Samsung MySono U5 Manual do Utilizador descarregar pdf (Página 39)

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Chapter 1 Safety

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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 potential for mechanical bioeects will be. There

are no set MI values that show whether mechanical bioeects are actually occurring. The MI should

be used as a guide for implementing the ALARA principle.

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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 temperature increase is aected by

various factors such as the tissue type, vascularity, operation mode, etc. This is because TI is used

only as a standard reference 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. You can select

either TIs or TIb using the TIs/TIb selection in the Miscellaneous system setups. TIc is displayed when

you select a trans-cranial application.

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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 for 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 for calculating the displayed output

values.

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Samsung MySono U5 Manual do Utilizador Página 39