Computerized Axial Tomography

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Computerized Axial Tomography

• The CAT Scanner

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Similar to X-rays

• CAT scanners produce X-rays
• A powerful form of electromagnetic energy
• X-ray photons have more energy than visible light
• They can pass through the body, but are absorbed
  by denser tissue such as bones

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But different..

• An X-ray is basically a shadow
• It gives a flat image, a 2 dimensional
  representation of the body part viewed
• CAT takes X-rays from more than one direction,
  enabling a 3-D image to be built
• Contrast dye can be injected to make the images
  clearer

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A 3-D Shadow

• The girl is holding a pineapple and banana.
• A conventional X-ray would miss one of the fruit
  as it would show only one aspect (shadow)
• CAT scanning would pick up both fruit

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How CAT scanning works

• The CAT scanner is like a doughnut
• The X-rays beam moves around the patient,
  scanning from hundreds of different angles
• The computer takes the information to build an
  image up.

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A rotating tube

• The patient lies down on a platform, which slowly
  moves through the hole in the machine. The X-ray
  tube is mounted on a movable ring around the
  edges of the hole. The ring also supports an
  array of X-ray detectors directly opposite the
  X-ray tube.

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• A motor turns the ring so that the X-ray tube and
  the X-ray detectors revolve around the body. Each
  full revolution scans a narrow, horizontal
  "slice" of the body. The control system moves the
  platform farther into the hole so the tube and
  detectors can scan the next slice.

A Scanned Liver Slice
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Benefits to CAT scanning

• Since they examine the body slice by slice, from
  all angles, CAT scans are much more comprehensive
  than conventional X-rays. CAT scans diagnose a
  wide variety of ailments, including head trauma,
  cancer and osteoporosis

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Are CAT scans safe?

• CAT scanning carries the same contraindications
  that X-rays do, but are considered safer
• Patients are exposed to small amounts of ionising
  radiation
• Scans during pregnancy are decided case by case
• All depends on the clinical urgency for a scan