The effect of errors in segmented attenuation maps on PET quantification

Keereman, Vincent; Holen, Roel Van; Mollet, Pieter; Vandenberghe, Stefaan

doi:10.1118/1.3651640

Cited by 99 publications

(104 citation statements)

References 24 publications

(25 reference statements)

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“…A study conducted by our group (9) showed an underestimation greater than 10% for 58% of osseous regions when a segmentation-based method that ignored bone was used. Keereman et al reported an underestimation of 10%-20% in spine and femur lesions if cortical bone was ignored, versus 10%-15% if soft bone was ignored (32).…”

Section: Discussionmentioning

confidence: 99%

MR-Based Attenuation Correction Methods for Improved PET Quantification in Lesions Within Bone and Susceptibility Artifact Regions

et al. 2013

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Hybrid PET/MR systems have recently entered clinical practice. Thus, the accuracy of MR-based attenuation correction in simultaneously acquired data can now be investigated. We assessed the accuracy of 4 methods of MR-based attenuation correction in lesions within soft tissue, bone, and MR susceptibility artifacts: 2 segmentation-based methods (SEG1, provided by the manufacturer, and SEG2, a method with atlas-based susceptibility artifact correction); an atlas-and pattern recognition-based method (AT&PR), which also used artifact correction; and a new method combining AT&PR and SEG2 (SEG2wBONE). Methods: Attenuation maps were calculated for the PET/MR datasets of 10 patients acquired on a whole-body PET/MR system, allowing for simultaneous acquisition of PET and MR data. Eighty percent iso-contour volumes of interest were placed on lesions in soft tissue (n 5 21), in bone (n 5 20), near bone (n 5 19), and within or near MR susceptibility artifacts (n 5 9). Relative mean volume-of-interest differences were calculated with CT-based attenuation correction as a reference. Results: For soft-tissue lesions, none of the methods revealed a significant difference in PET standardized uptake value relative to CT-based attenuation correction (SEG1, 22.6% 6 5.8%; SEG2, 21.6% 6 4.9%; AT&PR, 24.7% 6 6.5%; SEG2wBONE, 0.2% 6 5.3%). For bone lesions, underestimation of PET standardized uptake values was found for all methods, with minimized error for the atlas-based approaches (SEG1, 216.1% 6 9.7%; SEG2, 211.0% 6 6.7%; AT&PR, 26.6% 6 5.0%; SEG2wBONE, 24.7% 6 4.4%). For lesions near bone, underestimations of lower magnitude were observed (SEG1, 212.0% 6 7.4%; SEG2, 29.2% 6 6.5%; AT&PR, 24.6% 6 7.8%; SEG2wBONE, 24.2% 6 6.2%). For lesions affected by MR susceptibility artifacts, quantification errors could be reduced using the atlas-based artifact correction (SEG1, 254.0% 6 38.4%; SEG2, 215.0% 6 12.2%; AT&PR, 24.1% 6 11.2%; SEG2w-BONE, 0.6% 6 11.1%). Conclusion: For soft-tissue lesions, none of the evaluated methods showed statistically significant errors. For bone lesions, significant underestimations of 216% and 211% occurred for methods in which bone tissue was ignored (SEG1 and SEG2). In the present attenuation correction schemes, uncorrected MR susceptibility artifacts typically result in reduced attenuation values, potentially leading to highly reduced PET standardized uptake values, rendering lesions indistinguishable from background. While AT&PR and SEG2wBONE show accurate results in both soft tissue and bone, SEG2wBONE uses a two-step approach for tissue classification, which increases the robustness of prediction and can be applied retrospectively if more precision in bone areas is needed. Hybr id PET/MR systems have recently been introduced into clinical practice and are attracting increasing interest in the research and clinical communities (1-3). While PET/CT is an established hybrid modality with a wide range of applications, specific application trends for PET/MR are currently under investigation (4-7). MR-based atten...

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Section: Discussionmentioning

confidence: 99%

MR-Based Attenuation Correction Methods for Improved PET Quantification in Lesions Within Bone and Susceptibility Artifact Regions

et al. 2013

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“…In 3-or 4-class MRAC methods, bones are replaced by soft tissue and the inter-or intrapatient heterogeneity of attenuation coefficients in different tissue classes is ignored, which leads to quantification errors in the estimation of standardized uptake value (SUV) ranging between 4% and 25% in different organs (9)(10)(11)(12)(13). 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).…”

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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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“…In brain PET, ignoring bone has been suggested to cause quantification bias (29) . In whole‐body PET/MR imaging, however, neglecting bone in segmented attenuation images has been suggested to cause large errors only in regions that are inside or near bones 30 , 31 , 32 . In one example demonstrated by Samarin et al, (32) classifying bone as soft tissue resulted in less than 6% difference for PET voxels in the heart region.…”

Section: Discussionmentioning

confidence: 99%

Feasibility of using respiration‐averaged MR images for attenuation correction of cardiac PET/MR imaging

Pan

2015

J Applied Clin Med Phys

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Cardiac imaging is a promising application for combined PET/MR imaging. However, current MR imaging protocols for whole‐body attenuation correction can produce spatial mismatch between PET and MR‐derived attenuation data owing to a disparity between the two modalities' imaging speeds. We assessed the feasibility of using a respiration‐averaged MR (AMR) method for attenuation correction of cardiac PET data in PET/MR images. First, to demonstrate the feasibility of motion imaging with MR, we used a 3T MR system and a two‐dimensional fast spoiled gradient‐recalled echo (SPGR) sequence to obtain AMR images of a moving phantom. Then, we used the same sequence to obtain AMR images of a patient's thorax under free‐breathing conditions. MR images were converted into PET attenuation maps using a three‐class tissue segmentation method with two sets of predetermined CT numbers, one calculated from the patient‐specific (PS) CT images and the other from a reference group (RG) containing 54 patient CT datasets. The MR‐derived attenuation images were then used for attenuation correction of the cardiac PET data, which were compared to the PET data corrected with average CT (ACT) images. In the myocardium, the voxel‐by‐voxel differences and the differences in mean slice activity between the AMR‐corrected PET data and the ACT‐corrected PET data were found to be small (less than 7%). The use of AMR‐derived attenuation images in place of ACT images for attenuation correction did not affect the summed stress score. These results demonstrate the feasibility of using the proposed SPGR‐based MR imaging protocol to obtain patient AMR images and using those images for cardiac PET attenuation correction. Additional studies with more clinical data are warranted to further evaluate the method.PACS number: 87.57.uk

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The effect of errors in segmented attenuation maps on PET quantification

Cited by 99 publications

References 24 publications

MR-Based Attenuation Correction Methods for Improved PET Quantification in Lesions Within Bone and Susceptibility Artifact Regions

MR-Based Attenuation Correction Methods for Improved PET Quantification in Lesions Within Bone and Susceptibility Artifact Regions

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

Feasibility of using respiration‐averaged MR images for attenuation correction of cardiac PET/MR imaging

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