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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

RA 100 – Imaging I

Radioactivity, Electromagnetic Radiation

And Tissue Imaging


Radioactivity
RADIOACTIVITY

  • Emission of particles and energy from an atom

  • Disintegration or decay of the nucleus of unstable atoms

    • RADIONUCLIDES

    • RADIOISOTOPES


Radioactivity1
RADIOACTIVITY

  • Number of neutrons affects stability

  • Too few or too many cause instability

  • Particles or energy are ejected

  • Proper ratio is restored


Radioactivity2
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


Radioactivity3
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


Particulate radiation
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


Electromagnetic energy
ELECTROMAGNETIC ENERGY

  • Fluctuating magnetic and electrical fields

  • Contain no mass or charge

  • Photons – energy disturbances moving through space


Characteristics
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


Velocity
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


Wavelength
WAVELENGTH

  • Distance between crests or valleys on the sine wave

  • Top wave has a __________ wavelength

  • Bottom wave has a ___________wavelength


Frequency
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


Amplitude
AMPLITUDE

  • Height of the wave

  • ½ the distance from crest to valley

  • Not important in radiography


Wavelength vs frequency
WAVELENGTH VS FREQUENCY

  • What is the relationship between wavelength and frequency?


Energy vs wavelength frequency
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



Electromagnetic spectrum
ELECTROMAGNETIC SPECTRUM

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


X ray energy and tissue imaging
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


Factors affecting interaction with matter
FACTORS AFFECTING INTERACTION WITH MATTER

  • BEAM ENERGY

  • BEAM QUANTITY

  • TISSUE TYPE AND QUANTITY

    • TISSUE THICKNESS

    • ATOMIC NUMBER OF TISSUE

    • TISSUE DENSITY


Radiation and imaging
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?


Tissue factors and attenuation
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?


Tissue factors and attenuation1
TISSUE FACTORS AND ATTENUATION

  • TISSUE THICKNESS – QUANTITY

    • As tissue thickness increases, what happens to attenuation?

    • Why?


Tissue factors and attenuation2
TISSUE FACTORS AND ATTENUATION

  • TISSUE ATOMIC NUMBER

    • As tissue atomic number increases, what happens to attenuation?

    • Why?


Tissue factors and attenuation3
TISSUE FACTORS AND ATTENUATION

  • TISSUE DENSITY

    • As tissue density increases, what happens to attenuation?

    • Why?


Differential absorption
DIFFERENTIAL ABSORPTION

  • DIFFERENT TISSUE TYPES ABSORB DIFFERENT AMOUNTS OF RADIATION

  • In order of most to least absorption:

    • Bone

    • Muscle

    • Water density

    • Fat

    • Air - gas



Pathology and attenuation
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


Pathology and attenuation1
PATHOLOGY AND ATTENUATION

  • DESTRUCTIVE CONDITIONS:

    • ATROPHY

    • EMPHYSEMA

    • BOWEL OBSTRUCTION

    • DEGERERATIVE ARTHRITIS

    • OSTEOPOROSIS


Pathology and attenuation2
PATHOLOGY AND ATTENUATION

  • ADDITIVE CONDITIONS:

    • EDEMA

    • TUMORS

    • PLEURAL EFFUSIONS

    • PULMONARY EDEMA

    • CARDIOMEGALY

    • ASCITES

    • HYDROCEPHALUS




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