title: High performance MRI simulations of motion on multi-GPU systems.
abstract: BACKGROUND
  MRI physics simulators have been developed in the past for optimizing imaging protocols and for training purposes. However, these simulators have only addressed motion within a limited scope. The purpose of this study was the incorporation of realistic motion, such as cardiac motion, respiratory motion and flow, within MRI simulations in a high performance multi-GPU environment.
  
  
  METHODS
  Three different motion models were introduced in the Magnetic Resonance Imaging SIMULator (MRISIMUL) of this study: cardiac motion, respiratory motion and flow. Simulation of a simple Gradient Echo pulse sequence and a CINE pulse sequence on the corresponding anatomical model was performed. Myocardial tagging was also investigated. In pulse sequence design, software crushers were introduced to accommodate the long execution times in order to avoid spurious echoes formation. The displacement of the anatomical model isochromats was calculated within the Graphics Processing Unit (GPU) kernel for every timestep of the pulse sequence. Experiments that would allow simulation of custom anatomical and motion models were also performed. Last, simulations of motion with MRISIMUL on single-node and multi-node multi-GPU systems were examined.
  
  
  RESULTS
  Gradient Echo and CINE images of the three motion models were produced and motion-related artifacts were demonstrated. The temporal evolution of the contractility of the heart was presented through the application of myocardial tagging. Better simulation performance and image quality were presented through the introduction of software crushers without the need to further increase the computational load and GPU resources. Last, MRISIMUL demonstrated an almost linear scalable performance with the increasing number of available GPU cards, in both single-node and multi-node multi-GPU computer systems.
  
  
  CONCLUSIONS
  MRISIMUL is the first MR physics simulator to have implemented motion with a 3D large computational load on a single computer multi-GPU configuration. The incorporation of realistic motion models, such as cardiac motion, respiratory motion and flow may benefit the design and optimization of existing or new MR pulse sequences, protocols and algorithms, which examine motion related MR applications.
authors.forename: Christos G
authors.initials: CG
authors.lastname: Xanthis
authors.forename: Ioannis E
authors.initials: IE
authors.lastname: Venetis
authors.affiliation: Department of Computer Science and Biomedical Informatics, University of Thessaly, Lamia, Greece. aletras@hotmail.com.
authors.forename: Anthony H
authors.initials: AH
authors.lastname: Aletras
mesh_terms: D000465:Algorithms; D016477:Artifacts; D001783:Blood Flow Velocity; D003198:Computer Simulation; D003326:Coronary Circulation; D006321:Heart / Q000033:anatomy & histology / Q000502:physiology*; D006339:Heart Rate; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D019028:Magnetic Resonance Imaging, Cine; D008953:Models, Anatomic; D008955:Models, Cardiovascular; D009038:Motion; D009200:Myocardial Contraction; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D056152:Respiratory Rate; D012984:Software; D013997:Time Factors