How do you know it s SAFE EFSUMB Safety Committee Why are we concerned about safety The range of clinical applications is becoming wider The number of patients undergoing ultrasound examinations is increasing ID: 329995
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Slide1
Ultrasound ImagingHow do you know it’s SAFE?
EFSUMB Safety CommitteeSlide2
Why are we concerned about safety?The range of clinical applications is becoming wider The number of patients undergoing ultrasound examinations is increasing New techniques with higher acoustic output levels are being introduced.Slide3
What are bio-effects?The result of ultrasound interacting with biological molecules as it passes through tissue
Slide4
SafetyIs a bioeffect likely to cause a problematic change (e.g. cell, gene or DNA damage) ?Slide5
Mechanisms of ActionHeat (Ispta)
Cavitation (P-)Slide6
Attenuation=
Absorption
+Scatter
INCIDENT
BEAM
IMAGE
Scatter
20-40%
Absorption
60-80%
HEATSlide7
HEATING(Absorption)Increases with: frequency,
exposure duration,
pulse repetition frequencySlide8
2Pulsed Doppler
Colour
Doppler
Harmonic
imaging
B-mode
2D,3D
M-mode
Power
Heating potentialSlide9
ATL UM 9(Linear-Array L 10-5)Transducer Self Heating :
International limits for probe surface temperature due to self-heating :
T < 41 °C (in a water bath 2 l / 10 min) IEC 601-2-5 T < 43 °C (coupled to skin) T < 50 °C (emitting into air) IEC 60601-2-37
© CKollmann, Euroson 2010
Temperature distribution due to probe self-heating for diagnostic devices (maximum) :
B-Mode Pulsed Doppler Colour Doppler
I
spta
= 11 mW cm
2
, MI = 0,5
I
spta
= 533 mW cm
2
, MI = 0,9
I
spta
= 606 mW cm2, MI = 0,3Slide10
Biological consequences of heat depend on temperature rise and duration.
Thermal EffectsSlide11
Thermal EffectsTissues containing a large component of actively dividing cells are most sensitive to the effects of heat.Slide12
ACOUSTIC CAVITATION Slide13
CavitationSlide14
Formation/activity of gas filled bubbles in an ultrasound exposed mediumAt MHz frequencies bubble radius ~1 µmStable cavitation – bubbles oscillateInertial cavitation – bubbles expand too far then collapse very rapidly, releasing enough energy to damage tissue
Acoustic CavitationSlide15
Inertial CavitationSlide16
How does the risk of heating & cavitation change with imaging conditions?Slide17
All modes
Contact time
Cavitation
2
Heating
Cavitation
2
Heating
Output Power
Frequency
Cavitation
Heating
Increase
Increasing importance
Decreasing importanceSlide18
Imaging & M-mode
M-mode
Cavitation
2
Heating
Sector format
Heating
Deeper/more
focal zones
2
Heating
Narrow
Sector format
2
HeatingSlide19
2Pulsed Doppler
Other Factors which may influence
Heating and cavitationRange Gate Width
(pulse length may vary with gate width)
Range Gate Depth
(power may increase with depth)
Doppler Velocity Range
(pulse repetition frequency may increase)Slide20
2Receiver Gain
has
NO effect on heating or cavitation
So …..
Maximise
it!Slide21
A diagnostic exposure that produces a maximum in situ temperature rise of no more than 1.5C above physiological levels (37C) may be used clinically without reservation on
thermal grounds
WFUMB
’98 - 01
Thermal Effects
WFUMB 1992Slide22
A diagnostic exposure that elevates embryonic and fetal in situ temperature above 41oC
(by 4
oC) for
5 min should be considered to be potentially hazardous.
WFUMB
’
98 - 01
Thermal Effects
WFUMB 1992Slide23
“On Screen”
Labelling
Designed to provide safety related information
AIUM/NEMA O
utput
D
isplay
S
tandardSlide24
The Thermal index (TI) is an on-screen guide to the user of the potential for tissue heating.
