Radiologypart 1: x-ray

Dr Haddadi, PhD, MScAssistant prof. of Medical Physics

Fassa University of Medical Sciences

Electromagnetic radiation

Any charge in motion induces magnetic field

X-ray is a part of electromagnetic (EM) energy spectrum

Photons are part of the electromagnetic spectrum

Visible light

X-rays & Gamma raysUVInfraredRadio

Enough energyto cause ionization

The Electromagnetic Spectrum

EM properties

EM radiation propagates as a wave characterized by: - electric field - magnetic field - dielectric constant, and - electromagnetic properties of the medium

Wave length: distance of one complete cycle, λ,

Period: time for one cycle, T, and T=1/f Tc= λ and f λ=c c; 3 x 108 m/sec

Sinusoidal EM wave

For a monochromatic radiation: - Magnetic and electric fields are functions of time, t,

and space, x:

Ф(x,t)= Ф0 cos(ωt – kx)

Ф; electric field, ω=2πƒ; angular frequency, and k=2π/λ; for wave number

Ф(x,t) is a special form of the solution to the wave equation:

c= (1/με)-1/2, μ is permeability of the medium and

ε is permittivity of the medium

EM properties cont’d

The main difference between X-ray and light or radio waves:

frequency or wavelength (100-0.01 nm)

Dual characteristics of X-radiation: wave and particle interpretation of X- or

gamma radiation

Louis de Broglie equation (1924): λ = h/mv

The wave concept to explain:

Phenomena: - reflection - scattering - refraction - diffraction

Properties of X-Radiation as a particle:

Traveling at a speed of light; c Carrying an energy given by; E=hf

h;Planck constant (4.13 x 10-18 keV-sec, 1 ev= 1.6 x 10-19 joules)

These particles are called quanta, or photon Photons are capable of ionizing atoms and

molecules, so called ionizing radiation

Classification of Indirectly IonizingPhoton Radiation

Four distinct groups of photons**********

Characteristic (fluorescent) x rays result from electron transitions between atomic shells

Bremsstrahlung photons result from electron-nucleus Coulomb interactions

Gamma rays result from nuclear transitions Annihilation quanta result from positron-

electron annihilation

Characteristic x-ray

Bremsstrahlung photons

Annihilation quanta