The combined effect of ultrasonic exposure and protein restriction on maternal and fetal mice

Biological effects of high-frequency ultrasound exposure during mouse organogenesis

Little has been reported on bioeffects of high-frequency ultrasound (US) and guidelines for US use do not necessarily apply to high frequencies. Pregnant CD-1 mice were exposed to Doppler or B-mode US biomicroscopy (UBM) on embryonic day (E) 8.5 or E10.5, during organogenesis. Operating frequency was 40 MHz with a free field I(SPTA) of 11.9 W/cm(2) (Doppler) and 2.6 mW/cm(2) (B-mode), peak negative pressures of 6.61 MPa and MI of 1.05 (B-mode). Offspring were assessed weekly from 1 day postnatally to euthanasia at 6 weeks, with no significant difference in pup weight, body length or crown-rump length observed. E8.5 Doppler-exposed mice showed a small reduction in weight and length at 3 weeks and in weight at 6 weeks. E10.5 Doppler-exposed animals exhibited slight growth reduction in weeks 2 to 4, but were not significantly different at 6 weeks. Our results indicate similar exposures of mice should not cause significant adverse bioeffects.

A teratologic evaluation of continuous-wave, daily ultrasound exposure in unanesthetized pregnant rats

Pregnant Sprague-Dawley rats were trained to remain immobile when placed in water in an ultrasound exposure tank and exposed to 0, 0.1, 2.0, or 30.0 W/cm2 ISPTA (spatial peak, temporal average), 3.0-MHz continuous wave (cw) ultrasound on embryonic (E) days 4-19 for approximately 15 min/day. On E20 fetuses were removed; weighed; examined for external, skeletal, and visceral malformations; and uteri were examined for resorptions. Analyses revealed no increase in pre-implantation loss and no effects on maternal body weight, food, or water consumption. No increase in skeletal or visceral malformations was found, in fact exposed groups had a lower incidence of defects than controls. A significant increase in resorptions in the lowest exposure group (0.1 W/cm2) was obtained, but the effect was isolated, non-dose dependent and not credible as a treatment-related effect. No reduction in fetal weight was obtained, in fact the lowest (0.1-W/cm2) and middle (2.0-W/cm2) exposure level groups weighed slightly more than controls. The immobility procedure succeeded in avoiding anesthetization or forced restraint of the dams, thereby eliminating these factors as potential confounders. The results demonstrated that in unanesthetized, unrestrained rats in utero exposure to incident intensities of ultrasound of up to 30.0 W/cm2 cw ultrasound (or estimated internal exposures of 4-21 W/cm2, depending on body orientation to the incident beam) produced no evidence of embryotoxicity based on fetal necropsy data.

Medical sonography: reproductive effects and risks

While it is clear that the levels and types of medical sonography that have been used in the past have no measurable risks, it would be inaccurate to label the modality of ultrasound as totally safe regardless of exposure. Most agents have reproductive risks and even teratogenic risks if the exposure is raised sufficiently. Thus the prudent use of sonography means that clinicians and designers of equipment have to maintain exposures far below the risks that have been demonstrated in animal studies and from the knowledge obtained about the physical changes that can be produced in humans as the absorbed dose is elevated. The reproductive risks were evaluated using five criteria: 1) human epidemiology, 2) secular trend data, 3) animal experiments, 4) dose response relationships, and 5) biologic plausibility. The analysis reveals that the human epidemiology does not indicate that diagnostic ultrasound presents a measurable risk to the developing embryo or fetus. Animal studies also indicate that diagnostic levels of ultrasound are safe and do not elevate the fetal temperature into the region where deleterious embryonic and fetal effects will occur. Because higher exposures of ultrasound can elevate the temperature of the embryo, the use of diagnostic procedures and the design of sonographic equipment should take into consideration the hyperthermic potential of higher exposures of ultrasound and the hypothetical additional risk of performing sonography on pregnant patients who are febrile. It would appear that if the embryonic temperature never exceeds 39 degrees C, then there is no measurable risk. We suggest that sonography (the field) and sonogram (the procedure) are the most appropriate and least anxiety provoking terms.

Developmental exposure of mice to pulsed ultrasound

Exposure of pregnant mice on gestation day (gd) 8 to 1 MHz continuous-wave ultrasound (0, 0.05, 0.50, or 1.00 W/cm2) was reported previously to result in a slight (nonsignificant) increase in malformations. The present study was conducted in a similar fashion using pulsed ultrasound but was designed to maximize the likelihood of finding effects of gd 8 ultrasound exposure on prenatal development. Pregnant ICR mice (approximately 60 animals/group) were exposed on gd 8 to pulsed ultrasound with a center frequency of 1 MHz at levels of 0 (sham control), 0.05, 0.50, or 1.00 W/cm2 (spatial average, temporal average intensities; ISATA) with a spatial peak, pulse average intensity (ISPPA) of 90 W/cm2 and pulse duration of 6.5 microseconds. Anesthetized animals were placed in a degassed water bath (30 degrees C) and exposed for two 10 min intervals during which the beam was centered 1 cm on either side of the abdominal midline. On gd 17, dams were killed; the uterus and its contents were weighed and examined; and live fetuses were weighed and examined for external, visceral, and skeletal malformations. Although one female in the 0.50 W/cm2 group and seven animals in the 1.00 W/cm2 group died following exposure, no other significant change from controls was seen in any maternal or fetal parameter evaluated. Thus the results of this study indicate that there was no detectable effect on prenatal development of mice following exposure to ultrasound on gd 8 (a time of maximal sensitivity), even at exposure intensities that were lethal to some maternal animals.