Chapter 12 - System Safety and Maintenance
Acoustic Output Indices
Terason t3000 / Echo Ultrasound System User Guide
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ratio of the current power level from the transducer to the reference power level that
would cause a 1ºC steady-state temperature rise in bone located at the beam focus.
•
Mode type:
Calculated for all non-2D only operation, in both scanned and non-scanned
modes.
•
Tissue type and location:
In scanned modes, the model for soft tissue at the surface is
also used to calculate the maximum possible heating of bone at the beam focus. For
non-scanned modes, possible heating of bone near the beam focus is considered
directly.
•
Acoustic parameters:
For scanned modes, the time-average intensity at the transducer
surface is closely related to estimated heating effects. For unscanned modes, the
maximum product along the beam axis of both derated power and intensity is the basis
for calculating possible bone heating. Total heating effects for scanned and unscanned
modes are compiled separately, and the larger value is reported as TIB.
TIC: The Cranial (Bone) Thermal Index
TIC is of concern when bone is near the tissue surface and in close proximity to the
transducer aperture. Clinical applications of interest are specific to those involving
transcranial scanning. General information about the Cranial Thermal Index follows.
•
Potential bioeffect:
Thermal heating of cranial bone (with indirect heating of adjacent
brain tissue) due to absorption of ultrasound by the cranial bone. TIC is defined as the
ratio of the current transducer power level to the reference power level that would cause
a 1ºC steady-state temperature rise in cranial bone located at the transducer surface.
•
Mode type:
Calculated for all non-2D only operation, in both scanned and non-scanned
modes.
•
Tissue type and location:
Cranial bone, located near the tissue surface and near the
transducer aperture.
•
Acoustic parameter:
For each active mode, the product of estimated power and
intensity at the transducer surface is the basis for calculating cranial bone heating.
Heating effects of all modes are combined to calculate the TIC.
Relevant Acoustic Output Indices
When operating in any mode with the Freeze function disabled, the window displays the
indices relevant to the active transducer and operating mode. The definition of relevant
indices is as follows:
Acoustic Output Indices for Modes and Transducers
Mode Type Currently
Active
Allowed Transducer
Applications
Relevant
Indices
2D only
Include
neither
Adult Cephalic
nor
Neonatal Cephalic
MI, TIS, TIB
2D only
Include
either
Adult Cephalic
or
Neonatal Cephalic
MI, TIS, TIB, TIC
Any mode, other than 2D-
only
Include
neither
Adult Cephalic
nor
Neonatal Cephalic
TIS, TIB
