Safety, Technical Description, and Accuracy
10-28
ACUSON Cypress™ Operator’s Manual
Potential Sources of Error During Scanning
Table 57 shows the potential sources of error when conducting scans.
TABLE 57.
Potential Sources of Error
Source
Explanation of Error(s)
Patient
Variability
The technical difficulty of patients varies widely. Greater care
must be taken with technically difficult patients to obtain the best
images possible with the most optimum system control settings.
Operator
Variability
The skill, care, and experience of the person conducting the scan
is one of the most critical factors in obtaining accurate measure-
ments. Operator training should be consistent with the recom-
mendations of the relevant professional medical societies.
Speed of
Sound
The image processing and measurement algorithms of diagnostic
ultrasound assume that the speed of sound in body tissue is
1540 meters per second. Different types of body tissue have dif-
ferent sound speeds. In soft tissue there is approximately a 2%
error; this may be as high as 5%, especially if fatty tissue is
present in the area of the image being measured.
Doppler
Alignment
When performing Doppler scans try to align the beam as close to
parallel to flow as possible. Misalignment errors are typically
approximately ± 5%. Most cardiac clinical references assume
that the angle is under 20°.
Clinical
References
Numerous clinical references and studies have been published
which establish the accuracy of calculations formulas and algo-
rithms. It is important to be familiar with these references and
their descriptions of accuracy issues and limitations. These stud-
ies also describe any assumptions that may be made in the
development of the clinical formula. The calculations formulas
used in the Cypress system are derived solely from such pub-
lished data, and references are provided in the calculations sec-
tion of the manual.
Screen
Pixel
Resolution
The display screen provided in the Cypress system is comprised
of a rectangular array of square picture elements (pixels). Mea-
surement pixel resolution is assumed to be ± one pixel. The max-
imum potential error of this resolution accuracy is 0.4%.
