Cirs ATS539 - Grayscale Contrast Sensitivity

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2. Adjust the instrument settings (gain, TGC, output, etc.) as for a “normal” tech-
nique. Record these settings for use on subsequent testing
3. Orient the transducer to image the length of the vertical target wires, taking
care to adjust the tilt so that the wires are lined up in a vertical column.
4. Rotate the transducer 45° so that only a partial length of the wires is now vis-
ible.
5. Freeze the image and measure the length of each wire segment with the elec-
tronic calibers.
6. Record the measurements.
GRAYSCALE CONTRAST SENSITIVITY
Gray scale or gray scale processing uses the amplitude of the echoes received to
vary the degree of brightness of the displayed image. The adjustment of the echo
signal required to go from a just noticeable (lowest gray scale level) echo to the
maximum echo brightness is referred to as the displayed dynamic range. Clinically,
gray scale processing and displayed dynamic range allow echoes of varying de-
grees of amplitude to be displayed in the same image.Testing of grayscale contrast
is performed as follows:
1. Place the phantom on a clean, at surface with scan surface #4 positioned for
use.
2. Apply an adequate amount of low viscosity gel or water to the scan surface. If
water is used, ll the scanning well slowly to avoid introduction of air bubbles.
3. Adjust the instrument settings (TGC, output, etc.) to establish baseline values
for "normal" scanning. If the bottom of the phantom is seen, adjust the
gain settings until image goes entirely black. Record these settings on the
quality assurance record. These settings should be used for subsequent
testing.
4. Position the transducer over the gray scale target group until a clear image is
obtained.
5. Freeze the image and obtain a hard copy.
6. Examine the image. The targets should appear circular in shape, with clear
sharp edges and vary in the degree of brightness ranging from low to high
levels of contrast. The presence or absence of any shadowing behind the
structures should be noted.
7. All ndings should be documented on the quality assurance record.