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

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          Abstract

          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 dual-tracer protocol involving the assessment of myocardial perfusion ( 13N-NH 3: 813 ± 86 MBq) and metabolism ( 18F-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.

          Electronic supplementary material

          The online version of this article (10.1007/s12350-017-1118-2) contains supplementary material, which is available to authorized users.

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          Effects of noise, image resolution, and ROI definition on the accuracy of standard uptake values: a simulation study.

          Otto Hoekstra, Ronald Boellaard, Adriaan Lammertsma … (2004)
          Semiquantitative standard uptake values (SUVs) are used for tumor diagnosis and response monitoring. However, the accuracy of the SUV and the accuracy of relative change during treatment are not well documented. Therefore, an experimental and simulation study was performed to determine the effects of noise, image resolution, and region-of-interest (ROI) definition on the accuracy of SUVs. Experiments and simulations are based on thorax phantoms with tumors of 10-, 15-, 20-, and 30-mm diameter and background ratios (TBRs) of 2, 4, and 8. For the simulation study, sinograms were generated by forward projection of the phantoms. For each phantom, 50 sinograms were generated at 3 noise levels. All sinograms were reconstructed using ordered-subset expectation maximization (OSEM) with 2 iterations and 16 subsets, with or without a 6-mm gaussian filter. For each tumor, the maximum pixel value and the average of a 50%, a 70%, and an adaptive isocontour threshold ROI were derived as well as with an ROI of 15 x 15 mm. The accuracy of SUVs was assessed using the average of 50 ROI values. Treatment response was simulated by varying the tumor size or the TBR. For all situations, a strong correlation was found between maximum and isocontour-based ROI values resulting in similar dependencies on image resolution and noise of all studied SUV measures. A strong variation with tumor size of > or =50% was found for all SUV values. For nonsmoothed data with high noise levels this variation was primarily due to noise, whereas for smoothed data with low noise levels partial-volume effects were most important. In general, SUVs showed under- and overestimations of > or =50% and depended on all parameters studied. However, SUV ratios, used for response monitoring, were only slightly dependent of ROI definition but were still affected by noise and resolution. The poor accuracy of the SUV under various conditions may hamper its use for diagnosis, especially in multicenter trials. SUV ratios used to measure response to treatment, however, are less dependent on noise, image resolution, and ROI definition. Therefore, the SUV might be more suitable for response-monitoring purposes.
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            Effects of ROI definition and reconstruction method on quantitative outcome and applicability in a response monitoring trial.

            Nanda Krak, R. Boellaard, Otto Hoekstra … (2005)
            Quantitative measurement of tracer uptake in a tumour can be influenced by a number of factors, including the method of defining regions of interest (ROIs) and the reconstruction parameters used. The main purpose of this study was to determine the effects of different ROI methods on quantitative outcome, using two reconstruction methods and the standard uptake value (SUV) as a simple quantitative measure of FDG uptake. Four commonly used methods of ROI definition (manual placement, fixed dimensions, threshold based and maximum pixel value) were used to calculate SUV (SUV([MAN]), SUV15 mm, SUV50, SUV75 and SUVmax, respectively) and to generate "metabolic" tumour volumes. Test-retest reproducibility of SUVs and of "metabolic" tumour volumes and the applicability of ROI methods during chemotherapy were assessed. In addition, SUVs calculated on ordered subsets expectation maximisation (OSEM) and filtered back-projection (FBP) images were compared. ROI definition had a direct effect on quantitative outcome. On average, SUV[MAN), SUV15 mm, SUV50 and SUV75, were respectively 48%, 27%, 34% and 15% lower than SUVmax when calculated on OSEM images. No statistically significant differences were found between SUVs calculated on OSEM and FBP reconstructed images. Highest reproducibility was found for SUV15 mm and SUV[MAN] (ICC 0.95 and 0.94, respectively) and for "metabolic" volumes measured with the manual and 50% threshold ROIs (ICC 0.99 for both). Manual, 75% threshold and maximum pixel ROIs could be used throughout therapy, regardless of changes in tumour uptake or geometry. SUVs showed the same trend in relative change in FDG uptake after chemotherapy, irrespective of the ROI method used. The method of ROI definition has a direct influence on quantitative outcome. In terms of simplicity, user-independence, reproducibility and general applicability the threshold-based and fixed dimension methods are the best ROI methods. Threshold methods are in addition relatively independent of changes in size and geometry, however, and may therefore be more suitable for response monitoring purposes.
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              18F-FDG PET definition of gross tumor volume for radiotherapy of non-small cell lung cancer: is a single standardized uptake value threshold approach appropriate?

