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Author |
Gillam, J.E.; Solevi, P.; Oliver, J.F.; Casella, C.; Heller, M.; Joram, C.; Rafecas, M. |
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Title |
Sensitivity recovery for the AX-PET prototype using inter-crystal scattering events |
Type |
Journal Article |
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Year |
2014 |
Publication |
Physics in Medicine and Biology |
Abbreviated Journal |
Phys. Med. Biol. |
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Volume |
59 |
Issue |
15 |
Pages |
4065-4083 |
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Keywords |
positron emission tomography (PET); inter-crystal scattering; sensitivity |
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Abstract |
The development of novel detection devices and systems such as the AX-positron emission tomography (PET) demonstrator often introduce or increase the measurement of atypical coincidence events such as inter-crystal scattering (ICS). In more standard systems, ICS events often go undetected and the small measured fraction may be ignored. As the measured quantity of such events in the data increases, so too does the importance of considering them during image reconstruction. Generally, treatment of ICS events will attempt to determine which of the possible candidate lines of response (LoRs) correctly determine the annihilation photon trajectory. However, methods of assessment often have low success rates or are computationally demanding. In this investigation alternative approaches are considered. Experimental data was taken using the AX-PET prototype and a NEMA phantom. Three methods of ICS treatment were assessed-each of which considered all possible candidate LoRs during image reconstruction. Maximum likelihood expectation maximization was used in conjunction with both standard (line-like) and novel (V-like in this investigation) detection responses modeled within the system matrix. The investigation assumed that no information other than interaction locations was available to distinguish between candidates, yet the methods assessed all provided means by which such information could be included. In all cases it was shown that the signal to noise ratio is increased using ICS events. However, only one method, which used full modeling of the ICS response in the system matrix-the V-like model-provided enhancement in all figures of merit assessed in this investigation. Finally, the optimal method of ICS incorporation was demonstrated using data from two small animals measured using the AX-PET demonstrator. |
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Address |
[Gillam, John E.; Solevi, Paola; Oliver, Josep F.; Rafecas, Magdalena] Univ Valencia, CSIC, IFIC, Valencia, Spain, Email: john.gillam@sydney.edu.au |
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Iop Publishing Ltd |
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English |
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ISSN |
0031-9155 |
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Conference |
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Notes |
WOS:000340056800006 |
Approved |
no |
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Is ISI |
yes |
International Collaboration  |
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Call Number |
IFIC @ pastor @ |
Serial |
1879 |
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Author |
Oliver, J.F.; Rafecas, M. |
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Title |
Improving the singles rate method for modeling accidental coincidences in high-resolution PET |
Type |
Journal Article |
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Year |
2010 |
Publication |
Physics in Medicine and Biology |
Abbreviated Journal |
Phys. Med. Biol. |
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Volume |
55 |
Issue |
22 |
Pages |
6951-6971 |
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Keywords |
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Abstract |
Random coincidences ('randoms') are one of the main sources of image degradation in PET imaging. In order to correct for this effect, an accurate method to estimate the contribution of random events is necessary. This aspect becomes especially relevant for high-resolution PET scanners where the highest image quality is sought and accurate quantitative analysis is undertaken. One common approach to estimate randoms is the so-called singles rate method (SR) widely used because of its good statistical properties. SR is based on the measurement of the singles rate in each detector element. However, recent studies suggest that SR systematically overestimates the correct random rate. This overestimation can be particularly marked for low energy thresholds, below 250 keV used in some applications and could entail a significant image degradation. In this work, we investigate the performance of SR as a function of the activity, geometry of the source and energy acceptance window used. We also investigate the performance of an alternative method, which we call 'singles trues' (ST) that improves SR by properly modeling the presence of true coincidences in the sample. Nevertheless, in any real data acquisition the knowledge of which singles are members of a true coincidence is lost. Therefore, we propose an iterative method, STi, that provides an estimation based on ST but which only requires the knowledge of measurable quantities: prompts and singles. Due to inter-crystal scatter, for wide energy windows ST only partially corrects SR overestimations. While SR deviations are in the range 86-300% (depending on the source geometry), the ST deviations are systematically smaller and contained in the range 4-60%. STi fails to reproduce the ST results, although for not too high activities the deviation with respect to ST is only a few percent. For conventional energy windows, i.e. those without inter-crystal scatter, the ST method corrects the SR overestimations, and deviations from the true random rate are of the order of 1% or less. In addition, in the case of conventional energy window STi results reproduce ST results and therefore the former can be used to obtain the true random rate. |
