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brachial_plexus [2025/06/25 20:51] – scottbrachial_plexus [2026/04/27 16:51] (current) – [Tips and Tricks] scott
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 ======Brachial Plexus MRI====== ======Brachial Plexus MRI======
  
-=====Anatomy=====+=====Positioning=====
  
-The brachial plexus exam can be more difficult than a standard brain or spine exam, as there is more complex anatomy, different positioning requirements, and different scanning challenges.  A good sense of the anatomy is crucial to proper coverage and slice orientation. +Positioning for the brachial plexus exam is especially important. To ensure the nerves and forelimbs can be well assessed, both limbs should be positioned as __symmetrical__ as possible, and pulled __rostrally__ and well secured. Proper limb positioning will ensure that the peripheral brachial plexus nerves can be imaged closest to isocenter, compared slice-to-slice, and without excessive slice coverage. Typically dorsal recumbency is preferred, and any compatible coils that can be positioned over the elbows or sternum will help with SNR.
- +
-The brachial plexuses are bundles of nerves that originate from about C4/5 to T2/3 and extends into the forelimbs on both sides. When there is an injury or lesion in the brachial plexus, a patient may present with muscle atrophy or forelimb lameness without an orthopedic cause. Below are MIPs of the brachial plexus nerves in 3 planes. Keep in mind that the nerves extend deeper into the forelimb than visualized on these sequences, so the required coverage will be larger.+
  
 =====Scan Coverage and Planning===== =====Scan Coverage and Planning=====
  
 +==== A note on Localizers====
 +
 +When planning out your localizer images, be sure to use a LARGE FOV so that the forelimbs are well demonstrated, positioning can be checked, and coil extents can be seen. Use a LOT of slices to cover all the anatomy; you want to be able to find the shoulder joints, elbows,  and sternum on all three planes.
 ====Sagittal Plane==== ====Sagittal Plane====
 For brachial plexus scout images, add more slices on all planes to cover sternum to spine dorsally, shoulder to shoulder sagittal, and C3 to T3 axially. On the axial and dorsal scout imaging, plan the slices parallel to the center of the spinal cord. On the sagittal scout image, center the FOV on C6/7. For brachial plexus scout images, add more slices on all planes to cover sternum to spine dorsally, shoulder to shoulder sagittal, and C3 to T3 axially. On the axial and dorsal scout imaging, plan the slices parallel to the center of the spinal cord. On the sagittal scout image, center the FOV on C6/7.
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-{{::bpluexus_plan.png?600|}}+{{::bpluexus_plan.png?600|}}{{::bplexussagplan.png?600|}}
    
  
 ====Axial Plane==== ====Axial Plane====
-There are two common variations for planning axial slices in the cervical spine, parallel to the intervertebral disc or perpendicular to the spinal cord. Both variations will yield diagnostic images, so be sure to **check clinician preference**.  
-In the image below, axial slices prescribed parallel to the disc are in __orange__, and slices prescribed perpendicular to the cord are in __yellow__. Center the FOV in the middle of the intervertebral disc and check dorsal images to ensure that the slices are not tilted tot he left or right. If patient positioning is suboptimal, it may be necessary to rotate the slices to match any side-to-side curve of the neck. If axial slices are being prescribed caudally toward C5/C6/C7, check axial and dorsal images to ensure wrap won't occur. 
  
-{{:cspineaxplan.png?500|}}+Axial coverage for the brachial plexus should cover from typically C4/5 to T3/4 to ensure that the entire plexus is covered. Angling parallel to the intervertebral disc will generally display the nerves exiting the foramen more clearly. The FOV should relatively large and be centered at the inferior aspect at the vertebrae and large enough to include the sternum and mid shaft of the humerus on both sides. 
 + 
 +{{::bplexusaxplan.png?500|}}
  
