Ultrasound in obstetrics and gynecology: is this hot technology too hot?

The effect of nuchal umbilical cord on fetal cardiac and cerebral circulation-cross-sectional study

OBJECTIVES

The subject of our analysis is the influence of umbilical cord collision around the fetal neck on the fetal heart function and cerebral circulation.

METHODS

Our study was carried out on a group of 115 fetuses from single pregnancies with physiological course, during the 15th to 40th week of pregnancy. In our analysis, we examined the following parameters: Tei index for right ventricle, Tei index for left ventricle with Tei index components: isovolumetric contraction time, isovolumetric relaxation time, ejection time and cardiothoracic area ratio, middle cerebral artery peak systolic velocity (PS MCA), middle cerebral artery pulsatility index (PI MCA). Gestational age in our study was: 28+2±34. The study group of patients with fetal umbilical cord around neck group (fUCAN) included 38 fetuses (20 males, 18 females). The control group of patients with no fetal umbilical cord around neck group (NfUCAN) included 77 fetuses (43 males, 34 females).

RESULTS

In our study, we found no significant differences in the values obtained: Tei LV in fUCAN: 0.5±0.1 vs. in NfUCAN: 0.5±0.1; p=0.42), Tei RV in fUCAN: 0.5±0.2 vs. in NfUCAN: 0.4±0.1; (p=0.2). Tricuspid valve regurgitation-TR was observed with the following frequency: fUCAN: 7/38, 18% vs. NfUCAN: 13/77, 17%; p=0.8. MCA PS in study fUCAN group was significantly higher than in NfUCAN (40.2±11.5 vs. 32.5±9.5; p=0.003), although other hemodynamic and clinical variables did not differ between the study and control groups.

CONCLUSIONS

The fetal nuchal umbilical cord collision did not affect the fetal heart function expressed as Tei index, at the time of fetal heart examination (at mean gestational age 29+4 weeks). The fUCAN group presented elevated PS MCA, which was not related to other hemodynamic and clinical variables between the study and control groups.

Temperature Rise Caused by Shear Wave Elastography, Pulse Doppler and B-Mode in Biological Tissue: An Infrared Thermographic Approach

The aim of this study was to determine the interest in and relevance of the use of infrared thermography, which is a non-invasive full-field surface temperature measurement technique, to characterize the heterogeneous heating caused by ultrasound in biological tissue. Thermal effects of shear wave elastography, pulse Doppler and B-mode were evidenced in porcine tissue. Experiments were performed using a high-frequency echography Aixplorer system (Supersonic Imagine, Aix-en-Provence, France). For all three modes, ultrasound was applied continuously for 360 s while the temperature at the sample surface was recorded with a Cedip Jade III-MWIR infrared camera (Flir, Torcy, France). Temperature changes were detected for the three modes. In particular, "heat tunnels" crossing the sample were visualized from the early stages of the experiment. Heat conduction from the transducer was also involved in the global warming of the sample. The study widens the prospects for studies on tolerability, potentially in addition to classic approaches such as those using thermocouples.

Shear wave elastography safety in fetus: A quantitative health risk assessment

PURPOSE

To identify the effects of shear wave elastography in the fetus for evaluation in widespread use.

MATERIALS AND METHODS

The Health Risk Assessment method proposed by the National Research Council was used with literature to evaluate the safety of shear wave elastography for the fetus regarding its potential effects in human tissues.

RESULTS

The experimental and epidemiologic data from 25 articles showed that shear wave elastography maintained the same thermal effect as pulsed Doppler ultrasound already authorized in obstetrics, and that cavitation effect on fetal tissue is improbable. Nonetheless, the vibratory character of shear waves could induce displacement of fetal tissue while potential effects of very short duration energy peaks of the radiation force focused wave front remain unknown.

CONCLUSION

The actual knowledge does not provide enough information to assess the effects of shear wave elastography on fetal tissues, thus these points have to be explored by further experimental studies.

