Ultrasound imaging has been used for over 40 years and has an excellent safety record. It is based on non-ionizing radiation, so it does not have the same risks as X-rays or other types of imaging systems that use ionizing radiation. Although ultrasound imaging is generally considered safe when used prudently by appropriately trained health care providers, ultrasound energy has the potential to produce biological effects on the body. Ultrasound waves can heat the tissues slightly. In some cases, it can also produce small pockets of gas in body fluids or tissues (cavitation).
The long-term consequences of these effects are still unknown. Because of the particular concern for effects on the fetus, organizations such as the American Institute of Ultrasound in Medicine have advocated prudent use of ultrasound imaging in pregnancy.
Furthermore, the use of ultrasound solely for non-medical purposes such as obtaining fetal ‘keepsake’ videos has been discouraged. Keepsake images or videos are reasonable if they are produced during a medically-indicated exam, and if no additional exposure is required.
The medial indication for Pregnancy Center’s is the viability of pregnancy to prevent an unnecessary surgical procedure of abortion.. (See link for U/S indications)
Critical Ultrasound Safety Information
Doppler & Ultrasound Safety
As the FDA warned in 2004, “ultrasound is a form of energy, and even at low levels, laboratory studies have shown it can produce physical effect in tissue, such as jarring vibrations and a rise in temperature.”(9) This is consistent with research conducted in 2001 in which an ultrasound transducer aimed directly at a miniature hydrophone placed in a woman’s uterus recorded sound “as loud as a subway train coming into the station.”(10)
A rise in temperature of fetal tissue and in early 1st trimester heartbeat or umbilical cord doppler—especially since the expectant mother cannot even feel it—might not seem alarming, but temperature increases can cause significant damage to a developing fetus’s central nervous system and heart beat rate , according to research.(11) Across mammalian species, elevated maternal or fetal body temperatures have been shown to result in birth defects in offspring.(12) An extensive review of literature on maternal hyperthermia in a range of mammals found that “central nervous system (CNS) defects appear to be the most common consequence of hyperthermia in all species, and cell death or delay in proliferation of neuroblasts [embryonic cells that develop into nerve cells] is believed to be one major explanation for these effects.”(13)
Why should neurodevelopmental defects in rats or other mammals be of concern to expecting women? Because, as Cornell University researchers proved in 2001, brain development proceeds in the same manner “across many mammalian species, including human infants.”(14) The team found “95 neural developmental milestones” that helped them pinpoint the sequence of brain growth events in different species.(15) Therefore, if repeated experiments show that elevated heat caused by ultrasound damages fetal brains in rats and other mammals, one can logically assume that it can harm human brains and early embryonic hearts also.,
In fact, the FDA and professional medical associations confirmed on the prudent use of ultrasound and its risk which is why they have consistently warned against the non-medical or “keepsake” ultrasound portrait studios that have cropped up in malls throughout the country.(16)
These variables, along with factors such as cavitation (a bubbling effect caused by ultrasound that can damage cells) and on-screen safety indicators that may be inaccurate by a factor ranging from 2–6 (17), make the impact of Doppler ultrasound uncertain even in expert hands. Quite simply, if Doppler ultrasound can injure babies, it can cause the same damage whether done for routine, diagnostic or entertainment purposes.
Intensity of Doppler Ultrasound
Pulsed Doppler signal develops according to the subject velocity shown by the frequency of Doppler signal. In pulsed Doppler ultrasound, pulse wave is wider, pulse repetition frequency (PRF) is higher than B-mode, then pulsed Doppler ultrasound intensity tends higher than simple B-mode to clearly image the flow velocity curves. The PRF and ultrasound intensity are able to reduce by the user to keep TI and MI of pulsed Doppler ultrasound less than 1.0, when safety indices (TI or MI) are higher than 1.0 on the monitor display.
Comparison to B-mode
No hazardous thermal effect is expected in simple B-mode imaging device because of minimum heat production due to low ultrasound average intensity, i.e. World Federation of Ultrasound in Medicine and Biology (WFUMB) [1a] concluded that the use of simple imaging equipment is not contraindicated on thermal grounds. The real-time B-mode, simple three dimensional (3D) and four dimensional (4D) imaging devices are included in that category
Thermal and Mechanical Indices
The thermal effect is big concern in Doppler ultrasound study. Tissue temperature rises not only at the sample volume, but also in all tissues passed by the pulsed Doppler ultrasound beam. The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) discussed the safe use of Doppler ultrasound [6a]. Ultrasound intensity is less in color/power Doppler flow mapping due to its scanning procedure than stable irradiation of pulsed Doppler to fixed point.
