Now let’s put it all together & examine:
- Principles behind the use of ultrasound to obtain diagnostic information about internal structures
How do we use ultrasound to obtain diagnostic information about internal body structures?
|An ultrasound transducer is placed on the skin with a water-based jelly applied between the transducer & skin.|
|Short pulses of ultrasound are transmitted into the body.|
Some of the intensity is lost via attenuation & through transmission at a boundary.
|The reflected pulses return to the transducer where they are detected & converted to voltage pulses.|
|Voltage pulses can be amplified & processed to be displayed on screens (such as CROs).|
|Pulses are necessary so that reflected pulses can be detected in the time intervals between transmitted pulses.|
The time between transmission & detection can be used to calculate the distance between the boundary & the transducer.
How can we display the results of a scan?
|A-Scan||Ultrasound pulses are transmitted into the body (as described above).|
The pulse is reflected multiple times as it encounters different boundaries.
Reflected pulses detected later are amplified more, because their intensity will be very low compared to earlier reflected pulses (due to attenuation & loss at boundaries).
The peaks are shown on a CRO displaying intensity against time.
|B-Scan||A series of A-scans taken from different angles are composited to form a 2-dimensional image.|
What are the advantages of ultrasound scans over X-ray scans?
- Very low health risk to the patient & operator compared to X-rays
- Equipment is more portable & easier to use
How do we make ultrasound scanners more efficient?
Use higher frequency of ultrasound because it…
- has shorter wavelength, so…
- less diffraction occurs around small features, so…
- resolution obtained is greater