Radiology part 1: x-ray Dr Haddadi, PhD, MSc Assistant 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 rays UV Infrared Radio Enough energy to 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 10 8 m/sec

Sinusoidal EM wave  For a monochromatic radiation: - Magnetic and electric fields are functions of time, t, and space, x: Ф(x,t)= Ф 0 cos(ωt – kx) Ф; electric field, ω=2π ƒ ; 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 ( 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 keV-sec, 1 ev= 1.6 x joules)  These particles are called quanta, or photon  Photons are capable of ionizing atoms and molecules, so called ionizing radiation

Classification of Indirectly Ionizing Photon 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