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WFUMB Position Statement: How to perform a safe ultrasound examination and clean equipment in the context of COVID-19

On behalf of the WFUMB Safety Committee (Jacques S. Abramowicz, MD, Iwaki Akiyama, PhD, David Evans, PhD, F. Brian Fowlkes, PhD, Karel Marsal, MD, PhD, Yusef Sayeed, MD, Gail ter Haar, PhD,)

Abramowicz JS*1 and Basseal J*2

1 WFUMB and Department of Obstetrics and Gynecology, University of Chicago, Chicago, USA
Discipline of Infectious Diseases and Immunology, Faculty of Medicine and Health, The University of Sydney, NSW Australia and Australasian Society for Ultrasound in Medicine, Sydney, NSW Australia

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WFUMB Policy on Live Scanning at Commercial Exhibitions

While WFUMB does not object to live scanning at WFUMB meetings, the involvement of pregnant women and children, and the use of invasive scanning and contrast agents are not acceptable. In addition, the use of corporate employees to perform scans is acceptable, but such activities should not be considered educational. Scanning by physicians and/or technologists can be considered educational, but only if handled in an educational setting.

Specifically the following rules must be obeyed:

  1. Scanning should be performed with decorum, and in a manner respectful to the subject.
  2. Scanning of eyes, pregnant women and children are forbidden.
  3. If a previously unknown pregnancy is detected during a scan, the scanning session must be terminated immediately.
  4. Endoscopic, intra-cavity and intra-vascular scanning are forbidden.
  5. The use of ultrasonic contrast agents is forbidden.
  6. Subjects (models) must give consent by signing a form which explains the non-diagnostic nature of the scan. In the case of female subjects, they must also sign to confirm that they are not pregnant.
  7. Each exhibitor must have a written policy on how to deal with serious incidental findings.
  8. All those who perform live scanning must understand the significance of the on-screen display of thermal index and mechanical index, and be knowledgeable about ultrasound bioeffects and safety.
  9. The lowest acoustic output compatible with adequate imaging should be maintained, and TI should be kept below 1.0, except for peripheral vascular scanning where it may be raised to a maximum of 3.0.
  10. For reasons of subject comfort, individual scanning sessions should be limited to 30 minutes.

Approved by WFUMB Administrative Council, October 2015

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WFUMB/ISUOG Statement on the Safe Use of Doppler Ultrasound During 11-14 week scans (or earlier in pregnancy)
  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 to refine risks for trisomies.
  3. When performing Doppler ultrasound, the displayed Thermal Index (TI) should be less than or equal to 1.0 and exposure time should be kept as short as possible (usually no longer than 5-10 minutes) and not exceed 60 minutes.
  4. When using Doppler ultrasound for research, teaching and training purposes, the displayed TI should be less than or equal to 1.0 and exposure time should be kept as short as possible (usually no longer than 5-10 minutes) and not exceed 60 minutes. 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 the 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.

Approved by WFUMB Administrative Council, October 2015. This text is identical to that in the statement published by AFSUMB, AIUM, BMUS, EFSUMB and JSUMB

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WFUMB/ISUOG Policy Statement on Souvenir Imaging of the Fetus

The WFUMB disapproves of the use of ultrasound for the sole purpose of providing souvenir Images of the fetus. There have been no reported incidents of human fetal harm in over 40 years of extensive use of medically indicated and supervised diagnostic ultrasound. Nevertheless, ultrasound involves exposure to a form of energy, so there is the potential to initiate biological effects. Some of these effects might, under certain circumstances, be detrimental to the developing fetus. Therefore the uncontrolled use of ultrasound without medical benefit should be avoided. Furthermore, ultrasound should be employed only by health professionals who are trained and updated in ultrasound clinical usage and bioeffects.

Approved by WFUMB Administrative Council, October 2015

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(NEW)  WFUMB Statement on ultrasound exposure in the first trimester and autism spectrum

WFUMB Administrative Council endorses both AIUM Bioeffects Committee Statement1 on the paper by Webb et al.[2] and ISUOG statement on ultrasound exposure in the first trimester and autism spectrum disorders[3].

  1. http://www.aium.org/soundWaves/article.aspx?ald=965&ild=20160907
  2. Webb SJ, Garrison MM, Bernier R, McClinic AM, King BH, Mourad PD. Severity of ASD symptoms and their correlation with the presence of copy number variations and exposure to first trimester ultrasound. 2016. Autism research: official journal of the International Society for Autism Research 2016, DOI: 10.1002/aur.1690
  3. http://www.isuog.org/NR/rdonlyres/57A3E1B7-5022-4D7F-BE0E-93E1D239F29D/0/ISUOG_statement_on_ultrasound_exposure_in_the_first_trimester_and_autism_spectrum_disorders.pdf
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WFUMB Clinical Safety Statement for Diagnostic Ultrasound – an overview

Diagnostic ultrasound has been widely used in clinical medicine for many years with no proven deleterious effects. However, investigations into the possibility of subtle or transient effects are still at an early stage. Biological effects (such as localized pulmonary capillary bleeding) have been reported in mammalian systems at diagnostically relevant exposures but the clinical significance of such effects is not yet known. Consequently, diagnostic ultrasound can only be considered safe if used prudently. Ultrasound examinations should only be performed by competent personnel who are trained and updated in safety matters. It is also important that ultrasound devices are appropriately maintained.

The range of clinical applications is becoming wider, the number of patients undergoing ultrasound examinations is increasing and new techniques with higher acoustic output levels are being introduced. It is therefore essential to maintain vigilance to ensure the continued safe use of ultrasound.

