Obstetrical Ultrasound – Is all this safe for the fetus? - SD

Introduction

Hi, I'm Shaka bro.
I'm the co-director of the fetal
and neonatal medicine center
and professor in the Department of Obstetrics
and Gynecology at Rush University Medical Center in Chicago.
And today I'm going to speak about a topic
that is very important for anyone
who does obstetrical ultrasound, bio effects
and safety of ultrasound
obstetrical.
Ultrasound is all this safe for the fetus.

Understanding Risk and Bio Effects

Now, when one speaks about bio effects
and safety of ultrasound, there are two issues to consider.
One is risk. The other one is bio effects of ultrasound
and they're connected of course.
Now risk means the chance
or the possibility that something bad will happen.
There are three important characteristics when we speak
about risk, the probability that it will occur, the nature
of the risk and the magnitude of the harm.
But unfortunately, there's a complicating factor,
and that's personal views.
Now all these people may have a lot of fun
and think that they're doing something great.
I may think they're crazy.
That's the personal aspect of risk.

Evaluating Risk: Risk-Benefit Ratio and Precautionary Principle

Now, when we look at risk, the evaluation of a procedure
or an action can be done in one of two ways.
We can look at risk benefit ratio.
That means how much harm is acceptable
to obtain the desire result.
But we also can look at it with the precautionary principle.
How much harm can be avoided by not performing the action
or by performing it in a different way?
The precautionary principle says that if a certain action
in this case ultrasound may cause severe damage
to the public in the absence of a consensus
that there would not be harm, the burden
of proof falls on those who advocate taking the action.
In other words, those who say, do the ultrasound have
to prove that it is safe based on the
precautionary principle.

History of the Precautionary Principle

Now, this principle started in 1842.
In England, there was a bad epidemics of cholera
and John Snow, who was a physician, said, well, we have
to close one of the central fountains of London
to prevent the epidemics from spreading.
People thought it was crazy, but in fact he did that
and the epidemic stopped.
This was the first application of what was
to become the precautionary principle
that was used later in Germany,
particularly in the environmental laws, to try
and prevent some actions from the government
that could harm the environment
better safe than sorry is exactly the
application of this principle.
Premium non-natural.
First do no harm is another application.
And of course, ara the principle that we use in ultrasound
and radiology is another application of that principle.

David Toff's Statement on Ultrasound Use

Now, David Toms many years ago stated
that when one anticipates a specific benefit from ultrasound
examination that cannot be obtained by safer means
he today, we would say he or she should do it.
On the other hand, when one does not anticipate a specific
benefit from ultrasound examination, he should not do it.
So before we start, there's a question
that is very important to ask.
What is ti
and mi

Why Discuss Bio Effects and Safety?

Well,
Why do we speak about bio effects and safety of ultrasound?
Sometimes we see this type of headlines in the papers.
Could ultrasound scans cause harm
to unborn babies or this type?
And this was translated to me
by Professor Marcel Ultrasound can harm your baby,
and you see at the bottom of the page, the risk can be 30%.
So what is the rate of exposure to ultrasound?
Well, in 1984, there was an estimation that this was one out
of every two children born in the USA.
Today, 80%, 90%
of 4 million infants born in the USA are exposed
to ultrasound at least.
And in some European Asian South American countries,
it is close to a hundred percent with some countries
allowing for multiple ultrasounds reimbursed by companies
or by third party payers.
So should the practitioner worry,
should the mom and dad worry?
Should the feeders worry? Why do we even speak about this?
Yes, really, why even speak about bio effects
and safety of ultrasound?
We all know that ultrasound is safe.
Ultrasound is not thalidomide.
Many years ago there was a medication called thalidomide
that was used in pregnancy
to decrease anxiety in the patients.
And it worked very well for that goal,
except babies were born without arms and without legs.
So ultra ultrasound is certainly not thalidomide.
Ultrasound is not x-rays. It's certainly not atmic energy.
Show me the dead babies from ultrasound.
Well, ultrasound is a form of energy.
It's a waveform with positive and negative pressures,
and this energy can be transformed into thermal energy.
That's an indirect effect on tissues
or it can have a direct effect,
and that's mechanical energy.
Positive pressure causes movements in tissues.
Negative pressure can induce cavitation.
So ultrasound pulses when they go
through tissue can cause radiation, stress,
acoustic streaming, nerve ending stimulation, cavitation,
and possibly release of free radicals.

