Methods through which digital imaging helps in medical research in the brain include Computerized Axial Tomography (CAT or CT), Positron Emission Tomography (PET), Magnetic Resonance Imaging (MRI), Functional Magnetic Resonance Imaging (fMRI). Angiography and x-rays can now also be digitized. A new imaging mode, Magnetoencephalography (MEG) has recently been introduced. A CT scan is a type of x-ray machine. The patient lies on a special table that passes into the machine and the scanner takes the first image. The scanner then rotates in small movements around the head to take a series of photographs. The procedure is painless and takes half an hour or longer. Afterwards, the computer uses the images to form cross-sectional or even three-dimensional views of the head. Glucose and oxygen accumulate in areas of the brain that are metabolically active. When these materials are radioactively labelled and injected into the blood stream, they migrate to the areas where the brain is actively metabolizing. The radioisotopes break down to yield a neutrons and positrons. Eventually a positron encounters an electron. Both particles are destroyed and two gamma rays are produced. Using Positron Emission Tomography, gamma ray detectors record the areas of the brain where the gamma rays are emitted to produce a functional image of the brain. MRI uses strong magnetic fields and and radio waves to produce extremely detailed pictures of soft tissue like the brain. Unlike x-rays or CT scans, MRI does not use ionizing radiation. As with CT, the patient lies on a scanner table that glides into the machine. A very important aspect of the MRI scan is that patients may not wear any metal jewelry or have any implanted metal from a previous accident or operation. This can cause discomfort or even damage and interfere with the equipment. The first MRI scan was performed in 1977. Early MRI scanners were very tight and very slow, as long as 45 minutes or longer. This can make people very anxious, a condition known as 'claustrophobia'. The symptoms are so unpleasant that as many as one in five patients would refuse to proceed with the scans. Modern equipment is more open and there are even devices where the patient can remain standing throughout the scan. Refusals are now almost zero. Functional MRI (fMRI) is capable of detecting changes in metabolism and oxygen uptake as well as expanding blood vessels. These are all indications of activity in the area of the brain where they are observed. Like ordinary MRI, fMRI uses a strong magnetic field but unlike MRI, it also employs radio waves. Angiography provides information about the blood vessels of the brain. A series of x-rays is taken following injection of a special dye. A novel scanning technique called Magnetoencephalography (MEG) measures brain activity in real time. In patients who experience seizures, MEG can determine the precise location of the seizure with more accuracy than conventional MRI imaging. Using MEG and MRI together, scientists are able to identify and remove the damaged tissue without disturbing healthy brain.
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