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HD11 XE Getting Started
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Safety
longer than 3 cm and consists largely of fluid. When this model is used to esti-
mate maximum exposure to the fetus during transabdominal scans, a value of
1 dB/MHz may be used during all trimesters.
The maximum acoustic output levels of diagnostic ultrasound devices extend over
a broad range of values:
• A survey of 1990-equipment models yielded mechanical index (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. Maxi-
mum MI values are similar for real-time 2D, M-mode, pulsed Doppler, and
Color flow imaging.
• Computed estimates of upper limits to temperature elevations during trans-
abdominal scans were obtained in a survey of 1988 and 1990 pulsed Doppler
equipment. The vast majority of models yielded upper limits less than
1 degree C and 4 degrees C for exposures of first-trimester fetal tissue and
second-trimester fetal bone, respectively. The largest values obtained were
approximately 1.5 degrees C for first-trimester fetal tissue and 7 degrees C
for second-trimester fetal bone. Estimated maximum temperature elevations
given here are for a “fixed-path” tissue model and are for devices having I
SPTA
values greater than 500 mW/cm
2
. The temperature elevations for fetal bone
and tissue were computed based on calculation procedures given in Sections
4.3.2.1-4.3.2.6 in Bioeffects and Safety of Diagnostic Ultrasound (AIUM, 1993).
Acoustic Output Tables
Acoustic output tables are in the HD11 XE Acoustic Output Tables manual.
Acoustic Measurement Precision and 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
shown in Table 2-1 and Table 2-2.
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