|
|
|
|
Home | What
is CT? | What are the Radiation Risks From CT? | Should
I get "whole body" CT? |
How does FDA regulate CT? | Other
Resources | Radiation Quantities and Units | Contact
Us
All x-ray imaging is based on the absorption of x rays as they pass through the different parts of a patient's body. Depending on the amount absorbed in a particular tissue such as muscle or lung, a different amount of x rays will pass through and exit the body. The amount of x rays absorbed contributes to the radiation dose to the patient. During conventional x-ray imaging, the exiting x rays interact with a detection device (x-ray film or other image receptor) and provide a 2-dimensional projection image of the tissues within the patient's body - an x-ray produced "photograph" called a "radiograph." The chest x ray (Figure 1) is the most common medical imaging examination. During this examination, an image of the heart, lungs, and other anatomy is recorded on the film.
Figure 1: Chest X ray Image
Although also based on the variable absorption of x rays by different tissues, computed tomography (CT) imaging, also known as "CAT scanning" (Computerized Axial Tomography), provides a different form of imaging known as cross-sectional imaging. The origin of the word "tomography" is from the Greek word "tomos" meaning "slice" or "section" and "graphe" meaning "drawing." A CT imaging system produces cross-sectional images or "slices" of anatomy, like the slices in a loaf of bread. The cross-sectional images (Figure 2) are used for a variety of diagnostic and therapeutic purposes.
Figure 2: Cross-sectional Image of Abdomen
Figure 3: Patient in CT Imaging System
Figure 4: CT Fan Beam
Today most CT systems are capable of "spiral" (also called "helical") scanning as well as scanning in the formerly more conventional "axial" mode. In addition, many CT systems are capable of imaging multiple slices simultaneously. Such advances allow relatively larger volumes of anatomy to be imaged in relatively less time. Another advancement in the technology is electron beam CT, also known as EBCT. Although the principle of creating cross-sectional images is the same as for conventional CT, whether single- or multi-slice, the EBCT scanner does not require any moving parts to generate the individual "snapshots." As a result, the EBCT scanner allows a quicker image acquisition than conventional CT scanners.
|
|
|
|
Get the Savvy Consumer Newsletter! (FREE) |