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  1. 1. Magnetic resonance angiography (MRA)
  2. 2. Magnetic resonance angiography (MRA)  is a group of techniques based on magnetic resonance imaging (MRI) to image blood vessels.  This MRI technique presenting soft tissue contrast between blood vessels and surrounding tissues primarily dependent on by flow, rather than displaying the vessel lumen.  There are bright blood and black blood MRA techniques, named according to the appearance of the blood vessels.
  3. 3. Magnetic resonance angiography (MRA)  The three main types of MRA:  Time of flight angiography (TOF).  Phase contrast angiography (PCA).  Contrast enhanced magnetic resonance angiography (CE-MRA).
  4. 4. Magnetic resonance angiography (MRA)  Time of flight angiography (TOF).  Is a gradient echo sequences with short TR, acquired with slices perpendicular to the direction of blood flow.  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.
  5. 5. Magnetic resonance angiography (MRA)  Time of flight angiography (TOF).  These completely relaxed spins have full equilibrium magnetization and produce a much higher signal than stationary spins if a gradient echo sequence is generated.  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.  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.
  6. 6. Magnetic resonance angiography (MRA)
  7. 7. Magnetic resonance angiography (MRA)  Phase contrast angiography (PCA).  This method images of the blood flow-velocity are produced.  The phase information can be used with subtraction of images with and without a velocity encoding gradient.  The signal will be directly proportional to the velocity because of the relation between blood flow-velocity and signal intensity.  complete suppression of stationary tissue (no velocity - no signal).
  8. 8. Magnetic resonance angiography (MRA)  Phase contrast angiography (PCA).  Phase sensitization can only be acquired along one axis at a time.  Phase contrast angiographic techniques tend to be 4 times slower than TOF techniques with the same matrix.
  9. 9. Magnetic resonance angiography (MRA)
  10. 10. Magnetic resonance angiography (MRA)  Contrast enhanced magnetic resonance angiography (CE-MRA).  Is based on the T1 values of blood, the surrounding tissue, and paramagnetic contrast agent.  T1-shortening contrast agents reduces the T1 value of the blood (approximately to 50 msec, shorter than that of the surrounding tissues) and allow the visualization of blood vessels, as the images are no longer dependent primarily on the inflow effect of the blood.
  11. 11. Magnetic resonance angiography (MRA)  Contrast enhanced magnetic resonance angiography (CE-MRA).  Contrast enhanced MRA is performed with  A short TR to have low signal (due to the longer T1) from the stationary tissue.  Short scan time to facilitate breath hold imaging.  Short TE to minimize T2* effects.  A bolus injection of a sufficient dose of a gadolinium chelate.
  12. 12. THANKS FOR ALL.