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ULTRASOUND IMAGING (Basics (echo imaging (ultrasound pulses: (– Rather…

- - - - – Rather short: Generally 1-5 μs long (artificial damping in the crystal)
      - – It comprises a range of frequencies: larger for shorter pulses
      - – Velocity of sound in a medium nearly independent of frequency (otherwise the pulse would spread out as it traveled leading to pulse blurring)
      - – best for deep structures = low frequency
      - – best for high "axial" resolution = high frequency
    - - • Penetration: distance => ability to go through an object
      - • Attenuation =>how much energy is lost
      - • Reflection => when sound hits an object, it will bounce back to the sender
      - • Different tissues => different degrees => different appearances on the US screen
      - examples:
        
        • Bone: reflection close to 100%, strong echo, black shadow behind
        
        • Soft tissue, fat and organs: penetration, attenuation and reflection medium =>greys
        
        • Liquids (blood, urine, amniotic fluid, cysts): penetration high. Easy to see structures behind. Low reflection=>black US screen
        
        • Air/gas => lot of scatter=> useless snow storm