Ultrasound Flashcards
List the 4 key principles of safe US use.
- Only for medical diagnosis
- Exam times and output level should be as low and as short as possible
- Only used by fully trained staff
- Pregnancy scans should not be carried out for photo production only
What are biological effects of US?
Responses that occur when sound is introduced to the body
Define acoustic impedance?
The resistance a wave encounters as it passes through a tissue.
Explain the importance of acoustic impedance.
Acoustic impedance (AI) allows us to differentiate between the tissues the waves encounter. This is because each tissue type has a different density and therefore a different AI. The smaller the AI, the more useful it is for echo imaging.
What is the Doppler effect?
The difference between the frequency of sound as it leaves and arrives. When sound gets closer, the frequency and pitch of the wave increase.
Name and describe the 3 ultrasound modes.
- A Mode: produces graphs that show the strengths of reflections
- B Mode: produces 2D greyscale based on the strength of reflected sound echoes according to depth
- M Mode: produces a motion mode scan that shows motions and video images
A Doppler scan is…
…The measurement of change in sound frequency that shows the speed and direction of blood flow
What does “v = f x y” stand for?
velocity = frequency x wavelength
List 3 ways to follow the principles of ALARA
- Lowest acoustic exposure
- Making scans as short as possible
- Only scans for medical purpose
What do decibels (DB) do?
Measure the difference between sound intensities. The sound wave produced by the transducer and the returning echo wave.
State the difference between heating biological effects and mechanical biological effects.
Heating biological effects occur as a result of the mechanical friction of tissue moving as the US wave passes through.
Whereas a mechanical biological effect is the production and collapse of small bubbles in the inter/intracellular tissue fluid.
True or false?
The piezoelectric effect converts electrical energy into kinetic energy through crystal deformation.
False.
It is the conversion of kinetic energy into electrical energy through crystal deformation.
What happens when electric current is applied to Piezoelectric crystals?
The crystals vibrate and generate ultrasound waves.
What are Comet Tail artefacts?
When small calcific, crystalline, highly reflective objects come in contact with the ultrasound wave.
True or false?
Mirror artefacts are signal voids that appear behind structures that strongly absorb or reflect US waves.
False, those are Acoustic Shadow Image artefacts.
Mirror artefacts occur when the primary beam reflects from a surface and encounters another structure instead of returning to the transducer. This gives false readings of a deeper structure.
