title: Background suppression in time-resolved MR angiography without mask acquisition or operator intervention.
abstract: OBJECTIVE
  To suppress static and background tissue in time-resolved MRA studies of the full thorax or abdomen without the need of a mask image or operator intervention.
  
  
  METHODS
  The time course of each voxel is projected onto the orthogonal complement space of a matrix that spans static and linearly enhancing signal vectors. The norm of the solution, or the projection length, acts as a confidence measure for segmenting vascular and nonvascular tissue. Voxels whose confidence measures fall below an automatically detected threshold value are considered nonvascular. These voxels undergo an increasing level of suppression as the distance of the confidence measure from the threshold grows.
  
  
  RESULTS
  MIPs of processed volunteer studies were compared to the original unaltered studies to assess the improvement in clarity of vascular structures. Qualitative and quantitative comparisons of full body MIPs verify excellent suppression of nonvascular tissue in time-resolved three-dimensional image volumes.
  
  
  CONCLUSIONS
  Contrast increased by an average factor of 13 in five volunteer studies, quantitatively emphasizing the improvement in MIP processing achieved by this method. Improvement in the clarity of vascular structures in subvolume MIPs is also demonstrated to emphasize the significant increase in ease with which regions of interest can be identified.
authors.affiliation: Electrical Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA. arunacha@cae.wisc.edu
authors.forename: Arjun
authors.initials: A
authors.lastname: Arunachalam
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Thornton
authors.forename: Walter F
authors.initials: WF
authors.lastname: Block
mesh_terms: D000005:Abdomen / Q000473:pathology; D000465:Algorithms; D015901:Angiography, Digital Subtraction; D003198:Computer Simulation; D003287:Contrast Media / Q000494:pharmacology; D005583:Fourier Analysis; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D018810:Magnetic Resonance Angiography / Q000379:methods*; D013382:Subtraction Technique; D013909:Thorax / Q000473:pathology; D013997:Time Factors
chemical_list: D003287:Contrast Media