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Address |
[Oliver, Josep F.; Rafecas, Magdalena] Univ Valencia, CSIC, Inst Fis Corpuscular, IFIC, E-46003 Valencia, Spain, Email: josep.f.oliver@uv.es |
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Iop Publishing Ltd |
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English |
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ISSN |
0031-9155 |
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Expedition |
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Conference |
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Notes |
ISI:000283789700025 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
no |
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Call Number |
IFIC @ elepoucu @ |
Serial |
344 |
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Author |
Aguiar, P.; Rafecas, M.; Ortuño, J.E.; Kontaxakis, G.; Santos, A.; Pavia, J.; Rosetti, M. |
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Title |
Geometrical and Monte Carlo projectors in 3D PET reconstruction |
Type |
Journal Article |
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Year |
2010 |
Publication |
Medical Physics |
Abbreviated Journal |
Med. Phys. |
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Volume |
37 |
Issue |
11 |
Pages |
5691-5702 |
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Keywords |
3D PET; iterative reconstruction; list-mode reconstruction; ray-tracing techniques; Monte Carlo simulation; system response matrix |
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Abstract |
Purpose: In the present work, the authors compare geometrical and Monte Carlo projectors in detail. The geometrical projectors considered were the conventional geometrical Siddon ray-tracer (S-RT) and the orthogonal distance-based ray-tracer (OD-RT), based on computing the orthogonal distance from the center of image voxel to the line-of-response. A comparison of these geometrical projectors was performed using different point spread function (PSF) models. The Monte Carlo-based method under consideration involves an extensive model of the system response matrix based on Monte Carlo simulations and is computed off-line and stored on disk. Methods: Comparisons were performed using simulated and experimental data of the commercial small animal PET scanner rPET. Results: The results demonstrate that the orthogonal distance-based ray-tracer and Siddon ray-tracer using PSF image-space convolutions yield better images in terms of contrast and spatial resolution than those obtained after using the conventional method and the multiray-based S-RT. Furthermore, the Monte Carlo-based method yields slight improvements in terms of contrast and spatial resolution with respect to these geometrical projectors. Conclusions: The orthogonal distance-based ray-tracer and Siddon ray-tracer using PSF image-space convolutions represent satisfactory alternatives to factorizing the system matrix or to the conventional on-the-fly ray-tracing methods for list-mode reconstruction, where an extensive modeling based on Monte Carlo simulations is unfeasible. |
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Address |
[Aguiar, Pablo] Univ Santiago de Compostela, Dept Fis Particulas, Complexo Hosp Univ Santiago de Compostela, Fdn IDICHUS IDIS, Santiago De Compostela, Spain, Email: pablo.aguiar.fernandez@sergas.es |
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Amer Assoc Physicists Medicine Amer Inst Physics |
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English |
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Edition |
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ISSN |
0094-2405 |
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Conference |
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Notes |
ISI:000283747600015 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
no |
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Call Number |
IFIC @ elepoucu @ |
Serial |
338 |
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| Permanent link to this record |
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Author |
Cabello, J.; Rafecas, M. |
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Title |
Comparison of basis functions for 3D PET reconstruction using a Monte Carlo system matrix |
Type |
Journal Article |
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Year |
2012 |
Publication |
Physics in Medicine and Biology |
Abbreviated Journal |
Phys. Med. Biol. |
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Volume |
57 |
Issue |
7 |
Pages |
1759-1777 |
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Keywords |
