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Z. Hu,
S. Renisch,
B. Schweizer,
T. Blaffert,
N. Ojha, T. Guo,
J. Tang,
C. Tung,
J. Kaste,
V. Schulz,
I. Torres,
L. Shao
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ABSTRACT: Philips has introduced the world's first whole body sequential PET/MR system. We present the current status of MR-based attenuation correction (MRAC) technique. MRAC consists of MR image acquisition, segmentation, truncation compensation (TC), μ-value assignment, as well as correction for patient table and RF coils. These components have been described last year; this paper focuses on updates of the two most critical steps of MRAC: segmentation and TC. The segmentation algorithm attempts to distinguish 3 biological classes: air, lungs, and soft tissue. It combines an intensity-based region-growing technique with lung-model adaptation. For TC, the following three-step approach to correct for truncation in the MR-based attenuation maps has been developed and investigated: (A) Areas in the attenuation map which are possibly truncated are identified. (B) For these areas, an estimate of the outer patient contour is extracted from a registered PET image which is reconstructed without attenuation correction. (C) Truncation correction areas as extracted from the PET contours are added to attenuation map. The segmentation algorithm was applied to a number of datasets from a large pool of volunteers from multiple MR systems. The algorithm yields expected results except for susceptibility and motion artifacts. While the truncation compensation algorithm works for most cases, the robustness needs to be further improved.
Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE; 12/2010
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ABSTRACT: A sequential PET/MR system like Philips Gemini TF PET/MR system generates attenuation correction map from an MR image instead of a CT or transmission image for PET reconstruction. One problem in MR-based attenuation correction is that the MR table and coils are invisible in MR images but they may contain high density materials which have to be compensated for attenuation. This work investigates the attenuation impacts of the Gemini TF PET/MR table and several clinical MR coils to MR-based PET attenuation correction. To compensated the impacts of the MR tables and coils, a template inserting based approach is proposed. Templates of the MR table and coils are generated from transmission scans of the table and coils, which are pre-install on the PET/MR system. For each PET/MR scan, templates are inserted into the attenuation map generated from the MR image at the corresponding location before PET image reconstruction. Phantom studies have shown that with this template based attenuation correction approach, the PET/MR table and coils can be properly compensated for PET attenuation.
Nuclear Science Symposium Conference Record (NSS/MIC), 2009 IEEE; 12/2009
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Z. Hu,
N. Ojha,
S. Renisch,
V. Schulz,
I. Torres,
A. Buhl,
D. Pal,
G. Muswick,
J. Penatzer, T. Guo,
P. Bonert,
C. Tung,
J. Kaste,
M. Morich,
T. Havens,
P. Maniawski,
W. Schafer,
R.W. Gunther,
G.A. Krombach,
L. Shao
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ABSTRACT: In this paper MR-based attenuation method was implemented for a clinical whole-body PET/MR system. While awaiting future clinical evaluation, the algorithm seems promising from preliminary patient data evaluation, from both qualitative PET image quality and quantification accuracy. While the 3-segment MRAC resembles the results from short PET transmission scans, future work will be to implement and validate segmentation of more tissue classes, such as cortical bone. Robustness of MR image truncation compensation and incorporation of flexible coils need to be improved.
Nuclear Science Symposium Conference Record (NSS/MIC), 2009 IEEE; 12/2009
