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The complex circuitry interconnecting different areas in the brain, known collectively as white matter, is composed of millions of axons organized into fascicles and bundles. Upon macroscopic examination of sections of the brain, it is difficult to discern the orientation of the fibers. The same is true for conventional imaging modalities. However, recent advancements in magnetic resonance imaging (MRI) make such task possible in a live subject. By sensitizing an otherwise typical MRI sequence to the diffusion of water molecules it is possible to measure their diffusion coefficient in a given direction1. Normally, the axonal membrane and myelin sheaths pose barriers to the movement of water molecules and, thus, they diffuse preferentially along the axon2. Therefore, the direction of white matter bundles can be elucidated by determining the principal diffusivity of water. The three-dimensional representation of the diffusion coefficient can be given by a tensor and its mathematical decomposition provides the direction of the tracts3; this MRI technique is known as diffusion tensor imaging (DTI). By connecting the information acquired with DTI, three-dimensional depictions of white matter fascicles are obtained4. The virtual dissection of white matter bundles is rapidly becoming a valuable tool in clinical research.
Our journey begins with a transverse section of tightly packed axons as seen through light microscopy. Although represented as a two-dimensional "slice", we see that these axons in fact resemble tubes. A simulation of water molecules diffusing randomly inside the axons demonstrates how the membranes and myelin hinder their movement across them and shows the preferred diffusion direction --along the axons. The tracts depicted through DTI slowly blend in and we ride along with them. As we zoom out even more, we realize that it is a portion of the corpus callosum connecting the two sides of the brain we were traveling on and the great difference in relative scale of the individual axons becomes evident. The surface of the brain is then shown, as well as the rest of the white matter bundles--a big, apparently chaotic tangle of wires. Finally, the skin covers the brain.
With the exception of the simulated water molecules, all the data presented in the animation is obtained through microscopy and MRI. Computer algorithms for the extraction of the cerebral structures and a custom-built graphics engine make our journey through the brain's anatomy possible in a living person.
Micrograph courtesy of Dr. Christian Beaulieu, University of Alberta.
Music by Mario Mattioli.
References:
1. Stejskal, E.O., et al., J. Chem. Phys., 1965. 42:
2. Beaulieu, C., NMR Biomed., 2002. 15:435-55.
3. Basser, P.J., et al., J. Magn. Reson. B, 1994. 103:247-54.
4. Mori, S., et al., NMR Biomed., 2002. 15:468-80.
A C-reactive protein (CRP) test is a blood test that measures the amount of a protein called C-reactive protein in your blood. C-reactive protein measures general levels of inflammation in your body. High levels of CRP are caused by infections and many long-term diseases.
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Trabeculectomy, also called Filtration Surgery, is a surgical procedure performed for treatment of glaucoma. The treatment involves removing part of the trabecular meshwork and creating a new escape route for the aqueous humor. When successful, it allows the aqueous fluid to drain from the eye into an area underneath the conjunctiva where it is subsequently absorbed by the body's circulatory system or filtered into tears.
In this procedure:
- A conjunctival pocket is created and maybe treated with Mitomycin or other antimetabolites for a few minutes. These drugs are used to prevent scarring of the operation site. Scarring, if occurs, may clog the new drainage canal, and is therefore the major reason the procedure may fail.
- A half thickness flap is then made in the sclera and is dissected all the way to the clear cornea.
- A block of scleral tissue including part of the trabecular meshwork and Schlemm's canal is then removed to make a hole into the anterior chamber of the eye.
- As the iris may plug up this hole from the inside, a piece of the iris maybe removed at this time. This is called iridectomy.
- The scleral flap is then sutured loosely back in place. These sutures can be released gradually during a couple of weeks after surgery. This allows adjustment of the aqueous flow in order to achieve target pressure and to avoid the complication of having a too low intraocular pressure.
- The conjunctiva is sewn back in place to cover the area.
After surgery, aqueous humor drains into a filtering area called a "bleb" under the conjunctiva. Since the surgery is usually performed near the top of the eye, the bleb can easily be concealed behind the upper eyelid.
Herniated or Ruptured Disc: Between each of the vertebre of the spine is a disc which is filled with a gel type material to cushion the connection between the vertebre. With age or injury these intervertebral discs can rupture or herniate. This herniation causes them to push against the adjacent nerves which come from the spinal cord. This can frequently cause pain, numbenss and tingling. This animated video reviews herniated disc.
Dr. David Rivadeneira from Stony Brook University in Stony Brook, NY will host a panel discussion on how to obtain improved outcomes during open surgery through the application of advanced techniques and technologies, including the new LigaSure Impact™ instrument. "It provides excellent and reliable hemostasis on major blood vessels, but the big advancement is that it is faster than traditional techniques and leaves no foreign material behind."
The program will begin with a brief introduction of the topic, followed by video presentation of two procedures, a right hemicolectomy and a sigmoid colectomy. Dr. Rivadeneira will discuss the techniques that he uses. "You'll be able to see the impact of applying multifunctional energy-based instruments to enable rapid and reliable dissection of the mesentery and ligation of colonic blood supply. This is particularly evident on tough diverticular cases, where it works very well with complicated tissue." Joining Dr. Rivadeneira, to review and discuss the cases, will be Dr. Sang Lee from Weill Cornell Medical College, NY.
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Patent ductus arteriosus (PDA), in which there is a persistent communication between the descending thoracic aorta and the pulmonary artery that results from failure of normal physiologic closure of the fetal ductus (see image below), is one of the more common congenital heart defects.