Image artifacts from MR-based attenuation correction in clinical, whole-body PET/MRI

Keller, Sune H.; Holm, Søren; Hansen, Adam E.; Sattler, Bernhard; Andersen, Flemming; Klausen, Thomas Levin; Højgaard, Liselotte; Kjær, Andreas; Beyer, Thomas

doi:10.1007/s10334-012-0345-4

Cited by 117 publications

(107 citation statements)

References 21 publications

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“…This is especially behind the frontal sinus and in the skull base (Keller et al 2013, Dickson et al 2014. In the averaged %-difference images we see how the 8-15% error behind the sinuses and 5-8% error in the cerebellum near the skull base, when using the UTE technique, is significantly reduced when using our method (figures 6 and 9).…”

Section: Discussionmentioning

confidence: 76%

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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Section: Discussionmentioning

confidence: 76%

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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“…Three artifact types were subdivided into two subcategories; susceptibility artifacts: patients with sternotomy (STN) and patients with stents and other metallic artifacts (SMA), tissue inversion artifacts (TI): artifacts caused by inversions of lung and soft tissue (LSTI) as well as of soft and fat tissues (FSTI), respiratory misalignment artifacts: photopenic type artifacts observed at the diaphragm (PMA) and misalignment artifacts of the MR-AC maps and the emission data (Table 2, Figure 2). 25,26 Respiratory misalignment of PET-emission data and AC maps. MR-AC maps and nonAC-PET images were evaluated for spatial misalignment artifacts through visual inspection using the 3D application integrated into the working suite on the PET/MR console.…”

Section: Pet/mr Imagingmentioning

confidence: 99%

Assessment of attenuation correction for myocardial PET imaging using combined PET/MRI

Lassen

Rasul

Beitzke

et al. 2019

Journal of Nuclear Cardiology

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Objective. To evaluate the frequency of artifacts in MR-based attenuation correction (AC) maps and their impact on the quantitative accuracy of PET-based flow and metabolism measurements in a cohort of consecutive heart failure patients undergoing combined PET/MR imaging.Methods. Myocardial viability studies were performed in 20 patients following a dualtracer protocol involving the assessment of myocardial perfusion ( 13 N-NH 3 : 813 ± 86 MBq) and metabolism ( 18 F-FDG: 335 ± 38 MBq). All acquisitions were performed using a fully-integrated PET/MR system, with standard DIXON-attenuation correction (DIXON-AC) mapping for each PET scan. All AC maps were examined for spatial misalignment with the emission data, total lung volume, susceptibility artifacts, and tissue inversion (TI). Misalignment and susceptibility artifacts were corrected using rigid co-registration and retrospective filling of the susceptibility-induced gaps, respectively. The effects of the AC artifacts were evaluated by relative difference measures and perceived changes in clinical interpretations.Results. Average respiratory misalignment of (7 ± 4) mm of the PET-emission data and the AC maps was observed in 18 (90%) patients. Substantial changes in the lung volumes of the AC maps were observed in the test-retest analysis (ratio: 1.0 ± 0.2, range: 0.8-1.4). Susceptibility artifacts were observed in 10 (50%) patients, while six (30%) patients had TI artifacts. Average differences of 14 ± 10% were observed for PET images reconstructed with the artifactual AC maps. The combined artifact effects caused false-positive findings in three (15%) patients.Conclusion. Standard DIXON-AC maps must be examined carefully for artifacts and misalignment effects prior to AC correction of cardiac PET/MRI studies in order to avoid misinterpretation of biased perfusion and metabolism readings from the PET data. (J Nucl Cardiol 2017)

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“…Moreover, bones cannot be well delineated on conventional MR sequences because of their low water content and short transverse relaxation time. Truncation of MR imaging field of view and metal-induced susceptibility artifacts are other problems encountered in MRAC (4). Generally, MRAC methods can be categorized in 3 groups: segmentation-based approaches, which segment MR images into different tissue classes (background air, lung, fat, and soft tissue) and assign predefined attenuation coefficients to each class (5); atlas registration-based approaches, in which a coregistered MR-CT atlas dataset is used to derive a pseudo CT image from the patient's MR image (6); and emission-based approaches in which the attenuation map is directly estimated from TOF PET emission data with MR anatomic prior information (7,8).…”

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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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Image artifacts from MR-based attenuation correction in clinical, whole-body PET/MRI

Cited by 117 publications

References 21 publications

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

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

Assessment of attenuation correction for myocardial PET imaging using combined PET/MRI

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

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