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Abstract |
In emission tomography, iterative statistical methods are accepted as the reconstruction algorithms that achieve the best image quality. The accuracy of these methods relies partly on the quality of the system response matrix (SRM) that characterizes the scanner. The more physical phenomena included in the SRM, the higher the SRM quality, and therefore higher image quality is obtained from the reconstruction process. High-resolution small animal scanners contain as many as 10(3)-10(4) small crystal pairs, while the field of view (FOV) is divided into hundreds of thousands of small voxels. These two characteristics have a significant impact on the number of elements to be calculated in the SRM. Monte Carlo (MC) methods have gained popularity as a way of calculating the SRM, due to the increased accuracy achievable, at the cost of introducing some statistical noise and long simulation times. In the work presented here the SRM is calculated using MC methods exploiting the cylindrical symmetries of the scanner, significantly reducing the simulation time necessary to calculate a high statistical quality SRM and the storage space necessary. The use of cylindrical symmetries makes polar voxels a convenient basis function. Alternatively, spherically symmetric basis functions result in improved noise properties compared to cubic and polar basis functions. The quality of reconstructed images using polar voxels, spherically symmetric basis functions on a polar grid, cubic voxels and post-reconstruction filtered polar and cubic voxels is compared from a noise and spatial resolution perspective. This study demonstrates that polar voxels perform as well as cubic voxels, reducing the simulation time necessary to calculate the SRM and the disk space necessary to store it. Results showed that spherically symmetric functions outperform polar and cubic basis functions in terms of noise properties, at the cost of slightly degraded spatial resolution, larger SRM file size and longer reconstruction times. However, we demonstrate that post-reconstruction smoothing, usually applied in emission imaging to reduce the level of noise, can produce a spatial resolution degradation of similar to 50%, while spherically symmetric basis functions produce a degradation of only similar to 6%, compared to polar and cubic voxels, at the same noise level. Therefore, the image quality trade-off obtained with blobs is higher than that obtained with cubic or polar voxels. |
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Address |
[Cabello, Jorge; Rafecas, Magdalena] Univ Valencia, Inst Fis Corpuscular, CSIC, Valencia, Spain, Email: jorge.cabello@ific.uv.es |
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Publisher |
Iop Publishing Ltd |
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English |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
0031-9155 |
ISBN |
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Expedition |
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Conference |
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Notes |
WOS:000302121000004 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
no |
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Call Number |
IFIC @ pastor @ |
Serial |
955 |
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| Permanent link to this record |
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Author |
Gillam, J.E.; Solevi, P.; Oliver, J.F.; Rafecas, M. |
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Title |
Simulated one-pass list-mode: an approach to on-the-fly system matrix calculation |
Type |
Journal Article |
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Year |
2013 |
Publication |
Physics in Medicine and Biology |
Abbreviated Journal |
Phys. Med. Biol. |
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Volume |
58 |
Issue |
7 |
Pages |
2377-2394 |
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Keywords |
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Abstract |
In the development of prototype systems for positron emission tomography a valid and robust image reconstruction algorithm is required. However, prototypes often employ novel detector and system geometries which may change rapidly under optimization. In addition, developing systems generally produce highly granular, or possibly continuous detection domains which require some level of on-the-fly calculation for retention of measurement precision. In this investigation a new method of on-the-fly system matrix calculation is proposed that provides advantages in application to such list-mode systems in terms of flexibility in system modeling. The new method is easily adaptable to complicated system geometries and available computational resources. Detection uncertainty models are used as random number generators to produce ensembles of possible photon trajectories at image reconstruction time for each datum in the measurement list. However, the result of this approach is that the system matrix elements change at each iteration in a non-repetitive manner. The resulting algorithm is considered the simulation of a one-pass list (SOPL) which is generated and the list traversed during image reconstruction. SOPL alters the system matrix in use at each iteration and so behavior within the maximum likelihood-expectation maximization algorithm was investigated. A two-pixel system and a small two dimensional imaging model are used to illustrate the process and quantify aspects of the algorithm. The two-dimensional imaging system showed that, while incurring a penalty in image resolution, in comparison to a non-random equal-computation counterpart, SOPL provides much enhanced noise properties. In addition, enhancement in system matrix quality is straightforward (by increasing the number of samples in the ensemble) so that the resolution penalty can be recovered when desired while retaining improvement in noise properties. Finally the approach is tested and validated against a standard (highly accurate) system matrix using experimental data from a prototype system-the AX-PET. |
