PET/MR imaging of bone lesions – implications for PET quantification from imperfect attenuation correction

Samarin, Andrei; Burger, Cyrill; Wollenweber, Scott D.; Crook, David; Burger, Irene A.; Schmid, Daniel T.; Schulthess, Gustav K. von; Kuhn, Félix P.

doi:10.1007/s00259-012-2113-0

Cited by 233 publications

(162 citation statements)

References 14 publications

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“…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: 94%

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: 94%

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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“…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%

“…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. Ouyang et al (33) also concluded that three‐class segmentation can be sufficient for PET quantification in the heart, as it yields less than 5% quantification difference after compensation.…”

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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“…Cortical bone contains relatively few protons that contribute to the MR signal. Hence, standardized uptake values (SUVs) for osseous lesions have been reported to be underestimated by an average of 11 % and as much as 16 % for sclerotic spine lesions [9]. Despite also finding significantly lower SUVs for both FDG-avid focal bone lesions (FFBLs) and normal background bone (BB), Eiber et al have reported no significant qualitative differences in the visual conspicuity of FFBLs on PET/CT versus PET/MRI [10].…”

Section: Introductionmentioning

confidence: 99%

Conspicuity of FDG-Avid Osseous Lesions on PET/MRI Versus PET/CT: a Quantitative and Visual Analysis

Fraum

Fowler

McConathy

2016

Nucl Med Mol Imaging

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Background Because standard MRI-based attenuation correction (AC) does not account for the attenuation of photons by cortical bone, PET/MRI may have reduced sensitivity for FDG-avid focal bone lesions (FFBLs). This study evaluates whether MRI-based AC compromises detection of FFBLs, by comparing their conspicuity both quantitatively and qualitatively on PET/MRI versus PET/CT. Methods One hundred ninety general oncology patients underwent whole-body PET/CT followed by whole-body PET/MRI, utilizing the same FDG dose. Thirteen patients with a total of 50 FFBLs were identified. Using automated contouring software, a volumetric contour was generated for each FFBL. Adjacent regions of normal background bone (BB) were selected manually. For each contour, SUV-max and SUV-mean were determined. Lesion-to-background SUV ratios served as quantitative metrics of conspicuity. Additionally, two blinded readers evaluated the relative conspicuity of FFBLs on PET images derived from MRI-based AC versus CT-based AC. Visibility of an anatomic correlate for FFBLs on the corresponding CT and MR images was also assessed. Results SUV-mean was lower on PET/MRI for both FFBLs (-6.5 %, p = 0.009) and BB (-20.5 %, p < 0.001). SUV-max was lower on PET/MRI for BB (-14.2 %, p = 0.002) but not for FFBLs (-6.2 %, p = 0.068). The ratio of FFBL SUV-mean to BB SUV-mean was higher for PET/MRI (+29.5 %, p < 0.001). Forty of 50 lesions (80 %) were visually deemed to be of equal or greater conspicuity on PET images derived from PET/MRI. Thirty-five of 50 FFBLs (70 %) had CT correlates, while 40/50 FFBLs (80 %) had a correlate on at least one MRI sequence. The mean interval from tracer administration to imaging was longer (p < 0.001) for PET/MRI (127 v. 62 min). Conclusions Both FFBLs and BB had lower mean SUVs on PET/MRI than PET/CT. This finding was likely in part due to differences in the handling of cortical bone by MRI-based AC versus CT-based AC. Despite this systematic bias, FFBLs had greater conspicuity on PET/MRI, both qualitatively and quantitatively. This difference was likely due to the longer tracer uptake times for PET/MRI, which allowed for more tracer accumulation by FFBLs and more tracer washout from BB. Our results suggest that whole-body PET/MRI and PET/CT provide comparable sensitivity for detection of FDG-avid focal bone lesions.

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PET/MR imaging of bone lesions – implications for PET quantification from imperfect attenuation correction

Cited by 233 publications

References 14 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

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

Conspicuity of FDG-Avid Osseous Lesions on PET/MRI Versus PET/CT: a Quantitative and Visual Analysis

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