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Contrast Enhanced MR VenographyInfoSheet: - Sequences - 
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(CEMRV) A 3D dynamic contrast enhanced magnetic resonance venogram with acquisition timing to account for the later arrival of the contrast agent in the venous system. The pulse sequence used, is an enhanced 3D fast gradient echo sequence, the same sequence that is used for MR angiography.
For Ultrasound Imaging (USI) see Venous Ultrasound at
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 CE-MRA of the Carotid Arteries Colored MIP  Open this link in a new window
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 PCA-MRA 3D Brain Venography Colored MIP  Open this link in a new window

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Time of Flight AngiographyInfoSheet: - Sequences - 
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(TOF) The time of flight angiography is used for the imaging of vessels. Usually the sequence type is a gradient echo sequences with short TR, acquired with slices perpendicular to the direction of blood flow.
The source of diverse flow effects is the difference between the unsaturated and presaturated spins and creates a bright vascular image without the invasive use of contrast media. Flowing blood moves unsaturated spins from outside the slice into the imaging plane. These completely relaxed spins have full equilibrium magnetization and produce (when entering the imaging plane) a much higher signal than stationary spins if a gradient echo sequence is generated. This flow related enhancement is also referred to as entry slice phenomenon, or inflow enhancement.
Performing a presaturation slab on one side parallel to the slice can selectively destroy the MR signal from the in-flowing blood from this side of the slice. This allows the technique to be flow direction sensitive and to separate arteriograms or venograms. When the local magnetization of moving blood is selectively altered in a region, e.g. by selective excitation, it carries the altered magnetization with it when it moves, thus tagging the selected region for times on the order of the relaxation times.
For maximum flow signal, a complete new part of blood has to enter the slice every repetition (TR) period, which makes time of flight angiography sensitive to flow-velocity. The choice of TR and slice thickness should be appropriate to the expected flow-velocities because even small changes in slice thickness influences the performance of the TOF sequence. The use of sequential 2 dimensional Fourier transformation (2DFT) slices, 3DFT slabs, or multiple 3D slabs (chunks) are depending on the coverage required and the range of flow-velocities.
3D TOF MRA is routinely used for evaluating the Circle of Willis.
See also Magnetic Resonance Angiography and Contrast Enhanced Magnetic Resonance Angiography.
Images, Movies, Sliders:
 TOF-MRA Circle of Willis Inverted MIP  Open this link in a new window

 Circle of Willis, Time of Flight, MIP  Open this link in a new window
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Radiology-tip.comCT Angiography,  Coronary Angiogram
Radiology-tip.comColor Power Angio,  Doppler Ultrasound

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Magnetic resonance angiography: current status and future directions
Wednesday, 9 March 2011   by    
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