Phase Contrast With Body Imaging

1-Basic Principles for Phase Contrast

Phase contrast imaging is an MRI technique that can be used to detect any moving fluid based on velocity encoding (VENC) . Any Spins which are moving towards the magnetic field gradient develop a phase shift which is proportional to the velocity of the spins. By using bipolar gradients (two gradients with an equal magnitude but opposite direction -negative pulse) are used to encode the velocity of the spins. Fixed or unmoved spins have no net change in phase, after the two gradients are applied, moving spins will have a different magnitude of the second gradient compared to the first one, because of its different spatial position. This results in a net phase shift. This information can be used directly to determine the velocity of the spins. Alternatively, the image can be subtracted from one acquired without the velocity encoding gradients to obtain an angiogram.

2-Clinical Application For Phase Contrast

• MR angiography non-IV-contrast
• MR Venography as a non-IV-contrast
• CSF Flow Imaging
• Flow quantification( Aortic and Pulmonary valvar assessment) in cardiovascular MRI studies
• 4D Flow imaging (Aorta -vector Graph)
• MRI Electrography (quantifies waves from the tissue )

3- Velocity Encoding values

the VENC has to be identified before using the pulse imaging and it has to be accurate to the area of scanning to avoid any artifact

if it is to low, it will result in aliasing artifact and if it is to high, it may get in appropriate measurement

see the average values for the Phase contrast (VENC)

Thoracic Aorta 150-170cm/sec Abdominal Aorta 120-150cm/sec

Pulmonary artery 120 cm/sec

subclavian/ Brachial /carotids arteries 80-120cm/sec

cerebral arteries 30-60cm/sec

SSS(superior sagittal sinus) 15-20cm/sec

aqueduct      8-12 cm/sec

Pls note, theses values may be changing up and down according to the PT heart rate and age

next articles will be on How to use PC with image planning in various body regions

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