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Computed tomography (CT) or Computed Axial Tomography (CAT) is imaging tools use X-rays to make detailed pictures of structures inside of the body. This medical imaging method employs tomography. Tomography is the process of generating a two-dimensional image of a slice or section through a 3-dimensional object.
CT scanning was developed during the mid-1970s, a CT scanner emits a series of narrow beams through the human body as it moves through an arc, unlike an X-ray machine which sends just one radiation beam. The CT machine takes pictures of your body from different angles and gives a series of cross sections or 'slices' through the part of the body being scanned and often result in earlier diagnosis and more successful treatment of many diseases. X-rays are high energy photons (the energy "packets" of electromagnetic energy, similar to light but not in a visible wavelength) similar to gamma rays that pass through the body. More dense tissues such as bone block most x-rays while softer tissues let more x-rays pass completely through. Therefore, the image produced by an x-ray and CT scan is based on the density of tissues. Bones show up brightest while air is the darkest, this will make very detailed picture of the inside of the body can be built up in this way. In some CT scans, contrast agents or sedatives (iodine) may be used.
A CT machine resembles a large, square doughnut. A flat "patient couch" is situated in the circular opening, which is about 24 to 28 inches in diameter. The patient lies on the couch, which can be moved up, down, forward, and backward to position the patient for imaging. The CT scanner itself is a circular, rotating frame with an x-ray tube mounted on one side and a banana-shaped detector mounted on the other. A fan-shaped beam of x-rays is created as the rotating frame spins the x-ray tube and detector around the patient. For each complete rotation, one cross-sectional slice of the body is acquired. As the scanner rotates, the detector takes numerous snapshots called "profiles." Typically, about 1,000 profiles are taken in one rotation. Each profile is analyzed by computer, and the full set of profiles from each rotation is compiled into to form the slice-a two-dimensional image. The accuracy and speed of CT scans may be improved with the application of spiral CT. Refinements in detector technology allow new CT scanners to obtain multiple slices in a single rotation. These scanners, called "multislice CT" or "multidetector CT. The X-ray beam takes a spiral path during the scanning - it gathers continuous data with no gaps between images.
Risks of CT scans include:
- Being excessive exposure to radiation
- Allergic reaction to contrast dye (iodine)
- Not recommended for pregnant women and nursing mothers
CT Scans Benefits
- CT scanning is painless, noninvasive and accurate.
- CT examinations are fast and simple, about 30 minutes to complete
