Medical Imaging
X-ray production:
● X-rays are a form of electromagnetic radiation, produced when
high-speed electrons hit metal targets.
● X-rays are produced when fast-moving electrons are rapidly decelerated.
As the electrons slow down, their kinetic energy is transformed to
photons of electromagnetic radiation.
● The X-rays used in medical applications are usually described as soft
X-rays, because their energy is not very great, usually less than the
energies of 𝛾-rays produced by radioactive substances.
Production of X rays:
● Heated filament undergoes thermionic emission* releasing high-speed
electrons
● P.d between cathode and anode causes electrons to accelerate
● Electrons bombard metal target emitting X rays which leave through the
window
● Some kinetic energy of electrons transferred into the metal target as
thermal energy
● Metal target is cooled by water or spun around to increase target area
*The process by which free electrons are emitted from the surface of a metal
when external heat energy is applied is called thermionic emission.
, Tube current: the rate of arrival of electrons at a metal target
The width of the emerged X ray beam can be controlled using metal tubes
beyond the window to absorb X rays. This produces a parallel-sided beam
called a collimated beam.
Intensity Hardness
Depends on the # of electrons Depends on the acceleration of the
hitting the anode per unit time electrons
Proportional to the heater current Proportional to potential difference
between cathode and anode
A more intense X ray produces an The harder X ray has more
image quicker. penetrating power.
Hardness of an X ray beam: the measure of the penetration of the beam; the
greater the hardness, the greater the penetration/shorter wavelength/higher
frequency/higher photon energy.
Soft X rays are less penetrative (long wavelengths) so it is more likely to be
absorbed in the body hence it possesses a greater health hazard that short
wavelength radiation, minimised by using aluminium sheet filter placed in
the X rays beam from tube.
X-ray Spectrum:
● X-rays emerge from the tube with a range of frequencies
X-ray production:
● X-rays are a form of electromagnetic radiation, produced when
high-speed electrons hit metal targets.
● X-rays are produced when fast-moving electrons are rapidly decelerated.
As the electrons slow down, their kinetic energy is transformed to
photons of electromagnetic radiation.
● The X-rays used in medical applications are usually described as soft
X-rays, because their energy is not very great, usually less than the
energies of 𝛾-rays produced by radioactive substances.
Production of X rays:
● Heated filament undergoes thermionic emission* releasing high-speed
electrons
● P.d between cathode and anode causes electrons to accelerate
● Electrons bombard metal target emitting X rays which leave through the
window
● Some kinetic energy of electrons transferred into the metal target as
thermal energy
● Metal target is cooled by water or spun around to increase target area
*The process by which free electrons are emitted from the surface of a metal
when external heat energy is applied is called thermionic emission.
, Tube current: the rate of arrival of electrons at a metal target
The width of the emerged X ray beam can be controlled using metal tubes
beyond the window to absorb X rays. This produces a parallel-sided beam
called a collimated beam.
Intensity Hardness
Depends on the # of electrons Depends on the acceleration of the
hitting the anode per unit time electrons
Proportional to the heater current Proportional to potential difference
between cathode and anode
A more intense X ray produces an The harder X ray has more
image quicker. penetrating power.
Hardness of an X ray beam: the measure of the penetration of the beam; the
greater the hardness, the greater the penetration/shorter wavelength/higher
frequency/higher photon energy.
Soft X rays are less penetrative (long wavelengths) so it is more likely to be
absorbed in the body hence it possesses a greater health hazard that short
wavelength radiation, minimised by using aluminium sheet filter placed in
the X rays beam from tube.
X-ray Spectrum:
● X-rays emerge from the tube with a range of frequencies
