Fiber Connections of the Supplementary Motor Area Revisited: Methodology of Fiber Dissection, DTI, and Three Dimensional Documentation

The purpose of this study is to show each step of the fiber dissection technique on human cadaveric brains, the 3D documentation of these dissections, and the diffusion tensor imaging of the anatomically dissected fiber pathways.

Transcript

The overall goal of this project is to explore the fiber connections of the supplementary motor complex in humans using a combination of in vivo fiber tracking via MRI combined with cadaveric fiber microdissection. This method can help answer key questions in the field leading to white matter anatomy of the human brain, such as how microdissection and DTI technique are done and how 3D photography and documentation of these studies are performed. The main advantage of this technique is to understand the anatomy of the white matter pathways of supplementary motor area comprehensively.

The implications of this technique extending towards therapy and brain tumor surgery since the in vivo fiber tracking techniques can be applied in the preoperative setting to minimize postoperative complications. There, this method can provide insight into the fiber connections of the supplementary motor area can also be applied to virtually any other brain region to assess the fiber track connections. Generally, individuals new to MRI diffusion fiber tracking will struggle because they more widely-adopted diffusion tensor imaging has significant limitations in the ability to model crossing fibers amongst other limitations.

Therefore, we adopted the method of generalized Q-sampling modeling to allow more accurate fiber tracking. I will be demonstrating the procedure with Dr.Cevik, an neuroanatomy fellow from our laboratory. To begin, prepare formalin-fixed brains according to Klingler's method.

Place the cadaveric head in a three-pin skull clamp and use a scalpul to make a frontotemporal skin incision. Then, use a scalpel, forceps, and scissors to remove the skin and muscles from the head. Next, use a drill with a compact speed reducer and a 14 millimeter cranial perforator attachment to make one or more burr holes in the skull until the dura mater is reached.

Then, use a router with a burr attachment to cut the bone flap. Open the skull and expose the brain. Once exposed, remove the dura arachnoid and pia mater and place the tissue under a microscope at six to 40 times magnification.

Use a Penfield Dissector to decorticate the cerebral cortex and remove all frontocortical tissues to expose the short association fiber tracks. These can be identified as U-fibers, or intergyral fibers that interconnect neighboring gyri. With the assistance of a micro hook, gently remove the short association fibers to reach and expose the long association fibers, which interconnect distant areas in the same hemisphere.

White matter pathways are composed of myelinated fibers and examined in three main categories. Associated fibers are wide connections between the different cortical regions in the same hemisphere;commissural fibers provide connection between both hemispheres, and projection fibers provide connection between the cortex and the cargo part of the brain and the spinal cord. Then, use the surgical micro hook and Penfield Dissector to go deep into the long association fibers and remove the superficial association fibers.

Remove each fiber bundle to expose the projection commissural fibers. Start by placing the specimen in a designed black color platform. Select a scene with a full frontal view of the specimen.

And take one shot by focusing the camera on any point of the specimen close to the center point on the camera screen. Rotate the camera slightly left until the right-most point on the camera screen is the same as the focusing point above. Then slide the camera to the right until the middle point on the screen overlaps the original focusing point on the specimen.

Focus the camera on this point and take another shot. In the 3D software program, open the stereo images so that the left image is in the left slot and the right image is in the right slot. then select the Half Color Anaglyph RL2 option and generate the anaglyph in JPEG format.

Start by downloading pre-process diffusion data from the Human Connectome Project website. And post-process it using Diffusion Spectrum Imaging Studio. To accomplish this, load the dataset into the software by first selecting Step1 Open Source Images, and then selecting the data nii.

gz file. Next, select the Step2 Reconstruction button. After verifying the brain map, select generalized Q-sampling imaging as the reconstruction method.

Also, select r-squared weighting with a length ratio of 1.0. Leave the remaining the selections as default, and then select Run Reconstruction. Place seeds for the cortical spinal tract using a seed from the Atlas function in the Region window.

Select JHU White Matter labels 1 millimeter, and the cortical spinal tract region. Then, perform fiber tracking by first going to the Options window and setting the tracking parameters as shows here. Select the seed orientation as All, the see position as Subvoxel, and randomized seeding as On.Also, use Trilinear direction interpolation with a streamline tracking algorithm and choose Run Tracking in the fiber tract's window.

Due to the randomized nature of tracking, you may find so-called false fibers, or fibers that are not of interest. These can be cleared by using regions of avoidance that can be drawn by hand as a new region. In the Region window, click the Atlas button to place seeds for the superior longitudinal fasciculus 1.

Select FreeSurferDKT, left_superior_frontal and left_precuneus. Then in the Region window, set the left_precuneus type to Seed, and the left_superior_frontal type to ROI. Next, in the Region window, select New Region, and manually draw a region of inclusion in the most posterior aspect of the superior frontal gyrus in the coronal plane.

