Computed tomography synthesis from magnetic resonance images in the pelvis using multiple random forests and auto-context features

Daniel Andreasen, Jens M. Edmund, Vasileios Zografos, Bjoern H. Menze, Koen Van Leemput

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

29 Scopus citations


In radiotherapy treatment planning that is only based on magnetic resonance imaging (MRI), the electron density information usually obtained from computed tomography (CT) must be derived from the MRI by synthesizing a so-called pseudo CT (pCT). This is a non-trivial task since MRI intensities are neither uniquely nor quantitatively related to electron density. Typical approaches involve either a classification or regression model requiring specialized MRI sequences to solve intensity ambiguities, or an atlas-based model necessitating multiple registrations between atlases and subject scans. In this work, we explore a machine learning approach for creating a pCT of the pelvic region from conventional MRI sequences without using atlases. We use a random forest provided with information about local texture, edges and spatial features derived from the MRI. This helps to solve intensity ambiguities. Furthermore, we use the concept of auto-context by sequentially training a number of classification forests to create and improve context features, which are finally used to train a regression forest for pCT prediction. We evaluate the pCT quality in terms of the voxel-wise error and the radiologic accuracy as measured by water-equivalent path lengths. We compare the performance of our method against two baseline pCT strategies, which either set all MRI voxels in the subject equal to the CT value of water, or in addition transfer the bone volume from the real CT. We show an improved performance compared to both baseline pCTs suggesting that our method may be useful for MRI-only radiotherapy.

Original languageEnglish
Title of host publicationMedical Imaging 2016
Subtitle of host publicationImage Processing
EditorsMartin A. Styner, Elsa D. Angelini, Elsa D. Angelini
ISBN (Electronic)9781510600195
StatePublished - 2016
EventMedical Imaging 2016: Image Processing - San Diego, United States
Duration: 1 Mar 20163 Mar 2016

Publication series

NameProgress in Biomedical Optics and Imaging - Proceedings of SPIE
ISSN (Print)1605-7422


ConferenceMedical Imaging 2016: Image Processing
Country/TerritoryUnited States
CitySan Diego


  • Auto-context
  • CT synthesis
  • Magnetic resonance imaging
  • Pseudo CT
  • Radiotherapy
  • Random forest


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