Paediatrics Publications


A multi-centre evaluation of eleven clinically feasible brain PET/MRI attenuation correction techniques using a large cohort of patients


Claes N. Ladefoged, Rigshospitalet
Ian Law, Rigshospitalet
Udunna Anazodo, Lawson Health Research Institute
Keith St. Lawrence, Lawson Health Research InstituteFollow
David Izquierdo-Garcia, Massachusetts General Hospital
Ciprian Catana, Massachusetts General Hospital
Ninon Burgos, University College London
M. Jorge Cardoso, University College London
Sebastien Ourselin, University College London
Brian Hutton, UCL Institute of Nuclear Medicine
Inés Mérida, Laboratoire CNRS CERMEP Centre d'Exploration et de Recherche Médicales par Émission de Positons
Nicolas Costes, Laboratoire CNRS CERMEP Centre d'Exploration et de Recherche Médicales par Émission de Positons
Alexander Hammers, Laboratoire CNRS CERMEP Centre d'Exploration et de Recherche Médicales par Émission de Positons
Didier Benoit, Rigshospitalet
Søren Holm, Rigshospitalet
Meher Juttukonda, The University of North Carolina at Chapel Hill
Hongyu An, The University of North Carolina at Chapel Hill
Jorge Cabello, Klinikum rechts der Isar der Technischen Universität München
Mathias Lukas, Klinikum rechts der Isar der Technischen Universität München
Stephan Nekolla, Klinikum rechts der Isar der Technischen Universität München
Sibylle Ziegler, Klinikum rechts der Isar der Technischen Universität München
Matthias Fenchel, Siemens AG
Bjoern Jakoby, Siemens AG
Michael E. Casey, Siemens USA
Tammie Benzinger, Washington University School of Medicine in St. Louis, Mallinckrodt Institute of Radiology
Liselotte Højgaard, Rigshospitalet

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Aim To accurately quantify the radioactivity concentration measured by PET, emission data need to be corrected for photon attenuation; however, the MRI signal cannot easily be converted into attenuation values, making attenuation correction (AC) in PET/MRI challenging. In order to further improve the current vendor-implemented MR-AC methods for absolute quantification, a number of prototype methods have been proposed in the literature. These can be categorized into three types: template/atlas-based, segmentation-based, and reconstruction-based. These proposed methods in general demonstrated improvements compared to vendor-implemented AC, and many studies report deviations in PET uptake after AC of only a few percent from a gold standard CT-AC. Using a unified quantitative evaluation with identical metrics, subject cohort, and common CT-based reference, the aims of this study were to evaluate a selection of novel methods proposed in the literature, and identify the ones suitable for clinical use. Methods In total, 11 AC methods were evaluated: two vendor-implemented (MR-ACDIXON and MR-ACUTE), five based on template/atlas information (MR-ACSEGBONE (Koesters et al., 2016), MR-ACONTARIO (Anazodo et al., 2014), MR-ACBOSTON (Izquierdo-Garcia et al., 2014), MR-ACUCL (Burgos et al., 2014), and MR-ACMAXPROB (Merida et al., 2015)), one based on simultaneous reconstruction of attenuation and emission (MR-ACMLAA (Benoit et al., 2015)), and three based on image-segmentation (MR-ACMUNICH (Cabello et al., 2015), MR-ACCAR-RiDR (Juttukonda et al., 2015), and MR-ACRESOLUTE (Ladefoged et al., 2015)). We selected 359 subjects who were scanned using one of the following radiotracers: [18F]FDG (210), [11C]PiB (51), and [18F]florbetapir (98). The comparison to AC with a gold standard CT was performed both globally and regionally, with a special focus on robustness and outlier analysis. Results The average performance in PET tracer uptake was within ±5% of CT for all of the proposed methods, with the average±SD global percentage bias in PET FDG uptake for each method being: MR-ACDIXON (−11.3±3.5)%, MR-ACUTE (−5.7±2.0)%, MR-ACONTARIO (−4.3±3.6)%, MR-ACMUNICH (3.7±2.1)%, MR-ACMLAA (−1.9±2.6)%, MR-ACSEGBONE (−1.7±3.6)%, MR-ACUCL (0.8±1.2)%, MR-ACCAR-RiDR (−0.4±1.9)%, MR-ACMAXPROB (−0.4±1.6)%, MR-ACBOSTON (−0.3±1.8)%, and MR-ACRESOLUTE (0.3±1.7)%, ordered by average bias. The overall best performing methods (MR-ACBOSTON, MR-ACMAXPROB, MR-ACRESOLUTE and MR-ACUCL, ordered alphabetically) showed regional average errors within ±3% of PET with CT-AC in all regions of the brain with FDG, and the same four methods, as well as MR-ACCAR-RiDR, showed that for 95% of the patients, 95% of brain voxels had an uptake that deviated by less than 15% from the reference. Comparable performance was obtained with PiB and florbetapir. Conclusions All of the proposed novel methods have an average global performance within likely acceptable limits (±5% of CT-based reference), and the main difference among the methods was found in the robustness, outlier analysis, and clinical feasibility. Overall, the best performing methods were MR-ACBOSTON, MR-ACMAXPROB, MR-ACRESOLUTE and MR-ACUCL, ordered alphabetically. These methods all minimized the number of outliers, standard deviation, and average global and local error. The methods MR-ACMUNICH and MR-ACCAR-RiDR were both within acceptable quantitative limits, so these methods should be considered if processing time is a factor. The method MR-ACSEGBONE also demonstrates promising results, and performs well within the likely acceptable quantitative limits. For clinical routine scans where processing time can be a key factor, this vendor-provided solution currently outperforms most methods. With the performance of the methods presented here, it may be concluded that the challenge of improving the accuracy of MR-AC in adult brains with normal anatomy has been solved to a quantitatively acceptable degree, which is smaller than the quantification reproducibility in PET imaging.

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