6.1.13Waves
Ultrasound in Medical and Industrial Imaging
5 min read 6 parts Lesson 14 of 32 Unit quiz
Section 1 of 6How an Ultrasound Image Forms
Ultrasound images are built from echoes reflected at boundaries where the material changes.
Pulse
- Pulse Short pulses of ultrasound are sent into the body or material by a transducer.
Reflection
- Reflection Part of each pulse is reflected at every boundary between two different tissues or materials.
Detection
- Detection The transducer detects the returning echoes and records the time each one takes to arrive.
Image
- Image The time and strength of each echo are used to build a picture of the internal structure.
Section 2 of 6The Pulse-Echo Process
The same sequence is repeated many times a second to build up a moving image.
1
A transducer emits a short pulse of ultrasound into the material being examined.
2
The pulse travels through the material and is partly reflected at each boundary it meets.
3
The transducer receives each echo, and the time between sending the pulse and receiving the echo is measured.
4
The longer the echo takes, the deeper the boundary is, so the depth of each boundary can be worked out.
Section 3 of 6Uses in Medicine and Industry
Ultrasound is used widely because it is safe and can build images without cutting into the material.
Uses in Medicine and Industry
Medical scanning
- Medical scanning Used to monitor a developing foetus, and to image soft tissues and organs inside the body.
Industrial testing
- Industrial testing Used to detect cracks or flaws inside metal components, which reflect the pulse back earlier than the far surface.
Safety
- Safety Ultrasound is non-ionising, so repeated scans are safer for patients than X-rays.
| Use | Application | Why ultrasound is suitable |
|---|---|---|
| Medical imaging | Monitoring a developing foetus during pregnancy | Non-ionising, so it is safer than X-rays for repeated scans |
| Medical imaging | Imaging soft tissues and organs | Pulses reflect from the boundaries between soft tissues |
| Industrial testing | Detecting cracks or flaws inside metal | Pulses reflect from internal cracks and from the far surface |
Section 4 of 6Limitations of Ultrasound
Ultrasound has limits that affect where and how it can be used.
Bone
- Bone Ultrasound is almost entirely reflected by bone, so it cannot easily show what lies behind it.
Air and gas
- Air and gas Gaps of air reflect nearly all of the ultrasound, so a gel is used to remove air between the probe and the skin.
Speed in materials
- Speed in materials Ultrasound travels at different speeds in different materials, so depth calculations depend on the material being examined.
Section 5 of 6Worked Example
Question
- An ultrasound pulse is sent into soft tissue where its speed is 1500 m/s.
- An echo from a boundary returns after 0.0002 s.
- Calculate the depth of the boundary.
- Total distance travelled by the pulse = speed × time = 1500 × 0.0002 = 0.30 m.
- The pulse travels to the boundary and back, so depth = 0.30 ÷ 2 = 0.15 m.
- Convert to centimetres0.15 m = 15 cm.
Answer The boundary is 15 cm deep.
Section 6 of 6Exam Checklist & Tips
6.1.13 – Key Points for the Exam
- Ultrasound Sound waves with a frequency above the range that humans can hear.
- Transducer A device that emits ultrasound pulses and detects the returning echoes.
- Echo A reflected pulse of ultrasound that returns from a boundary between two materials.
- Pulse-echo technique The method of building an image from the times and strengths of reflected pulses.
- Non-ionising radiation Radiation that does not have enough energy to remove electrons from atoms.
Common Mistakes
- Using the total distance travelled by the pulse as the depth, instead of halving it because the pulse travels there and back.
- Saying ultrasound is ionising radiation in the same way as X-rays.
- Forgetting to convert metres into centimetres when a question asks for an answer in centimetres.
- Claiming ultrasound passes easily through bone and air, when both reflect it strongly.