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Transcript of Ultrasound 101
Cycles can be 7000/second
Returning waves are converted to Electrical Impulses
Brightness of signal depends on the intensity of the returned ultrasound Location (or deapth) of signal depends on the time it takes for the ultrasound beam to arrive back at the transducer (speed of ultrasound in tissue ~ 1540 m/s) Reflection Refraction Transmission Scattering Amount of reflection is proportional to the difference in acoustic impedance between adjacent tissues Greater difference in acoustic impedance, better differentiation with neighboring tissue
Acoustic Impedance = velocity x density Sciatic Nerve Interscalene Attenuation Progressive loss of acoustic energy as a wave passes through tissue Loss of signal is directly related to depth Attenuation is medium dependent
Represented by the Attenuation Co-efficient
Bone>>Air>>>Muscle>Brain>Fat>Blood>>>Water Choose lower frequency for deeper tissue Time gain compensation (TGC)
Artificially amplify signal (gain) for deeper (hence weaker) signal Resolution Axial Lateral Temporal Axial Resolution Ability to separat two structures at Different Depths Distance between objects must be greater the ½ pulse length to be seen as separate
Lateral Resolution Ability to separating two structures beside one another
Temporal Resolution Directly related to U/S Frame Rate (FR)
FR is limited by sweep speed
Sweep speed is limited by image depth
Image depth should be just below target