Automatic, three-segment, MR-based attenuation correction for whole-body PET/MR data

Schulz, Volkmar; Torres-Espallardó, I.; Renisch, Steffen; Hu, Zhiqiang; Ojha, Navdeep; Börnert, Peter; Perkuhn, Michael; Niendorf, Thoralf; Schäfer, Wolfgang; Brockmann, Holger; Krohn, Thomas; Buhl, Alexandra; Günther, Rolf W.; Mottaghy, Felix M.; Krombach, Gabriele A.

doi:10.1007/s00259-010-1603-1

Cited by 277 publications

(226 citation statements)

References 20 publications

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“…Furthermore, this survey MR pulse sequence should ideally also provide data for anatomical MRbased attenuation correction (AC) of PET data equivalent to that provided by CT. Currently, the proposed approaches for MR AC in torso imaging are mainly based on tissue segmentation, pattern recognition techniques, templates or atlases [18][19][20][21][22][23]. Apart from lesions in bone [24] and in the skull [25,26], MR AC based on such techniques has been shown to yield comparable results to CT AC of PET data.…”

Section: Introductionmentioning

confidence: 93%

Discrimination and anatomical mapping of PET-positive lesions: comparison of CT attenuation-corrected PET images with coregistered MR and CT images in the abdomen

Kuhn

Crook

Mader

et al. 2012

Eur J Nucl Med Mol Imaging

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Purpose PET/MR has the potential to become a powerful tool in clinical oncological imaging. The purpose of this prospective study was to evaluate the performance of a single T1-weighted (T1w) fat-suppressed unenhanced MR pulse sequence of the abdomen in comparison with unenhanced low-dose CT images to characterize PET-positive lesions. Methods A total of 100 oncological patients underwent sequential whole-body 18 F-FDG PET with CT-based attenuation correction (AC), 40 mAs low-dose CT and two-point Dixonbased T1w 3D MRI of the abdomen in a trimodality PET/CT-MR system. PET-positive lesions were assessed by CT and MRI with regard to their anatomical location, conspicuity and additional relevant information for characterization. Results From among 66 patients with at least one PETpositive lesion, 147 lesions were evaluated. No significant difference between MRI and CT was found regarding anatomical lesion localization. The MR pulse sequence used performed significantly better than CT regarding conspicuity of liver lesions (p<0.001, Wilcoxon signed ranks test), whereas no difference was noted for extrahepatic lesions. For overall lesion characterization, MRI was considered superior to CT in 40 % of lesions, equal to CT in 49 %, and inferior to CT in 11 %. Conclusion Fast Dixon-based T1w MRI outperformed lowdose CT in terms of conspicuity and characterization of PET-positive liver lesions and performed similarly in extrahepatic tumour manifestations. Hence, under the assumption that the technical issue of MR AC for whole-body PET examinations is solved, in abdominal PET/MR imaging the replacement of low-dose CT by a single Dixon-based MR pulse sequence for anatomical lesion correlation appears to be valid and robust.

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Section: Introductionmentioning

confidence: 93%

Discrimination and anatomical mapping of PET-positive lesions: comparison of CT attenuation-corrected PET images with coregistered MR and CT images in the abdomen

Kuhn

Crook

Mader

et al. 2012

Eur J Nucl Med Mol Imaging

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“…PET/MR is, however, limited by the lack of a direct measurement of photon attenuation to be used for attenuation correction (AC), which CT provides. Commercial PET/MR systems today segment the MR images into three classes (air, lung, and soft tissue) (Schulz et al 2011), or four classes (air, lung, fat, and soft tissue) (Martinez-Möller et al 2009) for MR-AC. Neither segmentation method accounts for bone, effectively assigning the linear attenuation coefficient (LAC) of soft tissue to bony areas.…”

Section: Introductionmentioning

confidence: 99%

Region specific optimization of continuous linear attenuation coefficients based on UTE (RESOLUTE): application to PET/MR brain imaging

et al. 2015

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The reconstruction of PET brain data in a PET/MR hybrid scanner is challenging in the absence of transmission sources, where MR images are used for MR-based attenuation correction (MR-AC). The main challenge of MR-AC is to separate bone and air, as neither have a signal in traditional MR images, and to assign the correct linear attenuation coefficient to bone. The ultra-short echo time (UTE) MR sequence was proposed as a basis for MR-AC as this sequence shows a small signal in bone. The purpose of this study was to develop a new clinically feasible MR-AC method with patient specific continuous-valued linear attenuation coefficients in bone that provides accurate reconstructed PET image data.A total of 164 [ 18 F]FDG PET/MR patients were included in this study, of which 10 were used for training. MR-AC was based on either standard CT (reference), UTE or our method (RESOLUTE). The reconstructed PET images were evaluated in the whole brain, as well as regionally in the brain using a ROI-based analysis. Our method segments air, brain, cerebral spinal fluid, and soft tissue voxels on the unprocessed UTE TE images, and uses a mapping of R * 2 values to CT Hounsfield Units (HU) to measure the density in bone voxels.

