Ultrasound is used during a scan to monitor the movement of a tissue boundary in the heart of a foetus.
A transducer sends short ultrasound pulses into the body and detects echoes from the same boundary. The speed of ultrasound in the tissue is 1540 m/s.
The table shows the echo time at different times during one movement of the boundary.
| Time in ms\text{ms}ms | Echo time in μs\mu\text{s}μs |
|---|---|
| 0 | 72 |
| 100 | 68 |
| 200 | 64 |
| 300 | 68 |
| 400 | 72 |
Calculate the distance moved by the tissue boundary between 0 ms and 200 ms.
Describe the movement of the tissue boundary during the 400 ms shown in the table.
At the first scanner setting, a wave train containing 20 complete wavelengths is 15.4 mm long in the tissue.
Calculate the frequency of the ultrasound.
A second scanner setting produces ultrasound with a frequency of 5.0 MHz.
Explain which setting should be used to show smaller details of the tissue boundary.