Ultrasound safety guidelines

Question 1

What are three of the main medical ultrasound societies in the UK

Answer 1

• World Federation for Ultrasound in Medicine & Biology (WFUMB).
• European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB).
• British Medical Ultrasound Society (BMUS).

Question 2

Is ultrasound considered safe?

Answer 2

• It is widely used with no reported deleterious effects.
• However, bioeffects have been reported in mammals, although the clinical significance is not yet known.
• Therefore, it is only considered safe if used prudently by competent personnel. Users must also remain vigilant of new techniques.

Question 3

What are some simple safety precautions a clinician could use when performing and ultrasound examination?

Answer 3

• Minimising mechanical index (MI) and thermal index (TI) (e.g. by considering technique, where PW & colour Doppler can produce higher TI values, and reducing output and adjusting other controls).
• Minimising scan time.

Question 4

When is ultrasound obstetric imaging performed in the UK?

Answer 4

First, second and third trimester.

Question 5

What must be considered regarding safety in obstetric ultrasound scanning?

Answer 5

• Fetus is particularly sensitive in early pregnancy (e.g. to temperature changes).
• Although little information known on possible bioeffects, care should be taken, particularly when TI > 0.7.
• Doppler should not be used routinely in first trimester.

Question 6

When may Doppler be used during obstetric scanning? What should be considered if doing this?

Answer 6

• PW Doppler may be used to refine risks for trisomies.
• TI should be less than or equal to 1.
• Exposure time should be 5-10 minutes.

Question 7

What are some additional areas of particular consideration of safety in ultrasound?

Answer 7

• Extra care required for eye, neonatal cardiac and cranial exams.
• Contrast agents can produce cavitation and microstreaming which increases with MI. High-MI echo examination should be avoided. Avoid using in patients with acute coronary syndrome and 24 hours prior to shock therapy.

Question 8

What temperature do BMUS consider as a potentially hazardous to a fetus? What techniques may incur this kind of temperature rise? What other examinations should be avoided?

Answer 8

• 4 degrees Celsius maintained for 5 mins or more.
• PW & colour Doppler may produce such temperature rises in bone.
• Unnecessary exposure of neonatal lung should be avoided as this can cause bruising.

Question 9

What is the general guidance regarding thermal indices and scanning time?

Answer 9

Guidance provides guideline scanning times depending on the TI value used for the scan.

Question 10

What mitigating factors might mean that adverse effects are still unlikely above MI/TI limits? Which society suggested this?

Answer 10

• Transducer movement.
• Perfusion.
• American Institute of Ultrasound in Medicine (AIUM).

Question 11

What are some potential issues with micro bubble contrast agents? How can these be avoided?

Answer 11

• Induction of premature ventricular contractions, microvascular leakage, glomerular capillary haemorrhage and local cell killing reported for MI > 0.4.
• Minimise dose, displayed MI and examination time when imaging MI > 0.4.