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RA 100 – Imaging I

RA 100 – Imaging I. Radioactivity, Electromagnetic Radiation And Tissue Imaging. RADIOACTIVITY. Emission of particles and energy from an atom Disintegration or decay of the nucleus of unstable atoms RADIONUCLIDES RADIOISOTOPES. RADIOACTIVITY. Number of neutrons affects stability

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RA 100 – Imaging I

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  1. RA 100 – Imaging I Radioactivity, Electromagnetic Radiation And Tissue Imaging

  2. RADIOACTIVITY • Emission of particles and energy from an atom • Disintegration or decay of the nucleus of unstable atoms • RADIONUCLIDES • RADIOISOTOPES

  3. RADIOACTIVITY • Number of neutrons affects stability • Too few or too many cause instability • Particles or energy are ejected • Proper ratio is restored

  4. RADIOACTIVITY • Radioactivity measured in Curies or Becquerels – disintegrations or nuclear transformations per unit of time • Half-life: time it takes for radioactivity to reach half its initial value

  5. RADIOACTIVITY • Results in the emission of: • Alpha particles • Beta particles • Gama rays • Alpha and Beta are particulate radiation • Gamma is electromagnetic radiation • All are capable of causing ionization

  6. PARTICULATE RADIATION • ALPHA PARTICLES • CONSIST OF 2 PROTONS AND 2 NEUTRONS (HELIUM NUCLEUS) • DOUBLE POSITIVE CHARGE • HIGHLY IONIZING BUT DON’T TRAVEL FAR IN TISSUE • BETA PARTICLES • CONSIST OF HIGH SPEED ELECTRONS • NEGATIVE CHARGE • NOT AS DAMAGING, BUT TRAVEL FURTHER

  7. ELECTROMAGNETIC ENERGY • Fluctuating magnetic and electrical fields • Contain no mass or charge • Photons – energy disturbances moving through space

  8. CHARACTERISTICS • Electromagnetic energy has four characteristics that identify or describe it • VELOCITY • WAVELENGTH • FREQUENCY • AMPLITUDE • Visually expressed through a sine wave • Two dimensional representation of the electromagnetic field

  9. VELOCITY • Speed is CONSTANT for all forms of electromagnetic radiation • All travel at the speed of light • 186,000 miles per second • 3 x 108 meters per second

  10. WAVELENGTH • Distance between crests or valleys on the sine wave • Top wave has a __________ wavelength • Bottom wave has a ___________wavelength

  11. FREQUENCY • Number of crests or valleys per unit of time • Rate of rise and fall of the wave • Top wave has a ____________frequency • Bottom wave has a ____________frequency

  12. AMPLITUDE • Height of the wave • ½ the distance from crest to valley • Not important in radiography

  13. WAVELENGTH VS FREQUENCY • What is the relationship between wavelength and frequency?

  14. ENERGY VS WAVELENGTH / FREQUENCY • Energy of electromagnetic radiation refers to its strength or ability to penetrate matter • High energy radiation is more capable of penetrating matter • What is the relationship between energy and wavelength? • What is the relationship between energy and frequency

  15. WAVELENGTH / FREQUENCY VS ENERGY

  16. ELECTROMAGNETIC SPECTRUM • All forms of electromagnetic radiation are arranged on a continuum according to their wavelengths or frequencies

  17. X-RAY ENERGY AND TISSUE IMAGING • Three potential interactions between x-rays and the body • Pass through unaffected • Formation of scatter • Absorption (attenuation) of radiation

  18. FACTORS AFFECTING INTERACTION WITH MATTER • BEAM ENERGY • BEAM QUANTITY • TISSUE TYPE AND QUANTITY • TISSUE THICKNESS • ATOMIC NUMBER OF TISSUE • TISSUE DENSITY

  19. RADIATION AND IMAGING • Beam energy • As beam energy increases, what will happen most frequently? • As beam energy decreases, what will happen most frequently? • Beam intensity (quantity) • What will happen if beam intensity is increased? • What will happen if beam intensity is decreased?

  20. TISSUE FACTORS AND ATTENUATION • Interaction between radiation and matter is at the atomic level • Interaction is a random chance • Radiation not attracted to any atom • If atom and electrons are in the path of the photon, interaction will occur • If not, no interaction • Increasing the number of atoms or electrons will increase chance for interaction • What will happen to attenuation? • What will happen to scatter?

  21. TISSUE FACTORS AND ATTENUATION • TISSUE THICKNESS – QUANTITY • As tissue thickness increases, what happens to attenuation? • Why?

  22. TISSUE FACTORS AND ATTENUATION • TISSUE ATOMIC NUMBER • As tissue atomic number increases, what happens to attenuation? • Why?

  23. TISSUE FACTORS AND ATTENUATION • TISSUE DENSITY • As tissue density increases, what happens to attenuation? • Why?

  24. DIFFERENTIAL ABSORPTION • DIFFERENT TISSUE TYPES ABSORB DIFFERENT AMOUNTS OF RADIATION • In order of most to least absorption: • Bone • Muscle • Water density • Fat • Air - gas

  25. DIFFERENTIAL ABSORPTION

  26. PATHOLOGY AND ATTENUATION • DESTRUCTIVE PATHOLOGY • Affected body tissue is decreased in thickness, effective atomic number and/or density • Less attenuation • ADDITIVE PATHOLOGY • Affected body tissue is increased in thickness, effective atomic number and/or density • Greater attenuation

  27. PATHOLOGY AND ATTENUATION • DESTRUCTIVE CONDITIONS: • ATROPHY • EMPHYSEMA • BOWEL OBSTRUCTION • DEGERERATIVE ARTHRITIS • OSTEOPOROSIS

  28. PATHOLOGY AND ATTENUATION • ADDITIVE CONDITIONS: • EDEMA • TUMORS • PLEURAL EFFUSIONS • PULMONARY EDEMA • CARDIOMEGALY • ASCITES • HYDROCEPHALUS

  29. ADDITIVE EXAMPLE

  30. DESTRUCTIVE EXAMPLE

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