Principles of ultrasound physics and equipment Flashcards
what is a wave
a mode of energy transfer from one place to another
what happens in longitudinal waves
particles move with a direction of travel
what is a sound wave
longitudinal waves that travel through a medium
what are ultrasound waves
very high frequency sound waves
what frequency are audible waves
20-20,000 Hz
what frequency are ultrasound waves
between 1-30 MHz
what is a wavelength
distance between consecutive wave crests or similar points on a wave
what is frequency (3 points)
1) number of cycles per second
2) measured in Hertz (Hz)
3) frequency affects penetrative power of the ultrasound beam
the higher the frequency…
less penetration power but more resolution
4 ways that sound is affected by tissue
1) reflection
2) attenuation
3) speed
4) absorption
when does reflection occur
when there is a difference in 2 types of tissue
what happens during attenuation
energy is lost as sound propagates through the tissue
what does speed depend on
the nature of the tissue
what happens during absorption
some ultrasound energy is converted into heat
How is an ultrasound image formed? 6 steps
1) transducer
2) Piezoelectric crystals
3) conversion of energy
4) sound attenuated, reflected and absorbed by tissue
5) reflected sound converted to electrical signals
6) grey scale image is formed
what is a B-mode image
a grey scale image
how is a B-mode image produced
by the piezoelectric effect
what is the piezoelectric effect
the conversion of electrical pulses to mechanical vibrations and the conversion of returned mechanical vibrations back into electrical energy
how is a Doppler image produced
utilises the Doppler principle
what is the Doppler principle
the change in observed frequency of the sound wave which occurs due to the relative motion between observer and source
Doppler imaging includes (3 types)
1) colour Doppler
2) power Doppler
3) spectral Doppler imaging
what is colour Doppler (2 things)
1) shows direction of blood flow
2) different colour indicates different direction of flow
what is power Doppler (3 things)
1) uses colour to indicate flow
2) non directional
3) can pick up very low velocities
what is spectral Doppler
indicates direction and velocity of flow
ultrasound safety (2 things)
1) no evidence of harm by ultrasound
2) there are thermal and mechanical effects
what must thermal indices and mechanical indices be
kept at recommended levels
clinical examples of ultrasound uses
1) obstetrics
2) gynaecology
3) general;abdo,superficial,paed
4) vascular
5) musculoskeletal
6) heart
7) emergency point of care
