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.

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A surgical video showing Femoro-Popliteal Bypass with a Saphenous Vein Graft

What is the spleen and what causes an enlarged spleen (splenomegaly)? The spleen sits under your rib cage in the upper left part of your abdomen toward your back. It is an organ that is part of the lymph system and works as a drainage network that defends your body against infection. White blood cells produced in the spleen engulf bacteria, dead tissue, and foreign matter, removing them from the blood as blood passes through it. The spleen also maintains healthy red and white blood cells and platelets; platelets help your blood clot. The spleen filters blood, removing abnormal blood cells from the bloodstream. A spleen is normally about the size of your fist. A doctor usually can't feel it during an exam. But diseases can cause it to swell and become many times its normal size. Because the spleen is involved in many functions, many conditions may affect it.

An intracranial hematoma occurs when a blood vessel ruptures within your brain or between your skull and your brain. The collection of blood (hematoma) compresses your brain tissue. An intracranial hematoma may occur because the fluid that surrounds your brain can't absorb the force of a sudden blow or a quick stop. Then your brain may slide forcefully against the inner wall of your skull and become bruised. Although some head injuries — such as one that causes only a brief lapse of consciousness (concussion) — can be minor, an intracranial hematoma is potentially life-threatening and often requires immediate treatment. An intracranial hematoma often, but not always, requires surgery to remove the blood.

Carpal tunnel release (part 1). Skin incision and retraction. Procedure performed by Deepak Kapila, MD, Broward Health, Fort Lauderdale, FL. Courtesy of BroadcastMed (http://ortho.broadcastmed.com/....4229/videos/carpal-t

There are hundreds more procedural videos as well as news, features, resources and references on Medscape.com. Join today for free.

Colonoscopy is a test that allows your doctor to look at the inner lining of your large intestine (rectum and colon). He or she uses a thin, flexible tube called a colonoscope to look at the colon. A colonoscopy helps find ulcers, colon polyps, tumors, and areas of inflammation or bleeding.

Doctors at the Mayo Clinic used 3D-printed models to prepare for their first-ever face transplant.

Hypoglycemia is a common and serious medical emergency which may occur in both daibetic and non-diabetic patients. The signs and symptoms of hypoglycaemia may be present in many individuals, but may also be masked in several individuals due to a condition called hypoglycaemia induced autonomic failure. This presentation aims to deal with the causes, clinical features, diagnosis and management of various causes of hypoglycaemia. The causes of hypoglycaemia may be divided into hypoglycaemia in ill or medicated individuals and hypoglycaemia in previously asymptomatic individuals. A variety of causes are discussed under both headings. Management of hypoglycaemia is also discussed in detail. There is also a brief discussion about management of insulinoma.

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The human brain is the command center for the human nervous system. It receives input from the sensory organs and sends output to the muscles. The human brain has the same basic structure as other mammal brains, but is larger in relation to body size than any other brains.

Hirschsprung's (HIRSH-sproongz) disease is a condition that affects the large intestine (colon) and causes problems with passing stool. The condition is present at birth (congenital) as a result of missing nerve cells in the muscles of the baby's colon. A newborn who has Hirschsprung's disease usually can't have a bowel movement in the days after birth. In mild cases, the condition might not be detected until later in childhood. Uncommonly, Hirschsprung's disease is first diagnosed in adults.

Periodontal Disease and Respiratory Infections

Medical students at Johns Hopkins University are getting a real-life birthing experience when a robot goes into labor. Kasey-Dee Gardner reports.

Electroconvulsive therapy (ECT) is a procedure, done under general anesthesia, in which small electric currents are passed through the brain, intentionally triggering a brief seizure. ECT seems to cause changes in brain chemistry that can quickly reverse symptoms of certain mental illnesses. It often works when other treatments are unsuccessful. Much of the stigma attached to ECT is based on early treatments in which high doses of electricity were administered without anesthesia, leading to memory loss, fractured bones and other serious side effects. ECT is much safer today. Although ECT still causes some side effects, it now uses electric currents given in a controlled setting to achieve the most benefit with the fewest possible risks.

The cell cycle or cell-division cycle is the series of events that take place in a cell leading to its division and duplication of its DNA (DNA replication) to produce two daughter cells.

A video showing bone marrow biopsy

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Heartburn is a burning pain in your chest, just behind your breastbone. The pain is often worse when lying down or bending over. Occasional heartburn is common and no cause for alarm. Most people can manage the discomfort of heartburn on their own with lifestyle changes and over-the-counter medications. Heartburn that is more frequent or interferes with your daily routine may be a symptom of a more serious condition that requires medical care