              Feng-Ming Spring Kong, Farrokh Dehdashti, Issam El-Rassi … (2006)
              PET with (18)F-FDG has been used in radiation treatment planning for non-small cell lung cancer (NSCLC). Thresholds of 15%-50% the maximum standardized uptake value (SUV(max)) have been used for gross tumor volume (GTV) delineation by PET (PET(GTV)), with 40% being the most commonly used value. Recent studies indicated that 15%-20% may be more appropriate. The purposes of this study were to determine which threshold generates the best volumetric match to GTV delineation by CT (CT(GTV)) for peripheral NSCLC and to determine whether that threshold can be generalized to tumors of various sizes. Data for patients who had peripheral NSCLC with well-defined borders on CT and SUV(max) of greater than 2.5 were reviewed. PET/CT datasets were reviewed, and a volume of interest was determined to represent the GTV. The CT(GTV) was delineated by using standard lung windows and reviewed by a radiation oncologist. The PET(GTV) was delineated automatically by use of various percentages of the SUV(max). The PET(GTV)-to-CT(GTV) ratios were compared at various thresholds, and a ratio of 1 was considered the best match, or the optimal threshold. Twenty peripheral NSCLCs with volumes easily defined on CT were evaluated. The SUV(max) (mean +/- SD) was 12 +/- 8, and the mean CT(GTV) was 198 cm(3) (97.5% confidence interval, 5-1,008). The SUV(max) were 16 +/- 5, 13 +/- 9, and 3.0 +/- 0.4 for tumors measuring greater than 5 cm, 3-5 cm, and less than 3 cm, respectively. The optimal thresholds (mean +/- SD) for the best match were 15% +/- 6% for tumors measuring greater than 5 cm, 24% +/- 9% for tumors measuring 3-5 cm, 42% +/- 2% for tumors measuring less than 3 cm, and 24% +/- 13% for all tumors. The PET(GTV) at the 40% and 20% thresholds underestimated the CT(GTV) for 16 of 20 and 14 of 20 lesions, respectively. The mean difference in the volumes (PET(GTV) minus CT(GTV) [PET(GTV) - CT(GTV)]) at the 20% threshold was 79 cm(3) (97.5% confidence interval, -922 to 178). The PET(GTV) at the 20% threshold overestimated the CT(GTV) for all 4 tumors measuring less than 3 cm and underestimated the CT(GTV) for all 6 tumors measuring greater than 5 cm. The CT(GTV) was inversely correlated with the PET(GTV) - CT(GTV) at the 20% threshold (R(2) = 0.90, P < 0.0001). The optimal threshold was inversely correlated with the CT(GTV) (R(2) = 0.79, P < 0.0001). No single threshold delineating the PET(GTV) provides accurate volume definition, compared with that provided by the CT(GTV), for the majority of NSCLCs. The strong correlation of the optimal threshold with the CT(GTV) warrants further investigation.
              Article 0 comments Cited 54 times – based on 0 reviews     Review now
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                Author and article information

                Contributors
                Martin Lyngby Lassen: martin.lassen@meduniwien.ac.at
                Journal
                Journal ID (nlm-ta): J Nucl Cardiol
                Journal ID (iso-abbrev): J Nucl Cardiol
                Title: Journal of Nuclear Cardiology
                Publisher: Springer International Publishing (Cham )
                ISSN (Print): 1071-3581
                ISSN (Electronic): 1532-6551
                Publication date (Electronic): 22 November 2017
                Publication date PMC-release: 22 November 2017
                Publication date (Print): 2019
                Volume: 26
                Issue: 4
                Pages: 1107-1118
                Affiliations
                [1 ]ISNI 0000 0000 9259 8492, GRID grid.22937.3d, QIMP Group, Center for Medical Physics and Biomedical Engineering, General Hospital Vienna, , Medical University of Vienna, ; 1090 Vienna, Austria
                [2 ]ISNI 0000 0000 9259 8492, GRID grid.22937.3d, Division of Nuclear Medicine, Department of Biomedical Engineering and Image-guided Therapy, , Medical University of Vienna, ; Vienna, Austria
                [3 ]ISNI 0000 0000 9259 8492, GRID grid.22937.3d, Division of Cardiovascular and Interventional Radiology, Department of Biomedical Engineering and Image-guided Therapy, , Medical University of Vienna, ; Vienna, Austria
                [4 ]ISNI 0000 0000 9259 8492, GRID grid.22937.3d, Department of Cardiac Surgery, , Medical University of Vienna, ; Vienna, Austria
                Article
                Publisher ID: 1118
                DOI: 10.1007/s12350-017-1118-2
                PMC ID: 6660490
                PubMed ID: 29168158
                SO-VID: 2e539755-ddd9-4399-b16a-1ec9588e4245
                Copyright © © The Author(s) 2017
                License:

                Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

                History
                Date received : 19 May 2017
                Date revision received : 18 October 2017
                Categories
                Subject: Original Article
                Custom metadata
                issue-copyright-statement © American Society of Nuclear Cardiology 2019

                ScienceOpen disciplines: Cardiovascular Medicine
                Keywords: attenuation correction,cardiac pet,artifacts,pet/mr
                Data availability:
                ScienceOpen disciplines: Cardiovascular Medicine
                Keywords: attenuation correction, cardiac pet, artifacts, pet/mr

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