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Ladefoged CN, Hansen AE, Keller SH, et al. Impact of incorrect tissue classification in Dixon-based MR-AC: fat-water tissue inversion. EJNMMI Phys. 2014;1(1):101doi: 10.1186/s40658-014-0101-0.
Ladefoged, C. N., Hansen, A. E., Keller, S. H., Holm, S., Law, I., Beyer, T., Højgaard, L., Kjær, A., & Andersen, F. L. (2014). Impact of incorrect tissue classification in Dixon-based MR-AC: fat-water tissue inversion. EJNMMI physics, 1(1), 101. https://doi.org/10.1186/s40658-014-0101-0
Ladefoged, Claes Nøhr, et al. "Impact of incorrect tissue classification in Dixon-based MR-AC: fat-water tissue inversion." EJNMMI physics vol. 1,1 (2014): 101. doi: https://doi.org/10.1186/s40658-014-0101-0
Ladefoged CN, Hansen AE, Keller SH, Holm S, Law I, Beyer T, Højgaard L, Kjær A, Andersen FL. Impact of incorrect tissue classification in Dixon-based MR-AC: fat-water tissue inversion. EJNMMI Phys. 2014 Dec;1(1):101. doi: 10.1186/s40658-014-0101-0. Epub 2014 Dec 14. PMID: 26501459; PMCID: PMC4545462.
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EJNMMI Phys. 2014 Dec;1(1):101. doi: 10.1186/s40658-014-0101-0. Epub 2014 Dec 14.

Impact of incorrect tissue classification in Dixon-based MR-AC: fat-water tissue inversion.

EJNMMI physics

Claes Nøhr Ladefoged, Adam Espe Hansen, Sune Høgild Keller, Søren Holm, Ian Law, Thomas Beyer, Liselotte Højgaard, Andreas Kjær, Flemming Littrup Andersen

Affiliations

  1. Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100, Copenhagen, Denmark. [email protected].
  2. Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100, Copenhagen, Denmark. [email protected].
  3. Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100, Copenhagen, Denmark. [email protected].
  4. Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100, Copenhagen, Denmark. [email protected].
  5. Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100, Copenhagen, Denmark. [email protected].
  6. Centre for Medical Physics and Biomedical Engineering, Medical University of Vienna, Waehringer Guertel 18-20/4L, Vienna, A-1090, Austria. [email protected].
  7. Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100, Copenhagen, Denmark. [email protected].
  8. Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100, Copenhagen, Denmark. [email protected].
  9. Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100, Copenhagen, Denmark. [email protected].

PMID: 26501459 PMCID: PMC4545462 DOI: 10.1186/s40658-014-0101-0

Abstract

BACKGROUND: The current MR-based attenuation correction (AC) used in combined PET/MR systems computes a Dixon attenuation map (MR-ACDixon) based on fat and water images derived from in- and opposed-phase MRI. We observed an occasional fat/water inversion in MR-ACDixon. The aim of our study was to estimate the prevalence of this phenomenon in a large patient cohort and assess the possible bias on PET data.

METHODS: PET/MRI was performed on a Siemens Biograph mMR (Siemens AG, Erlangen, Germany). We visually inspected attenuation maps of 283 brain or head/neck (H/N) patients, classified them as non-inverted or inverted, and calculated the fat/water tissue fraction. We selected ten FDG-PET brain patients with non-inverted attenuation maps for further analysis. Tissue inversion was simulated, and PET images were reconstructed using both original and inverted attenuation maps. The FDG-PET images of the ten brain patients were analyzed using 11 concentric annulus regions of 5 mm width placed over a central transaxial image plane traversing PETDixon.

RESULTS: Out of the 283 patients, a fat/water inversion in 23 patients (8.1%) was observed. The average fraction of fat in the correct MR-ACDixon was 13% for brain and 17% for H/N patients. In the inverted cases, we found an average fat fraction of 56% for the brain patients and 41% for the H/N patients. The effect of the simulated tissue inversion in the brain studies was clearly seen on AC-PET images. The percent-difference image revealed a radial error where the largest difference was at the ventricles (30% ± 3%) and smallest at the cortical region (10% ± 2%).

CONCLUSIONS: Tissue inversion in Dixon MRI is well known and can occur when there is an error in the off-resonance correction method. Tissue inversion needs to be considered if, based on Dixon-AC, the construction of normal PET databases is performed or any quantitative physiological parameters are fitted. Visual inspection is needed if Dixon-AC is to be used in clinical routine.

Keywords: DWFS; Fat-water inversion; Image artifacts; PET/MR

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