Zero TE-based pseudo-CT image conversion in the head and its application in PET/MR attenuation correction and MR-guided radiation therapy planning

Florian Wiesinger, Mikael Bylund, Jaewon Yang, Sandeep Kaushik, Dattesh Shanbhag, Sangtae Ahn, Joakim H. Jonsson, Josef A. Lundman, Thomas Hope, Tufve Nyholm, Peder Larson, Cristina Cozzini

Research output: Contribution to journalArticlepeer-review

52 Scopus citations

Abstract

Purpose: To describe a method for converting Zero TE (ZTE) MR images into X-ray attenuation information in the form of pseudo-CT images and demonstrate its performance for (1) attenuation correction (AC) in PET/MR and (2) dose planning in MR-guided radiation therapy planning (RTP). Methods: Proton density-weighted ZTE images were acquired as input for MR-based pseudo-CT conversion, providing (1) efficient capture of short-lived bone signals, (2) flat soft-tissue contrast, and (3) fast and robust 3D MR imaging. After bias correction and normalization, the images were segmented into bone, soft-tissue, and air by means of thresholding and morphological refinements. Fixed Hounsfield replacement values were assigned for air (-1000 HU) and soft-tissue (+42 HU), whereas continuous linear mapping was used for bone. Results: The obtained ZTE-derived pseudo-CT images accurately resembled the true CT images (i.e., Dice coefficient for bone overlap of 0.73 ± 0.08 and mean absolute error of 123 ± 25 HU evaluated over the whole head, including errors from residual registration mismatches in the neck and mouth regions). The linear bone mapping accounted for bone density variations. Averaged across five patients, ZTE-based AC demonstrated a PET error of -0.04 ± 1.68% relative to CT-based AC. Similarly, for RTP assessed in eight patients, the absolute dose difference over the target volume was found to be 0.23 ± 0.42%. Conclusion: The described method enables MR to pseudo-CT image conversion for the head in an accurate, robust, and fast manner without relying on anatomical prior knowledge. Potential applications include PET/MR-AC, and MR-guided RTP.

Original languageEnglish (US)
Pages (from-to)1440-1451
Number of pages12
JournalMagnetic resonance in medicine
Volume80
Issue number4
DOIs
StatePublished - Oct 2018
Externally publishedYes

Keywords

  • attenuation correction
  • PET/MR
  • pseudo-CT
  • radiation therapy planning
  • RTP
  • RUFIS
  • synthetic CT
  • ZTE

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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