They are referred to as noninvasive and include (1) computed tomography (CT scans), (2) magnetic resonance imaging (MRI), and positron emission tomography (PET) scans.

In a CT scan differences in how the brain tissues absorb x rays are used to construct a three-dimensional image. Unlike older techniques, it is not necessary to inject a a contrast material into the individual to be examined, and the dose of x rays needed for a CT scan is very much lower.

The MRI is a procedure in which an externally applied magnetic field is used to detect differences in the way hydrogen nuclei (protons, 1H) of water molecules in the tissues of the brain vibrate. The vibration of these water molecules will differ when the chemical surroundings differ. In addition to hydrogen, there now exist MRI methods for detecting the vibration of other nuclei of abundant, naturally occurring atoms.

*This includes fluorine (19F), sodium (23Na), phosphorus (31P) and nitrogen (15N.).*

Note: in the paragraph above: one can review the Periodic Table of Elements, in the event they do not understand what is written above.

For example, it is possible to distinguish where ATP is most abundant by looking at phosphorus resonance. In this way it has become possible to learn a great deal about metabolic processes within the brain.

CT and MRI scans provide different types of information about the location of tumors, site of hemorrhage following injury, and other abnormalities. I.E, bleeding following a concussion is revealed by both the MRI and CT scans.

* More information about the site and extent of intracranial bleeding is available in the MRI because the MRI technique has greater contrast resolution than the CT scan, and bony structures do not obscure the MRI images.*

Both CT and MRI scans have been used to noninvasively locate tumors and other abnormalities in other parts of the body. In many applications, MRI have become the diagnostic tool of choice, because it does not require that a patient receive x-rays.

However, if information about the presence of bony structures in relation to the site of injury or abnormality is needed, then the other diagnostic tools may be more effective than the MRI.

The PET scan is based on the fact small amounts of the naturally occurring isotopes of several elements spontaneously emit positrons.

A positron is like an electron, except that it has a positive charge rather than a negative charge. Positron-emitting isotopes include 13N, 15O, and 11C:

Again review the Periodic Table of Elements and Table of Atomic Numbers and Atomic Masses if what is written above do not make sense.

For what you may see as "150" is not one hundred and fifty. However, if you know nothing about chemistry, don"t worry about it!

Like the MRI, the PET scan involves forming the three-dimensional image of where these molecules are located. It differs in that compounds labelled with these isotopes are given to an individual before the PET scan is performed.

For example, if you want to know where CNS-active drugs bind, all that is necessary is to prepare a drug labelled with one of these isotopes.

The PET scan is also a useful way of measuring blood flow in the brain, glucose utilization, and oxygen consumption.

It has great potential for diagnosing psychiatric disorders, brain tumors, epilepsy, and the degenerative changes characteristics of Alzheimer's disease.

A common feature of all these imaging techniques is computer-assisted reconstruction of an image of the brain. However, CT scans, MRIs, and PETs would not be feasible without the advances in computer speed and memory capacity that have developed over the past two decades.

After viewing the three different scans of the same brain taken with the three different medical diagnostic tools. I am quite sure that one would much prefer to have their brain scanned with the PET considering it is the most efficient of the three, and produces more detail though the most expensive.

Secondly, the MRI machine is better than the CT scan in that it produces better detail of the brain and tissues of the body when scanned. It is however, also more expensive than the CT scan. So it is safe to conclude that an MRI machine is a much better piece of equipment, and could serve a much better purpose in a hospital, or an institution which specializes in diagnostics, using such diagnostic tools.