Samsung MYSONO U6 Manual do Utilizador descarregar pdf (Página 41)

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Chapter 1 Safety

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 a steady state to

be reached.

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 variability 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 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 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 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 measured according to AIUM measurement standards but not based on errors caused during

the measurment. They are also independent of the eects of non-linear loss on the measured values.

Control Eects - 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.

 Power

Power controls the system’s 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 MYSONO U6 Manual do Utilizador Página 41