A4.3.2 Ti (Thermal Index); A4.3.3 Measurement Uncertainty - EDAN F9 User Manual

F9, F9 Express Fetal & Maternal Monitor User Manual Ultrasound Intensity and Safety
MI = P
r, α
× C
f
awf MI
C = 1 (MPa / MHz )
MI

A4.3.2 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 1º C (1.8º F).
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.

A4.3.3 Measurement Uncertainty

The uncertainties in the measurements were predominantly systematic in origin; the random
uncertainties were negligible in comparison. The overall systematic uncertainties were
determined as follows.
1. Hydrophone Sensitivity
Based on the HNP-0400 hydrophone calibration certificate, the hydrophone measurement
uncertainty for 1-15MHz is 1 dB, which is equivalent to an uncertainty of ± 12.20% for intensity
and ± 6.10% for pressure. This uncertainty is used in PW measurement uncertainty assessment.
2. Digitizer
Based on the oscilloscope calibration certificate, the oscilloscope uncertainty is ± 1.16% for
intensity and ± 0.58% for pressure.
3. Temperature
Based on the temperature variation of the water bath, the uncertainty is ± 1.6% for intensity and
± 0.8% for pressure.
4. Spatial Averaging
± 10.2% for intensity, and ± 6.1% for pressure.
5. Non-linear Distortion:
N/A. No effects of nonlinear propagation were observed.
Since all the above error sources are independent, they may be added on an RMS basis, giving a
total uncertainty of ± 26.62 percent for all intensity values reported, ± 13.31 percent for all the
pressure values and ± 14.52 percent for the Mechanical Index.
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