80. A-Mode and B-Mode ultrasound diagnosticsrename
yaboiemil's version from 2016-06-13 05:59
Section1. All diagnostic methods are based on the detection of Ultrasound waves reflected
at boundaries between different tissues.
2. Time delay between sent and received ultrasound pulse is due to PROPAGATION
SPEED and PATH LENGTH.
3. Echo sound intensity is diminished because of:
a) Reflected ultrasound is dependent on ACOUSTIC IMPEDANCE of tissues on boundary
b) Intensity of ultrasound decreases exponentially with DEPTH OF PENETRATION
4. There are 3 scanning Methods:
|A-mode||Amplitude Modulated||1D - measures depth of echo-producing boundaries|
|B-mode||Brightness Modulated||2D - Processing of A-mode to produce image with brightness increasing with echo amplitude.|
|M-mode||Motion Modulated||3D - Processing of B-scan curves laid side by side (shift of boundary vs. time)|
5. A-mode and B-mode have the disadvantage that they are not in real time and cannot trace moving structures
6. The shape of the probe defines the cross-section shape and the ultrasonic field.
7. When you move the probe across the body you get a cross-section of the structures in that ultrasonic field.
Some probe shapes:
Sector and convex used for deep structures.
Linear used for superficial.
8. A higher frequency yields a higher resolution BUT penetration decreases
9. Solved by the use of multifrequency probes, which produce real-time images by switching between several
transducer elements, eliminating the need for mechanical movement of the probe.
10. A problem: Deep structures need a low frequency repetition rate. Fast structures need a high-frequency
repetition rate. There are problems displaying the fast, deep structures.