Ultrasound

Question 1

Frequency range in US

Answer 1

2-20MHz (audible sound 20-20kHz)

Question 2

How does frequency affect US image quality?

Answer 2

Higher frequency = higher resolution, however lower penetration

Seeing deeper structures require lower frequency

Question 3

How is attenuation influenced by frequency?

Answer 3

Higher frequency = higher attenuation

Question 4

How does scattering affect US imaging?

Answer 4

Not all energy will be reflected to add to image quality - scattering results in speckles due to fluctuations of echo intensities

Question 5

Refraction

Answer 5

Changes in the direction of the US beam when passing through an interphase between tissues of different densities (and hence waves propagate at different speeds)

Question 6

How do the refraction and the incident angle affect US imaging?

Answer 6

Larger incidence angle = less reflected waves detected by probe = miss some structural information (ie changing probe angle can make some structures “disappear”

Question 7

Describe the Doppler principle

Answer 7

Echoes from moving scatterers and reflectors have a slightly different frequency to the transmitted frequency.
The Doppler shift is proportional to the speed