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Safety and Care
Accuracies
Measurement Accuracies
The
Freestyle may be used to provide measurements and calculations derived from
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ultrasound images. The quantified image data may be used along with other clinical information
to assist a physician in making a patient diagnosis.
The sole reliance on diagnostic ultrasound data to make a clinical diagnosis is not
recommended. Numerous factors related to the accuracy of ultrasound image data must be
taken into account. This section describes some of these factors. Measurement accuracies are
also influenced by operator experience, scanning technique, interpreting physician experience,
and the technical difficulty of the patient. Many of these variables are not associated with the
Freestyle system. This limits the ability to fully specify the clinical accuracy of the
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measurements and calculations provided by the system.
Accuracy by Transducer Type
All transducer types have been verified for measurement accuracy in the modes appropriate to
each measurement type.
Because the moderate transducer frequency range of the system, measurement accuracies for
the system are not expected to vary significantly based on transducer used.
Accuracy of Primary Measurements
All reported accuracies are +/– one-half the least significant digit.
Distance
The system assumes that the speed of sound in tissue is 1540 meters per second and that
this speed is homogeneous in all tissues. The diagnostic ultrasound literature states that
differences in the speed of sound in the body do exist because of the differing tissue types. In
Clinical Sonography – A Practical Guide, (2nd Edition, Roger C. Sanders, ed., Little Brown and
Company 1991) the range is cited as from 1500 to 1600 meters per second. These differences
would produce an inaccuracy of up to +/– 4%.
The distance measurements on the system are verified using an AIUM standard phantom
with a fluid having an acoustic speed of approximately 1540 meters per second at room
temperature. The accuracy of this measurement is +/– 5%. The maximum range of this
measurement is 24 cm (dependent on the probe).
Area
The accuracy of the area measurement is +/– 10%.
The maximum range of this measurement is 733 cm
(dependent on the probe).
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Freestyle User Manual
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