User's Manual

Clarius Ultrasound Scanner - HD3 Scanners Safety Topics
revision 1 56
The maximum acoustic output levels of diagnostic ultrasound scanners extend over a broad
range of values:
• A survey of 1990-equipment models yielded MI values between 0.1 and 1 at their highest
output settings. Maximum MI values of approximately 2 are known to occur for currently
available equipment. Maximum MI values are similar for real-time B-Mode, M-mode, and
PW Doppler.
• Computed estimates of upper limits to temperature elevations during transabdominal
scans were obtained in a survey of 1988 and 1990 Doppler equipment. The vast majority
of models yielded upper limits less than 1°C and 4°C (1.8°F and 7.2°F) for exposures of
first-trimester fetal tissue and second-trimester fetal bone, respectively. The largest values
obtained were approximately 1.5°C (2.7°F) for first-trimester fetal tissue and 7°C (12.6°F)
for second-trimester fetal bone. Estimated maximum temperature elevations given here
are for a “fixed-path” tissue model and are for scanners having I
spta
(derated) values
greater than 500 mW/cm
2
. The temperature elevations for fetal bone and tissue were
computed based on calculation procedures given in Sections 4.3.2.1 through 4.3.2.6 in
“Bioeffects and Safety of Diagnostic Ultrasound” (AIUM Report, January 28, 1993).
Acoustic Measurement Precision & Uncertainty
All table entries have been obtained at the same operating conditions that give rise to the
maximum index value in the first column of the tables. Measurement precision and
uncertainty for power, pressure, intensity, and center frequency are listed in the following
tables.
Measurement precision on the following quantities is determined by making
repeated measurements and stating the standard deviation as a percentage.
ACOUSTIC MEASUREMENT PRECISION
Quantity Precision
(Percentage Standard Deviation)
Pr is the underated peak rarefactional pressure measured in megapascals (MPa) Pr: 5.4%
Wo is the ultrasonic power in milliwatts (mW) 6.2%
f
c
is the center frequency in megahertz (MHz) (NEMA UD-2 definition) <1%
PII.3 is the derated spatial-peak pulse intensity integral in joules per square centimeter (J/cm
2
)
PII.3: 3.2%
ACOUSTIC MEASUREMENT UNCERTAINTY
Quantity Measurement Uncertainty
(Percentage, 95% Confidence Value)
Pr is the underated peak rarefactional pressure measured in megapascals (MPa) Pr: ±11.3%
Wo is the ultrasonic power in milliwatts (mW) ±10%