1.2 Ultrasound Flashcards
What frequency are ultrasound waves?
Above 20,000Hz (20kHz)
How do ultrasounds work?
Ultrasound waves are transmitted through a substance and when they reach a boundary between 2 different materials with different densities they are partly reflected back to the receiver. It measures the time between each reflection
What happens to ultrasound waves when they reach different substances with different densities?
They are partly reflected back, partly absorbed through and partly refracted into the substance they are in
How can the time taken between reflections be used to work out the distance between each material?
You use the time taken and the known speed that the waves were travelling at to work out the distance by doing SPEED X TIME
Why must you divide the distance (speed x time) by 2 in the exam?
Because the time is for the wave to be sent from the transmitter to the substance and back to the receiver so it made two journeys so divide the distance found by 2
Calculation for distance in ultrasound
Distance (m) = speed (m/s) x time (s)
Remember to divide the answer by two because the waves travelled twice the distance (from the transmitter to the tissue and then back to the receiver)
Why is ultrasound safer to use for scanning that X-Rays?
It is non ionising so doesn’t cause cancer
How can ultrasounds be used for prenatal scans?
Fire ultrasound waves at the mothers abdominals, ultrasound goes through different densities, builds up a picture of baby, and can measure heart beats and blood flow
How can ultrasounds be used to remove kidney stones?
The ultrasounds are such a high frequency that when aimed at the kidney stones, they vibrate so vigorously that they are crushed and can be released through urine
Why are ultrasound waves restricting?
They don’t pass through bone and make echoes so the waves are reflected
What frequency waves can the human ear detect?
20-20,000Hz
