Bolus Chase Peripheral MRA

Overview:

Several approaches can be used for peripheral 3D MRA. We prefer to perform a series of 3D acquisitions following a single bolus injection of contrast media. The bolus is chased while it is running down to the legs. This is sometimes referred to as a runoff examination.

Scheduling Guidelines :

• First Ask:
  1. Diabetes?
  2. Aneurysm?
  3. Heart disease or CHF?
  4. Hypertension?
  5. Non-healing ulceration? Location?______________
  6. What are the symptoms?__________Which leg?___________
  7. Ankle-brachial pressures available? Fax non-invasive labs to 212-752-8908.
  8. Any bypass grafts?__________________________
  9. How long can you hold your breath?____________
• Scheduling preferences: 90 minute slot
• Ask patient to bring reports and films from any prior arteriograms
• Light meal prior to MRA is acceptable
• If patient is claustrophobic request: Valium (5-10 mg po) Xanax (1-2 mg po)

Patient Preparation:

• Change all clothes
• Start IV: If there is no injector available, use the SmartSet. An angiocatheter of 20 or 22 Guage is adequate when using SmartSet (for more information, please contact: 734-623-6400). Be sure that all iv connections are tight so they do not pop apart or leak. Load 30 cc of saline flush in 30 cc syringe and use 10 cc to prime flush Smart Set and test iv. Save remaining 20 cc saline to use later for flushing Gadolinium through tubing. When using automatic injector, load 60 cc of saline into flush syringe.
• Mark any surgical scars, masses or areas of ulceration with Vitamin E capsule or MR compatible marker.
• Sedation: Valium (5-10 mg po) or Xanax (1-2 mg po) are recommended for patients who are claustrophobic or anxious about the MRA examination. This will also reduce motion artifact and reduce cardiac output to maximize MRA image quality.
• Coil: Initially use head coil for ankle to knee for 2D time-resolved MRA. Then use the body coil or preferably phased array extremity coil for bolus chase Gd-enhanced 3D MRA.
• Patient Positioning: Feet First, Supine. Support patient’s head with comfortable pillows. Cover legs with blanket if patient is cold. This will help for avoiding peripheral vasoconstriction.

Time-Resolved Peripheral MRA

Time-resolved Gd-MRA techniques are useful when they are combined with 3D Gd-MRA. These are 3D TRICKS and 2D projection MRA of the calves and the feet. Time-resolved images shows the contrast arrival time to the calf and gives an idea about how fast the blood flow is. The bolus timing of subsequent 3D bolus chase Gd-MRA can be determined based on this information. If the contrast arrival time to the calf is less than 25 s, acquisition of 3D Gd-MRA without venous enhancement is almost impossible. In these fast flow patients, tourniquets (Smart Tourniquet) applied on the thighs are especially important for decreasing venous contamination.

Time-resolved 2D-projection MRA (calves and feet)

• SPGR pulse sequence which acquires 30 sequential images of a thick slab (60-120 mm). Display rate of the images is 2 frames/s.
• Position the coil over the area from above the knee to mid-tibia as shown on the figure.
• Landmark on mid-coil
• First acquire the pre-contrast sagittal localizer images
• On sagittal images prescribe a coronal thick slab for imaging the trifurcations of both legs
• For contrast enhanced image acquisition, fill the tubing with Gd, and then attach to the angiocatheter. Begin administering 6 ml of Gd bolus by hand as fast as possible and simultaneously press the ‘Scan’ button. As soon as the Gd administration finishes, switch to 20 ml saline flush at the same rate. If you are using an injector; 3.5 ml/s Gd followed with 25 ml saline flush as 3.5 ml/s.
• Move the coil down to image ankle and the feet. Position with cushion under knees to that foot will point more horizontally. The toes should be sticking out slightly beyond the end of the coil. Tape feet together to remind the patient to hold still.
• First acquire coronal localizer images. Coronal T1 of ankle-foot is ready to run. No adjustment necessary.
• Prescription of sagittal 2D projection MRA: On the coronal localizer (chose a slice 10-30 mm posterior to isocenter) set slab thickness to width of foot-ankle. Use “shift” to place one sagittal thick slab on each ankle-foot.
• Use sufficient phases so that total scan time is > 1 minute. If patient is older or expected to have really slow flow, make sure there are sufficient slices to image for at least 90 seconds.
• Using similar parameters and another bolus injection of 6 mL of gadolinium, acquire sagittal time-resolved ankle and foot images.
• An image obtained before the contrast arrival (visually identified on unsubtracted images) was used as the mask for complex subtraction from the subsequent image data. This is done both calves and feet)
• Reconstruction from remote terminal:

  telnet (IP address=192.168.30.21)
  login: signa
  password: adw2.0
  cd /usr/g/mrraw
  plist
  lx2dsam
  if uncertain about mask use image 5
  usually there are 2 locations
  If telnet does not work use utilities: command window: cd /usr/g/mrraw

3D TRICKS (Time Resolved Imaging of Contrast Kinetics):

TRICKS is a multi-phase and single station contrast enhanced time-resolved MRA technique. Imaging parameters are adjusted based on the patient’s flow kinetics.

