U60 Diagnostic Ultrasound System User Manual Ultrasound Intensity and Safety
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A2.3.2. TI (Thermal Index)
Heating of tissues is caused by absorption of ultrasound when the ultrasound energy is applied.
The temperature rise is determined by the acoustic intensity, exposed area and thermophysical
properties of the tissue.
In order to indicate the potential for temperature rise caused by thermal effects, the AIUM and
NEMA formulate thermal index (TI). It is defined as the ratio of the total acoustic power to the
acoustic power required to raise the tissue temperature by 1ºC.
According to different thermophysical properties of the tissue, TI is divided into three kinds: TIS,
TIB and TIC.
TIS (Soft Tissue Thermal Index): It provides an estimate of potential temperature rise in soft or
similar tissues.
TIB (Bone Thermal Index): It provides an estimate of potential temperature rise when the
ultrasound beam passes through soft tissue and a focal region is in the immediate vicinity of
bone.
TIC (Cranial Bone Thermal Index): It provides an estimate of potential temperature rise in the
cranial bones or superficial bones.
A2.3.3. Display of MI/TI
The system provides real-time display of MI/TI values in the upper right part of the screen. The
start point of MI/TI value is 0.0. You can preset which TI item is to be displayed through Set
up>System Preset.
The operator should monitor these values during examinations and keep the exposure time and
output level at the minimum amounts needed for effective diagnosis.
The display precision is 0.1.
MI display error:
When tested MI ≤0.6, the absolute display error ﹤0.39;
When tested MI﹥0.6, the relative display error ＜±65%.
TI display error:
When tested TI ≤1.2, the absolute display error ﹤0.78;
When tested TI﹥1.2, the relative display error ＜±65%.
A2.4: Acoustic Output
A2.4.1. Factors that Contribute to Uncertainty in the Output Display
A number of factors should be considered in display accuracy determination methods, such as:
Transducer variability
System variability
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