GE LOGIQ 500 Advanced Reference Manual page 190

Bioeffects
Acoustic output
6–6
Awareness of the acoustic output level can be a difficult task for
the operator, especially when the objective is to obtain a quality
image. Older ultrasound equipment had limited means, if any,
for indicating the acoustic output level. In most cases, the
operator had to be familiar with the output intensities as
described in the operator manual. To improve operator
awareness of acoustic output, this system incorporates an
output display that directly indicates the potential for mechanical
and thermal bioeffects as equipment controls are adjusted.
The output display consists of four numeric index values that
indicate the potential for producing bioeffects (three indices are
for heating effect and one for cavitation). As the user changes
equipment settings that alter the acoustic output, the output
display indices are immediately updated to reflect the change in
potential for producing bioeffect. The indices are based on
mathematical models and each is normalized so that the
potential for bioeffect becomes more significant as the indices
reach a value 1.0 or larger.
A mechanical index (MI) provides an indication of the potential
for the possible onset of transient cavitation within tissue while
the three thermal indices provide an indication of the potential
for heat generation within tissue. The different thermal indices
may be used depending on the type of tissue being examined:
S
Soft Tissue Thermal Index (TIS) is used as an indicator of
the potential to generate heat within soft tissues. This is the
most used thermal indicator.
S
Bone Thermal Index (TIB) is used as an indicator of the
potential to generate heat at the beam focus when focusing
on or near bone that is adjacent to very sensitive tissue.
This index is intended as a thermal indicator for second and
third trimester fetal examination or transfontanelle neonatal
cephalic exams.
S
Cranial Bone Thermal Index (TIC) is used as an indicator of
the potential to generate heat in the near-field when the
beam passes through bone at the surface as with adult or
pediatric cranial applications.
LOGIQ 500 Advanced Reference Manual
2276614–100 Rev. 0