Ultrasound

Question 1

How are high frequency sound waves created?

Answer 1

Alternating current with high frequency across crystal causes mechanical changes in crystal which gives ultrasound. This is the inverse piezoelectric effect

Question 2

How are high frequency waves detected?

Answer 2

Mechanical stress from US pressure waves causes charge separation in atoms in the crystal lattice which gives a changing electric field. This is detected as an AC signal. This is the piezoelectric effect

Question 3

How might the doppler effect be used in US imaging?

Answer 3

Used to quantise blood flow, eg. to check if blood is flowing to particular organs, or to assess blood vessels feeding tumour

Question 4

What are some advantages of US imaging?

Answer 4

• Non-ionising
• Low cost
• Portable

Question 5

What are some disadvantages of US imaging?

Answer 5

• Operator dependent as it is a “live” process
• Cannot penetrate gas / bone
• Presence of artifacts such as shadows behind areas which have a different acoustic impedance to surrounding tissue