title: Comprehensive 4D velocity mapping of the heart and great vessels by cardiovascular magnetic resonance.
abstract: BACKGROUND
  Phase contrast cardiovascular magnetic resonance (CMR) is able to measure all three directional components of the velocities of blood flow relative to the three spatial dimensions and the time course of the heart cycle. In this article, methods used for the acquisition, visualization, and quantification of such datasets are reviewed and illustrated.
  
  
  METHODS
  Currently, the acquisition of 3D cine (4D) phase contrast velocity data, synchronized relative to both cardiac and respiratory movements takes about ten minutes or more, even when using parallel imaging and optimized pulse sequence design. The large resulting datasets need appropriate post processing for the visualization of multidirectional flow, for example as vector fields, pathlines or streamlines, or for retrospective volumetric quantification.
  
  
  CONCLUSIONS
  Multidirectional velocity acquisitions have provided 3D visualization of large scale flow features of the healthy heart and great vessels, and have shown altered patterns of flow in abnormal chambers and vessels. Clinically relevant examples include retrograde streams in atheromatous descending aortas as potential thrombo-embolic pathways in patients with cryptogenic stroke and marked variations of flow visualized in common aortic pathologies. Compared to standard clinical tools, 4D velocity mapping offers the potential for retrospective quantification of flow and other hemodynamic parameters.
  
  
  CONCLUSIONS
  Multidirectional, 3D cine velocity acquisitions are contributing to the understanding of normal and pathologically altered blood flow features. Although more rapid and user-friendly strategies for acquisition and analysis may be needed before 4D velocity acquisitions come to be adopted in routine clinical CMR, their capacity to measure multidirectional flows throughout a study volume has contributed novel insights into cardiovascular fluid dynamics in health and disease.
authors.affiliation: Department of Radiology, Medical Physics, University Hospital Freiburg, Germany. michael.markl@uniklinik-freiburg.de
authors.forename: Michael
authors.initials: M
authors.lastname: Markl
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Kilner
authors.forename: Tino
authors.initials: T
authors.lastname: Ebbers
mesh_terms: D001783:Blood Flow Velocity; D001808:Blood Vessels / Q000503:physiopathology*; D002318:Cardiovascular Diseases / Q000175:diagnosis* / Q000503:physiopathology; D003326:Coronary Circulation; D006321:Heart / Q000503:physiopathology*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D021621:Imaging, Three-Dimensional; D019028:Magnetic Resonance Imaging, Cine; D011237:Predictive Value of Tests; D012039:Regional Blood Flow; D015656:Respiratory Mechanics; D013997:Time Factors