Magnetoencephalography

Magnetoencephalography (MEG )

How It Works

* Currents in neurons create very tiny magnetic fields
* MEG uses SQUIDs to detect these magnetic fields.
* Magnetic signals from the brain are only a few fT in strength.
* Needs a magnetically shielded room


History

* First measured by David Cohen in 1968.
* He used a copper induction coil
* Presently, MEG technology uses SQUIDS
* Today, MEG machines can contain as many as 300 SQUID sensors


Diagram of MEG setup

SQUIDS

* Superconducting Quantum Interference Devices
* Superconducting material is niobium or lead alloy with gold/indium
* Cooled to low temperature with either liquid He (4K) or N (77K)
* Manufactured at NIST in Boulder!
* Noise levels about 3 fT*Hz^-1/2

Josephson Junctions

* Two superconductors separated by a thin insulating barrier
* A small current will tunnel across the barrier
* The constant current Ic depends on temperature and magnetic field
* SQUIDS measure fractions of the phase difference in terms of the flux quantum h/2e

Detecting Brain Activity

* 50,000 neurons need to fire to generate a readable signal
* Neurons near the outside of the brain generate the strongest signals

Magnetic Shielding
Forward Problem
The Inverse Problem
Synthetic Aperture Magnetometry
Magnetic Source Imaging
Dipole Model Source Localization
Lead-field-based imaging approach
Independent Component Analysis
Uses of MEG

* MEGs are used in research to measure the time course of brain activity
* MEGs can detect epilepsy, as well as detect areas of the brain that are most important to avoid during surgery

Advantages/Disadvantages

* High 1 ms time resolution
* Completely non-invasive
* Does not depend on head geometry like EEG
* Magnetic fields decay faster over distance than electric fields
* MEG is best used to complement other imaging techniques


References
Magnetoencephalography (MEG).ppt

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Diagnosing a Traumatic Head Injury

Diagnosing a Traumatic Head Injury

How are head injuries diagnosed? The full extent of the problem may not be completely understood immediately after the injury, but may be revealed with a comprehensive medical evaluation and diagnostic testing. The diagnosis of a head injury is made with a physical examination and diagnostic tests. During the examination, the physician obtains a complete medical history of the child and family and asks how the injury occurred. Trauma to the head can cause neurological problems and may require further medical follow up.

Diagnostic Tests

Blood Tests - your child may need to have blood obtained to check for normal levels. Sometimes we need to stick your child for blood each day until normal levels are reached. We have special lab staff that specializes in drawing blood from children.

CT scan - computer-enhanced procedure for obtaining x-ray images of the body. The machine looks like a big doughnut and your child will be placed on a platform that slides into the middle of the machine. During the scan an X-ray tube rotates around the body, generating hundreds of images. Your child must remain still during this test. The machine does not touch the child and is not painful. The scan will take 30-60 minutes.

MRI scan - uses a magnetic field to create two-dimensional images of the body. The machine looks like a big doughnut shaped tube. The child will be placed on a platform that slides into the middle of the machine. The MRI machine will make a loud knocking noise as the images are taken. Your child must remain still during this test. Young children, or a child with a fear of closed-in spaces, may need to be sedated for the procedure. If sedation is required your child may not be able to eat or drink before the test. The scan can last 60-90 minutes. One parent can go with the child to the MRI suite.

Ophthalmology Exam - this test is performed by a doctor specially trained to examine your child's eyes. The doctor may dilate the eyes with eye drops in order to visualize the internal structures of the eyes. The doctor may also examine how your child can see close-up and far away.

ICP monitor - this is a device that measures the pressure inside the head. This monitor is placed by a neurosurgeon either in the intensive care unit or operating room. The device is attached to a monitor that gives a constant reading of pressure inside the head. If the pressure goes up, it can be treated right away.

Modified Barium Swallow - an X-ray exam that assesses your child's oral skills and swallowing safety. A speech language pathologist will monitor this test. Based on the results your child's diet may be changed.

Neuropsychology Evaluation - this involves giving the child different types of tests by a doctor to determine the way the brain functions. These can include mental tests and physical skill tests. There is no invasive procedure involved.

Electroencephalography (EEG) - this test is used to record ongoing electrical brain waves. Sometimes children may have seizures after a traumatic head injury, and this test can help diagnose or evaluate for seizures. This test can determine if any brain waves are abnormal. This test is not invasive; the child will have the electrodes temporary glued to the scalp while monitored.

Source: LeBonheur Children Medical Centre

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Chiropractic Care for High Blood Pressure

Chiropractic Care for High Blood Pressure

Chiropractic is a system of health care that emphasizes the relationship between structure and function in the body. Doctors of chiropractic believe that good health depends, in part, on the normal alignment of the body's parts, and that is alignments called subluxations - can be a major factor in illness. Chiropractors consider proper alignment of the spine to be of critical importance because of its central role in nervous system's function. Proper nerve function is essential in restoring and maintaining good health.

A video from ABC news about the effects of chiropractic care on high blood pressure.

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