Important safety considerations
Vscan Extend – User Manual 2-19
5721203-100 Rev. D
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.
Reference to calculation of TI can be found in:
• NEMA Standards Publication UD 3: “Standard for Real-Time
Display of Thermal and Mechanical Acoustic Output Indices
on Diagnostic Ultrasound Equipment”, Revision 2
• EN/IEC 60601-2-37. Medical electrical equipment.
Part 2-37: Particular requirements for the safety of
ultrasonic medical diagnostic and monitoring equipment
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
guidance of September 9, 2008 for diagnostic ultrasound
systems and transducers.
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 guidance of September 9, 2008 for diagnostic ultrasound
systems and transducers.
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