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Peripheral CE-MRA (MobiFlex) Maastricht

ExamCard
Leiner, Tim, M.D., Ph.D. Maastricht University Medical Center

 
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* Dr Leiner's procedure was developed at Release 9, but this

downloadable ExamCard is for Intera 1.5T Release 11.

ExamCard purpose

This ExamCard outlines a CE-MRA protocol for the assessment of the peripheral vasculature of patients with suspected intermittent claudication.

 

This ExamCard specifies four simple steps: 1) localizer scan, 2) mask scans, 3) contrast agent injection, assisted by BolusTrak, 4) contrast-enhanced 3D acquisition. If SENSE is used, it becomes a 5-step process in which a reference scan is performed (for each station separately) after the localizer scan.

 

Anatomy covered is from the infrarenal aorta down to the pedal arch in the foot. Total examination time, encompassing the steps above and using SENSE, is less than 15 minutes.

 

Maastricht's ExamCard for patients with suspected chronic critical ischemia divides the contrast bolus into two injections: the first part is used to scan the lower leg, and the second part is used to image the iliac and upper leg stations). This Exam Card is not available on NetForum yet.

ExamCard overview

MobiFlex_PV_Maastricht
Scan 1Localizer
Scan 2SENSE reference scan iliac
Scan 3SENSE reference scan upper leg
Scan 4SENSE reference scan lower leg
Scan 5Lower leg (mask)
Scan 6Upper leg (mask)
Scan 7Iliac (mask)
Scan 8BolusTrak-assisted contrast agent injection
Scan 9Iliac (CE)
Scan 10Upper leg (CE)
Scan 11Lower leg (CE)

ExamCard final result

 MobiFlex_Maastricht1.jpg   (FS25)
MobiFlex_Maastricht1.jpg (FS25)
Subtracted, fused image.

Patient preparation

Coil(s): 3-station Synergy Peripheral Vascular coil

OR:  integrated Body coil (upper two stations) + SENSE Body coil (lower leg).

 

Patient positioning: feet first, supine. If using the Synergy Peripheral Vascular coil, place a cushion beneath the popliteal fossa (posterior knee depression) to suspend the calf muscles. If using the Body coil + SENSE Body coil for the lower legs, use the standard MobiTrak foot support.

 

Special patient preparation: IV line for administration of contrast agent. Practicing the breath-hold command familiarizes the patient with the command and can be used to determine how long the patient can hold his/her breath.

Contrast agent / injection protocol

35-45 ml of 0.5 mmol/ml gadolinium contrast agent.

Alternatively 18-23 ml of 1.0 mmol/ml gadolinium contrast agent can be used.

 

Contrast injection is initiated based on the BolusTrak technique. After acquiring the three mask scans, injection of contrast medium (35-40 ml) is started, followed by injection of 20 ml of saline using an MR-compatible remote-controlled power injector (Medrad Spectris). The injection rate is set at 2.0 ml/sec for the first half of the contrast agent (~15-20 ml) and reduced to 1.0 ml/sec for the remainder (~20 ml).

Extended information per scan

1. Localizer: Low-resolution axial time-of-flight scan

Provides rough outline of arteries to facilitate positioning of the three-dimensional volume that will be imaged in mask and contrast-enhanced scans. The localizer assists in tailoring the thinnest 3D volume (slab) necessary to encompass the arteries in a given station, without including extraneous tissue. This saves considerable scan time and affords the option to increase resolution within the volume if desired. The localizer (survey) scan is run from the feet to the abdomen.

 

2, 3, 4. SENSE reference scan: for 3-station Synergy Peripheral Vascular coil

The reference scan determines the signal profile of each element of the 12-element coil. Perform this scan after the localizer and position it over the area to be examined. The SENSE reference scan needs to be performed separately in every station where SENSE is used but it can be used for all subsequent SENSE and CLEAR (Constant Level AppEARance) scans. The result is superb image quality even if the patient moves.

 

5, 6, 7. Lower leg, upper leg and iliac masks: non-contrast-enhanced 3D mask scan

Obtained for each station/FOV, 3D mask scan increases vessel-to-background contrast. It is later subtracted from identical scan obtained during injection of contrast material. The preparation phase of the mask scan is stored and this information is available when the same sequence is executed again (i.e. during the injection of contrast material). Therefore, preparation phases can be skipped during the injection of contrast material.

 

8. BolusTrak-assisted contrast agent injection

To time arrival of contrast medium before starting the contrast-enhanced scans, a real-time bolus monitoring (BolusTrak) is used. BolusTrak uses a coronal 2D thick-slice gradient echo acquisition in combination with real-time complex subtraction to visualize the arrival of contrast in the left ventricle. Upon contrast arrival, the 2D sequence is aborted and the 3D sequences are started with a delay time of approximately 5-8 seconds, which is used to give patients a breath-hold command.

 

9, 10, 11. Iliac, upper and lower leg contrast-enhanced scans

The contrast-enhanced scans are run by reversing the mask scans. The table moves automatically in between, the mask images are automatically subtracted from the contrast-enhanced scans and orthogonal MIPs are produced for each station. To ensure that the 3D contrast-enhanced acquisition is not started prior to completion of the breath-hold command, the scan start needs to be set to 'manual start'.

Background information

As an alternative to digital subtraction angiography (DSA), MobiTrak (i.e. moving-bed) peripheral CE-MRA has enabled clinicians to rapidly image multiple FOV (up to 120-130 cm), employing a single contrast bolus covering three separate stations (iliac, upper leg, lower leg), thereby avoiding venous enhancement and improving vessel-to-background contrast.

 

However, because a single contrast injection is used, speed is critical to avoid venous enhancement. Using the exact same scanning parameters (e.g. iliac station parameters) for all stations doesn't account for decreasing arterial vessel diameters from iliac to upper leg and particularly from the iliac to the lower leg station. This potentially reduces image quality, especially due to insufficient spatial resolution in lower leg arteries. MobiFlex moving-bed imaging allows flexible choice of scan parameters for each station, resulting in optimal spatial resolution for iliac, upper leg and lower leg arteries.

Literature references

  1. Leiner T, Ho KY, Nelemans PJ, de Haan MN, and van Engelshoven JM.
    Three-dimensional contrast-enhanced moving-bed infusion-tracking (MobiTrak) peripheral MR angiography with flexible choice of imaging parameters for each field of view.
    J Magn Reson Imaging 2000;11:368-377.
  2. Leiner T, Nijenhuis RJ, Maki JH, Lemaire E, Hoogeveen R, and van Engelshoven JM.
    Use of a three-station phased array coil to improve peripheral contrast-enhanced magnetic resonance angiography.
    J Magn Reson Imaging 2004;20:417-425.
  3. de Vries M, Nijenhuis RJ, Hoogeveen RM, de Haan MW, van Engelshoven JMA, Leiner T.
    Contrast-enhanced peripheral MR angiography using sensitivity encoding (SENSE) in multiple stations: feasibility study.
    In Press, J Magn Reson Imaging.


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ExamCard
Intera 1.5T
Release 10, Release 11, Release 9
Peripheral MRA, Vascular
 

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