• In slow flow patients, set more temporal output phases to increase the scan time, so that you can capture at least one arterial phase. In fast flow patients, less temporal output phases may be enough for capturing both arterial and venous phases. The number of the output phases only changes the total scan time.
• Complete the prescription and save the protocol, then click on ‘Prepare to Scan’ and then ‘Scan’ buttons. The system runs a scan for mask image acquisition and then pauses. Mask images will be used for automatic subtraction of the source images.
• Begin injecting 12 ml of Gd at the rate of 1 ml/s, and simultaneously press to ‘Scan’ button. When the Gd injection finishes, immediately switch to 20 ml saline flush at the same injection rate.
• When you look at the browser, you will see subtracted individual phases as different series and collapsed images of each phases as a separate series. On the subtracted images you will see the delay time (DT) which indicates the time interval between the start of the scan and the start of the phase. The DT on the image that you see the contrast in the arteries is the contrast arrival time.
• The number of scan locs determines the spatial resolution. While the number of scan locs increases, the maximum allowed number of output temporal phases decreases.
• It is possible to decrease scan time by setting a Phase FOV < 1, using a wide bandwidth and/or selecting a ‘Turbo’ mode. Turbo mode allows shorter TR, which in turn results in shorter scan time and high temporal resolution.

General Imaging Strategy:

If the contrast travel time to the foot-ankle is 35 seconds or less then go straight to bolus chase using a delay determined by assuming it takes 20 seconds to fill the pelvis. If the contrast travel time to the ankle is greater than 40seconds then perform a test bolus in the thigh to determine optimal timing for each station.

3D Gadolinium Enhanced Bolus Chase MRA

Preparations :

• Position the patient on the table so that the feet line up with the end of the table.
• Position the arms either above the head or crossed over the chest.
• Place the blood pressure cuffs (Smart Tourniquet) on both thighs.
• Place cushions under the ankles and knees so that the calf and thigh are perfectly horizontal and in line with the aorta.
• Strap feet together with curlex. Be careful with patients who have foot ulcers.
• Wide strap over knees to help the patient cooperate with holding perfectly still during the exam.
• Then "Landmark" 2-3 fingers above umbilicus.
• Advance to scan.

Here we describe the automatic table motion available in some of the MR scanners.

Prescribing 3D Volume

• Perform axial 2D TOF along the pelvis, thighs, and lower legs.
• Determine the greatest anterior extent of peripheral arteries = A? Usually this is in the groin area anterior to femoral head.
• Determine greatest posterior extent of peripheral arteries = P? Usually this is the popliteal artery.

• Prescribe the fast 3D SPGR pulse sequence in the coronal plane with sufficient slice thickness and number of slices to cover the arteries on the axial 2D TOF locator in the A-P direction.
• Slab thickness = thickness to encompass all peripheral arteries = A?-P? Typically this is 80-100 mm.
• Graphically prescribe off an axial scout image at S0.
• Adjust number and thickness of slices to obtain sufficient coverage with <30s .
• Thickness may be increased up to 4mm as necessary.
• For patients with really slow flow, use full second station.
• Timing:

  For fast or average flow rate: use fast second station (i.e 10-15 seconds for thigh).
  Scan delay = time to fill pelvis – (scan time)/2 + 5 second safety margin
  Bolus duration = 3/2 scan time – 1/3(time to feet), ~35 seconds
  

Pre-Gd Mask Images:

Subtraction of the pre-contrast mask images from the post-contrast images reduces the background signal and improves the vessel-to-background contrast. This is especially important for small vessels.

