Safety
HD11 XE Getting Started
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Mechanical Index (MI) Display
Mechanical bioeffects 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 bioeffects varies with peak rarefactional pressure
and ultrasound frequency. The MI accounts for these two factors. The higher the
MI value, the greater the likelihood of mechanical bioeffects occurring. There is
no specific MI value that means that a mechanical effect is actually occurring. The
MI should be used as a guide for implementing the ALARA principle.
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 tem-
perature 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 heat-
ing within soft homogeneous tissue.
➤ To display TIS, TIC, or TIB
1. Press Setup.
2. In the System widow, click the System tab.
3. Under Thermal Index, select the appropriate index.
4. Click Close.
TIC is displayed when you select a transcranial application.
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