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Appendicitis is one of the most common surgical problems. One out of every 2,000 people has an appendectomy sometime during their lifetime. Treatment requires an operation to remove the infected appendix. Traditionally, the appendix is removed through an incision in the right lower abdominal wall. In most laparoscopic appendectomies, surgeons operate through 3 small incisions (each ¼ to ½ inch) while watching an enlarged image of the patient’s internal organs on a television monitor. In some cases, one of the small openings may be lengthened to complete the procedure.
The words “laparoscopic” and “open” appendectomy describes the techniques a surgeon uses to gain access to the internal surgery site. Most laparoscopic appendectomies start the same way. Using a cannula (a narrow tube-like instrument), the surgeon enters the abdomen. A laparoscope (a tiny telescope connected to a video camera) is inserted through a cannula, giving the surgeon a magnified view of the patient’s internal organs on a television monitor. Several other cannulas are inserted to allow the surgeon to work inside and remove the appendix. The entire procedure may be completed through the cannulas or by lengthening one of the small cannula incisions. A drain may be placed during the procedure. This will be removed later by your surgeon.
Peripheral vascular disease, also called PVD, refers to any disease or disorder of the circulatory system outside of the brain and heart. The term can include any disorder that affects any blood vessels. It is, though, often used as a synonym for peripheral artery disease. PVD is the most common disease of the arteries. The build-up of fatty material inside the vessels, a condition called atherosclerosis or hardening of the arteries, is what causes it. The build up is a gradual process. Over time, the artery becomes blocked, narrowed, or weakened.
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.