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Address |
[Gillam, J. E.; Solevi, P.; Oliver, J. F.; Rafecas, M.] Univ Valencia, CSIC, IFIC, Inst Fis Corpuscular, Valencia, Spain, Email: john.gillam@ific.uv.es |
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Publisher |
Iop Publishing Ltd |
Place of Publication |
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English |
Summary Language |
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Original Title |
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Series Volume |
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Edition |
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ISSN |
0031-9155 |
ISBN |
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Expedition |
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Conference |
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Notes |
WOS:000316181300024 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
no |
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Call Number |
IFIC @ pastor @ |
Serial |
1370 |
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| Permanent link to this record |
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Author |
Llosa, G.; Trovato, M.; Barrio, J.; Etxebeste, A.; Muñoz, E.; Lacasta, C.; Oliver, J.F.; Rafecas, M.; Solaz, C.; Solevi, P. |
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Title |
First Images of a Three-layer compton Telescope prototype for Treatment Monitoring in hadron Therapy |
Type |
Journal Article |
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Year |
2016 |
Publication |
Frontiers in Oncology |
Abbreviated Journal |
Front. Oncol. |
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Volume |
6 |
Issue |
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Pages |
14 - 6pp |
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Keywords |
Compton camera; Compton telescope; hadron therapy; treatment monitoring; LaBr3 |
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Abstract |
A Compton telescope for dose monitoring in hadron therapy is under development at IFIC. The system consists of three layers of LaBr3 crystals coupled to silicon photomulti-plier arrays. Na-22 sources have been successfully imaged reconstructing the data with an ML-EM code. Calibration and temperature stabilization are necessary for the prototype operation at low coincidence rates. A spatial resolution of 7.8 mm FWHM has been obtained in the first imaging tests. |
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Address |
[Llosa, Gabriela; Trovato, Marco; Barrio, John; Etxebeste, Ane; Munoz, Enrique; Lacasta, Carlos; Oliver, Josep F.; Rafecas, Magdalena; Solaz, Carles; Solevi, Paola] Inst Fis Corpuscular IFIC CSIC UVEG, Valencia, Spain, Email: gabriela.llosa@ific.uv.es |
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Publisher |
Frontiers Media Sa |
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English |
Summary Language |
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Edition |
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ISSN |
2234-943x |
ISBN |
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Expedition |
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Conference |
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Notes |
WOS:000369799800001 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
no |
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Call Number |
IFIC @ elepoucu @ |
Serial |
2785 |
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Author |
Blume, M.; Martinez-Moller, A.; Keil, A.; Navab, N.; Rafecas, M. |
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Title |
Joint Reconstruction of Image and Motion in Gated Positron Emission Tomography |
Type |
Journal Article |
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Year |
2010 |
Publication |
IEEE Transactions on Medical Imaging |
Abbreviated Journal |
IEEE Trans. Med. Imaging |
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Volume |
29 |
Issue |
11 |
Pages |
1892-1906 |
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Keywords |
Gating; motion compensation; positron emission tomography (PET); reconstruction |
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Abstract |
We present a novel intrinsic method for joint reconstruction of both image and motion in positron emission tomography (PET). Intrinsic motion compensation methods exclusively work on the measured data, without any external motion measurements. Most of these methods separate image from motion estimation: They use deformable image registration/optical flow techniques in order to estimate the motion from individually reconstructed gates. Then, the image is estimated based on this motion information. With these methods, a main problem lies in the motion estimation step, which is based on the noisy gated frames. The more noise is present, the more inaccurate the image registration becomes. As we show both visually and quantitatively, joint reconstruction using a simple deformation field motion model can compete with state-of-the-art image registration methods which use robust multilevel B-spline motion models. |
