Magnetic resonance angiography (MRA) and Magnetic resonance venography (MRV)
1. Sequence: Time-of-flight
Abbr.: TOF
Physics: Blood entering the imaged area is not yet magnetically saturated, giving it a much higher signal when using short echo time and flow compensation.
Main Clinical distinctions: Detection of aneurysm, stenosis, or dissection.
MRI image appearance
The easiest way to identify TOF images is to look for blood vessels in the body (circle of wcarotids). Blood vessels usually appear bright on TOF image.
Tissues and their TOF appearance
- Muscles: - darker than fat signal
- Fat – dark gray
- White matter - dark gray
- Bone marrow: - dark
- Moving blood- bright
- Gray matter - dark gray
- Fluids – dark
- Bone - dark
- Air - dark
Use
- Very useful for circle of willis imaging
- Very useful for carotid arteries imaging
- Very useful for dural venous sinus imaging
- Can be useful for arterial imaging in the legs
2. Sequence: 3D Phase contrast( PC) sequence used in MRV brain imaging
Abbr.: PC-MRV
Physics: Two gradients with equal magnitude, but opposite direction, are used to encode a phase shift, which is proportional to the velocity of spins.
Main Clinical distinctions: Detection of aneurysm, stenosis, or dissection (pictured).
Use
- Very useful for dural venous sinus imaging
- Useful for circle of willis imaging
- Useful for carotid arteries imaging
- Can be useful for arterial imaging in the legs