• Inflate the blood pressure cuffs up to the pressure of 50 mmHg for reducing the venous contamination. This pressure should be applied to the thighs during entire study (both pre- and post-contrast imaging).
• Table is positioned at first station (abdomen-pelvis), press "start scan".
• After first scan finishes, table automatically moves to second (thighs) station, press "start scan".
• Finally table moves to third station (calves), press "start scan".
• Check images to be sure they appropriately cover the anatomy and make sure the level of transition from one station to the next are in suitable locations so complex branching anatomy (e.g. the trifurcation) will be easy to evaluate. It is useful if the first and second stations both cover the common femoral bifurcation so that in the event of a timing error, it will be well visualized on at least on station.
• The actual arterial phase run is very complicated because you have to coordinate injection, breath holding and scanning. Generally it is also necessary to have the patient hyperventilate before hand to make sure breath holding will be easy. Getting all this to work requires standing in the scanner room next to the patient during the injection.

Dynamic Gd Enhanced Images:

• The actual arterial phase run is very complicated because you have to coordinate injection, breath holding and scanning. Generally it is also necessary to have the patient hyperventilate before hand to make sure breath holding will be easy. Getting all this to work requires standing in the scanner room next to the patient during the injection.
• Contrast injection: Typically the injection rate is 1.5 ml/s. For 30 ml at an injection rate of 1.5 ml/s, the bolus duration would be 45 seconds.
• For more precise measurement of infusion rate and scan delay, measure the time for a Gd test bolus to reach the aorta with a sagittal 2D SPGR sequence. Prescribe one thick slice centered on the aorta and repeat 2D SPGR scan at 1-2 second intervals for 60 seconds after initiating test bolus injection. Also consider Doppler Ultrasound contrast agent to determine the circulation time from the iv site to the infrarenal abdominal aorta, the common femoral artery and the popliteal artery. Ideally measure the circulation time to both legs but at a minimum, measure the most symptomatic leg. Then calculate infusion rate and scan delay with the following formulas assuming partial Fourier imaging (0.5 NEX) with center of k-space acquired at the end of the acquisition:

  Scan Delay = Time to aorta peak bolus – Scan Time/2
  Bolus Duration = 2.5 x Scan time + Table motion time – Popliteal peak time + Aorta peak time – US bolus duration

• If there is a full acquisition of k-space with sequential mapping such that the center of k-space acquired in the middle of the scan then use the following formula:

  Scan Delay = Time to aorta peak bolus – Scan Time/4

• Each station should be prepped to scan before contrast injection.
• First station (abdomen and pelvis):
• Check to be sure that phorder = 0 (sequential mapping of k-space), arm the pump if using an automatic injection, and press "prep to scan".
• Start hyperventilating the patient ("deep breath in", "breathe out"…)
• Start the contrast infusion at the calculated rate.
• After scan delay (calculated above or empirically use 10-15 seconds or longer in patients who are older, have CHF or aortic aneurysm), start the scan during breath holding.
• Second station (thighs) and third (calf): All the while the contrast infusion continues at 1.5 ml/s and switches automatically to saline flush out 1.5 ml/s the moment the 60 ml Gd syringe is empty.
• Transfer images to computer workstation.
• Subtract mask images from dynamic enhanced images.

3D Phase Contrast (Renal Arteries):

The 3D PC is sensitive to in-plane and turbulent flow. If there is a hemodynamically significant stenosis, turbulent flow results in signal loss in the vessel lumen. Scanning and reconstruction time are long. After Gd injection the SNR is higher than no contrast images. Therefore, using this sequence as a last study is appropriate.

There is a common association of renal artery stenosis with peripheral vascular disease. Therefore, all patients who are being imaged for peripheral vascular disease should have an evaluation of the renal arteries. Since the 3D Gd MRA in the abdomen is not optimized for the renal arteries, it is always helpful to perform post-Gd 3D PC sequence for complete renal artery evaluation.

VENC settings: Default = 40 cm/s

1. Young patients = 50-60 cm/s
2. Old patients (>70) = 30 cm/s
3. Poor renal function (Cr>2) = 30 cm/s
4. AAA or CHF = 30 cm/s
5. Obtain collapse image but do not reconstruct any projection images
6. Reconstruct phase difference images
7. Recently we have discovered that the sequence will not always work properly unless you select the magnitude images

• Set the phase contrast parameters in ‘Vascular’ section:

  Projection: 0
  Compression: on
  Flow analysis: off
  Acquisition flow direction: all
  Additional flow images: Magnitude

• Prescribe axial slices to cover both renal arteries all the way down to the renal parenchyma.
• Do not use saturation pulses

Billing Instructions:

MRA Abdomen: 774185

MRA Pelvis: 772198

MRA lower extremity: 773725

Reimbursable ICD9 codes:

Report Template :

Clinical Statement:

Technique:

Findings:

 No abnormal masses are identified; however this study was not optimized to evaluate abdominal and pelvic organs or soft tissues.

Impression: