LETTE
RS TO THE
EDITOR
Postpartum survival of mice exposed in utero to ultrasound P. D. Edmonds, S. J. Stolzenberg, a)C. A. Torbit, b)S. M. Madan,andD. E. Pratt SR! International 333 RavenswoodAvenue,Menlo Park, California 94025 (Received 14 November 1978; acceptedfor publication 10 May 1979)
We found no credible enhancementof neonatalmortality in mice exposedin utero on Day 8 of gestation
to ultrasound at 0.44W/cm• (ñ20%) spatialaverage intensity, 2 MHz, continuous wave,for 60-180s in a 37øC water bath. This result is comparedwith the adverseeffect on neonatal survival reported by Curto [in Ultrasoundin Medicine (Plenum, New York, 1976), Vol. 2, pp. 535-536] for exposureon
Day 14 of gestation at about0.125to 0.5 W/cm•, 1 MHz, continuous wave,for 180s in a 30øCbath. It is concludedthat a temporaryreductionin fetal viability, lastingfrom 4 daysto lessthan 10 daysafter exposure,could account for both setsof data. It is also evident from thesedata that improved methodsof determiningintensitieswithin mammaliantissuesare highly desirable. PACS numbers: 43.80.Gx, 43.35.Wa
During a study of biological effects of ultrasound on pregnant CFW Swiss Webster mice and their offspring,
whichwill be reported separately,1 we observedgrowth and mortality
rates of neonares for 25 days postpartum.
Curto2 reported a significant increase in neonatal mortality through 21 days postpartum following exposure of
CF1 mice on Day 143of gestationto 1 MHz, continuous wave ultrasound at spatial average intensities ranging
from 0.125 to 0.5 W./cm2 for 180 s. Curto'• results have been cited among those used to determine a prob-
able thresoldof bioeffectsin mammaliantissuesa;they lie near a critical intersection of asymptotes deduced from the cited data. The acoustic output of diagnostic ultrasonic equipment is frequently compared with these asymptotes; therefore it is important to obtain independent
data
under
similar
conditions.
In our data, which relate to exposureon Day 8 of gestation, there was only one barely significant difference
by X2 test amongthe postpartumdeathsof offspringof untreated
controls,
sham-treated
controls,
and mice
exposedto approximately0.5 W/cm 2 ultrasoundat 2 MHz, continuous wave, delivered for 60, 100, 140, and 180 s. In that apparently significant case, six of the seven deaths occurred in a single litter; the result is therefore possibly unrelated to the ultrasound exposure.
The foregoing intensities represent free fields in a water bath, the mouse being absent. It should be noted
in the context of the following discussionthat Curto's data have been plotted by others4'5at the spatial average intensity in such a free field.
Table I shows the comparison of our data with Curto's; exposure parameters
were combined to show the energy
flux (equalto intensityx time, in W-s/cm 2 or J/cm2), to which the energy absorbed by the tissue is proportional. This is an appropriate measure of exposure for a thermal tissue.
mechanism The
first
12 of 25 neonatal
of interaction
column
deaths
shows
were
of ultrasound our
raw
confined
data.
and Because
to two of 90 lit-
a)Nowat the Department of Pharmacology, University of California School of Medicine,
San Francisco,
CA 94143.
b)Nowat the Departmentof ObstetricsandGynecology,Vanderbilt University, 590
Nashville,
TN 37232.
J. Acoust. Soc. Am. 66(2), Aug. 1979;
ters, we also show the result of excluding these two abnormal litters. In none of our groups, with or without exclusion, did our neonatal mortality approach the rates reported by Curto, as shown in the last column. We estimated the spatial average intensity in the water bath, at the position occupied by the mice, from the pressure amplitude profiles of the near field; these profiles which were plotted with a Mediscan piezoelectric probe, exhibited seven maxima and six minima with excursions
of +1.5
dB in the field
slice
of interest.
The
calibration of these profiles was obtained from measurement of total ultrasonic power ,output of the trans.ducer
by meansof a Wells vane radiometer,6 whichis known to be accurate within +10% from calculation and comparison with NBS- and BRH-calibrated transducers. From consideration of the impedance difference at the water-skin interface, we initially estimated that 95% of the incident power was transmitted into the mouse abdomen; however, our servo-controlled power amplifier increased the incident power to compensate for power reflected from tlie mouse and then collected by the transducer. Therefore, the power transmitted into our mice
should have closely corresponded (within< 5%) to the free
field
value.
