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 video from Loyola medical school, Chicago showing the cardiovascular medical and clinical medical examination

are you a medical student, a resident, a primary care physician or you practice in an emergency department, you can improve your suture skills with this detailed instruction. As you practice towards a cosmetically perfect technique, your confidence will increase, especially when dealing with complex wounds. Areas of study include: methods of closure, closure materials, anesthetics, suture removal, infection, prophylaxis, when to call in a plastic surgeon, recapping techniques and more

Fistulectomy surgery procedure video

Removal of pregnancy within the fallopain tube using laparoscopic keyhole surgery. A segment of the tube together with the pregnancy within is removed video.

Access to processes within the skull base with lateral extension to the pterygopalatine fossa are reached by combined subfrontal osteotomy and Le Fort I osteotomy

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Diabetes contributes to Perio Disease

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A "Hallux Valgus" or "Hallux Abducto-Valgus" deformity, is commonly referred to as a "Bunion." This describes a pathological condition involving the position of the "hallux" in relation to the first metatarsal.

A bunion deformity can clinically present with a variety of characteristics. The foot itself may present with a wide splaying of the forefoot and a painful bump on the medial aspect of the first metatarsal phalangeal joint. In addition, the hallux may be abducted from the midline of the body, with a valgus rotation in the frontal plane.

A radiographic analysis of a bunion deformity in the Anterior/Posterior or Dorsal/Plantar view will reveal a variety of pathological components. Most notably so, is the exaggerated inter-metatarsal angle between the first and second metatarsal. This may be accompanied by a displacement of the first metatarsal from its position over the sesamoids, such that the metatarsal demonstrates a medial alignment away from the sesamoids which lie to the lateral side.

In some cases, the proximal articular set angle at the head of the first metatarsal may be off-set. This "PASA" is one of the factors which determines the position of the proximal phalanx on the metatarsal during movement as well as at rest.

Although conservative care may involve shoe modifications, padding, strapping, and custom orthosis; surgical reconstruction may be required to alleviate painful and immobilizing bunion conditions.

Soft tissue components of the bunion deformity are primarily addressed by means of a capsular modification, as well as a tenotomy of the adductor tendon at its insertion on the base of the proximal phalanx. The fibular sesamoid may be repositioned by a release of the surrounding ligaments.

Surgical management of the bone or osseous components of a bunion deformity will commonly include an osteotomy and correction to re-establish a more functional position of the first metatarsal within the forefoot. This capital fragment of bone is held in place with hardware fixation in order to secure a proper alignment during the healing phase, thus allowing the hallux to return to a more functionally useful position in the sagittal plane.

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