Spring 2024 SPI Ch 5***

• what's intensity?

  • the energy concentration in a sound beam
  • describes the "bigness" of a wave
  • how power in a wave is distributed in space
• what's the formula for intensity?

  intensity = power (W) / area (cm2)
• what's spatial?

  refers to location or space
• how is spatial reported? list the 2 ways:

  • spatial peak intensity (Isp)
  • spatial average intensity (Isa)
• what's Isp?

  • spatial peak intensity
  • measures the maximum intensity
• what's Isa?

  • spatial average intensity
  • average intensity of the beam's entire cross-sectional area
• what does this signify?

  intensity

  A) intensity

  
• what's temporal?

  refers to time
• transmit / talking / on time

  
• receiving / listening / off time

  
• list the 5 terms related to intensity

  • spatial
  • temporal
  • peak
  • average
  • pulsed
• the center of the beam is the strongest, the outside is the weakest
• T or F: Spatial peak intensity is always higher than the spatial average intensity

  True
• what's Ita?

  • temporal average intensity
  • measures the average intensity of the beam during PRP (aka both the transmit and receive times)
• what's duty factor?

  the amount of time that the sound energy is present compared to the off time
• what's Ipa?

  measures the average intensity during the pulse duration (aka transmit time)

  
• what's Ita?

  temporal average intensity

  • measures the average intensity of the beam during PRP (aka both the transmit and receive times)

  
• what's Itp?

  • temporal peak intensity
  • measures the max intensity of the beam at the exact moment of its max value

  
• what's Im or Imax?

  • mean intensity of the max peak
  • measures the average intensity of the bean during the most intense half cycle

  
• temporal intensities largest to smallest

  Itp > lm > Ipa > Ita
• intensities may be reported in various ways with respect to time and space
• these different measurements are important in the study of bioeffects. SPTA is the most relevant intensity with respect to tissue heating
• the units for all intensities are watts/centimeter squared (W/cm2)
• peak measurements are larger than average measurements therefore, SPTP has the highest value and SATA has the lowest
• the beam uniformity coefficient (SP/SA factor) describes the spread of the beam in space. this is a unitless number with a value greater than 1
• duty factor describes the relationship of beam intensitieswith respect to time. this is a unitless number between 0 and 1
• with continuous wave ultrasound (CW) the beam is always transmitting. therefore the pulse average and temporal average are the same. SPTA = SPPA, SATA = SAPA
• when pulsed and CW beams have the same SPTP, the CW beam has the higher SPTA. when pulsed and CW beams have the same SATP, the CW beam has the higher SATA. CW beam have higher intensities than PW beams