Fetal thermal effects of diagnostic ultrasound

Processes that can produce a biological effect with some degree of heating (ie, about 1 degrees C above the physiologic temperature) act via a thermal mechanism. Investigations with laboratory animals have documented that pulsed ultrasound can produce elevations of temperature and damage in biological tissues in vivo, particularly in the presence of bone (intracranial temperature elevation). Acoustic outputs used to induce these adverse bioeffects are within the diagnostic range, although exposure times are usually considerably longer than in clinical practice. Conditions present in early pregnancy, such as lack of perfusion, may favor bioeffects. Thermally induced teratogenesis has been shown in many animal studies, as well as several controlled human studies; however, human studies have not shown a causal relationship between diagnostic ultrasound exposure during pregnancy and adverse biological effects to the fetus. All human epidemiologic studies, however, were conducted with commercially available devices predating 1992, that is, with acoustic outputs not exceeding a spatial-peak temporal-average intensity of 94 mW/cm2. Current limits in the United States allow a spatial-peak temporal-average intensity of 720 mW/cm2 for fetal applications. The synergistic effect of a raised body temperature (febrile status) and ultrasound insonation has not been examined in depth. Available evidence, experimental or epidemiologic, is insufficient to conclude that there is a causal relationship between obstetric diagnostic ultrasound exposure and obvious adverse thermal effects to the fetus. However, very subtle effects cannot be ruled out and indicate a need for further research, although research in humans may be extremely difficult to realize.

The commodification of obstetric ultrasound scanning in Hanoi, Viet Nam

Growing numbers of pregnant women across the world now routinely have ultrasound scans as part of antenatal care, including in low-income countries. This article presents the findings of anthropological research on the use of obstetric ultrasonography in routine antenatal care in Hanoi, Viet Nam. The findings come from observation, a survey and interviews with women seeking ultrasound scans at a main maternity hospital and interviews with doctors providing ultrasound there. We found a dramatic overuse of ultrasound scanning; the 400 women surveyed had had an average of 6.6 scans and 8.3 antenatal visits during pregnancy, while one-fifth had had ten scans or more. Doctors considered obstetric ultrasound an indispensable part of modern antenatal care. For two-thirds of the women, the main reason for frequent scans was reassurance of normal fetal development. However, the women often also said their doctor had recommended the scans. This overuse must be seen in the context of growing commercialisation in the Vietnamese health care system, where ultrasound provides an important source of revenue for both private and public providers. There is an urgent need in Viet Nam for policy and practice guidelines on the appropriate use of ultrasonography in pregnancy and how best to combine it with essential antenatal care, and information dissemination to women.

Sonography and Sociality: Obstetrical Ultrasound Imaging in Urban Vietnam

This article is about new reproductive technologies, maternal anxieties, and existential uncertainties. It explores the question of why pregnant women in Vietnam's capital, Hanoi, have become avid consumers of obstetrical ultrasound scanning even while expressing profound doubts regarding the reliability and safety of this new technology of pregnancy. Through a phenomenological analysis of the social production of women's sense of reproductive risks and uncertainties, the article shows how Hanoian women's paradoxical stances toward ultrasound imaging can be explained through a consideration of embodied and historically generated experiences within everyday local worlds. The article argues that the "scientific stories" of fetal well-being and normality that are produced through ultrasonography are challenged by vivid and continual exchanges in everyday lives of stories of the inherent uncertainties of existence in general and of human reproduction in particular.

First-trimester sonography: is the fetus exposed to high levels of acoustic energy?

PURPOSE

As a form of energy, diagnostic ultrasound has bioeffects on living tissues. The thermal index (TI), TIS (TI for soft tissue), TIB (TI for bone), TIC (TI for cranial bone) expresses the potential for rise in temperature at the ultrasound beam's focal point. The mechanical index (MI) indicates the potential for the ultrasound beam to induce inertial cavitation in tissues. The goal of this study was to characterize the acoustic output of clinical ultrasound instruments, as expressed by TI and MI, during routine first-trimester sonographic examinations.

METHODS

A prospective observational study was conducted. First-trimester patients were randomly selected from those scheduled for viability scans. An obstetrician collected data. Sonographers were blinded to the data being sought, which included gestational age, duration of the examination, and every variation in the MI and TI during each sonographic examination.

RESULTS

A total of 52 first-trimester examinations were evaluated. The mean gestational age was 8.9 +/- 1.9 weeks. The mean duration of the sonographic examinations was 8.1+/- 1.4 minutes. During the examinations, there were 178 MI variations (mean +/- SD, 0.9 +/- 0.3) and 167 TI variations (mean +/- SD, 0.2 +/- 0.1).

CONCLUSION

First-trimester sonographic examinations are associated with a negligible rise in TI.

An increased thermal index can be achieved when performing Doppler studies in obstetric sonography

OBJECTIVE

The present study was aimed at evaluating acoustic outputs during clinical ultrasound examinations, as expressed by the thermal index (TI) and the mechanical index (MI), during the second half of pregnancy and comparing acoustic outputs between B-mode and Doppler examinations.