Bio Effects: Thermal and Mechanical

Cavitation is one of two things.
Non inertial cavitation is when bubbles
that are in tissues do not collapse, but have a back
and forth motion, and that motion can cause streaming
or radiation forces or heat production.
The second type is inertial cavitation
where the bubbles in tissue grow
and collapse under the influence of those waves.
And when they collapse, there's a very, very high elevation
of the temperature for a very brief moment of time.
So ultrasound going through living tissues causes effects.
These are called bio effects,
but there are no epidemiological studies demonstrating
harmful bio effects in humans.
Yes, but all epidemiological studies are about exposure
before 1992.
Why is 1992 so important?
Because in 1992, the maximal output
for fetal applications was allowed to be increased
by a factor of eight.
So before 1992, the maximal out acoustic output
for fetal application was 94 milliwatt percenters square
was allowed to be increased
to 720 milliwatt percenters square,
which was the upper limit for general ultrasound.
At that time, the FDA under the pressure
of A IUM public representative manufacturers decided that
we would, they would increase the allowed output
and they created the output display standard or ODS.
This stated that manufacturers may indeed increase the
maximal output, as we said, up to 720 milliwatt per square
on the condition that two indices appeared on screen.
One was the thermal index of TI expressing the potential
for thermal effects, and the other one was the mechanical
index or MI expressing the potential for non-thermal,
also called mechanical effects.
But in addition, a particular effort was to be made
to educate the end users about bio effect safety and TI
and mi and we'll see a little later if this was successful.

Thermal Index (TI) and Mechanical Index (MI)

So the thermal index is a unitless estimate
of the possible tissue temperature rise in degrees
centigrade again, possible temperature rise.
It is a ratio of the total acoustic power divided
by the acoustic power needed to raise the temperature
by one degree centigrade.
Now it predicts the potential for temperature increase.
It is not a real temperature measurement
and important no time information is given
with this index.
And there are three thermal indices, TIS
for soft tissues used primarily in the first trimester
TIB for bones used in the second and third trimester.
Both these indices are the most used in obstetrics
and TIC for cranium when we do ultrasound through the,
skull as we do in adults or in fetuses.
And the reason being that bone is the most absorbing tissue
for acoustic energy,
therefore the highest possible temperature is in the
vicinity of cranium.
The mechanical index expresses the potential
to induce cavitation.
So of course bubbles must be present.
I said earlier that cavitation needs bubbles to occur.
Well, there are no bubbles in the fetal lungs or the bowels,
therefore the risk due to this effect,
the mechanical risk appears to be low.
So manufacturers must display the ti on the MI on screen.
Where is it? Well, it's somewhere on the screen
and every machine is different in this case,
in the upper right corner can be in other places.

End User Knowledge of TI and MI

But what do end users know about these indices?
Well, a few years back we published an article
where we ask people and users what they knew about safety
and we ask people who perform more than five
OB ultrasound a day.
So we didn't want people who did not perform a lot
of ultrasound and the knowledge was quite low.
In fact, we compared this with a publication a few years
before that looking at end users in Sweden,
Carol Marshall published this
and we both found that about 25% of end users knew
what TI and MI stand for.
So 75% did not know
about two third did not know
that these indices appear on screen during the examination.

Potential Risks: Heat and Fetal Damage

Why is this so important?
It's important because heat is dermatological.
It can cause fetal damage.
This has been shown in animal experiments.
This has been shown
where maternal fever in early pregnancy can cause anomalies
as well as external factors such as sauna or hot bath.
So heat has been shown to cause defect.
This is not heat generated by ultrasound as can be seen.
How hot can it get?
Well, here is an example of an ultrasound
or a commercial commercially available machine,
and you can see that the TIB in the Corona is 5.7.
So in theory, the temperature could rise
by 5.7 degrees centigrade,
although again, this is an estimate.
It could be more, it could be less.

Recommended Maximum Exposure Times

What are the recommended maximum exposure times
for embryo fetus?
Well, the British Medical Ultrasound Society published these
numbers in 2000 and reaffirmed them in 2010.
So if the TI is 0.7, you can expose the fetus
for about 60 minutes without risk.
If the TI is one, this goes down to 30 minutes.
The TI is 1.5 15 minutes ti of two four minutes
ti of 2.5, one minute, one minute
of safe exposure.

