Image Formation

Question 1

What is A-mode?

Answer 1

Displays amplitude of echos as a function of time (e.g. depth)

Question 2

What is B-mode?

Answer 2

Converts A-mode signal into brightness value

Question 3

What is M-mode?

Answer 3

Displays B-mode signal as a function of time

Question 4

How do contrast agents work (physical property, type of interaction)? Given an example of an element used as a contrast agent

Answer 4

Ultrasound uses microbubble-based contrast agents to help visualize the structure of vessels as well as the flow of blood.

They utilize acoustic responses, oscillating non-linearly when pressure is applied by the ultrasound wave. Contrast-enhanced ultrasound uses resonant scattering and non-linear harmonic generation; microbubbles resonate and scatter the soundwaves upon impact with the ultrasound waves. This helps to increase the visibility of blood.

Example: perfluorocarbon

Question 5

You are asked to perform an abdominal ultrasound scan of the liver. Given the following setup: the field of view spans an angle of 30 degrees, the depth is 10 cm in depth from the skin, and the lateral resolution is 2mm; calculate:

the acquisition time for the image

the frame rate

Answer 5

Arc length:
L = theta * r = (30 * pi/180) * 10 cm = 5.23 cm = 52.3 mm

A-lines:
N = (2L)/lat_res = (252.3 mm) / 2 mm =~ 53

Echo time:
T = (2*D) / c = (2 * 100 mm) / (1540 m/s * 1000 mm/m) = 0.00013 s

Acquisition time:
T_acq = N * T_echo = … = 0.0069 s = 6.9 ms

Frame rate:
FR = 1 / (N * T_echo) = … = 145 s^-1