Samsung SONOACE R3 Instrukcja Użytkownika Pobierz pdf (Strona 41)

Chapter 1 Safety

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The measured water tank values 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 assumed in the industry standard TI models, and the assumption is

made that the ultrasound probe is held steady in one position long enough for steady state to be

reached.

A number of factors are considered when estimating the accuracy of display values: hardware variations,

algorithm accuracy estimation and measurement variability. Variability among probes and systems

is a significant factor. Probe variability results from piezoelectric crystal efficiencies, process-related

impedance dierences, and sensitive lens focusing parameter variations. Dierences in the system pulse

voltage control and eciencies are also a contributor to variability. There are inherent uncertainties in

the algorithms used for estimating acoustic output values over the range of possible system operating

conditions and pulse voltages. Inaccuracies in laboratory measurements are related to differences

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 calculation of the accuracy

estimate displayed. Neither linear propagation, nor uniform attenuation at the 0.3dB/cm-MHz rate,

occur in water tank 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 water tank 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 measurement variability. Display accuracy estimates are not based

on errors in, or caused by measuring according to, the AIUM measurement standards. They are also

independent of the eects of non-linear loss on the measured values.

Control aecting the indices

As various system controls are adjusted, the TI and MI values may change. This will be most apparent as

the POWER control is adjusted; however, other system controls will aect the on-screen output values.

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Power

Power controls the system acoustic output. Two real-time output values are on the screen: a TI and a MI.

They change as the system responds to POWER adjustments.

In combined modes, such as simultaneous Color, 2D-mode and pulsed Doppler, the individual modes

each add to the total TI. One mode will be the dominant contributor to this total. The displayed MI will

be from the mode with the largest peak pressure.

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Samsung SONOACE R3 Instrukcja Użytkownika Strona 41