Differences in Ultrasound Modes and Examiner Control

So what will you say? I use an FDA approved machine?
There's no problem. Well, yes,
but one should know that the mode
of ultrasound used is very important
for the acoustic output.
For instance, in B mode, the acoustic output expressed
by the I-S-P-T-A-A form of intensity
is 34 milliwatt per square.
That jumps to 1001 80
for spectral doppler.
So the output is more dependent doppler being more than MB
than B mode, but the output is under examiner control.
And this is very important.
So whether you use an improved machine
or not, you the examiner control the output.
For instance, if you move the focus
or the GA sample in Doppler, you will change the output.
Now the additional problem is
that every machine behaves differently.
So in one machine you can rise, raise the output
by moving the focus up in another machine.
This will occur when you move the focus down.
So you have to know your machine.
Here is an example of a collar box, large collar box
with a TI 0.7
and the MI 1.2, we're going to move the box up
and make it smaller and this causes the ti to jump to 1.2.
So just moving the box, just changing the size
of the box changes the output.
Here is an example of a doppler of the umbilical artery
where the ti is 2.4 relatively high.
You can obtain a good signal with a ti of 0.4.
What I did is I decreased the power.
Now I purposely decreased it to a maximal way so
that there's still a signal,
but it is not as good as before.
So if you decrease it from 2.4 to 0.8,
let's say you would still have a wonderful signal
with very low power.
Now, most machine, the default is the high power.
We've been able to convince manufacturers
that in fact they should try to start with a low power
and the examiner will increase the power only if needed.

First Trimester Considerations

Is early pregnancy worse?
Well, in the past we used a full bladder.
We rarely use this in today.
And of course, ultrasound travels
through fluid without impairment and
therefore the risk was
that the fetus would in fact get a higher
amount of exposure.
We are closer to intonated tissues when we do transvaginal
ultrasound and there is some transducer fa
transducer face heating.
That is possible. We've said already
that the worst effect is a bone tissue interface,
but of course there's very little bone in the first
trimester fetus.
We're not sure about how much heat is dissipated
by the early fetus in the early pregnancy.
The other side of the equation, of course,
is the fetus susceptibility.

Critical Periods of Fetal Development

Now this is a table
that we've all seen in our embryology books,
which shows the development of the fetus.
And as Brent Etal stated, the critical period
for structural teratogen sensitivity is about the third
to the eighth post fertilization week.
And that's five to 10 weeks gestational age.
Another way of looking at this is looking at critical
periods of development.
And if we look at the different organs, we see
that the central nervous system starts at about four
and five weeks and goes on to 12 and later.
The heart as in this is in this time period, the arms,
the eyes, the legs, the teeth, the palate,
the external genitalia, and the ears.
Now 10 to 11 weeks is
the mean entry into prenatal care,
but it's also the time where
major morphological manifestation will occur before
and minor or functional manifestations
will occur after this.
And in fact, in 1999, Francis Duck in an editorial
asked, stated that no epidemiological
or other evidence was then,
and he meant in the early nineties, around 1992 when the
output were changed or is now available
to support the assertion of safety at these high exposures.
So there's essentially no data showing that it is safe,
although naturally this is very difficult to show.

Exposure in the First Trimester

So we asked the question
during the first trimester is the fetus exposed
to high levels of acoustic energy?
And our conclusion was that in fact,
during the first trimester,
and we were speaking about B mode,
the rise in ti was minimal.
Is doppler worse? Here's an example of a doppler
of the doctor's osis in a very early fetus,
and you can see that the AirWave is reversed.
So this happened to be a fetus with down syndrome,
but we perform now a lot
of these examinations in the first trimester with doppler,
we perform doppler of the doctor's venosus,
trans valvular blood flow,
and particularly the tricuspid valve.
And we can start now to look at cardiac anatomy
and function very early in pregnancy.
Well, the publishing
of papers on first trimester doppler was questioned
by Stuart Campbell and Larry Platt in 2000.
Another article in the same journal asked the question
of whether it is ethical
to perform research using dopper ultrasound
in the first trimester.