To obtain another estimate of intensity at the uterus,
we made use of data obtainedfrom anotherexperiment.1 In that study we had made a dorsolateral incision and implanted a small thermister (YSI type 511, time con-
stant =0.2 s) enclosed in a polyethylene tube (0.024 in. diameter) in one laterally displaced uterine horn of three nonpregnant mice. We then measured the temperature-time profiles with the mice immersed in the water bath and in the same spatial relationship to the transducer as the pregnant mice but exposed to >0.95
W/cm•' spatial average intensity, estimatedby the first method. The initial slope (dT/dt) o of the profile for dorsal exposurewas 0.09øCs'l, yielding an estimated intensityof 0.75 W/cm"from the relation?'8I= (DCJ/2•)
(dT/dt)o, wherepC=0.90 cal deg'l cm'3 is the heatcapacity per unit volumeof soft tissue at 2 MHz,9 and o•= o•xf, where c•1 is the absorption coefficient at 1 MHz. The initial slope of the temperature profile with ventral exposure was not significantly different from the one for
0001-4966/79/080590-04500.80
(D1979Acoustical Society ofAmerica
590
Redistribution subject to ASA license or copyright; see http://acousticalsociety.org/content/terms. Download to IP: 84.88.136.149 On: Wed, 03 Dec 2014 08:53:32
TABLE I. Postpartum mortality of neonate mice exposedin utero to ultrasound. a
Totalneonatal Nominal
Mortalityafter
mortality
exposure b
Number/sample
(W- s/cm 2)
Curtod
exclusions c
(1976)
Number/sample size
Number/sample
size
%
%
4/84 e
4.8
0/80
0
3/84
3.6
3/84
3.6
size
Untreated
controls
......
Sham
controls
22.5
............
30
6/90 e
45
4.2
19/132h 6.6
0/84
0
............
50
5/120
14.4
......
14/108h
3/84
3.6
3/84
3.6
70
7/90 f'g
90
2/108
7.7
1/84
1.1
......
1.9
2/108
1.9
24/90h
13.0
......
26.7
Exposureson day 8 (SRI) or day 14 (Curto) of gestation.
Expressed in termsof theintensityin thebathin theabsence of themouse;multiplyby 0.88(SRI) or -
RS TO THE
EDITOR
Postpartum survival of mice exposed in utero to ultrasound P. D. Edmonds, S. J. Stolzenberg, a)C. A. Torbit, b)S. M. Madan,andD. E. Pratt SR! International 333 RavenswoodAvenue,Menlo Park, California 94025 (Received 14 November 1978; acceptedfor publication 10 May 1979)
We found no credible enhancementof neonatalmortality in mice exposedin utero on Day 8 of gestation
to ultrasound at 0.44W/cm• (ñ20%) spatialaverage intensity, 2 MHz, continuous wave,for 60-180s in a 37øC water bath. This result is comparedwith the adverseeffect on neonatal survival reported by Curto [in Ultrasoundin Medicine (Plenum, New York, 1976), Vol. 2, pp. 535-536] for exposureon
Day 14 of gestation at about0.125to 0.5 W/cm•, 1 MHz, continuous wave,for 180s in a 30øCbath. It is concludedthat a temporaryreductionin fetal viability, lastingfrom 4 daysto lessthan 10 daysafter exposure,could account for both setsof data. It is also evident from thesedata that improved methodsof determiningintensitieswithin mammaliantissuesare highly desirable. PACS numbers: 43.80.Gx, 43.35.Wa
During a study of biological effects of ultrasound on pregnant CFW Swiss Webster mice and their offspring,
whichwill be reported separately,1 we observedgrowth and mortality
rates of neonares for 25 days postpartum.
Curto2 reported a significant increase in neonatal mortality through 21 days postpartum following exposure of
CF1 mice on Day 143of gestationto 1 MHz, continuous wave ultrasound at spatial average intensities ranging
from 0.125 to 0.5 W./cm2 for 180 s. Curto'• results have been cited among those used to determine a prob-
able thresoldof bioeffectsin mammaliantissuesa;they lie near a critical intersection of asymptotes deduced from the cited data. The acoustic output of diagnostic ultrasonic equipment is frequently compared with these asymptotes; therefore it is important to obtain independent
data
under
similar
conditions.
