3D Brachial Plexus MRI/MRA/MRV Technique

[by James D. Collins, M.D. of UCLA Radiology]

Plain chest radiographs (PA and lateral) and C-spine radiograph are obtained and reviewed prior to the MRI. The procedure is discussed, the patient is examined, and the clinical history is reviewed. Respiratory gating is applied throughout the procedure to minimize motion artifact. The patient is supine in the body coil with arms down to the side, and imaging is monitored at the MRI station.

The body coil is used because the signal intensity of a surface diminishes above and below the coil, and the images are suboptimal for landmark anatomy. Intravenous contrast agents are not administered. A water bag (500 ml normal saline) is placed on the right and the left side of the neck above the shoulder girdle to increase signal-to-noise ratio for high resolution imaging. A full field of view (44 cm) of the neck and the thorax is used to image both supraclavicular fossae. Contiguous (4-5 mm) coronal, transverse (axial), oblique transverse, and sagittal T1-weighted images are obtained. If there is clinical evidence of scarring, tumor, and/or lymphatic obstruction, Fast Spine Echo T2-weighted images are selectively obtained. Seven imaging sequences are acquired, coronal, transverse, oblique transverse (all right and left), and sagittal. Selected images are annotated for the physicians review.

The coronal sequence is the first to be imaged. The brachial plexus envelopes the artery (forming a neurovascular bundle), and the nerves are best imaged when the cursors are aligned to the arterial blood supply. The axillary artery margins vary in each patient, and the cursors must be adjusted for each MRI brachial plexus examination. The cursors are positioned on the skin surface of the posterior chest wall to the skin surface of the anterior chest wall for symmetry, 3-D reconstruction, and to detect abnormalities that trigger brachial plexopathies. The superior landmark is set above the orbits and the inferior landmark set at the level of the kidneys. The image that best demonstrates the arterial blood flow to the upper extremities is selected as the baseline image for the remaining sequences. The transverse sequence is set from the baseline coronal image above the orbits to the carina. The lateral margins of the shoulder girdle are imaged to insure bilateral, simultaneous display of the brachial plexus. The transverse oblique sequence is set by aligning the cursors to the arterial blood supply of each upper extremity using the baseline coronal sequence. The cursors are centered to the plane of the axillary artery 2 cm below the inferior cord of the brachial plexus to the superior margin of the coracoid process. This sequence is necessary to detect signal intensity, architecture, and compression of the long axis of the nerves, arteries and veins.

The sagittal sequence is obtained by aligning the cursors lateral to the coracoid processes (right and left). The sagittal plane is necessary to detect compression of the neurovascular bundle by the coracoid process, pectoralis minor muscle, clavicle and/or subclavius muscle, axillary masses, abnormalities of the scalene triangle, and evaluation of the cervicothoracic spine. The 2D Time Of Flight MRA/MRV sequence is obtained after the sagittal sequence. Veins and arteries of the neck, supraclavicular fossae, and the great vessels are imaged. The images are reconstructed and displayed as a single 2D stacked image and 3D reconstructed coronal display. These images are cross referenced to the T1-weighted images above.

Bilateral coronal and sagittal abduction external rotation of the upper extremities imaging sequences are obtained. After the routine sequences are completed, the patient is brought out from the gantry, and the arms are fully extended behind the head (without change in patient position). The patient is then returned to the gantry for completion of the sequences. This imaging plane displays the posterior inferior rotation of the clavicles and subclavius muscles, tension on the scalene triangles, increased intrathoracic pressure effects on cardiovascular structures, lungs, soft tissues, posterior inferior displacment of the acromioclavicular joints, and increased intraabdominal contents. The rotation of clavicle(s) may be measured in degrees, and inner diameters of the subclavian arteries and veins may be obtained in cm. A comparison may then be made to the above structures in the arms at the side positions. The coronal imaging parameters are set from the routine coronal T1-weighted sequence. The posterior setting is the same as the coronal sequence arms at the side and anterior to the sternoclavicular joints. This best displays the clavicles, neurovascular bundles, and the scalene triangles. The sagittal abduction external rotation sequence begins following the bilateral coronal abduction external rotation of the upper extremities sequence has been completed. The images are continuously acquired from the left coracoid process to the right coracoid process. The bilateral coronal and sagittal abduction external rotation of the upper extremities may then be cross-referenced to the coronal and sagittal routine sequence with arms at the side.

When an image sequence is completed, it is immediately transferred to another screen at an independent workstation for review and 3-D reformat display. The software for this 3-D reconstruction is already prepared in the 1.5 Tesla G.E. Signa MRI unit. The images are stored on optical disks for 3-D color reconstruction. The entire study is monitored by the radiologist and requires one and a half hours. Selected Kodak color, black and white laser prints, and transparencies are obtained for lectures and poster presentations. Annotated images are preserved on DVD/CD, radiographs, and optical disks.

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[Last update: Friday October 16th, 2009]