AAA Protocol

Common Indications:

• Pre-op for AAA repair
• Measure aorta diameter (only Sag and Axial T1 black blood necessary)
• Map aorto-renal anatomy for stent graft planning

Patient Preparation:

• Start intravenous line (20 or 22 gauge iv). If using a small caliber iv (i.e. 22 gauge) then pre-warm the gadolinium contrast to body temperature to reduce its viscosity.
• Oxygen, 2-4 liters/min by nasal canulae is essential if the patient is short of breath.
• Valium (5-10mg po) or Xanax (1-2 mg po) if patient is claustrophobic may be given.

Coil: Body coil is best because of its large field-of-view that allows imaging from diaphragm to femoral heads. If using the torso array, consider rotating 90 degrees for greater S/I coverage.

Patient Positioning: Supine, feet first,

Landmark: on lower rib margin or just above iliac crest

Series 1: Sagittal Locator

• For AAA the sagittal locator is the best orientation. You may consider landmarking high to also cover the thoracic aorta in case the patient is suspected of a thoraco-abdominal aneurysm. Make sure to use a large FOV (48 cm) so you will still see low enough to locate the iliac and femoral arteries.
• Single shot fast spin echo (SSFSE) is also a good initial (localizer) sequence but it will not show the thoracic component of the aorta and it is not available on all scanners. It can be performed without breath-holding although it is preferred. Use 8 skip 0, TE=180 and do not use fat saturation.
• Breath-hold fast multiplanar spoiled gradient echo (FMPSPGR) is the fastest sequence but is not recommended because it does not show the abdominal aorta well especially if there is trouble with the breath holding.
• When using the spin echo sequence with interleaved acquisition (as recommended) half of the images are reconstructed half way through the scan. These images can be used to set-up series 2 while you are waiting for series 1 to finish.

This is the main sequence for showing the aorto-iliac and renal artery anatomy in a presentation that is suitable for pre-operative planning. It is essential to have perfect gadolinium infusion timing so that central k-space data will be acquired during the arterial phase of the bolus.

• ADDITIONAL PARAMETERS
• Vascular Screen:
• Projection Images: 0
• Collapse: on
• User CVs Screen:
• Max. Monitor Period: 40
• Image Acq. Delay: 8
• SPECIAL: off
• Multi Phase Screen:
• Phases per Location: 3
• Delay After Acq: minimum (550)

• To determine where to position the 3D Volume, first find the celiac and SMA, the right and left kidneys and trace the path of the right and left iliac and common femoral arteries.
• Scanning range
• Posterior to the iliac arteries where they loop in the pelvis
• Anterior to the celiac and SMA origins and anterior to the common femoral arteries as the pass over the femoral heads
• Make sure the acquisition time is short enough so that the patient can suspend breathing for the entire scan. To make the scan time shorter consider
• Decreasing NEX to 0.5
• Decreasing matrix to 128
• Decreasing number of slices and increasing slice thickness
• Covering only the essential anatomy
• Use the "fallback" for optimal right-left alignment
• Check "#of Locs Before Pause" to be sure it is set to 1.
• Place the patient’s arms over head or on cushions to get them out from along side the patient where they will wrap around into the imaging volume.
• Test the iv with saline and then fill the SmartSet with Gd contrast (about 7ml).
• Instruct the patient on when to suspend breathing: "This is the most important scan. You will need to hold your breath for 1/2 of the scan, the second half. You can tell when to hold your breath by the change in the sound. Just to be sure there is no confusion, I will squeeze your arm when the sound changes so that you will know exactly when to take in a deep breath and hold it."
• Start scan: Do not begin injecting until the clock begins to count down: about 15 seconds after starting the scan.
• When the clock begins counting down, starting injecting at about 1-2 cc/sec.
• When the sound changes (bolus detected), signal the patient to Breath Hold by squeezing arm.
• When Gd infusion is complete, flush with 20 cc normal saline.
• At the end of the arterial phase scan, have the patient take 3-4 quick breaths and then scan again to catch the portal venous phase. Then allow the patient to breath several times until relaxed and breath hold for one final scan during the equilibrium phase.

The purpose of this series of images is to provide high resolution axial images for measuring aneurysm size, to determine the extent of intraluminal thrombus and to identify periaortic enhancement that occurs with inflammatory aneurysms. This is especially important in the pelvis where large aneurysms of the iliac arteries may be missed when lined with thrombus that obscures the true aneurysm diameter. Patients with AAA may also have aneurysms of the common femoral arteries, popliteal arteries, renal arteries, splanchnic arteries, thoracic aorta and great vessels and iliac arteries. Consider adding fat saturation to this sequence to improve contrast at the expense of small increase in scan time.

