- ‘Spatial pulse length’ is the product of the wavelength and the number of cycles in a pulse
- A shorter wavelength (and thus higher frequency) results in a shorter spatial pulse length
- Resolution is determined by the ‘spatial pulse length’ of the wave
- The minimum distance that can be reflected between two points is equal to half the ‘spatial pulse length’
- Therefore Resolution is high when the ‘spatial pulse length’ is short and the wave frequency is high
- Higher frequency waves have a greater resolution but at the expense of deeper penetration
- The absorption of an ultrasound wave is proportional to the frequency
- When more energy is absorbed the wave is less able to penetrate deep into tissues
- Therefore lower frequency waves penetrate deeper but at the expense of resolution