ce) may produce different interactions with the three oxyorthosilicate scintillators. In addition a possible DOI detector comprising LuAG:Pr pixels with a thin LSO:Ce layer at one end has been evaluated. A Bollinger-Thomas set-up was used to measure luminescence rise and luminescence decay time characteristics in all cases. When using LaCl3:Ce, the phoswich combinations with YSO:Ce and GSO:Ce showed phoswich decay time characteristics as expected for a simple convolution of the decay times of the two phoswich components. A correction was needed, however, for the LaCl3:Ce-LSO:Ce phoswich due to the LSO:Ce intrinsic activity. For the LaBr3:Ce-LSO:Ce phoswich, corrections were needed for noninteracting LaBr3:Ce light in addition to the expected phoswich interaction.

Keywords
High resolution PET, Phoswich detectors, Lutetium oxyorthosilicate LSO, Gadolinium oxyorthosilicate GSO, Yttrium oxyorthosilicate YSO, Lanthanum Bromide LaBr3, Lanthanum chloride LaCl3, Scintillator interactions
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-79698 (URN)10.1016/j.nima.2010.11.049 (DOI)000305376900071 ()
Note

AuthorCount:6;

Available from: 2012-09-14 Created: 2012-09-11 Last updated: 2022-03-15Bibliographically approved
Eriksson, L., Conti, M., Melcher, C. L., Townsend, D. W., Eriksson, M., Rothfuss, H., . . . Bendriem, B. (2011). Towards Sub-Minute PET Examination Times. IEEE Transactions on Nuclear Science, 58(1), 76-81
Open this publication in new window or tab >>Towards Sub-Minute PET Examination Times
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2011 (English)In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 58, no 1, p. 76-81Article in journal (Refereed) Published
Abstract [en]

The main performance parameters in positron camera system design are sensitivity and spatial resolution. This paper concerns sensitivity, which is a function of the scintillation material, the solid angle subtended by the detector array, and the scintillator packing fraction. The solid angle can be increased by extending the axial extent of cylindrical detector systems. Most commercial positron camera systems are based on rings of detector blocks with lutetium oxyorthosilicate, LSO:Ce or LYSO:Ce, as the scintillator of choice. By adding more rings, the solid angle and thus the absolute sensitivity increases while the singles detection efficiency remains fairly constant assuming the same crystal thickness. It has been shown that Ca co-doping of LSO:Ce reduces the scintillation decay time to similar to 30 ns with a light output over 30000 ph/MeV. This improvement may give a time-of-flight (TOF) advantage with time resolution of 500 ps or less. If the count rate sensitivity of a large axial field-of-view (AFOV) system is combined with the TOF sensitivity increase, we have the means to create examination times in the sub-minute range with no compromise in image quality. In the present study we have compared the existing Siemens molecular CT (mCT) systems to future 6, 8, 12, 20 and higher block ring systems with and without TOF. The mCT 4 block ring system has been used as a reference. The time for acceptable image quality with this system is then extrapolated to other systems based on planar sensitivity. However, the planar sensitivity is related to the solid angle, and reaches saturation for large AFOVs. This implies that there is an upper count rate sensitivity limit. A 20 block ring system may cover a 70 cm examination range at a certain planar count rate and could provide acceptable quality images in approximately 10 seconds by combining the high planar sensitivity count rate provided by the multi-ring feature, the high stopping power of LSO and the TOF gain due to the improved timing resolution. The increased sensitivity may be used to reduce patient dose.

Keywords
Molecular imaging, positron emission tomography (PET), time-of-flight imaging (TOF)
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-67509 (URN)10.1109/TNS.2010.2096542 (DOI)000287086900010 ()
Note
authorCount :8Available from: 2011-12-29 Created: 2011-12-28 Last updated: 2022-02-24Bibliographically approved
Bauer, F., Aykac, M., Eriksson, L. & Schmand, M. (2010). Depth of interaction with a 3-dimensional checkerboard arrangement LSO-LSO block. IEEE Transactions on Nuclear Science, 57(3), 971-975
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, p. 971-975Article 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

Keywords
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: 2022-02-25Bibliographically approved
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