• The 2D time-of-flight sequence is fast and heavily T1-weighted and is our preferred sequence. An alternative approach to achieving the bright blood effect and enhancement effect is to use a spin echo T1-weighted sequence with flow compensation, the shortest possible echo time and possibly fat saturation to better appreciate areas of enhancement.
• Scan from above the celiac axis down to the femoral heads. This will help in identifying AAA, iliac and common femoral artery aneurysm size. To avoid excessively long scan times, it is acceptable to use large gaps (e.g. 8 mm thick slices with a 5, 10 or even 20 mm gap).
• Flow compensation and Respiratory compensation with multiple NEX are all essential.
• Initiate this scan immediately after the coronal 3D Gd:MRA so that the data are acquired before the contrast agent is eliminated from the intravascular space.

Series 4: Axial 3D Phase Contrast

This sequence provides another high resolution look at the renal arteries and helps in the evaluation of the hemodynamic significance of any renal artery lesions that are present.

• ADDITIONAL PARAMETERS
• Vascular Screen:
• Projection Images: 0
• Flow Recon Type: Phase Diff
• Velocity Encoding: 30
• Acq. Flow Direction: ALL
• Collapse: on
• Flow Analysis: off
• Additional Flow Images: none

• Set the Venc = 30cm/sec as the default since all patients with AAA tend to have relatively slow renal blood flow. Lower it to 20 or 25 cm/sec in patients who also have renal insufficiency with serum creatinine >2.5 mg/dl
• When positioning the 3D volume, remember that the position of the kidneys will be lower during the breathhold in inspiration for the 3D Gd:MRA. So anticipate that the kidney will move 1-2 cm superiorly during free breathing for the 3D PC.
• It is acceptable to have the FOV slightly smaller than the right-left dimension of the patient’s abdomen since phase is mapped A-P and frequency is R-L.
• If there are accessory renal arteries, then instead of 28 slices that are each 2.5 mm thick, change to 60 slices each 2.0 mm thick with 128 phase encoding steps in order to cover more S-I distance.

Billing Codes:

• MRA Abdomen 74185
• MRI Abdomen 74181
• MRA Pelvis 72198
• Computer Recontructions 76375

 

Note that if the study is just to measure the aneurysm size: (e.g. to determine if the AAA is growing) then it may be sufficient to perform sagittal or coronal SSFSE and axial T1 for size measurements. This saves time and does not require gadolinium contrast. Detailed mapping of the vascular anatomy is only necessary for pre-operative or pre-stent planning.

Sample typical dictation:

The patient was imaged with Sagittal (T1 or SSFSE), axial T2, 3D coronal spoiled gradient echo with dynamic gadolinium enhancement, axial 2D time-of-flight post gadolinium and 3D phase contrast post gadolinium sequences. Following image acquisition, reformations and MIPs were obtained on a computer workstation optimized for each of the major vessels.
There is a (infra, juxta, para, supra-) renal abdominal aortic aneurysm extending down to (above the bifurcation, the bifurcation, below the bifurcation). The maximum diameter measures ____. There is (not) evidence for peri-aortic inflammation.
The celiac axis and superior mesenteric artery origins are widely patent The inferior mesenteric artery is not identified and presumed occluded. A single right renal artery is identified which is widely patent and the right kidney measures 11 cm in length. A single left renal artery is identified which is widely patent and the left kidney measures 11.5 cm in length. No signal dephasing is identified in the renal arteries on 3D PC. No accessory renal arteries are identified. The retroperitoneal and renal venous anatomy is normal.
The common iliac arteries are normal (ectatic or aneurysmal). The internal iliac arteries are widely patent but not aneurysmal. The external iliac arteries are widely patent (stenotic?). The common femoral arteries are normal in caliber (ectatic or aneurysmal)


Vascular Measurements (cm)

Aorta diameter above celiac
Aorta diameter at renal arteries
Aorta diameter at top of AAA
Maximum AAA diameter
Aorta diameter at bifurcation
Diameter of right common iliac artery
Diameter of left common iliac artery
Diameter of right external iliac artery
Diameter of left external iliac artery
Length of neck between right renal and AAA
Length of neck between left renal and AAA
Length of normal diameter R CIA above IAA
Length of normal diameter L CIA above IAA

No abdominal masses are identified.
Impression:
6 cm infrarenal AAA extending to bifurcation with widely patent renal arteris, celiac and SMA. IMA occluded.

ICD9 Codes: