Medical Imaging and Radiotherapy: Foundational Concepts

Flashcards covering medical imaging and radiotherapy physics, including mechanics, atomic structure, radiation interactions, dosimetry, and imaging modalities from Weeks 1 through 12.

Work

The force applied to an object multiplied by the distance moved by the object, measured in the SI unit Joule ($J$).

Electron Volt ($eV$)

The work required to move an electron through a potential difference of $1\,V$, commonly used in radiation physics.

Power

The rate at which energy is used or converted from one form to another, measured in Joules per second ($J/s$) or Watts ($W$).

Conduction

The mechanism of heat transfer through a material.

Convection

The mechanism of heat transfer via the movement of fluids, such as liquids or gases.

Ultrasound

An application of sound in medicine with frequencies in the range of $2-18\,MHz$.

Doppler Effect

An effect observed in medical imaging when sound waves are reflected from moving red blood cells.

Bohr Model

A model of the atom consisting of a central nucleus with protons and neutrons, orbited by electrons in levelled outer shells at fixed radii.

Electron Binding Energy

The energy required to completely remove an electron from an atom.

Ionisation

The complete removal of an electron from an atom.

Excitation

The process where electrons move from one level to another within an atom without escaping.

Alpha Decay

A type of radioactive decay where $2$ protons and $2$ neutrons (a Helium atom) are ejected from the nucleus.

Beta- Decay

A decay process where a neutron turns into a proton, ejecting a negatively charged electron and a massless antineutrino.

Positron Beta+ Decay

A decay process where a proton turns into a neutron, ejecting a positively charged electron and a massless neutrino.

Attenuation

The reduction of intensity or number of X-rays due to absorption or scattering processes.

Half-Value Thickness (HVT)

The thickness of a material required to reduce the intensity of an X-ray beam to $50\%$.

Tenth-Value Thickness (TVT)

The thickness of a material required to reduce the intensity of an X-ray beam to $10\%$.

Photoelectric Effect

An absorption process where an incident X-ray photon is completely absorbed by an inner electron, which is then ejected; probability increases with atomic number ($Z$) and decreases with photon energy.

Compton Scattering

A scattering process where an X-ray photon collides with an orbital electron, transferring energy and changing direction.

Pair Production

An absorption process occurring at energies greater than $1.02\,MeV$ where a photon is absorbed by the nucleus to create an electron and a positron.

Mass Attenuation Coefficient

The linear attenuation coefficient divided by the material's density, removing the effect of the physical environment.

Absorbed Dose

The energy absorbed per unit mass, measured in Gray ($Gy$).

Equivalent Dose

The absorbed dose weighted for the harmful effects of different types of radiation, measured in Sieverts ($Sv$).

Effective Dose

The equivalent dose weighted for the susceptibility of different tissues to harm.

Linear Energy Transfer (LET)

The average energy deposited per unit length by a charged particle.

Computed Radiography (CR)

An indirect digital radiography method using photostimulable phosphor screens, such as $BaFBr:Eu$, scanned by a red laser to emit blue light.

Direct Digital Radiography (DDR)

A method that converts X-rays directly into electron-hole pairs using an amorphous selenium or silicon semiconductor layer.

Thermionic Emission

The release of electrons from a heated tungsten filament in the X-ray tube current circuit.

Heel Effect

The self-absorption of X-rays in the anode, resulting in reduced intensity at the anode end of the X-ray field.

X-Ray Quality

A measure of beam penetration related to average photon energy, expressed in millimeters of aluminum ($mm\,Al$) as the Half-Value Layer.

Overdiagnosis

The detection and treatment of early disease that would not have manifested during the patient’s natural life, identified as a risk in screening mammography.

Slip Ring Technology

The technology that enabled the 5th Generation (Helical CT), allowing the X-ray source to rotate continuously as the patient moves through the scanner.

Cobalt-60

A teletherapy radionuclide with a half-life of $5.26$ years that decays via gamma emission.

Bragg Peak

The phenomenon where protons and heavy ions deposit most of their energy at a specific depth, followed by virtually no exit dose.

Technetium-99m

A radioactive gamma emitter used in nuclear medicine that is absorbed in high-metabolism regions like tumours.