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“…Using the PET/CT datasets of 35 patients, Martinez-Möller et al reported an average SUV error of 8.0% 6 3.3% in 21 bone lesions and less than 5% in all other lesions (5). Schulz et al reported, using 15 whole-body PET/CT/MR patient scans, an average error of 6.5% 6 4.1% in 7 bone lesions and a maximum error of 213.4% in a pelvic bone lesion (14). Ouyang et al demonstrated that if the bones can be identified in MR images to produce a 5-class MRAC map, SUV errors in all bones are reduced to less than 10% (10).…”

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confidence: 99%

Impact of Time-of-Flight PET on Quantification Errors in MR Imaging–Based Attenuation Correction

Mehranian

Zaidi

2015

J Nucl Med

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Time-of-flight (TOF) PET/MR imaging is an emerging imaging technology with great capabilities offered by TOF to improve image quality and lesion detectability. We assessed, for the first time, the impact of TOF image reconstruction on PET quantification errors induced by MR imaging-based attenuation correction (MRAC) using simulation and clinical PET/CT studies. Methods: Standard 4-class attenuation maps were derived by segmentation of CT images of 27 patients undergoing PET/CT examinations into background air, lung, soft-tissue, and fat tissue classes, followed by the assignment of predefined attenuation coefficients to each class. For each patient, 4 PET images were reconstructed: non-TOF and TOF both corrected for attenuation using reference CT-based attenuation correction and the resulting 4-class MRAC maps. The relative errors between non-TOF and TOF MRAC reconstructions were compared with their reference CT-based attenuation correction reconstructions. The bias was locally and globally evaluated using volumes of interest (VOIs) defined on lesions and normal tissues and CT-derived tissue classes containing all voxels in a given tissue, respectively. The impact of TOF on reducing the errors induced by metal-susceptibility and respiratory-phase mismatch artifacts was also evaluated using clinical and simulation studies. Results: Our results show that TOF PET can remarkably reduce attenuation correction artifacts and quantification errors in the lungs and bone tissues. Using classwise analysis, it was found that the non-TOF MRAC method results in an error of -3.4% ± 11.5% in the lungs and -21.8% ± 2.9% in bones, whereas its TOF counterpart reduced the errors to -2.9% ± 7.1% and -15.3% ± 2.3%, respectively. The VOI-based analysis revealed that the non-TOF and TOF methods resulted in an average overestimation of 7.5% and 3.9% in or near lung lesions (n 5 23) and underestimation of less than 5% for soft tissue and in or near bone lesions (n 5 91). Simulation results showed that as TOF resolution improves, artifacts and quantification errors are substantially reduced. Conclusion: TOF PET substantially reduces artifacts and improves significantly the quantitative accuracy of standard MRAC methods. Therefore, MRAC should be less of a concern on future TOF PET/MR scanners with improved timing resolution. Hybr id PET/MR imaging has recently emerged as a new modality enabling simultaneous molecular and morphologic assessment of a variety of physiopathologic conditions (1). Over the last 2 decades, PET/MR technology has experienced considerable technical advances toward addressing the challenges encountered in system design and quantitative performance. With the advent of avalanche photodiodes and silicon photomultipliers, the challenge of mutual compatibility between PET and MR subsystems has now been well addressed, thus paving the way toward fully integrated time-of-flight (TOF) PET/MR systems (2). However, accurate PET quantification using MR imaging-based attenuation correction (MRAC) remains a major challenge (3)....

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Automatic, three-segment, MR-based attenuation correction for whole-body PET/MR data

Abstract: Our MR-based attenuation correction method offers similar correction accuracy as offered by segmented CT. According to the specialists involved in the blind study, these differences do not affect the diagnostic value of the PET images.

Cited by 277 publications

References 20 publications

Discrimination and anatomical mapping of PET-positive lesions: comparison of CT attenuation-corrected PET images with coregistered MR and CT images in the abdomen

Discrimination and anatomical mapping of PET-positive lesions: comparison of CT attenuation-corrected PET images with coregistered MR and CT images in the abdomen

Region specific optimization of continuous linear attenuation coefficients based on UTE (RESOLUTE): application to PET/MR brain imaging

Impact of Time-of-Flight PET on Quantification Errors in MR Imaging–Based Attenuation Correction

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