Safety Biological Safety
42 Lumify Ultrasound System
Philips Healthcare 4535 618 58571_A/795 * MAY 2016
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 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 “Setting the
Thermal Index Display” on page 79.
Mechanical and Thermal Indices Display Precision and Accuracy
The MI and TI precision is 0.1 unit on the system.
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