 ====Dorsal Plane==== ====Dorsal Plane====
-The dorsal plane angulation is tailored to the clinical scenario, and may not be consistent between exams. A sample slice planning is below in __orange__. Due to the natural curve of the spine, there isn't one angle that will get all the spinal cord in one slice, to be sure to adjust the angle to best emphasize pathology noted on prior axial or sagittal images. It is good practice to extend slice coverage ventrally beyond the vertebral bodies, as the __Brachial Plexus__ nerves exit ventrocaudally  from C4/5 to T1/2. Incidental findings are also frequently located on the dorsal plane (Right image, red arrow)+The dorsal plane is particularly useful when scanning for brachial plexus pathology, as it provides a good overview of both forelimbs symmetrically. As a first screening sequence, the dorsal should cover from the sternum to just past the vertebral bodies, with the FOV large enough to demonstrate both forelimbs. The __Brachial Plexus__ nerves exit ventrocaudally  from C4/5 to T1/2 and extend into the forelimbs and dorsal to the humeral head. Incidental findings are also frequently located on the dorsal plane (Right image, red arrow)
  
-{{:cspinedorplan.png?500|}}{{:dorincidental.png?500|}}+{{::bplexusdorplan.png?500|}}{{:dorincidental.png?500|}}
  
 =====Tips and Tricks===== =====Tips and Tricks=====
  
 ===Selecting Phase Direction=== ===Selecting Phase Direction===
-In the cervical spine, either A/P or S/I may be selected, but require slightly different acquisition strategies. 
-If choosing the phase direction S/I, motion artifact from respiration and flow the vessels in the cranial thorax will propagate S/I. Unlike awake human patients, there should be no motion artifact from swallowing. In the S/I direction there will be anatomy that extends beyond the FOV, and will require significant oversampling to prevent wrap artifact. This can add quite a bit of time, but will afford some extra SNR, so it may be possible to reduce time by reducing NEX/Averages. Note the flow artifact from the vessels (red arrow). If selecting the phase direction as A/P, it is possible to not only remove all the oversampling, but even to reduce the phase FOV to further reduce time. It is necessary with this method to prescribe a sat band over the cranial thorax to prevent flow artifact from propagating through the caudal cervical spine. It is important to note, this is not an appropriate method when brachial plexus pathology is suspected, as the sat band will obscure the nerve bundles.  
  
-==Phase S/I==+When imaging the brachial plexus, any phase direction may be used, but the A/P direction will allow for greater flexibility. A/P phase direction may allow for a rectangular FOV and reduced oversampling, both of which will save time that can be used for other motion reduction strategies. Unlike the cervical spine, saturation bands should not be used ventral to the spine to reduce flow and respiration artifact, as the nerves of interest run parallel to all the vessels and would be obscured.  
 + 
 +===Reducing Motion and Flow=== 
 + 
 +As the use of saturation bands would obscure important anatomy, motion reduction must be achieved with other methods. Here are a few parameter changes that can be made to reduce the effect of respiratory motion in the brachial plexus area: 
 + 
 +  * Increase NEX/Averages; 4 or more 
 +  * Square matrix; ie 256x256 select a slightly lower resolution to save time and keep it square  
 +  * Utilize higher bandwidth 
 +  * If applicable to your system, try PROPELLER/BLADE; pretty good for motion and also reduces flow artifact 
 + 
 +To reduce the effect of flow artifact: 
 + 
 +  * Use a slightly longer ETL/Turbo factor 
 +  * Select a later TE (second echo for T1's) 
 +  * If applicable to your system, 3D FSE's like CUBE/SPACE will naturally do an excellent job suppressing signal from vessels in all contrasts 
 + 
 +===Find Pathology=== 
 + 
 +Locating pathology in brachial plexus scans can be difficult when a large lesion isn't present. There are a few things that can be done to help: 
 + 
 +  * Run a dorsal early in the exam, preferably a STIR 
 +  * Check for symmetry; denervation changes are more easily spotted as fluid like intensity in muscles 
 +  * Good fat saturation; use Dixon techniques whenever possible. If no Dixon is available, be sure to manually shim the area of interest
  
-{{stirphasesi.png?500}} +===Fat Saturation===
  
-==Phase A/P==+Fat saturation can be tricky in the cervical/plexus area due the uneven anatomy, presence of microchips, and large FOV's required. 
  
-{{stirphaseAP.png?500}}+{{::poorfatsat.png?400|}}
  
 +  * Use Dixon techniques for fat saturation (Dixon, FLEX, IDEAL)
 +  * SPAIR/SPECIAL techniques may be a bit more homogenous if available
 +  * Manually shim to the area around the thoracic inlet
 +  * Position and scan close the isocenter
 +  * Use the smallest appropriate FOV