Safety and Care
Potential Sources of Measurement Error During Scanning
The table below identifies potential sources of measurement error that may occur during
scanning. Awareness of these sources can help you avoid errors they may cause.
Speed of Sound
Explanation of Error
The technical difficulty of patients in ultrasound imaging varies widely.
Greater care must be taken with technically difficult patients to obtain
the best images possible with the optimal transducer and system
The skill, care, and experience of the person conducting the scan is
one of the most critical factors in obtaining accurate measurements.
Operator training should be consistent with the recommendations of the
appropriate professional medical societies.
The image processing and measurement algorithms of diagnostic
ultrasound assume that the speed of sound in body tissue is 1540
meters per second. Different body tissues have different 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 being measured.
When performing Doppler scans, try to align the Doppler sample as
close to parallel as possible.
The display screen provided in the
comprised of a rectangular array of square picture elements (pixels).
Measurement pixel resolution is assumed to be +
maximum potential error of this resolution accuracy is 0.4%
Occasionally, a pixel or a group of pixels of the display may enter a fault
condition and become stuck in an on or off position. If stuck pixels occur
at a place where a measurement value is displayed, it could cause the
operator to misread the result. Pixels stuck in the on position may be
detected by looking at the screen with a dark background. Pixels stuck
in the off position will show up as dark against a bright video image. You
should periodically examine your system for stuck pixels and be aware
of this potential condition when reading measurements. If you believe
your system has stuck pixels, contact your Service Representative.
Freestyle system is
one pixel. The
Freestyle User Manual