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 homogeneous tissue.
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 preset.
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
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Safety
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