METHODS

Patients with suspected fetal growth problems undergoing Doppler studies of the fetal circulation in addition to B-mode sonography were selected. Examinations took place between 21 and 40 weeks' gestation. An obstetrician collected data prospectively. Sonographers were unaware of the data being sought. The analysis of variance test was applied for differences in continuous variables.

RESULTS

A total of 63 examinations were evaluated. The mean gestational age +/- SD was 31.6 +/- 5.1 weeks. The mean duration of the total examinations was 17.6 +/- 8.6 minutes, whereas the Doppler studies lasted 0.9 +/- 0.8 minutes. The TI was significantly higher in the pulsed wave Doppler studies (mean, 1.5 +/- 0.5; range, 0.9-2.8) and color flow imaging studies (mean, 0.8 +/- 0.1; range, 0.6-1.2) compared with B-mode sonography (mean, 0.3 +/- 0.1; range, 0.1-0.7; P < .01). During the examination, 190 B-mode MI variations were recorded (mean, 1.1 +/- 0.1), which were comparable with those of the 31 color flow Doppler studies (mean, 1.0 +/- 0.1; P = .09) but higher than the 190 pulsed wave Doppler MI variations (mean 0.9 +/- 0.2; P < .001).

CONCLUSIONS

Increased acoustic output levels, as expressed by TI levels, are reached during obstetric Doppler studies. In particular, TI levels may reach 1.5 and higher. Doppler procedures should be performed with caution and be as brief as possible during obstetric sonography.

Acoustic output as measured by mechanical and thermal indices during routine obstetric ultrasound examinations

OBJECTIVE

The purpose of this study was to quantify the acoustic output of clinical ultrasound instruments, as expressed by the thermal index (TI) and mechanical index (MI), during routine obstetric examinations.

METHODS

A prospective, observational study was conducted. Sonographers were unaware of the data being sought. Data were collected regarding duration of the examination and specific duration spent at each MI and TI.

RESULTS

A total of 11 first-trimester, 14 second-trimester, and 12 third-trimester examinations were evaluated. The mean duration of the first-trimester examination was 8.9 minutes. The mean MI was 0.73 (range, 0.3-1.3), and the mean TI was 0.34 (0.1-1.7). The mean duration of the second-trimester examination was 31.8 minutes. The mean MI was 1.04 (0.5-1.5), and the mean TI was 0.28 (0.1-2.4). The mean duration of the third-trimester examination was 16.3 minutes. The mean MI was 1.06 (0.2-1.5), and the mean TI was 0.32 (0.1-2.4). Statistical significance existed across trimesters with regard to examination durations and MI (P < .001). However, no statistical significance existed in the TI across trimesters. During the third trimester, 3.5% of the examinations had a TI of greater than 1.0. Of these, 2.4% were between 1.0 and 1.49 and 1.1% were greater than 1.5. These changes (of TI > or = 1) were brief (mean +/- SD, 0.17 +/- 0.08 minutes) and were observed during the short periods of color Doppler imaging.

CONCLUSIONS

Output levels during routine obstetric ultrasound examinations, as expressed by the MI and TI, are generally low. However, higher output levels, particularly TI levels of greater than 1.5, can be achieved, although they account for only a very small proportion of examination time.

Incidence of cardiac arrhythmias with therapeutic versus diagnostic ultrasound and intravenous microbubbles

OBJECTIVE

The purpose of this study was to determine the type of arrhythmias induced with therapeutic versus diagnostic transthoracic low-frequency ultrasound (TLFUS) transducers in the presence of intravenous microbubbles.

METHODS

Intravenous perfluorocarbon-exposed sonicated dextrose albumin (PESDA) microbubbles were infused or given as a bolus injection while TLFUS was applied in the standard parasternal and apical views with either a 1-MHz therapeutic ultrasound transducer or high-mechanical-index diagnostic ultrasound (1.7 MHz).

RESULTS

Significantly more ectopy was produced by the therapeutic transducer, especially at higher-intensity settings in the continuous wave mode after bolus injections of PESDA (P < .001 compared with lower intensities and lower continuous infusion rates). Six patients (15%) had either clinical supraventricular tachycardia or nonsustained ventricular tachycardia after intravenous PESDA with therapeutic TLFUS. In comparison, diagnostic high-mechanical-index ultrasound produced only isolated ventricular ectopy and no sustained ventricular arrhythmias.

CONCLUSIONS

Intravenously injected microbubbles and low-frequency therapeutic transducers operating at longer duty cycles and wide beam widths have the capability of eliciting clinically important arrhythmias in patients at high risk for such events.

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.