Estimate of the tissue temperature rise in ºC which might be possible under "reasonable worst-case conditions”
THERMAL INDEX (TI)Slide25
TI = Acoustic Power Output (Acoustic Power to produce a 1oC rise)
THERMAL INDEXSlide26
Soft tissue index TISBone
TIB
TIC – bone near transducer
THERMAL INDEXSlide27
The Mechanical index (MI) is an on-screen guide of the likelihood and magnitude of nonthermal effects.
MECHANICAL INDEXSlide28
MI = p/fP: in situ pressuref: frequency
MECHANICAL INDEX (MI)Slide29
Power setting
High power
low gain
Lower power
high gainSlide30
Power setting
High power
low gain
Lower power
high gainSlide31
From scientific evidence of ultrasound-induced biological effects to date, there is NO REASON to withhold diagnostic scanning during pregnancy
,
provided it is 1. medically indicated
2. is used prudently by fully trained operators.
This includes routine scanning
of pregnant women.Slide32
Ultrasound exposure during pregnancy
With increasing mineralisation of fetal bones, the possibility of heating sensitive tissues such as brain and spinal cord increases.
So …. extra vigilance is advisedSlide33
3D imagingNo additional safety considerations (particularly if there are significant pauses during scanning to study or manipulate the reconstructed images)Slide34
4D imaging(real-time 3D) Involves
continuous exposure
Guard against prolonging examination times unduly to improve the recorded image sequence beyond that necessary for diagnostic purposes.Slide35
Ultrasound Contrast Agents (UCAs)
UCAs are not licensed for pregnancy Caution should be exercised when using in tissues for which damage to microvasculature may be important (eg. eye, brain, neonate)Exercise caution when using UCAs in patients with severe coronary artery disease and pulmonary hypertension.
Keep MI low, and avoid long exposure times
Refer to EFSUMB CEUS guidelines (2011)Slide36
http://www.bmus.org/policies-guides
0
0.5
1.0
1.5
2.0
2.5
3.0
0.7
RECOMMENDED
RANGE
PROVIDED
ADEQUATE IMAGES
CAN BE OBTAINED
(especially in 1st trimester)
Unlimited time
Observe ALARA
< 60
mins
< 30
mins
< 15
mins
< 4
mins
< 1
min
NOT
RECOMMENDED forOBscanning
Recommended scanning time limits for these TIs(observe ALARA)
THERMAL INDEX
OBSTETRIC SCANNINGMonitor TIS up to 10 weeks post-LMP, TIB thereafter.Slide37
Epidemiological safety studiesRecent systematic reviews:Torloni MR. WHO systematic review of the literature and meta-analysis.
UOG 2009;33:599-608
Whitworth M. Ultrasound for fetal assessment in early pregnancy. Cochrane Database Syst Rev 2010Salvesen KÅ. Ultrasound in pregnancy and non-right handedness: meta-analysis of randomized trials.
UOG 2011;38:267-71Slide38
Only one controversial issuePrenatal ultrasound is associated with left-handedness
Published studies
Year Journal 1. author Type of study
1993 BMJ Salvesen RCT1998 Early Hum Dev Kieler RCT
2001 Epidemiology Kieler Cohort
Epidemiology Kieler Cohort
Ultrasound Obstet Gynecol Heikkilä RCT
2011 Ultrasound Obstet Gynecol Salvesen Meta-analysisSlide39
Meta-analysis Forrest plot from Salvesen UOG 2011;38:267-71Slide40
We should worry – why?
5
epidemiological
studies demonstrate an
increased
risk
of
left
-
handedness
of
15-30%
No
other
epidemiological
study on ultrasound and handedness has been publishedExperimental studies indicate effects on the brain in some animal modelsModern scanners produce higher outputsSlide41
We should not worry – why? Being left-handed is normal (10-15% of population)
A statistical association does
not imply a causal relationshipThe biological plausibility of this association is questionableSlide42
European Committee for Medical Ultrasound Safety
www.efsumb.org/ecmus
British Medical Ultrasound Society
www.bmus.org
World Federation for Ultrasound in Medicine & Biology
www.wfumb.org
Safety Statements