17-Medical Physics definitions Flashcards
Tube current
The rate of arrival of electrons at a metal target
Braking radiation
X-ray photons released when electrons decelerate as it strikes anode, attracted by the nucleus of an atom in the anode, and loses energy
Characteristic radiation
Rearrangement of electrons in anode when a high speed electron strikes, excites orbital electrons which then de-excite, emitting photons and giving rise to spectrum lines; specific to material of anode.
Sharpness
Ease with which edge of a structure can be determined
Contrast
The visual difference between the areas of darkness and light.
Half value thickness
Thickness of a medium required to reduce the transmission to one half of its initial value.
Voxel
A small cube in a 3D image
Specific acoustic impedance (z)
Product of density of medium and speed of sound in medium
Intensity reflection coefficient (alpha)
Ratio of intensity of reflected wave and intensity of incident wave
A-scan
Measured distance of different boundaries from transducer held in one position graphically
B-scan
Repeats A scan from multiple angles to form 2d image
Atomic spin
Fundamental property (like charge or mass) of a subatomic particle that defines how a particle rotates on its axis.
Precession
The movement of the axis of rotation on a spinning object (proton) around another external axis.
Larmour frequency
Angular frequency of the circular path of precession of the object.
Relaxation time
Time taken for a nucleus to fall back into lower energy state.
