Equipment Performance

Question 1

What is spatial resolution

Answer 1

The ability to discern two objects as separate
- the minimum distance between them

Axial resolution is 3 times smaller than lateral which is 3 times smaller than slice thickness

Question 2

Discuss the issues related to accuracy of measurement in ultrasound

Answer 2

Axial resolution - dependent on transmit pulse duration (PRF, frequency)

Lateral resolution - dependent on beam width (aperture diameter, frequency)

Artifacts

Question 3

What detemines axial resolution

Answer 3

The echoes from the two targets need to not overlap in time
This is determined by the duration of the transmit pulse
The axial resolution = propagation speed x pulse duration / 2

Improved with increased frequency (reduced penetration depth)

Question 4

What determines lateral resolution

Answer 4

Point targets are smeared out laterally by an amount equal to the beam width
Therefore targets need to be separated by at least beam width to be seen as separate

Beam width is reduced with increasing frequency (and increased aperture diameter)

Question 5

What are the factors determining contrast resolution

Answer 5

Contrast resolution is the ability to detect differences between tissue’s echogenicity

Artifacts
Speckle
Machine settings
- Gain, TGC, dynamic range, frequency

Question 6

What determines temporal resolution

Answer 6

TR = ability to produce good images when tissues are moving or the probe is moving

Key parameter is frame rate (Hz)

(FR x P x L x E) / M = c / 2 = 77,000cm/s

P = depth of penetration
L = number of lines in each image
E = number of pulses needed for each line