Interactive Transcript
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There are multiple indications for
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performing MRI during pregnancy.
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Some of them are unrelated to the pregnancy
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itself and may include neurological
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indications, and musculoskeletal indications.
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Acute abdominal pain is something
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for which we very frequently
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perform MRI in pregnant patients.
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Common conditions occurring in pregnancy
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for which we would do MRI include
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appendicitis, acute or chronic hepatobiliary
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pathology, and nephrolithiasis.
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We can also use MRI to evaluate obstetric
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abnormalities, and in those cases, MRI
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may be extremely useful for operative
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planning for this patient population.
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MRI is an extremely safe imaging
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modality to use during pregnancy.
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We have decades of data regarding the use
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of MRI in pregnant patients, none of which
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suggests that MRI is harmful to the fetus.
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One of those reasons, of course, is
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because we're using radiofrequency
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pulses within a magnetic field, again,
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instead of ionizing radiation for CT.
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MRI is wonderful because we can get large
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field of view images with excellent tissue
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characterization, and the images are often
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diagnostic without intravenous contrast.
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I want to point out that MRI is safe to perform
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in pregnancy in all three trimesters, both at 1.5
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tesla and 3 tesla.
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There were initially, at the advent of
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MRI, concerns about tissue heating and
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specific absorption rate for the fetus.
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However, we know now that most of the
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tissue heating that occurs in the context
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of MRI really happens at the skin's surface,
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which is maternal tissue, and the
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uterus and fetus are deep to that.
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Additionally, the amniotic fluid
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that's surrounding the fetus continues
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to circulate, so it's dissipating
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any heat that may reach the fetus.
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There is also a theoretical risk to the
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fetal ossicles due to the noise that may
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happen during the exam, particularly in
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the context of gradient echo imaging.
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However, this hasn't really panned out in many
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of the human studies that we've performed.
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We've not seen a lot of babies born with
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hearing-related issues thought to be
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due to noise exposure during the MRI.
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Let's also talk about the use of gadolinium-
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based contrast agents in pregnant patients.
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Gadolinium contrast is water-soluble,
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so it does cross the placenta.
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And because gadolinium is renally excreted, it
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can lead to cyclic re-exposure to the fetus,
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because as the gadolinium crosses the placenta,
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it enters the fetal circulation, is excreted
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by the fetal kidneys, and then is urinated
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out by the fetus into the amniotic fluid.
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Because the fetus also swallows the
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amniotic fluid, there's a continuous
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re-exposure to the gadolinium contrast.
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Because the gadolinium contrast is persisting
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for longer than we would like in the fetal
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circulation and the amniotic fluid, there is the
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potential for that free gadolinium to dissociate
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from the chemical chelate to which it's bound.
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And so there are recent studies that have
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come out showing that fetuses exposed
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to gadolinium-based contrast agents
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are at increased risk of rheumatologic,
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inflammatory, or infiltrative skin conditions.
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Gadolinium-based contrast agents
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are also considered a class C drug
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because some animal studies have
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shown the potential for teratogenesis.
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And so for all of these reasons, there is
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really almost no reason to use gadolinium-
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based contrast in pregnant patients,
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and it is not routinely indicated.
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