Studies on Ultrasound Effects

A very interesting study was published a few years ago
on ultrasound exposure of the fetal chick brain.
Now chicks can learn
and memorize the position of certain plates
where food is situated.
So you can teach a chick that food, for instance,
is in the blue plate and not in the red plate.
When you remove the plates and you bring the plates back
and the chicks back, they will go directly to the blue plate
because they know that the food is there.
So they learned it and they memorize it.
So this group of researcher exposed the brain
of chicks on day 19 of a 21 day incubation period to B mode
for five or 10 minutes
or two pulse doppler for 1, 2, 3, 4, and five minutes.
They assessed then the learning
and memory function that I just talked about on day two post
hatch, and they found
that B mode exposure did not affect memory function at all.
But following four
and five minutes of doper exposure, two hours
after training, there was significant memory impairment.
The chicks did not remember where the food was.
In fact, in separate groups of chicks, the short,
the intermediate and long-term memory were impaired,
which suggested
that they could not learn where the food was.
Furthermore, when they were received a second training
session, five minutes
after completion of the initial testing,
they we're still unable to learn.

So today we do NT nasal bone, some do maxillary angle.
All these are obtained with B mode,
which is low ultrasound energy.
But to do an entire assessment of the fetus in the early
trimester, we should use or can use tricuspid valve
and Drs Venus, and this is of course done with doppler.

Calculating Energy Exposure

Can we calculate how much energy is in fact
applied to the fetus?
Well, the answer to that question is simple.
No, we can't, but we can do a little exercise
that will give us an idea of the differences in exposure.
So let's assume two minutes each to obtain the BPD,
the head circumference,
the abdomen circumference, and the female length.
All these of course with B mode.
So the total energy that we will apply to the fetus,
remember B mode is 34 milliwatt persona.
Meter square is about 34 times two, two minutes
times four, four elements
or total of 272 milliwatt PERA meter square.
If we do doppler and we assume five minutes
to find the doctor's venosus and the tricuspid,
and those of you who perform those know
that it can be much more than five minutes.
Now the total energy is going to be 1180.
Remember we said dopper is 1180 milliwatt per meter square
times five, five minutes times two, two elements,
or 11,800 milliwatt per centimeter square.
This is 42 times higher than what was used for the bmo.

Rat Liver Study

Another interesting study recently published showed the
ultrasound effects in rat liver
where they quantified the damage to the liver
after pause doppler.
And they did find after longer exposure,
there was more tissue damage in the liver
and they established that ten second was the maximum
exposure time to ensure that there was no damage
to the tissue in that particular model.
So doppler in the her early pregnancy
should be used with caution, how to keep it safe.

Recommendations for Safe Use

Well, here is again that table from
the British Medical Ultrasound Society
and they again look at the ti
and in fact, you see at the right side that above a ti I
of three, they don't recommend any use.
And depending on the other tis, the times are,
as we showed earlier, Many societies in the world have
statements regarding safety of ultrasound.
In particular doppler, the IUM is beamus and w
and it is just an example of the IUM statement of 2011
stating that the use of doppler
during the first trimester is being promoted
as a diagnostic aid.
In screening for some congenital anomalies,
the procedure requires skill
and subjects the fetus to extended period
of relatively high ultrasound exposure levels as we showed
because of the increased risk, the use of spectral doppler
with high TI in the first trimester needs
to be viewed with caution.
And spectral doppler should be employed only when there's a
clear benefit, risk advantage, and both ti
and the examination duration should be kept low.
In general, keeping the TI less than one will reflect
minimal risk.
The potential for the potential impact
of ultrasound has never been as high as now
with an ever increasing number of practitioner.
Worldwide performing Doppler examination from the first
trimester onwards has was stated by Kristo Binga,
remember the whole first trimester,
and that includes week 10 to 12 is the most
sensitive time in gestation.
Then of course, there's the issue of the lawyers
and the issue that not only is it important for the patient
and the fetus to keep the exposure low,
but it is important also from a legal standpoint.
So perform the exam only if it's indicated,
keep the output as low as possible, keep the exam
as short as possible.
Both of these, of course, need to be compatible
with accurate diagnosis
and this is exactly the elara principle as low
as reasonable, achievable.
Watch the ti and mi and keep them below one.
And when you start performing ultrasound, please
think about the MI and the ti.

Conclusion

Thank you.