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Effect of local TOF Kernel miscalibrations on contrast-noise in TOF PET

Enrico Clementel (UGent), Pieter Mollet (UGent) and Stefaan Vandenberghe (UGent)
Author
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Project
EU FP7 project Sublima (grant agreement 241711)
Abstract
TOF PET imaging requires specific calibrations: accurate characterization of the system timing resolution and timing offset is required to achieve the full potential image quality. Current system models used in image reconstruction assume a spatially uniform timing resolution kernel. Furthermore, although the timing offset errors are often pre-corrected, this correction becomes less accurate with the time since, especially in older scanners, the timing offsets are often calibrated only during the installation, as the procedure is time-consuming. In this study, we investigate and compare the effects of local mismatch of timing resolution when a uniform kernel is applied to systems with local variations in timing resolution and the effects of uncorrected time offset errors on image quality. A ring-like phantom was acquired on a Philips Gemini TF scanner and timing histograms were obtained from coincidence events to measure timing resolution along all sets of LORs crossing the scanner center. In addition, multiple acquisitions of a cylindrical phantom, 20 cm in diameter with spherical inserts, and a point source were simulated. A location-dependent timing resolution was simulated, with a median value of 500 ps and increasingly large local variations, and timing offset errors ranging from 0 to 350 ps were also simulated. Images were reconstructed with TOF MLEM with a uniform kernel corresponding to the effective timing resolution of the data, as well as with purposefully mismatched kernels. To CRC vs noise curves were measured over the simulated cylinder realizations, while the simulated point source was processed to generate timing histograms of the data. Results show that timing resolution is not uniform over the FOV of the considered scanner. The simulated phantom data indicate that CRC is moderately reduced in data sets with locally varying timing resolution reconstructed with a uniform kernel, while still performing better than non-TOF reconstruction. On the other hand, uncorrected offset errors in our setup have a larger potential for decreasing image quality and can lead to a reduction of CRC of up to 15% and an increase in the measured timing resolution kernel up to 40%. However, in realistic conditions in frequently calibrated systems, using a larger effective timing kernel in image reconstruction can compensate uncorrected offset errors.
Keywords
SCANNER, Biomedical image processing, POSITRON-EMISSION-TOMOGRAPHY, image reconstruction, positron emission tomography

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Citation

Please use this url to cite or link to this publication:

Chicago
Clementel, Enrico, Pieter Mollet, and Stefaan Vandenberghe. 2013. “Effect of Local TOF Kernel Miscalibrations on Contrast-noise in TOF PET.” Ieee Transactions on Nuclear Science 60 (3): 1578–1588.
APA
Clementel, E., Mollet, P., & Vandenberghe, S. (2013). Effect of local TOF Kernel miscalibrations on contrast-noise in TOF PET. IEEE TRANSACTIONS ON NUCLEAR SCIENCE, 60(3), 1578–1588.
Vancouver
1.
Clementel E, Mollet P, Vandenberghe S. Effect of local TOF Kernel miscalibrations on contrast-noise in TOF PET. IEEE TRANSACTIONS ON NUCLEAR SCIENCE. 2013;60(3):1578–88.
MLA
Clementel, Enrico, Pieter Mollet, and Stefaan Vandenberghe. “Effect of Local TOF Kernel Miscalibrations on Contrast-noise in TOF PET.” IEEE TRANSACTIONS ON NUCLEAR SCIENCE 60.3 (2013): 1578–1588. Print.
@article{4145131,
  abstract     = {TOF PET imaging requires specific calibrations: accurate characterization of the system timing resolution and timing offset is required to achieve the full potential image quality. Current system models used in image reconstruction assume a spatially uniform timing resolution kernel. Furthermore, although the timing offset errors are often pre-corrected, this correction becomes less accurate with the time since, especially in older scanners, the timing offsets are often calibrated only during the installation, as the procedure is time-consuming. In this study, we investigate and compare the effects of local mismatch of timing resolution when a uniform kernel is applied to systems with local variations in timing resolution and the effects of uncorrected time offset errors on image quality. A ring-like phantom was acquired on a Philips Gemini TF scanner and timing histograms were obtained from coincidence events to measure timing resolution along all sets of LORs crossing the scanner center. In addition, multiple acquisitions of a cylindrical phantom, 20 cm in diameter with spherical inserts, and a point source were simulated. A location-dependent timing resolution was simulated, with a median value of 500 ps and increasingly large local variations, and timing offset errors ranging from 0 to 350 ps were also simulated. Images were reconstructed with TOF MLEM with a uniform kernel corresponding to the effective timing resolution of the data, as well as with purposefully mismatched kernels. To CRC vs noise curves were measured over the simulated cylinder realizations, while the simulated point source was processed to generate timing histograms of the data. Results show that timing resolution is not uniform over the FOV of the considered scanner. The simulated phantom data indicate that CRC is moderately reduced in data sets with locally varying timing resolution reconstructed with a uniform kernel, while still performing better than non-TOF reconstruction. On the other hand, uncorrected offset errors in our setup have a larger potential for decreasing image quality and can lead to a reduction of CRC of up to 15\% and an increase in the measured timing resolution kernel up to 40\%. However, in realistic conditions in frequently calibrated systems, using a larger effective timing kernel in image reconstruction can compensate uncorrected offset errors.},
  author       = {Clementel, Enrico and Mollet, Pieter and Vandenberghe, Stefaan},
  issn         = {0018-9499},
  journal      = {IEEE TRANSACTIONS ON NUCLEAR SCIENCE},
  keyword      = {SCANNER,Biomedical image processing,POSITRON-EMISSION-TOMOGRAPHY,image reconstruction,positron emission tomography},
  language     = {eng},
  number       = {3},
  pages        = {1578--1588},
  title        = {Effect of local TOF Kernel miscalibrations on contrast-noise in TOF PET},
  url          = {http://dx.doi.org/10.1109/TNS.2013.2255134},
  volume       = {60},
  year         = {2013},
}

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