The MI also regulated below 1.0, because the main mechanical ultrasound bioeffect is the cavitation, which accompanies high pressure, high temperature and free radical formation, will not occur in the cell plasma of high viscosity and no gas bubble, and free radical formed in the liquid does not reach the cell due to its short life span, but high intensity ultrasound developed hemorrhage in neonatal animal lung, the MI is regulated less than 1.0 in obstetrical setting.
In general, it is emphasized that ultrasonic examination should be performed only by medical indications, because diagnostic ultrasound users should recognize the sensitivity of young biological tissues of developing embryos and fetuses to intense ultrasound. The users also should know ultrasonic intensity of their devices, the mechanisms of ultrasound bioeffect, and the prudent use of the devices, because the ultrasound user is responsible to the ultrasound safety [7a].An important ultrasound bioeffect is thermal effect due to temperature rise induced by ultrasound absorption, because malformations were reported after the exposure of animal embryos and fetuses to high temperature in biological experiments [8a]. Inertial cavitation and other mechanical effects are concerned in the non-thermal bioeffects of ultrasound. In clinical situations, the thermal and mechanical indices (TI and MI) of ultrasonic devices are less than 1.0 in obstetrical setting, and an ultrasound user reduces the output intensity of ultrasound devices to control the thermal and mechanical indices less than 1.0, when they are higher than 1.0.
Although the pulsed Doppler is useful to study the blood flow, peak flow velocity, peripheral blood flow impedance (RI and PI), and a bad fetal outcome was known in cases of the loss and reverse flow of Doppler diastole in fetal artery, the study should be prudent, if the fetal body is exposed to pulsed Doppler ultrasound due to its potential high intensity caused by the long ultrasound pulse, high repetition frequency and FFT frequency analysis of Doppler wave.
Pulsed Doppler Ultrasound in the First Trimester
Although chromosomal abnormalities were detected in the reversed atrial diastole (a-wave) of fetal ductus venosus pulsed Doppler and useful in the prenatal diagnosis of chromosomal abnormalities in the first trimester [9a], a recent study on the pulsed Doppler ultrasound exposure of rat fetal ductusvenosus in early pregnancy resulted the transient increase of fetal liver apoptosis index [10a], thus the ultrasound bioeffect and safety committee of ISUOG declared a statement on the use of pulsed ultrasonic Doppler ultrasound not be used in early pregnancy.
In 11–13 weeks of pregnancy in the first trimester as follows [11a];
1. Pulsed Doppler (spectral, power and color flow imaging) ultrasound should not be used routinely.
2. Pulsed Doppler ultrasound may be used for clinical indications such as refine risks for trisomies.
3. When performing Doppler ultrasound, the displayed thermal index (TI) should be =<1.0 and exposure time should be kept as short as possible (usually no longer than 5-19 min) and should not exceed 60 min. 4. When using Doppler ultrasound for research, teaching and training purposes, the displayed TI should be ≤ 1.0 and exposure time should be kept as short as possible Informed consent should be obtained. 5. In educational settings, discussion of first trimester pulsed or color Doppler should be accompanied by information on safety and bioeffects (e.g. TI, exposure times and how to reduce output power). 6. When scanning maternal uterine arteries in the first trimester, there are unlikely to be any fetal safety implications as long as the embryo/fetus lies outside the Doppler ultrasound beam.
The use of pulsed Doppler ultrasound should be prudent in fetal study, because of its tendency to be high. The TI and MI should be lower than 1.0 in the obstetrical setting. The user should depress TI or MI below 1.0, if the monitor screen shows higher index than 1.0. The use of pulsed Doppler is regulated in the first trimester.
1 “National Autism Treatment Plan for Excellence in IDEA” Petition to the President of the United States.www.petitiononline.com/natpidea/petition.html. Accessed 23 Sep 2006.
2 “How Common Are Autism Spectrum Disorders (ASD)?” Centers for Disease Control and Prevention.www.cdc.gov/ncbddd/autism/asd_common.htm. Accessed 23 Sep 2006.
3 “Autism in schools: Crisis or challenge?” The National Autistic Society.www.nas.org.uk/nas/jsp/polopoly.jsp?d=160&a=3464. Accessed 23 Sep 2006.
4 “International Programme on Chemical Safety. Environmental Health Criteria 22. Ultrasound.” 1982. United Nations Environment Programme, International Labour Organisation and International Radiation Protection Association. www.inchem.org/documents/ehc/ehc/ehc22.htm. Accessed 22 May 2006.
