Samsung PT60A Manual do Utilizador descarregar pdf (Página 43)

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Chapter 1 Safety

underwater are de-rated using a conservative, industry standard, attenuation coecient of 0.3dB/

cm-MHz.

Conservative values for tissue characteristics were selected for use in the TI models. Conservative

values for tissue or bone absorption rates, blood perfusion rates, blood heat capacity, and tissue

thermal conductivity were selected.

Steady state temperature rise is an assumption inherent in the industry standard TI model, which

assumes that the ultrasound probe has been in one location for a long enough duration for it to

be considered to be in a steady state.

A number of factors are considered when estimating the accuracy of display values; hardware

variations, algorithm accuracy estimation, measurement variability, and variability among probes

and systems are signicant factors. Probe deviation results from piezoelectric crystal eciencies,

process-related impedance dierences, and sensitive lens focusing parameter variations.

Dierences in the system pulse voltage control and eciencies also contribute to variability.

There are inherent uncertainties in the algorithms used to estimate acoustic output values over

the range of possible system operating conditions and pulse voltages. Inaccuracies in laboratory

measurements are related to dierences in hydrophone calibration and performance, positioning,

alignment and digitization tolerances, and variability among test operators.

The conservative assumptions of the output estimation algorithms of linear propagation,

at all depths, through a 0.3dB/cm-MHz attenuated medium are not taken into account in

the calculation of the accuracy estimate displayed. Neither linear propagation nor uniform

attenuation at the 0.3dB/cm-MHz rate occurs in underwater measurements, or in most

tissue paths in the body. In the body, dierent tissues and organs have dissimilar attenuation

characteristics. In water, there is almost no attenuation. In the body, and particularly in underwater

measurements, non-linear propagation and saturation losses occur as pulse voltages increase.

The display accuracy estimates take into account the variability ranges of probes and systems,

inherent acoustic output modeling errors, and the measurement variability. Display accuracy

estimates are measured according to AIUM measurement standards but not based on errors

caused during measurement or inherent errors. They are also independent of the eects of non-

linear loss on the measured values.

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Samsung PT60A Manual do Utilizador Página 43