Structural brain imaging techniques are used to evaluate the structure, or anatomy, of the brain. Computerized axial tomography (CAT or CT) was the first such technique. Strangely enough, it was invented in the 1970s by researchers at EMI, a British music recording company that couldn’t capitalize on it, although they did get the Nobel Prize for their invention. CT scanners take a large number of X rays in different planes and use computer technology to “reconstruct” the internal brain structure, which then becomes crystal clear to the viewer.
MRI works on a different principle. A strong magnetic field is applied around the head, and the distance traveled by individual protons (subatomic particles) in response to the magnetic field is measured in various parts of the brain. The MRI’s computers use this information to produce clear, fine-grained images of internal brain structures. Unlike CT, MRI involves no radiation exposure. In any case, the risk of damage from radiation is low for the brain because it has few dividing or reproducing cells, making DNA damage unlikely.
Claustrophobia can develop in the MRI machine, which makes a loud banging noise. “Open” MRI is a method recently developed for people who have claustrophobia, but because it is open (the head is only partially enclosed) the magnetic field used is weaker and the sensitivity of the technique is much lower than that of a regular MRI.
Both SPECT and PET involve the intravenous injection of a radioactive tracer that is taken up by the brain. A combination of high-resolution cameras and sophisticated computers produces a 3-D image of radioactive tracer counts, representing blood flow or glucose metabolism (consumption), throughout the brain. SPECT or PET can reveal subtle deficits in blood flow or glucose consumption that have not led to changes in brain structure— the subject may still have a normal MRI. The first patient described in the introduction, David Finestone, had a subtle blood flow deficit on SPECT in the presence of a normal MRI, and this information proved very useful in his clinical management.
Taken From: The Memory Program How to Prevent Memory Loss
and Enhance Memory Power
