title: Simulation of spatiotemporal CT data sets using a 4D MRI-based lung motion model.
abstract: OBJECTIVE
  Four-dimensional CT imaging is widely used to account for motion-related effects during radiotherapy planning of lung cancer patients. However, 4D CT often contains motion artifacts, cannot be used to measure motion variability, and leads to higher dose exposure. In this article, we propose using 4D MRI to acquire motion information for the radiotherapy planning process. From the 4D MRI images, we derive a time-continuous model of the average patient-specific respiratory motion, which is then applied to simulate 4D CT data based on a static 3D CT.
  
  
  METHODS
  The idea of the motion model is to represent the average lung motion over a respiratory cycle by cyclic B-spline curves. The model generation consists of motion field estimation in the 4D MRI data by nonlinear registration, assigning respiratory phases to the motion fields, and applying a B-spline approximation on a voxel-by-voxel basis to describe the average voxel motion over a breathing cycle. To simulate a patient-specific 4D CT based on a static CT of the patient, a multi-modal registration strategy is introduced to transfer the motion model from MRI to the static CT coordinates.
  
  
  RESULTS
  Differences between model-based estimated and measured motion vectors are on average 1.39 mm for amplitude-based binning of the 4D MRI data of three patients. In addition, the MRI-to-CT registration strategy is shown to be suitable for the model transformation.
  
  
  CONCLUSIONS
  The application of our 4D MRI-based motion model for simulating 4D CT images provides advantages over standard 4D CT (less motion artifacts, radiation-free). This makes it interesting for radiotherapy planning.
authors: Institute of Medical Informatics, University of Lübeck, Ratzeburger Allee 160, 23538 , Lübeck, Germany, marx@imi.uni-luebeck.de.
authors: Mirko
authors: M
authors: Marx
authors: Jan
authors: J
authors: Ehrhardt
authors: René
authors: R
authors: Werner
authors: Heinz-Peter
authors: HP
authors: Schlemmer
authors: Heinz
authors: H
authors: Handels
mesh_terms: D016477:Artifacts; D003198:Computer Simulation; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology; D008175:Lung Neoplasms / Q000175:diagnosis*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008962:Models, Theoretical; D009038:Motion; D012119:Respiration