2. Ultrasonography Flashcards
(44 cards)
What is Ultrasonography?
using ultrasonic waves in the frequency wave >20000 megahertz to create images of body structures based on the pattern of echos reflected from the tissues and organs being imaged.
What are the 3 physical properties of an ultrasound?
Sound- a wave of energy that must be transmitted through a medium
Sound waves- described by their frequency, wavelength and velocity
Frequency- the number of cycles or waves completed every second, and the wavelength is the distance needed to create one cycle
How does ultrasonography work?
Piezoelectric crystals are contained within the transducer.
An electric current causes the crystals to vibrate inducing a compressed sound wave.
Transducer produces ultrasound beams in pulses and each pulse travels through the skin tissue.
When the waves meet different tissue structures they will either:
- Continue deeper
- Reflect back to the probe
- Refract or dissipate as heat
- Be absorbed
Returning echos then convert to electrical signals via the piezoelectric effect.
The electronic system of the computer translates the info, measuring electric difference and displays the data as an image.
What advantages are there to using ultrasonography?
- No risk of ionisation energy
- No additional risks from anaesthesia
- Real time imaging
What is the Piezoelectric effect?
Ceramic crystals in the transducer deform due to pressure causing an ultrasound beam.
The frequency of the wave is determined by the crystals.
The returning echoing sound causes the crystals to vibrate and create an electrical current to be fed to the computer.
What is the pulse-echo principle?
Ultrasound beams are produced in pulses. In the time between pulses, the beam enters the body and is bounced or reflected back to the machine.
Define ‘Attenuation’
The gradual weakening of the ultrasound beam as it passes through tissue
Define ‘Echogenicity’
Tendency of a tissue to reflect sound waves
How does a deep tissue or structure effect attenuation and echogenicity?
The further away the tissue is the more the waves become attenuated.
It will take longer for the echo to return to the probe. A focal point can be set and the machine can ‘time’ the echoes ensuring the image appears at the appropriate place on the screen.
Define ‘reflection’
Occurs when ultrasound waves are bounced back to the transducer
Define ‘Acoustic impedance’
The product of a tissue’s density and the velocity of the soundwaves passing through it
Define ‘scattering’
Refers to the redirection of ultrasound waves as they interact with small, touch, uneven structures
Define ‘Absorption’
When the energy from the ultrasound is converted into heat. This then results in cavitation.
Define ‘cavitation’
Gas pockets
Define ‘refraction’
When an ultrasound beam hits a structure at an oblique angle. The change in tissue density causes the beam to bend
Define ‘interface’
Hitting a boundary (usually displayed as white)
What is the difference between hyperechoic and Hypoechoic?
Hyperechoic= high intensity
Hypoechoic= low intensity
Should surgical spirit be used during an ultrasound?
In moderation as it is proven to damage the transducer
How does frequency effect image quality?
Higher frequency= shorter sound wave.
Short wave- clear image, but not deep scan
Long wave- low resolution, deep scab
Free air affects image quality.
Define ‘brightness’
The intensity (strength) of the echoes
What is B-mode?
B-mode is used during abdominal ultrasounds. It’s 2D, grayscale imaging.
What is M-mode?
M-mode is used for echocardiograms. It is a 2D, colour imaging, Doppler ultrasound test which identifies blood flow.
Define ‘anechoic’
Black- represents fluid such as blood or urine
How does none appear on an ultrasound?
White- Hyperechoic
More sound waves are reflected back to the probe - high density no penetration of sound waves
