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Departments of Radiology and Medical PhysicsDepartments of Radiology and Medical PhysicsUniversity of Wisconsin-MadisonUniversity of Wisconsin-Madison
Vessel Branch Segmentation of Phase Contrast Vastly undersampled PRojection Magnetic
Resonance Imaging
Kevin Johnson Kevin Johnson
Overview
• Background• Motivation• Theory
– Phase Coherence Mixture Model– Discrepancies
• Methods– Segmentation– Traces
• Results• Conclusions
Phase Contrast MR • MRI
– Fourier encodes atoms of non-zero spin– Complex Acquisition
• Phase Contrast MR– Encoded velocity in phase– 5-Images per Acquisition:
1H Density Vascular Velocity A/P Velocity L/R Velocity S/I
PC VIPR • Highly efficient acquisition• More accurate than conventional methods• High Resolution (0.5x0.5x0.5mm)
Motivation
• Phase image is difficult to analyze due to noise
• Segmentations allows visualization
• In neurological cases vasculature is complex– Need to separate branches
Frydrychowicz et al. ICVTS 2006. 340-342
Theory (Chung et al.)
• Phase Coherence
• May allow for automated separation
Mixture Model
Phase Coherence Thresholds
Theory in Practice
• Phase Coherence Histogram
• Simply due to the higher accuracy– In paper they had phase offsets – Shift PDF of Tissue– No effect on background
Methods
• Segmentation1) Determine phase coherence
2) Threshold phase coherence (T=0)
3) Threshold CD Image (T manually set)
4) Take intersection of images
5) Open image
6) Determine connected regions
7) Remove small regions
• Centerline1) Filter with LPF
2) Initialize by 3D watershed filling up to threshold
3) 3D Watershed with bridges built as connectivity
Results: Segmentation
Complex Difference Initial Threshold Eroded Image
Dilated Image Cleanup/Connectivity 3D Final Result
Results: Segmentation• Separate out individual components
• Remove components
ECA Branch ICA Branch Sap Vein Branch
No ECA/SAP Un-segmented
Results: Centerline
Initial Connectivity Connectivity (50% max)
Final
Conclusions
• Phase Coherence mixture model ineffective for PC VIPR
• Segmentation effective at separating components• Small vessels lost due to opening mask• Center line effective in most vessels• Failures in cases of complex flow