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Address |
[Blume, Moritz; Rafecas, Magdalena] Univ Valencia, CSIC, IFIC, E-46071 Valencia, Spain, Email: moritz.blume@cs.tum.edu |
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Publisher |
Ieee-Inst Electrical Electronics Engineers Inc |
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Language |
English |
Summary Language |
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Original Title |
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Edition |
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ISSN |
0278-0062 |
ISBN |
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Conference |
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Notes |
ISI:000283941800007 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ elepoucu @ |
Serial |
340 |
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| Permanent link to this record |
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Author |
Llosa, G.; Barrio, J.; Cabello, J.; Crespo, A.; Lacasta, C.; Rafecas, M.; Callier, S.; de la Taille, C.; Raux, L. |
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Title |
Detector characterization and first coincidence tests of a Compton telescope based on LaBr3 crystals and SiPMs |
Type |
Journal Article |
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Year |
2012 |
Publication |
Nuclear Instruments & Methods in Physics Research A |
Abbreviated Journal |
Nucl. Instrum. Methods Phys. Res. A |
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Volume |
695 |
Issue |
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Pages |
105-108 |
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Keywords |
Hadron therapy; Compton imaging; LaBr3; Continuous crystal; SiPM; MPPC; G-APD |
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Abstract |
A Compton telescope for dose monitoring in hadron therapy consisting of several layers of continuous LaBr3 crystals coupled to silicon photomultiplier (SiPM) arrays is under development within the ENVISION project. In order to test the possibility of employing such detectors for the telescope, a detector head consisting of a continuous 16 mm x 18 mm x 5 mm LaBr3 crystal coupled to a SiPM array has been assembled and characterized, employing the SPIROC1 ASIC as readout electronics. The best energy resolution obtained at 511 key is 6.5% FWHM and the timing resolution is 3.1 ns FWHM. A position determination method for continuous crystals is being tested, with promising results. In addition, the detector has been operated in time coincidence with a second detector layer, to determine the coincidence capabilities of the system. The first tests are satisfactory, and encourage the development of larger detectors that will compose the telescope prototype. |
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Address |
[Llosa, G.; Barrio, J.; Cabello, J.; Crespo, A.; Lacasta, C.; Rafecas, M.] UVEG, CSIC, IFIC, Inst Fis Corpuscular, Valencia, Spain, Email: gabriela.llosa@ific.uv.es |
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Publisher |
Elsevier Science Bv |
Place of Publication |
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Language |
English |
Summary Language |
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Original Title |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
0168-9002 |
ISBN |
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Medium |
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Area |
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Expedition |
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Conference |
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Notes |
WOS:000311469900020 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
1235 |
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Author |
Beltrame, P. et al; Oliver, J.F.; Rafecas, M.; Solevi, P. |
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Title |
The AX-PET demonstrator-Design, construction and characterization |
Type |
Journal Article |
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Year |
2011 |
Publication |
Nuclear Instruments & Methods in Physics Research A |
Abbreviated Journal |
Nucl. Instrum. Methods Phys. Res. A |
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Volume |
654 |
Issue |
1 |
Pages |
546-559 |
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Keywords |
PET; Axial geometry; Geiger-mode Avalanche Photo Diodes (G-APD); SiPM |
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Abstract |