5 Keiler, H., et al. 2001. Sinistrality—a side-effect of prenatal sonography: A comparative study of young men. Epidemiology 12(6): 618–23; Campbell, J.D., et al. 1993. Case-controlled study of prenatal ultrasonography exposure in children with delayed speech. Can Med Assoc J 149: 10, 1435–40.
6 “Ultrasound Can Affect Brain Development.” Truth Out Issues.www.truthout.org/issues_06/080806HA.shtml. Accessed 25 Sep 2006.
8 Ang, E.S., Jr., et al. 2006. Prenatal exposure to ultrasound waves impacts neuronal migration in mice.PNAS 103(34): 12903–10. www.pnas.org/cgi/content/abstract/103/34/12903?maxtoshow. Accessed 11 Aug 2006.
9 Rados, Carol. 2004. FDA Cautions Against Ultrasound “Keepsake” Images. FDA Consumer Magazine. www.fda.gov/fdac/features/2004/104_images.html. Accessed 11 Sep 2005. [Editor’s note: See Avoid Fetal “Keepsake” Images, Heartbeat Monitors.]
10 Samuel, Eugenie. 2001. Fetuses can hear ultrasound examinations. New Scientist.www.newscientist.com/article/dn1639-fetuses-can-hear-ultrasound-examinations-.html. Accessed 11 May 2006.
11 Miller, M.W., et al. 2002. Hyperthermic teratogenicity, thermal dose and diagnostic ultrasound during pregnancy: implications of new standards on tissue heating. Int J Hyperthermia 18(5): 361–84.
13 Graham, Jr., M., M.J. Edwards and M.J. Edwards. 1998. Teratogen Update: Gestational Effects of Maternal Hyperthermia Due to Febrile Illnesses and Resultant Patterns of Defects in Humans. Teratology58: 209–21.
14 Clancy, B., R.B. Darlington and B.L. Finlay. 2001. Translating developmental time across mammalian species. Neuroscience 105(1): 7–17.
15 Ibid.16 See note 9 above.
1a Barnett SB, Kossoff G (1992) WFUMB symposium on safety and standardisation in medical ultrasound: Issues and recommendations regarding thermal mechanisms for biological effects of ultrasound. Hornbick. Ultrasound Med Biol 18: 731-814.
2a Ang ES Jr, Gluncic V, Duque A, Schafer ME, Rakic P (2006) Prenatal exposure to ultrasound waves impacts neuronal migration in mice. Proc Natl Acad Sci U S A 103: 12903-12910.
3a Ide M (1986) Japanese policy and status of standardisation. Ultrasound Med Biol 12: 705-706.
4a Maeda K, Ide M (1986) The limitation of the ultrasound intensity for diagnostic devices in the Japanese industrial standards. IEEE Trans Ultrason Ferroelectr Freq Control 33: 241-243.
5a Maeda K, Murao F, Yoshiga T, Yamauchi C, Tsuzaki T (1986) Experimental studies on the suppression of cultured cell growth curves after irradiation with CW and pulsed ultrasound. IEEE Trans Ultrason Ferroelectr Freq Control 33: 186-193.
6a ISUOG Bioeffects and Safety Committee, Abramowicz JS, Kossoff G, Marsal K, Ter Haar G (2002) Safety statement, 2000 (reconfirmed 2002). Ultrasound Obstet Gynecol 2002 19: 105.
7a American Institute of Ultrasound in Medicine (1992) Standard for Real Time Display of Thermal and Mechanical Acoustic Output Indices on Diagnostic Ultrasound Equipment. National Electrical Manufacturers Association.
8a National Council on Radiation Protection and Measurements (1992) Exposure Criteria for Medical Diagnostic Ultrasound: I. Criteria Based on Thermal Mechanisms. NCRP Report No.113.
9a Florianski J, Fuchs T, Zimmer M, Homola W, Pomorski M, et al. (2013) The role of ductus venosus Doppler flow in the diagnosis of chromosomal abnormalities during the first trimester of pregnancy. Adv Clin Exp Med 22: 395-401.
10a Pellicer B, Herraiz S, TÃ¡boas E, Felipo V, Simon C, et al. (2011) Ultrasound bioeffects in rats: quantification of cellular damage in the fetal liver after pulsed Doppler imaging. Ultrasound Obstet Gynecol 37: 643-648.
11a Salvesen KÃ…, Lees C, Abramowicz J, Brezinka C, Ter Haar G, et al. (2011) Safe use of Doppler ultrasound during the 11 to 13+ 6-week scan: is it possible? Ultrasound Obstet Gynecol 37: 625-628.