User Guide

7
BEAM PROFILE, FOCAL ZONE AND LATERAL RESPONSE WIDTH
The beam prole is the shape of the ultrasound beam. A typical beam prole is
shown in Figure 1. The narrowest region within the beam prole is indicative of the
focal point. By convention, the region surrounding the focal point with intensity
within 3 dB of maximum is the focal zone. The best images are obtained while
within the focal zone. The vertical wire target group is useful for determining the
beam prole and the focal zone of a system, as follows:
1. Apply coupling gel to the scanning surface or ll the water trough with tap
water.
2. Position the transducer in a vertical plane. (The wires should appear as dots,
not lines).
3. Adjust the instrument settings (gain, TGC, output, etc.) as for a “normal”
technique. Record these settings for use on subsequent testing.
4. Align the probe so that all the vertical targets are displayed at their maximum
intensity level to ensure the transducer is imaging a vertical plane.
5. Freeze the image and obtain a hard copy. Note: Some of the targets will ap-
pear as short horizontal lines rather than dots on the frozen image.
6. Measure the horizontal length of the targets. These measurements represent
the lateral response width of the system at the different depths and setup.
The minimum length is indicative of the location of the focal point.
Figure 1 - Typical Beam Profile
7. If a smooth curve is drawn to connect the edges of
the targets, the beam prole is easily discernible.
8. If using a variable focused transducer, repeat the
above procedure for several different focal zones
(those settings most commonly used are recom-
mended).
9. Record the focal point and save the hard copy.
VERTICAL DISTANCE MEASUREMENTS
A vertical distance is dened as the distance along the axis of the beam. The verti-
cal wire targets are used to assess the accuracy of vertical distance measurements
as follows:
1. Apply coupling gel to the scanning surface or ll the water trough with tap
water.
2. Position the transducer in a vertical plane. (The wires should appear as dots,
not lines). Do not apply excessive pressure as this may temporarily
compress the target and skew the measurements.
3. Adjust the instrument settings (gain, TGC, output, etc.) as for a “normal”
technique. Record these settings for use on subsequent testing.