Mindray Zonare ZS3, Инструкция по эксплуатации

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ZS3 Instructions for Use
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18.
Display Accuracy and Precision
The output display indices are calculated with the accuracy described below. Also listed is the
precision of the displays. A discussion of the accuracy statements follows their specification.
Thermal Index Display Accuracy and Precision
It is estimated that 90% of TI values will be +/– 45% of the displayed TI value or
+/– 0.15 of the displayed value, whichever value is larger. This is approximately
+/– 2 dB. The TI is displayed with a precision of 0.1. A displayed value of 0.0 for TI means that
the calculated value is less than 0.05.
Mechanical Index Display Accuracy and Precision
It is estimated that 90% of MI values will be /– 25% of the displayed value, or +/– 0.15
of the displayed MI value, whichever value is larger. This is approxi/– 2 dB.
The MI is displayed with a precision of 0.1.
Discussion of Display Accuracy
The stated display accuracy values are determined relative to the MI and TI models, equations,
and measurement methods specified in the
"Standard for Real-Time Display of Thermal and
Mechanical Acoustic Output Indices on Diagnostic Ultrasound Equipment, Revision 2" (NEMA
UD3)
. The TI and MI are relative indicators for the likelihood of tissue thermal rise and
mechanical bioeffects, respectively. The accuracy statements listed here are not bound on the
deviation of the displayed indices from actual temperature rise or pressure levels in the body.
The TI and MI values are determined from measurements in water and derated for tissue
attenuation using an assumed homogenous tissue model with attenuation of 0.3 dB/cm/MHz
and the sound propagation properties of water. Most tissues attenuate ultrasound at a greater
rate. Fluids such as amniotic fluid attenuate less. In addition, the propagation of ultrasound is a
nonlinear one in most cases, to different degrees in water and various tissues, with varying
resultant effects on actual MI or TI values. The MI is a relative indicator for the likelihood of a
mechanical bioeffect, such as cavitation, and its model assumes the presence of nucleation
sites needed for cavitation. The TI models assume a blood perfusion length of 1 cm. Tissue
perfusion lengths and rates are dependent on vasculature and blood flow and the thermal
properties of the surrounding tissue, which vary greatly. The bone TI derivation assumes all
ultrasound energy is absorbed by the impinged bone.
The accuracy estimates stated are based on the variability in acoustic output of probes and
systems, uncertainties in measurements made per the AIUM / NEMA standards, and
uncertainties or approximations introduced in implementing the MI and TI algorithms in system
software. They are not based on errors in the AIUM/NEMA MI or TI models, errors introduced
by the measurement standards, differences between actual tissue paths and properties and
those of water, or the effects of nonlinear propagation on the measured values.
Measurement Uncertainty of Acoustic Output Values
The measurement uncertainty of quantities are listed in the table below. They are measured
as part of determining MI or TI values. Quantities are listed as one standard deviation, in