Imaging Receptors In X-ray And MRI

6 Pages 1514 Words

Introduction:
Two landmarks in non-invasive medical diagnosis took place with the introduction of x-ray and Magnetic Resonance Imaging (MRI) facilities. Each system has its pros and cons and its unique features making it invaluable.

Operational overview:
X-ray machines have several components including the source, an intensifying grid and a film. The source is the x-ray tube, a glass or metal envelope containing the anode and cathode within a vacuum. X-rays are generated by converting electrical energy into intense heat in the cathode where electrons leave its external surfaces. This stream of electrons is shot against the tungsten anode with the great force created from the large potential difference. When the electrons collide with tungsten atoms they dislodge electrons from the atoms’ lower orbits. Electrons from higher orbitals fill the lower energy level and release energy in the form of x-ray photons with high energy levels. Electrons slowed by other atoms’ nuclei also give off extra energy as x-ray photons which are focused through a window in the x-ray tube onto the target area of the patient.
The x-rays produced by the tube pass through objects to create images of their structures. The body’s tissues have varying densities; each absorbs and transmits photons differently. This difference in the absorption of waves creates visible variations on the radiographic image. More energy is absorbed by the denser bone than its surrounding softer tissues.

The MRI machine is basically a magnetic box. Running through it is a longitudinal tube (the magnetic bore) where the patient lies. The principal component of an MRI scanner is its magnet. This is rated in units called tesla, ranging from 0.5 - 2.0 tesla in medical MRI devices. Four basic types of magnets are used in MRI systems: - Resistive magnets where current is passed through wire windings to create a magnetic field.
Permanent magnets which are always working.
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