TWIST\TRICKS Dynamic MRA Upper Arm
TWIST (Time-resolved Angiography With Interleaved Stochastic Trajectories) MRA
TWIST (Time-resolved Angiography With Interleaved Stochastic Trajectories) is an advanced and innovative 3D Magnetic Resonance Angiography (MRA) technique that offers exceptionally high temporal (sub-second) and spatial resolution (sub-millimeter). This unique capability allows for the acquisition of multiple arterial, mixed, and venous phase images, capturing the passage of a contrast agent through the vascular anatomy in real-time.
TWIST MRA is based on a special k-space sampling technique. The k-space, a mathematical representation of image data, is divided into two regions. The central region of k-space provides information related to image contrast, while the peripheral region primarily contributes to achieving high spatial resolution.
The acceleration of the sequence acquisition is achieved by more frequently sampling k-space lines in the center during the passage of the contrast medium bolus through the covered 3D volume. This random and interleaved sampling technique optimizes both temporal and spatial resolution, enabling the real-time visualization of blood flow dynamics and vascular structures.
TWIST MRA is particularly beneficial in pediatric populations with soft-tissue vascular anomalies in the head and neck region. Compared to conventional contrast-enhanced MRI (CE-MRI), TWIST MRA with gadofosveset trisodium, a blood-pool contrast agent, offers detailed temporal information of VA hemodynamics and flow characteristics without the need for invasive procedures.
Indications for MRA upper arm
- Arteriovenous malformation
- Brachial artery dissection
- Brachial vein thrombosis
- Brachial Artery stenosis
- Atherosclerotic disease
- Aneurysms
- Vasculitis
Contraindications
- Any electrically, magnetically or mechanically activated implant (e.g. cardiac pacemaker, insulin pump biostimulator, neurostimulator, cochlear implant, and hearing aids)
- Intracranial aneurysm clips (unless made of titanium)
- Pregnancy (risk vs benefit ratio to be assessed)
- Ferromagnetic surgical clips or staples
- Metallic foreign body in the eye
- Metal shrapnel or bullet
Patient preparation for TWIST MRA
- A satisfactory written consent form must be taken from the patient before entering the scanner room
- Ask the patient to remove all metal objects including keys, coins, wallet, cards with magnetic strips, jewellery, hearing aid and hairpins
- Ask the patient to undress and change into a hospital gown
- Contrast injection risk and benefit must be explained to the patient before the scan.
- Gadolinium should only be given to the patient if GFR is > 30
- An intravenous line must be placed with extension tubing extending out of the magnetic bore
- Intravenous line must be placed in the unaffected side e.g if the problem exists in RT arm the canula should be in LT side
- Claustrophobic patients may be accompanied into the scanner room e.g. by staff member or relative with proper safety screening
- Offer headphones for communicating with the patient and ear protection
- Explain the procedure to the patient and answer questions
- Note the weight of the patient
Positioning for TWIST MRA upper arm
- Position the patient in supine position with head pointing towards the magnet (head first supine)
- Position the patient over the spine coil and place the body coil over the upper arm (shoulder down to elbow)
- Securely tighten the body coil using straps to prevent respiratory artefacts
- Give a pillow under the head and cushions under the legs for extra comfort
- Centre the laser beam localiser over the mid humerus
- Register the patient on the scanner as 'head first supine'
Recommended TWIST MRA Upper Arm Protocols and Planning
Localiser
A three-plane TrueFISP\HASTE localizer must be taken initially to localize and plan the sequences. These are fast single-shot localizers with an acquisition time under 25s, which are excellent for localizing vascular structures. Take at least 5-8 slices in all planes to get the best results.
TWIST coronal 1mm 3pre and 30 post
Plan the coronal TWIST 3D block 0n the axial plane, and angle the positioning block parallel to the clavicle (i.e., parallel to the subclavian artery). Check the positioning block in the other two planes. An appropriate angle must be used in the sagittal plane (parallel to the humerus). Slices must be sufficient to cover the whole upper arm from anterior to posterior. Ensure that the slices adequately cover the entire upper arm from anterior to posterior. Use a sufficiently large field of view (FOV) to encompass the shoulder and elbow joints. For phase direction, either choose right to left or head to feet with 100% oversampling to prevent wrap-around artifacts.
Parameters TWIST
TR 4-5 | TE 1.25 | FLIP 14 | NEX 1 | SLICE 1MM | MATRIX 384X320 | FOV 380-420 | PHASE R>L | DYNAMIC 30 SCAN | IPAT ON |
A dynamic TWIST sequence consists of 30 1mm 3D scans, with each acquisition taking around 3-4 seconds. The contrast injection must be administered after the third dynamic sequence.
T1 vibe 3d DIXON axial post contrast 1mm
Plan the axial slices on the coronal plane and angle the positioning block perpendicular to the humerus. Check the positioning block in the other two planes. An appropriate angle must be used in the sagittal plane (perpendicular to the humerus). Slices must be sufficient to cover the whole upper arm, from the acromioclavicular joint to the elbow joint. Adding a saturation band over the chest will help reduce breathing artifacts. The phase direction must be anteroposterior to avoid wrap-around and motion artifacts from the chest.
Parameters
TR 6-7 | TE 2.39 4.77 | FLIP 10 | NXA 1 | SLICE 1 MM | MATRIX 288×288 | FOV 250-300 | PHASE A>P | OVERSAMPLE 20% | BH NO |