Safety
26 Vivid S5/Vivid S6 User Manual
R2424458-100 Rev. 2
Acoustic output
Definition of the acoustic output
parameters
Thermal Index
TI is an estimate of the temperature increase of soft tissue or
bone. There are three thermal index categories:
• TIS: Soft tissue thermal index. The main TI category. Used
for applications that do not image bone.
• TIB: Bone thermal index (bone located in a focal region).
Used for fetal application.
• TIC: Cranial bone thermal index (bone located close to the
surface). Used for transcranial application.
Mechanical Index
MI is the estimated likelihood of tissue damage due to
cavitation. The absolute maximum limits of the MI is 1.9 as set
by the FDA 510 (k) guidance of 1997.
Note: Further explanation on "cavitation" appears in the
Reference Manual Chapter 3 - Nonthermal Bioeffects.
Ispta
The Ispta is the Spatial Peak Temporal Average Intensity. The
absolute maximum limit of Ispta is 720 MW/cm
2
as set by the
FDA 510(k) guidance of 1997.
ALARA
Ultrasound procedures should be performed using output
levels and exposure times As Low As Reasonably Achievable
(ALARA) while acquiring clinical information.
Training
During each ultrasound examination the user is expected to
weigh the medical benefit of the diagnostic information that
would be obtained against the risk of potential harmful effects.
Once an optimal image is achieved, the need for increasing
acoustic output or prolonging the exposure cannot be justified.
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