Samsung MYSONO U6 Manual do Utilizador descarregar pdf (Página 40)

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Operation Manual

 Mechanical Index (MI) Display

Mechanical bioeects are threshold phenomena that occur when a certain level of output is

exceeded. The threshold level varies, however, with the type of tissue. The potential for mechanical

bioeects varies with peak pressure and ultrasound frequency. The MI accounts for these two

factors. The higher the MI value, the greater the likelihood of mechanical bioeects occurring.

However, there is no specic MI value that means that a mechanical eect will actually occur. The

MI should be used as a guide for implementing the ALARA principle.

 Thermal Index (TI) Display

The TI informs the user about the potential for temperature increase occuring at the body surface,

within body tissue, or at the point of focus of the ultrasound beam on bone. The TI is an estimate

of the temperature increase in specic body tissues. The actual amount of any temperature rise is

inuenced by factors such as tissue type, vascularity, and mode of operation. The TI should be used

as a guide for implementing the ALARA principle.

The bone thermal index (TIb) informs the user about potential heating at or near the focus after

the ultrasound beam has passed through soft tissue or uid, for example, at or near second or

third trimester fetal bone. The cranial bone thermal index (TIc) informs the user about the potential

heating of bone at or near the surface, for example, cranial bone. The soft tissue thermal index (TIs)

informs the user about the potential for heating within soft homogeneous tissue. Tic is displayed

when you select a trans-cranial application.

 Mechanical and Thermal Indices Display Precision and Accuracy

The Mechanical and Thermal Indices on the system are precise to 0.1 units.

The MI and TI display accuracy estimates for the system are given in the Acoustic Output Tables

manual. These accuracy estimates are based on the variability range of probes and systems, inherent

acoustic output modeling errors and measurement variability, as described below.

The displayed values should be interpreted as relative information to help the system operator

achieve the ALARA principle through prudent use of the system. The values should not be

interpreted as actual physical values investigated tissue or organs. The initial data that is used

to support the output display is derived from laboratory measurements based on the AIUM

measurement standard. The measurements are then put into algorithms to calculate the displayed

output values.

Many of the assumptions used in the process of measurement and calculation are conservative in

nature. Over-estimation of actual in situ exposure, for the vast majority of tissue paths, is built into

the measurement and calculation process. For example, 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

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Samsung MYSONO U6 Manual do Utilizador Página 40