Then, perform fiber tracking as previously described. next, perform the same process for the superior longitudinal fasciculus two. First, use New Region from the Region window and draw the seed region in the posterior aspect of the middle front gyrus white matter in the coronal plane.

Then, choose a region of inclusion using Atlas a FreeSurferDKT regions, left_rostral_middle_frontal, and left_caudal_middle_frontal. And FreeSurferSeg Atlas region ctx_lh_G_pariet_inf-Angular. Complete this process by performing fiber tracking as previously described.

For fiber tracking of the superior longitudinal fasciculus 3, place seeds with a seed region using Atlas. Choose ctx_lh_G_pariet_inf-Supermar of the FreeSurferSeg atlas. Then, select the region of inclusion from Atlas in ctx_lh_G_front_inf-Opercular from the FreeSurferSeg atlas.

Complete this process by performing fiber tracking as previously described. For the callossal fibers, place seeds using a new region and draw a seed in the sagittal plane encompassing the corpus callosum. Complete this process by performing fiber tracking as previously described after increasing Terminate if to 900 tracts.

For cingulate fibers, place seeds using a new region and draw a seed region the mid cingulate gyrus on the coronal view. Use New Region to draw a region of inclusion in the posterior cingulate gyrus under coronal view. Complete this process by performing fiber tracking as previously described.

Next, place seeds for claustrocortical fibers using the Atlas function to place a region in Claustrum under the talairach atlas. Next, select Atlas and add regions left_superior_parietal and left_superior_frontal from the FreeSurferDKT atlas. In the Region window, set Claustrum to End and the other two regions to Seed.

Based on the accuracy of the registration, the regions may need some modification in position, particularly the claustrum due to the small size of structure. These are found by right-clicking the region in the Region window and selecting the change in position from the Move Region options. Perform fiber tracking as in previous steps.

Place seeds for the frontal aslant tract by first selecting the Atlas function and selecting the left_pars_opercularis from the FreeSurferDKT atlas, and then another region using the Atlas function and selecting Supp_Motor_Area_L from the aal atlas. Next, set left_pars_opercularis to End in the Region window, and the set Supp_Motor_Area_L to Seed. For the frontal striatal tract, again, select the Atlas function and then Supp_Motor_Area_L from the aal atlas.

Next, choose the Atlas function and then select Striatum_L from the ATAG_basal_ganglia atlas. In the Region window, set Striatum_L to End, and Supp_Motor_Area_L to Seed. Then, generate a surface rendering of the brain by selecting Slices and Add Isosurface.

The threshold value may vary based on the dataset and may have to be adjusted until the results are satisfactory. It is critical to gain a better understanding of topographical anatomy, particularly through 3D anatomical studies and to use clinical features of these connections to plan surgery in order to prevent permanent damage. The supplementary motor area complex consists of two parts:the Pre-SMA anteriorly, shown here in purple, and the SMA-Proper posteriorly, shown in green.

The cortical and subcortical connections of these two parts are shown here, using fiber dissection and DTI techniques. After decortication, the short association fibers, called U-fibers, are exposed. U-fibers connect neighboring gyri to each other, such as the pre-SMA to the SMA-Proper, and the SMA-Proper to the motor cortex.

In this lateral view, the connections made by the SLF 1, 2, and 3 can be seen. After removing a part of the SLF 2 at the corona level, the FAT was exposed. FAT fibers travel obliquely from the SMA region to the inferior frontal gyri and become superficial in the Pars Opercularis.

Here, the exposed borderline of the claustrocortical fiber distribution on the cortical area can be seen. This is between the anterior part of the pre-SMA, and the posterior part of the parietal lobe. The DTI technique is powerful for visualizing the location of fibers throughout the brain.

The images shown here highlight the position of the SLF fibers, as well as describe the relationship of the FAT and FST. In addition, the technique can be used to show the position of callosal fibers, cingular fibers, and claustrocortical fibers. While attempting the MRI tracking procedure, it's important to remember that data quality is critical to success.

In this project, we utilize high quality data from the Human Connectome Project database. We routinely replicate such results on our 3D clinical scanners, but it's important to remember that acquisition of such high quality data may require lengthy MRI acquisitions, depending on the MRI scanner available. An understanding of the fiber tract connections of the supplementary motor area complex is essential for planning the frontal lobe surgery.

After watching this video, you should have a good understanding of microsurgical entangled with anatomy of the supplemental motor area complex.

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Journal (Neuroscience)

Journal (Neuroscience)

Fiber Connections of the Supplementary Motor Area Revisited: Methodology of Fiber Dissection, DTI, and Three Dimensional Documentation

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