Thermal Index (TI) Displays
The TI informs the user about the conditions that exist that might lead to an increase in
temperature at the surface of the body, within the body tissue, or at the point of focus of the
ultrasound beam on bone. That is, the TI informs the user of the potential for temperature rise
in body tissue. It is an estimate of temperature increase in body tissue with specific properties.
The actual amount of any temperature rise is influenced by factors such as tissue type,
vascularity, mode of operation, and others. 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 fluid; 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
You can choose to display TIS, TIC, or TIB. (For details on changing the TI display, see the system
Help.) On systems with transcranial applications, TIC is displayed when you select a transcranial
Mechanical and Thermal Indices Display Precision and Accuracy
The MI and TI precision is 0.1 unit on the system.
The MI and TI display accuracy estimates for the system are given in Acoustic Output Tables, on
your user information CD. Those accuracy estimates are based on the variability range of
transducers and systems, inherent acoustic output modeling errors, and measurement
variability, as discussed in this section.
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 in interrogated tissue or organs. The initial data that is
used to support the output display is derived from laboratory measurements based on the
American Institute of Ultrasound in Medicine (AIUM) measurement standard. The
measurements are then put into algorithms for calculating the displayed output values.
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