Available safety information during clinical scanning Ultrasound produces heating, pressure changes and mechanical disturbances in tissue. Diagnostic levels of ultrasound are capable of producing temperature rises that may be hazardous to sensitive organs and the embryo/fetus. Biological effects of non-thermal origin have been reported in animals but, to date, no such effects have been demonstrated in humans, except when a microbubble contrast agent is present.

The Thermal index (TI) is an on-screen guide to the user of the potential for tissue heating. The Mechanical index (MI) is an on-screen guide of the likelihood and magnitude of non-thermal effects. Users should remain aware of both indices while scanning, especially when changing scan modes, and should adjust the machine controls to keep them as low as reasonably achievable (ALARA principle) without compromising the diagnostic value of the examination. Where low values cannot be achieved, examination times should kept as short as possible.

Scanners should be set up so the default (switch-on) power for a given examination is no greater than the minimum level necessary for that type of examination. In obstetric applications this default power should result in a TI no higher than 0.7. The output should only be increased during the examination if this is necessary to produce a satisfactory diagnostic result.

Some modes are more likely than others to produce significant acoustic outputs and, when using these modes, particular care should be taken to regularly check the TI and MI indices. Spectral pulse wave Doppler and Doppler imaging modes (colour flow imaging and power Doppler imaging) in particular can produce more tissue heating and hence higher TI values, as can B-mode techniques involving coded transmissions. Tissue harmonic imaging mode can sometimes involve higher MI values. 3D (three dimensional) imaging does not introduce any additional safety considerations, particularly if there are significant pauses during scanning to study or manipulate the reconstructed images. However, 4D scanning (real-time 3D) involves continuous exposure and users should guard against the temptation to prolong examination times unduly in an effort to improve the recorded image sequence beyond that which is necessary for diagnostic purposes.

Ultrasound exposure during pregnancy The embryo/fetus in early pregnancy is known to be particularly sensitive. In view of this and the fact that there is very little information currently available regarding possible subtle biological effects of diagnostic levels of ultrasound on the developing human embryo or fetus, care should be taken to limit the exposure time and the Thermal and Mechanical Indices to the minimum commensurate with an acceptable clinical assessment, particularly when the Thermal Index exceeds 0.7. It is recommended that TIs of less than 3.0 are used.

Temperature rises are likely to be greatest at bone surfaces and adjacent soft tissues. With increasing mineralisation of fetal bones, the possibility of heating sensitive tissues such as brain and spinal cord increases. Extra vigilance is advised when scanning such critical fetal structures, at any stage in pregnancy. Based on scientific evidence of ultrasound-induced biological effects to date, there is no reason to withhold diagnostic scanning during pregnancy, provided it is medically indicated and is used prudently by fully trained operators. This includes routine scanning of pregnant women. However, Doppler ultrasound examinations should not be used routinely in the first trimester of pregnancy.

The power levels used for fetal heart rate monitoring (cardiotocography – CTG) are sufficiently low that the use of this modality is not contra-indicated on safety grounds, even when it is to be used for extended periods.

Safety considerations for other sensitive organs Particular care should be taken to reduce the risk of thermal and non-thermal effects during investigations of the eye and when carrying out neonatal cardiac and cranial investigations.

Ultrasound contrast agents (UCA) These usually take the form of stable gas filled microbubbles, which can potentially produce cavitation or microstreaming, the risk of which increases with MI value*. Data from small animal models suggest that microvascular damage or rupture is possible. Caution should be considered for the use of UCA in tissues where damage to microvasculature could have serious clinical implications, such as in the brain, the eye, and the neonate. As in all diagnostic ultrasound procedures, the MI and TI values should be continually checked and kept as low as possible. It is possible to induce premature ventricular contractions in contrast enhanced echocardiography when using high MI and end-systolic triggering. Users should take appropriate precautions in these circumstances and avoid cardiac examinations in patients with recent acute coronary syndrome or clinically unstable ischaemic heart disease. The use of contrast agents should be avoided 24 hours prior to extra-corporeal shock wave therapy.

BMUS. Guidelines for the safe use of diagnostic ultrasound equipment. Ultrasound 2010; 18: 52-59. Also available at https://www.bmus.org/policies-statements-guidelines/safety-statements/

While not being an ultrasound related bio-effect, it should be noted that life threatening anaphylactic reactions have been reported following contrast agent administration, with a rate of less than 0.002%. Investigators should therefore take the necessary precautions.

Approved by WFUMB Administrative Council, September 29, 2012

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WFUMB Recommendations on Non-medical Use of Ultrasound
  • The WFUMB disapproves of the use of ultrasound for the sole purpose of providing keepsake or souvenir images of the fetus.

  • Ultrasound imaging for non-medical reasons is not recommended unless carried out for education, training or demonstration purposes.

  • In the absence of supporting evidence of safety, caution should be used to minimize ultrasound exposure to the fetus.
  • The use of ultrasound to provide keepsake images or videos of the fetus may be acceptable if it is undertaken as part of a clinical diagnostic ultrasound examination, provided that it does not increase exposure to the fetus.
  • The use of ultrasound without medical indication to determine the fetal gender is inappropriate, and contrary to responsible medical practice.
  • Live scanning of pregnant models for equipment exhibitions at ultrasound congresses is considered a non-medical practice that should be prohibited since it provides no medical benefit, and risks to the embryo or fetus cannot be excluded.
  • Ultrasonography is a medical procedure that should only be carried out in the clinical setting where there is a medical indication and when carried out under the supervision of a physician or an appropriately trained expert in diagnostic ultrasound.
  • When using ultrasound for non-medical reasons the ultrasound equipment display should be used to ensure that TI < 0.7 and MI < 0.3.

Approved by WFUMB Administrative Council, October 2015

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