Energy. Mechanical Energy

Transcription

1 Principles of Imaging Science I (RAD119) Electromagnetic Radiation Energy Definition of energy Ability to do work Physicist s definition of work Work = force x distance Force acting upon object over distance expends energy Mechanical Energy Action of physical movement Two types: Potential Kinetic 1

2 Chemical Energy Energy released from chemical reaction Examples: Body converts chemical energy from food into mechanical energy or movement Battery converts chemical energy into electrical energy Heat Energy Also known as thermal energy Results from movement of molecules Temperature measures thermal energy Example: Toaster converts electrical energy into heat energy Electrical Energy Electricity Results from movement of electrons in conductor Example: Light bulb converts electric energy to light 2

3 Electromagnetic Energy Exists independently of objects Present ubiquitously and spans an energy continuum Endless ordered arrangement Combination of electrical and magnetic bundles called photons or quantum Electromagnetic Energy (EM) All types of electromagnetic radiation are a form of energy EM energy is the result of electric and magnetic disturbances traveling through space Typically, only the electric wave is depicted in illustrations Electromagnetic Energy (EM) Pure energy travels through space at speed of light Electric and magnetic waves 90 degrees to each other Does not need a medium to be transmitted unlike mechanical waves in water or sound waves in air Can travel in a vacuum Entire band of energies is grouped in the EM spectrum 3

4 PHOTONS Smallest quantity of any electromagnetic energy Have no mass, no form Quantum refers to a small bundle of energy that travels through space at the speed of light Speed of light = 186,400 miles/sec = x 10 5 miles/sec = 3 x 10 8 m/sec Velocity of all electromagnetic radiation PHOTON PROPERTIES Electric & magnetic fields that continuously change in a wavelike motion Field: Interaction among the electric and magnetic energies Sine Wave: Variation of the interactions is represented as a sine wave SINE WAVE DEFINITION & TERMS Disturbance in a medium Amplitude One half the range of the wave that varies from crest to valley Height of the wave 4

5 Sine Wave Terms Wavelength Distance between adjacent crests or valleys Measured in metric meters Represented by lambda (λ) SINE WAVE TERMS Frequency # of wavelengths that pass a given point per second Cycles/sec Oscillations/sec Measured in Hertz (Hz) 1 Cycle/second = 1 Hz Wavelength & Frequency Relationship 5

6 SINE WAVE TERMS Period: Time to complete one cycle of a wave TIME /#CYCLES Wave with a frequency of one cycle per second = 1.0 sec period Wave with a frequency of two cycles per second = 0.5 sec period Two Sine Wave Comparison 1 sec/2cps = 0.5 Period 1 sec/4cps = 0.25 Period WAVE EQUATION Relationship between the sine wave parameters Change in one parameter affects the value of one or both parameters Amplitude is not related to frequency or wavelength Equation Velocity = Frequency x Wavelength As velocity decreases, frequency decreases to maintain wavelength As velocity is maintained, frequency and wavelength are inversely proportional frequency = Velocity/Wavelength Wavelength = Velocity/frequency 6

7 PARTICLE MODEL Applied to electromagnetic radiation Planck s Quantum Theory Direct relationship between photon energy and frequency E = hf E = Photon Energy h = Planck s constant 4.15 X evs f = Frequency Velocity (c) = frequency x wavelength EM SPECTRUM Continuum of electromagnetic energies The full range of all of the different types of electromagnetic radiations arranged in order of increasing energy: Radio Radar/microwaves Infrared Visible light Ultraviolet X-rays and gamma rays Represents frequency, wavelength, and energy EM SPECTRUM 7

8 EM SPECTRUM EM SPECTRUM Wavelength and frequency are inversely proportional. Wavelength and energy are inversely proportional. Energy and frequency are directly proportional. Electromagnetic Interactions EM interaction with matter is based upon wavelength EM energy interacts with objects that have a size similar to the wavelength Radio/TV (km) antennae Microwaves (cm) food X-ray, Gamma ray atoms Visible light acts more like a wave when it interacts with matter»has particle properties X-rays behave more like particles due to ionizing potential 8

9 Light Characteristics Wave and particle characteristics Visible light refers to the light we can see (wave) Infrared light, ultraviolet light Warmth and sunburn are the manifestations of UV energy (particles) The intensity of light is related to how many particles are emitted from the source and distance Light Characteristics Transmission Passing of light rays through a substance Air, clear glass, or the near vacuum of space Light photons are transmitted, attenuated, or absorbed Wave Model 9

10 Wave Model X-ray photons that interact with the body are attenuated or absorbed RADIOGRAPHIC TERMINOLOGY Radiopaque Anatomical structures that absorb x-ray photons Demonstrate anatomical structures white in the image Bones Radiolucent Anatomical structures that partially absorb or attenuate x-ray photons Demonstrate structures grey in the image Soft tissue, organs, muscle Radiographic Terminology Density (Brightness) Degree of blackening in the image High Density (Dark) Low Density (White) Contrast (Grey Scale) Long Scale Contrast Many shades of grey Low contrast CXR, Abdomen Short Scale Contrast Black and white High contrast Bony anatomy 10

11 Radiopaque or Radiolucent? Density Long Scale vs Short Scale Contrast 11

12 Scale of Contrast Contrast INVERSE SQUARE LAW Demonstrates the similarity of x-rays and light rays The intensity of radiation decreases with the square of the distance from the source Doubling the distance from the source decreases the intensity 4x. Halving the distance from the source increases the intensity 4x. 12

13 Inverse Square Law Light also acts like particles Even though these photons are steadily emitted by the light source, as you move farther away from the source, fewer photons reach you They spread out as they travel in a wider area away from the source THE INVERSE SQUARE LAW THE INVERSE SQUARE LAW The intensity of the radiation decreases with an increase of distance from the source (and vice versa) Intensity is inversely proportional to the square of the distance Formula: I 2 = I 1 (d 1 /d 2 ) 2 I 1 = Old intensity d 1 = Old distance Formula may also be expressed as: I 1 /I 2 = d 12 /d 2 2 I 2 = New intensity d 2 = New distance 13

14 INVERSE SQUARE LAW I 1 = D 2 2 I 2 D 1 2 I 1 = Original Intensity I 2 = New Intensity D = Original Distance 1 D = New Distance 2 Examples 14