DMS 209

• The hydrophone is also called a:

  microphone
• In a hydrophone, the acoustic pressure is measured:

  at specific location within the sound beam
• What is dosimetry ?

  Science of identifying and measuring sound beam potential for biological effects
• What are the three dosimetric qualities ?

  Pressure, power, and intensity
• What is acoustic exposure ?

  Amount of acoustic energy a patient receives
• What determines the sound beam intensity ?

  Ultrasound system output control (source)
• Acoustic exposure is determined by what 2 things ?

  Sound beam intensity and exposure time
• What three things should you do to avoid over-exposure ?

  Only perform exam when medically indicated, with proper equipment settings, and limit exposure time
• What are the 2 types of intensity ?

  Spatial and temporal
• Spatial peak:

  area of beam with the highest intensity
• Spatial average:

  average beam intensity
• Temporal Peak:

  highest intensity during "ON" time
• Temporal Average:

  Average intensity during "ON" and "OFF" time
• What has the minimum intensity ?

  SATA
• What is the most common measurement for ultrasound bioeffects ?

  SPTA
• What does the acronym SATP mean ?

  Spatial Average; Temporal Peak
• What has the maximum intensity ?

  SPTP
• What are the three types of bioeffects research ?

  In vivo, in vitro, and epidemiological
• What is in vivo research ?

  Within a living body
• What is in vitro research ?

  Outside the living body in an artificial environment; in glass (test tubes or petri dishes); Very high intensities can cause genetic damage and cell death
• What is epidemiological research ?

  long term studies of people who have had ultrasounds; mostly human fetuses; no known effects when compared to fetuses without exposure
• Mechanical index is used to describe output in terms of:

  possible cavitation
• If less than 1, the risk of cavitation is:

  low
• If higher than 1, then the risk for cavitation is:

  high
• What is cavitation ?

  interaction of sound beam with microscopic bubbles in tissue
• Mechanical index is related to:

  Temporal Peak
• What are the two forms of cavitation ?

  Stable and transient
• What happens in stable cavitation ?

  Bubbles grow and oscillate at lower MI levels; results in microstreaming in fluid surrounding cells and in cell shear stresses
• What happens in transient cavitation ?

  bubbles expand and collapse causing implosion at higher MI levels; results in shock waves and colossal temperatures
• Thermal index used to describe ratio between output power and the amount of power it takes to raise tissue temperature by 1 degree Celsius.
• What is Thermal Index dependent on ?

  TDR frequency, acoustical power, beam area, absorption, attenuation properties of tissue, and thermal properties of tissue
• What is TIS ?

  Thermal index in soft tissue
• What is TIB ?

  Thermal index in bone near focus
• What is TIC ?

  Thermal index in cranium in near field
• How can the effect of heating be reduced ?

  By reducing scan time
• What does ALARA stand for ?

  ALARA stands for "As Low As Reasonably Achievable.
• A peak is always greater than or equal to an average.
• Duty Factor = TA (temporal average) / PA (pulse average)
• Dosimetric quantities that are measured are:

  Acoustic pressure; acoustic power, acoustic intensity, radiation force