MRA AND MRV OF ABDOMEN
Indications for MRA and MRV abdomen
Magnetic Resonance Angiography(MRA) of abdomen
- Pre surgical planning for stent-grafts
- Abdominal aortic aneurysm
- For the evaluation vasculitis
- Mesenteric Ischaemia
- Post-surgical Follow-up
- Renal artery stenosis
- Aortic Dissection
Magnetic resonance venography (MRV) of abdomen
- For the assessment of post radiotherapy changes
- Portal vein assessment in liver transplant
- Portal hypertension varices
- Hepatic venous thrombosis
- Arteriovenous malformation
- Portal vein thrombosis
- Venous thrombosis
- IVC tumor invasion
- IVC occlusion
- Leg swelling
- IVC tumor
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
- 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
- Instruct the patient to hold their breath for the breath hold scans (its better to coach the patient two to three times before starting the scan)
- An intravenous line must be placed with extension tubing extending out of the magnetic bore
- Contrast injection risk and benefits must be explained to the patient before the scan
- Gadolinium should only be given to the patient if GFR is >30
- If possible provide a chaperone for claustrophobic patients (e.g. relative or staff )
- Offer earplugs or headphones, possibly with music for extra comfort
- Explain the procedure to the patient
- Instruct the patient to keep still
- Note the weight of the patient
Positioning
- 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 coils over abdomen and pelvis (nipple down to elbow three inches below symphysis pubis).
- 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 localizer over the iliac crest.
Suggested protocols, parameters and planning
localiser
A three-plane TrueFISP localizer needs to be acquired initially for localization and sequence planning purposes. These fast single-shot localizers have an acquisition time of under 25 seconds, making them highly effective for localizing vascular structures. It’s recommended to obtain a minimum of 5-8 slices in all planes to achieve optimal results.
T1 vibe 3d DIXON axial pre contrast 4 mm
Plan the axial slices on the coronal plane. Angle the positioning block parallel to the line along the right and left iliac crests. Check the positioning block in the other two planes. Ensure an appropriate angle is used in the sagittal plane (perpendicular to the lumbar spine). The slices should sufficiently cover the entire abdomen from the diaphragm down to the symphysis pubis. The field of view (FOV) should be large enough to encompass the entire abdomen (usually 350mm-400mm).
Parameters
TR 6-7 | TE 2.39 4.77 | FLIP 10 | NXA 1 | SLICE 4 MM | MATRIX 320×320 | FOV 320-350 | PHASE A>P | OVERSAMPLE 20% | BH YES |
T1 flash 3D coronal .9mm -1.1mm pre-contrast
Plan the coronal slices on the axial plane, angling the positioning block parallel to the midline along the right and left kidneys. Verify the positioning block in the other two planes. An appropriate angle must be applied in the sagittal plane, parallel to the Inferior vena cava, ensuring slices cover the entire Inferior vena cava. Utilize phase oversampling and, for 3D blocks, slice oversample, to prevent wrap-around artifacts. The field of view (FOV) must adequately encompass the entire IVC. Instruct the patient to hold their breath during image acquisition (In our department, we instruct patients to breathe in and out twice before the “breath in and hold” instruction). Using the Parallel acquisition technique is highly recommended to reduce scan time (scan time should be under 15 seconds for optimal results).
Parameters
TR 4-5 | TE 2-3 | FLIP 10 | NEX 1 | SLICE 1 MM | MATRIX 320×320 | FOV 400-450 | PHASE R>L | OVERSAMPLE 100% | IPAT ON |
Contrast administration and timing of scans
Guess timing technique:- This is one of the simplest methods. It works by estimating the time of contrast travel from the site of injection to the vascular structure of the abdomen. This technique is highly dependent upon the site of contrast injection, age of the patient, cardiac output, and vascular anatomy. Generally, the contrast takes about 18-25 seconds to travel from the antecubital vein to the abdominal aorta. Therefore, the post-contrast T1 acquisition should start within 20 seconds of contrast administration.
Care bolus technique:- Care bolus is the most commonly used bolus detection technique. This technique utilizes a coronal fast gradient refocused sequence to obtain real-time images of the vascular structure of interest, typically positioned over the heart, at a frequency of one image per second. The operator can observe the arrival of the contrast bolus in the heart and subsequently switch to the centric 3D sequence.
Planning care bolus
Plan the coronal care bolus slice on the sagittal plane. Position the block over the mid-heart and angle the slice parallel to the ascending aorta. Verify the position in the other two planes. Establish the appropriate angle in the axial plane, aligning it horizontally across the heart.
Care bolus scans should commence one second before contrast administration. The operator can then observe the scans in real-time and monitor the arrival of the contrast bolus in the heart. Once the contrast reaches the heart, the care bolus should be promptly halted, and the patient should be instructed to hold their breath before initiating the centric 3D dynamic sequence.
T1 flash dynamic 3D coronal .9mm - 1.1mm post-contrast 3 measurements
Plan the coronal slices on the axial plane, angling the positioning block parallel to the midline along the right and left kidneys. Verify the positioning block in the other two planes. An appropriate angle must be applied in the sagittal plane, parallel to the Inferior vena cava, ensuring slices cover the entire Inferior vena cava. Utilize phase oversampling and, for 3D blocks, slice oversample, to prevent wrap-around artifacts. The field of view (FOV) must adequately encompass the entire IVC. Instruct the patient to hold their breath during image acquisition (In our department, we instruct patients to breathe in and out twice before the “breath in and hold” instruction). Using the Parallel acquisition technique is highly recommended to reduce scan time (scan time should be under 15 seconds for optimal results).
A dynamic flash 3D sequence comprises three flash 1mm 3D scans, with a 15-second delay between the first and second scans and a 20-second delay between the second and third scans. The initial scan captures the arterial phase, followed by the venous phase in the second scan, and finally, the delayed venous phase in the third scan. Precise timing is crucial for each scan, particularly during the arterial and venous phases. Providing accurate breathing instructions is vital during the first and second scans, as well as between the second and third scans. Instruct the patient to breathe normally after the arterial phase scan and then to hold their breath when approximately 4 seconds remain for the venous scan. Repeat this procedure between the second and third scans.
Parameters
TR 4-5 | TE 2-3 | FLIP 10 | NXA 1 | SLICE 1 mm | MATRIX 320X320 | FOV 400-450 | PHASE R>L | DYNAMIC 3 SCANS | IPAT ON |
T1 vibe 3d fat sat axial post contrast 4mm
Plan the axial slices on the coronal plane. Angle the positioning block parallel to the line along the right and left iliac crests. Check the positioning block in the other two planes. Ensure an appropriate angle is used in the sagittal plane (perpendicular to the lumbar spine). The slices should sufficiently cover the entire abdomen from the diaphragm down to the symphysis pubis. The field of view (FOV) should be large enough to encompass the entire abdomen (usually 350mm-400mm).
Parameters
TR 6-7 | TE 2.39 4.77 | FLIP 10 | NXA 1 | SLICE 4 MM | MATRIX 320×320 | FOV 320-350 | PHASE A>P | OVERSAMPLE 20% | BH YES |
