Samsung PT60A User Manual download pdf (Page 42)

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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, but there is no specic MI value that means that a mechanical eect will denitely

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

 Thermal Index (TI) Display

The TI informs the user of the potential for temperature increase occurring 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 only 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, such as the skeletal structure of a 2-3

month old fetus. The cranial bone thermal index (TIc) informs the user about the potential heating

of bone at or near the surface, for example, the 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.

You can select the TI to display at Setup > Imaging > Display.

 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

section of this operation manual. These accuracy estimates are based on the variability ranges of

probes and systems, inherent acoustic output modeling errors, and the 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 of 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 is built into the measurement and calculation

process for the vast majority of tissue paths. For example, the acoustic output values measured

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Samsung PT60A User Manual Page 42