S
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R
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6
6
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U
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r
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M
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～61～
ultrasound impact on these small bubbles, temperature and pressure around the space of the bubbles will
increase, or even oscillate and explode, which may result in physical or chemical effects on the surrounding
tissues.
Relevant Parameters
The main parameters related to acoustic power are: transmit frequency, transmit focus number, transmit
voltage, transmit angle, element pitch, etc. These parameters vary subject to exam modes. Follow ALARA
principle to select the appropriate power for scanning.
A multiplicative factor applied to acoustic output parameters intended to account for ultrasonic attenuation of
tissue between the source and a particular location in the tissue. In the calculation of all mechanical, the
average ultrasonic attenuation is assumed to be 0.3dB/cm-MHz along the beam axis in the body.
References
(1) AIUM: ”Acoustic Output Measurement Standard For Diagnostic Ultrasound Equipment,” Revision 3,
NEMA Standard Publication UD 2-2004, National Electrical Manufacturers Association,2004
(2) AIUM/NEMA: “Standard for real-time display of thermal and mechanical acoustic output indices on
diagnostic ultrasound equipment,” Revision 2, NEMA Standard Publication UD 3-2004, National
Electrical Manufacturers Association,2004
(3) Measurement and characterization of ultrasonic fields using hydrophones in the frequency range
0.5MHz to 15MHz
(4) Ultrasonic Power measurement in liquids in the frequency range 0.5MHz to 25MHz
(5) 5.FDA:”510(K) Guide for Measuring and Reporting the Acoustic Output Diagnostic Ultrasound
Medical Devices,” Center for Devices and Radiological Health, Food and Drug Administration
Statistics
Statistical Analysis of Measurement Data
A statistical analysis was performed on the base of a tolerance limit approach. The mean and standard deviation of
the Spatial-Peak, Temporal-Average Intensityand the Spatial-Peak, Pulse-Average Intensity were found, and the
upper output limits were calculated from the following formula : X=
+KS
Where X is the upper output parameter limit,
is the average of the measured output parameter, S is the
standard deviation of the measured output parameter, and K is a factor from Reference [M.G. Natrella,
Experimental Statistics NBS Handbook 91, 1966 Table A-7].
When sample size is 3 and P=γ=90%, the K value
was 4.258. A value of K was chosen which corresponds to a 90% probability that 90% of all probes would fall
below the calculated limits X. The following table presents the calculated values using the 4.258 value for K.
Table 2 Results for SRF618B6 Transducers
Transducers
Wired FHR Transducer Wireless FHR Transducer
Sample Size
3 3
Mode
PW PW
I
SATA
(mW/cm²)
Mean (
)
0.802 0.811
Std Dev (S) 0.050 0.084
Limit (X) 1.019 1.172
I
SAPA
(mW/cm²)
Mean (
)
11.02 11.13
Std Dev (S) 0.699 1.157
Limit (X) 13.99 16.06
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