Vascular MR In Practice Flashcards
What is required for Non -MR angiography?
→ Insertion of a catheter into a vein or artery etc
→ Sedatives - local anaesthetic
→ IV contrast
→ 30 min - 2hours
→ Few hours rest after wards
→ Significant radiation dose to pt and staff
→ Can treat at the same time
What is Vascular MRI?
- non-invasive (only may need a cannula)
- Multiple-planar imaging
- no ionising radiation
- can show functional and anatomical information
What Key areas can VMRI be used to investigate?
Brain, neck, heart, chest, abdomen, pelvis, as well as upper and lower extremities.
Although it is impossible due to all the positioning required to scan all these areas in one session .
What are the 2 methods of Non-con MRA ?
TOF and Phase contrast
See other lecture for more info
TOF recap
TOF angio is based upon the flow-related enhancement of spins that are entering an image slice.
GE sequences with very short TR periods are used to saturate the signal from stationary tissue
The blood flowing into the slice has not been saturated, so it signal is stronger than that of the stationary tissue.
TOF be performed in 2D or 3-D and can be performed with multiple stacks.
It can be combined with pre-saturation bands to suppress either the arterial or Venus flow
It uses the difference in longitudinal magnetisation for image contrast.
MIPS can be created from the source image so that the vessels can be isolated from surrounding soft tissue.
What are the Limitations of TOF ?
The vessles have to be relatively straight in order for the TOF to work.
Phase contrast recap
PC angio relies on detecting changes in the phase of bloods transverse magnetisation as it moves along the magnetic field gradient
Exploits difference in the spin phase for image contrast
Regularly used in cardiac MR, sagittal sinus and CSF flow
CE-MRA recap
Uses gad to enhance the signal by shortening the T1 of blood
Requires very quick imaging - eg: Fast GE, short TE and TR
Comparatively small volumes of contrast
Parameters must be optimised, using breath hold for abdominal vessles
Often on coronal - largest possible coverage
What are the 3 Types of aquiring CE-MRA ?
- Time bolus Ed CE-MRA
- Using a ‘fluoro’ sequences
- Using a series of acquisitions to see both arterial and venous phases
What is involved in Time bolus CE-MRA?
Involves the use of a test injection to determine a precise travel time for the bolus contrast injection
A mask scan with no contrast is performed first
The care bolus image looks similar to the T1 localiser scans with contrast in the blood vessels appearing bright
Travel time can be calculated
Another 3D sequence is performed after the contrast. The mask sequence and the post-con sequence are then subtracted - the resulting shows contrast filled vessels.
What is Fluoro CE-MRA?
• Uses MR fluoro to observe the arrival of the contrast bolus
• No need for a test injection.
• The mask, and post contrast scan have the same scan parameters
• Once the contrast is observed the 3D live scan is triggered
• Both the mask and live scan are 3D sequences. The fluoro scan is 2D
What is involved during Time resolved CE-MRA ?
- Time resolved acquisition involves the use of multiple dynamic scans to capture not only the anatomy of the vessels but also the blood flow.
- It does not require precise timing of the contrast bolus.
- Multiple 2D or 3D sequences are acquired to get arterial, venous and equilibrium phases of blood flow.
What is MRV (MR venogram) TOF-Brain used for?
- evaluation of thrombosis
- Venous sinus Tumour
- Drowsiness and confusion accompanying a headache
What are the clinical indications for a MRA TOF Brain ?
- ? Aneurism
- stroke
- vasculitis: internal carotid, cerebral, basilar artery
- occlusion and stenosis
- arteriovenous malformation (AVM)
What are MR of Carotid arteries used to look for?
What is the advantage?
Atherosclerosis
Ulceration
Stenosis
Complete occlusion
Advantage- minimal dephasing through tight stenosis
