Echo Made Easy - Chapter 2

Question 1

How is a 2D image created by ultrasound?

Answer 1

Ultrasound reflected from a tissue interface distorts the
piezoelectric crystal and generates an electrical signal. The
signal produces a dot (spot) on the display screen.

The location of the dot indicates the distance of the structure
from the transducer. The brightness of the dot indicates the
strength of the returning signal.

To create a 2-D image, the ultrasound beam has to be swept
across the area of interest. Ultrasound is transmitted along
several (90 to 120) scan lines over a wide (45° to 90°) arc
and many (20 to 30) times per second.

Question 2

What does the M in M-mode stand for?

How does it differ from standard B-mode? What is it useful for?

How is M-mode displayed? What does each axis represent?

Answer 2

In the M (motion)-mode tracing, ultrasound is transmitted and received along only one scan line, perpendicular to the structure being studied.

M-mode is displayed as a continuous tracing with two axes. The vertical axis represents distance between the moving structure and the transducer. The horizontal axis represents time.

Since only one scan line is imaged, M-mode echo provides greater sensitivity than 2-D echo for studying the motion of moving cardiac structures. Motion and thickness of ventricular walls, changing size of cardiac chambers and opening and closure of valves is better displayed on M-mode

Question 3

What can CW doppler be used for (5)?

Answer 3

CW doppler is used:

• for rapid scanning of the heart in search of high velocity signals and abnormal flow patterns
• as basis for placement of sample volume to obtain PW spectral trace
• for grading of severity of valvular stenosis and regurgitation
• for quantifying VSD
• for calculating pulmonary artery pressure (by using CW signal of triscuspid valve)

Question 4

What is PW doppler used for (3)?

Answer 4

PW doppler is used:

• to localise velocity signals and abnormal flow patterns picked up by CW doppler and colour flow mapping.
• MV inflow signal is used to asses LV diastolic dysfunction
• AV outflow signal is used to calculate SV and cardiac output