|images (slices) of the tissue being examined. This method provides clearer and more detailed information than X rays used by themselves. CT scan also has the advantage of minimizing the amount of radiation exposure. Figure 1 is a schematic of the equipments with a rotating X rays source and detector. Before the scan is carried out, a contrast medium may be injected to make blood vessels, organs, or abnormalities show up more clearly; a drink of contrast medium may be given to highlight loops of intestine. The amount
Figure 1 CT Scan
Figure 2 CT Image
|of X rays absorbed by different tissues is recorded by the detector and transformed by a computer into an image. Figure 2 shows a CT cross-section of the chest.
|11, nitrogen 13, oxygen 15). These substances are injected into the blood-stream and are taken up in greater concentrations by areas of tissue that are more metabolically active. In the tissue, the substances emit positrons, which, in turn, release X-rays. It is the detection of these X-rays that actually forms the basis of PET scanning. By surrounding the patient with an array of detectors linked to a computer, the origin of the X-rays can be computed and a picture built of the distribution of the radio- active isotopes. Figure 4 is a sample of the PET brain scan.
Figure 3 PET Scan
Figure 4 PET Image
|detectable radio signal as they fall back into alignment. Magnetic field gradient is required to translates the signals into separate spatial locations. Magnetic coils in the machine detect these signals and a computer changes them into a cross-sectional or three dimensional image based on the strength of signal produced by different types of tissue. Tissues that contain a lot of hydrogen (such as fat) produce a bright image; those that contain little or no hydrogen (such as bone) appear dark. Figure 6 is a MRI image of the head.
Figure 5 MRI Scan
Figure 6 MRI Image [view large image]