In our data, which relate to exposureon Day 8 of gestation, there was only one barely significant difference
by X2 test amongthe postpartumdeathsof offspringof untreated
controls,
sham-treated
controls,
and mice
exposedto approximately0.5 W/cm 2 ultrasoundat 2 MHz, continuous wave, delivered for 60, 100, 140, and 180 s. In that apparently significant case, six of the seven deaths occurred in a single litter; the result is therefore possibly unrelated to the ultrasound exposure.
The foregoing intensities represent free fields in a water bath, the mouse being absent. It should be noted
in the context of the following discussionthat Curto's data have been plotted by others4'5at the spatial average intensity in such a free field.
Table I shows the comparison of our data with Curto's; exposure parameters
were combined to show the energy
flux (equalto intensityx time, in W-s/cm 2 or J/cm2), to which the energy absorbed by the tissue is proportional. This is an appropriate measure of exposure for a thermal tissue.
mechanism The
first
12 of 25 neonatal
of interaction
column
deaths
shows
were
of ultrasound our
raw
confined
data.
and Because
to two of 90 lit-
a)Nowat the Department of Pharmacology, University of California School of Medicine,
San Francisco,
CA 94143.
b)Nowat the Departmentof ObstetricsandGynecology,Vanderbilt University, 590
Nashville,
TN 37232.
J. Acoust. Soc. Am. 66(2), Aug. 1979;
ters, we also show the result of excluding these two abnormal litters. In none of our groups, with or without exclusion, did our neonatal mortality approach the rates reported by Curto, as shown in the last column. We estimated the spatial average intensity in the water bath, at the position occupied by the mice, from the pressure amplitude profiles of the near field; these profiles which were plotted with a Mediscan piezoelectric probe, exhibited seven maxima and six minima with excursions
of +1.5
dB in the field
slice
of interest.
The
calibration of these profiles was obtained from measurement of total ultrasonic power ,output of the trans.ducer
by meansof a Wells vane radiometer,6 whichis known to be accurate within +10% from calculation and comparison with NBS- and BRH-calibrated transducers. From consideration of the impedance difference at the water-skin interface, we initially estimated that 95% of the incident power was transmitted into the mouse abdomen; however, our servo-controlled power amplifier increased the incident power to compensate for power reflected from tlie mouse and then collected by the transducer. Therefore, the power transmitted into our mice
should have closely corresponded (within< 5%) to the free
field
value.
To obtain another estimate of intensity at the uterus,
we made use of data obtainedfrom anotherexperiment.1 In that study we had made a dorsolateral incision and implanted a small thermister (YSI type 511, time con-
stant =0.2 s) enclosed in a polyethylene tube (0.024 in. diameter) in one laterally displaced uterine horn of three nonpregnant mice. We then measured the temperature-time profiles with the mice immersed in the water bath and in the same spatial relationship to the transducer as the pregnant mice but exposed to >0.95
W/cm•' spatial average intensity, estimatedby the first method. The initial slope (dT/dt) o of the profile for dorsal exposurewas 0.09øCs'l, yielding an estimated intensityof 0.75 W/cm"from the relation?'8I= (DCJ/2•)
(dT/dt)o, wherepC=0.90 cal deg'l cm'3 is the heatcapacity per unit volumeof soft tissue at 2 MHz,9 and o•= o•xf, where c•1 is the absorption coefficient at 1 MHz. The initial slope of the temperature profile with ventral exposure was not significantly different from the one for
0001-4966/79/080590-04500.80
(D1979Acoustical Society ofAmerica
590
Redistribution subject to ASA license or copyright; see http://acousticalsociety.org/content/terms. Download to IP: 84.88.136.149 On: Wed, 03 Dec 2014 08:53:32
TABLE I. Postpartum mortality of neonate mice exposedin utero to ultrasound. a
Totalneonatal Nominal
Mortalityafter
mortality
exposure b
Number/sample
(W- s/cm 2)
Curtod
exclusions c
(1976)
Number/sample size
Number/sample
size
%
%
4/84 e
4.8
0/80
0
3/84
3.6
3/84
3.6
size
Untreated
controls
......
Sham
controls
22.5
............
30
6/90 e
45
4.2
19/132h 6.6
0/84
0
............
50
5/120
14.4
......
14/108h
3/84
3.6
3/84
3.6
70
7/90 f'g
90
2/108
7.7
1/84
1.1
......
1.9
2/108
1.9
24/90h
13.0
......
26.7
Exposureson day 8 (SRI) or day 14 (Curto) of gestation.
Expressed in termsof theintensityin thebathin theabsence of themouse;multiplyby 0.88(SRI) or -