Axial PET is a novel geometrical concept for Positron Emission Tomography (PET), based on layers of long scintillating crystals axially aligned with the bore axis. The axial coordinate is obtained from arrays of wavelength shifting (WLS) plastic strips placed orthogonally to the crystals. This article describes the design, construction and performance evaluation of a demonstrator set-up which consists of two identical detector modules, used in coincidence. Each module comprises 48 LYSO crystals of 100 mm length and 156 WLS strips. Crystals and strips are readout by Geiger-mode Avalanche Photo Diodes (G-APDs). The signals from the two modules are processed by fully analog front-end electronics and recorded in coincidence by a VME-based data acquisition system. Measurements with point-like (22)Na sources, with the modules used both individually and in coincidence mode, allowed for a complete performance evaluation up to the focal plane reconstruction of point sources. The results obtained are in good agreement with expectations and proved the set-up to be ready for the next evaluation phase with PET phantoms filled with radiotracers. |
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Address |
[Casella, C; Dissertori, G; Djambazov, L; Lustermann, W; Nessi-Tedaldi, F; Pauss, F; Renker, D; Schinzel, D] ETH, Inst Particle Phys, CH-8093 Zurich, Switzerland, Email: Chiara.Casella@cern.ch |
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Publisher |
Elsevier Science Bv |
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English |
Summary Language |
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Original Title |
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Series Editor |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
0168-9002 |
ISBN |
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Medium |
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Area |
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Expedition |
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Conference |
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Notes |
WOS:000295765100078 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
790 |
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Author |
Bolle, E.; Casella, C.; Chesi, E.; De Leo, R.; Dissertori, G.; Fanti, V.; Gillam, J.E.; Heller, M.; Joram, C.; Lustermann, W.; Nappi, E.; Oliver, J.F.; Pauss, F.; Rafecas, M.; Rudge, A.; Ruotsalainen, U.; Schinzel, D.; Schneider, T.; Seguinot, J.; Solevi, P.; Stapnes, S.; Tuna, U.; Weilhammer, P. |
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Title |
AX-PET: A novel PET concept with G-APD readout |
Type |
Journal Article |
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Year |
2012 |
Publication |
Nuclear Instruments & Methods in Physics Research A |
Abbreviated Journal |
Nucl. Instrum. Methods Phys. Res. A |
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Volume |
695 |
Issue |
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Pages |
129-134 |
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Keywords |
PET; Axial geometry; Geiger-mode Avalanche Photo Diodes (G-APD); SiPM |
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Abstract |
The AX-PET collaboration has developed a novel concept for high resolution PET imaging to overcome some of the performance limitations of classical PET cameras, in particular the compromise between spatial resolution and sensitivity introduced by the parallax error. The detector consists of an arrangement of long LYSO scintillating crystals axially oriented around the field of view together with arrays of wave length shifter strips orthogonal to the crystals. This matrix allows a precise 3D measurement of the photon interaction point. This is valid both for photoelectric absorption at 511 key and for Compton scattering down to deposited energies of about 100 keV. Crystals and WLS strips are individually read out using Geiger-mode Avalanche Photo Diodes (G-APDs). The sensitivity of such a detector can be adjusted by changing the number of layers and the resolution is defined by the crystal and strip dimensions. Two AX-PET modules were built and fully characterized in dedicated test set-ups at CERN, with point-like Na-22 sources. Their performance in terms of energy (Renew approximate to 11.8% (FWMH) at 511 key) and spatial resolution was assessed (sigma(axial) approximate to 0.65 mm), both individually and for the two modules in coincidence. Test campaigns at ETH Zurich and at the company AAA allowed the tomographic reconstructions of more complex phantoms validating the 3D reconstruction algorithms. The concept of the AX-PET modules will be presented together with some characterization results. We describe a count rate model which allows to optimize the planing of the tomographic scans. |
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Address |
[Heller, M.; Joram, C.; Schneider, T.; Seguinot, J.] CERN, PH Dept, CH-1211 Geneva, Switzerland, Email: Matthieu.Heller@cern.ch |
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Corporate Author |
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Thesis |
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Publisher |
Elsevier Science Bv |
Place of Publication |
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Editor |
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Language |
English |
Summary Language |
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Original Title |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
0168-9002 |
ISBN |
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Medium |
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Area |
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Expedition |
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Conference |
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Notes |
WOS:000311469900026 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
1236 |
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