Ultrasound Flashcards
What is ultrasound?
1 ) A procedure that uses high frequency sound waves to produce images of internal organs or the interior of the body
2) works similar to sonar tech or echolocation in animals
At what frequencies does ultrasound work at?
> 20,000Hz (20kHz)
How should you measure wave lengths?
1) peak-to-peak
OR
2) trough-to-trough
What is soft tissue propagation?
1) how fast the sound wave travels through soft tissue
2) speed is 1540 m/s and can’t be altered
3) can change the frequency to change the sound wave
What is reflection as it relates to ultrasound?
1) it is when the sound waves produced by the transducer hit an object and come back
2) it occurs between two tissues with very different acoustic impedances
What is specular reflection?
1) when sound waves encouter tissue boundaries that are large and smooth it reflects back in a uniform way
What is backscatter as it relates to ultrasound?
1) a type of reflection
2) occurs on rough surface and small structures
3) no uniform way to reflect
What is attentuation as it relates to ultra sound?
1) is the absorption of energy to the body
2) sound energy is converted to heat
3) results from specular reflection and backscatter
What is refraction as it relates to ultrasound?
1) refraction is the bending (changing direction) of a sound wave as it encounters an interface between two materials with different speeds of sound
2) can lead to artifacts
Why is ultrasound gel used?
1) it allows ultrasound waves to penetrate the body from the transducer
2) reduces reflection and refraction (waves travel better through water than air)
3) without it less than 1% of the signal goes into patient, 99% with it
How does a transducer work?
1) it converts electrical energry into mechanical energy
2) uses piezoelectric effect
3) it then sends out a signal which comes back and causes the crystals to vibrate
What are some properties of a curved tranducer? What whould it be used for?
1) it can penetrate deeply (up to 30cm)
2) uses low frequency
3) ex: abdominal aorta
What are some properties of a linear tranducer? What whould it be used for?
1) can’t scan deeply (8-10cm) so superficial structures
2) high frequency
3) ex: duplex carotid
What are some properties of a phased array tranducer? What whould it be used for?
1) goes deeper (30cm)
2) low frequency
3) it is smaller in size
4) ex: heart examinations
What is lateral resolution?
1) the ability to distinguish objects that are side-by-side
2) narrower the beam, the better the resolution
What is axial resolution?
1) ability to distinguish two objects that are longitudinally adjacent
2) higher frequency means better axial resolution
How is the doppler effect used in ultra sound?
1) it can be used to asess the flow of blood
2) red blood cells move towards the transducer = high frequency
3) red blood cells move away from the transducer = low frequency
What is pulsed-wave (PW) doppler?
1) measures blood flow velocity at one specific location
2) sends a signal and wait to receive a signal back
3) used with a curved transducer
4) low velocities
What it continuous wave (CW) doppler?
1) there are two crystals working simultaneously
2) one always sends and one always receives
3) measures high velocities
4) obtains the signal along the entire length of the ultrasound beam
What is colour flow Doppler?
1) is a visualisation of flow direction and velocity within a user defined area
2) BART = Blue Away, Red Towards
What are image artefacts?
Imaging artefacts are incorrect representations of anatomy or function
What is reverberation?
1) images artifact
2) ultrasound beam bounces several times between two strong specular reflectors
3) takes longer for the signal to return so machine misinterprets the info
What is acoustic shadowing?
1) image artefact
2) highly echo reflective structure that blocks the ultrasound from penetrating
3) can’t see under the shadow
What is a shadow artifact?
1) ultrasound beam encounters a strong reflector and the energy of the forward beam becomes degraded = blocked signal
2) can fix by angling in with different waves
What is beam width artifact?
1) something from the edge of the image but the machine “thinks” is from the center
How can you minimize risks during an ultrasound?
1) only perform ultrasound for appropriate clinical indications
2) keep power output as low as possible
3) keep exposure time to a minimum
4) M-mode and 2D have the lowest intensity, PW doppler has the highest, colour doppler in the middle
5) check for risk of electric shock
6) injury risk with trips and falls
7) risk of infection