Download pregnant patients and mri procedures

MRISAFETY.COM
ANNEXURE C
Magnetic resonance (MR) imaging has been used to evaluate obstetrical, placental, and fetal abnormalities in
pregnant patients for more than 25 years. MR imaging is recognized as a beneficial diagnostic tool and is utilized to
assess a wide range of diseases and conditions that affect the pregnant patient as well as the fetus.
Initially, there were substantial technical problems with the use of MR imaging primarily due to image degradation
from fetal motion. However, several technological improvements, including the development of high-performance
gradient systems and rapid pulse sequences, have provided major advances especially useful for imaging pregnant
patients. Thus, MR imaging examinations for obstetrical and fetal applications may now be accomplished routinely
in the clinical setting.
PREGNANCY AND MRI SAFETY
The use of diagnostic imaging is often required in pregnant patients. Thus, it is not surprising, that the question of
whether or not a patient should undergo an MR examination during pregnancy will often arise. Unfortunately, there
have been few studies directed toward determining the relative safety of using MR procedures in pregnant patients.
Safety issues include possible bioeffects of the static magnetic field of the MR system, risks associated with
exposure to the gradient magnetic fields, the potential adverse effects of radiofrequency (RF) energy, and possible
adverse effects related to the combination of these three electromagnetic fields.
MR environment-related risks are difficult to assess for pregnant patients due to the number of possible
permutations of the various factors that are present in this setting (e.g., differences in field strengths, pulse
sequences, exposure times, etc.). This becomes even more complicated since new hardware and software is
developed for MR systems on an on-going basis.
There have been a number of laboratory and clinical investigations conducted to determine the effects of using MR
imaging during pregnancy. Most of the laboratory studies showed no evidence of injury or harm to the fetus, while a
few studies reported adverse outcomes for laboratory animals. However, whether or not these findings can be
extrapolated to human subjects is debatable.
By comparison, there have been relatively few studies performed in pregnant human subjects exposed to MR
imaging or the MR environment. Each investigation reported no adverse outcomes for the subjects. For example,
Baker et al. reported no demonstrable increase in disease, disability, or hearing loss in 20 children examined in
utero using echo-planar MRI for suspected fetal compromise. Myers et al. reported no significant reduction in fetal
growth vs. matched controls in 74 volunteer subjects exposed in utero to echo-planar MRI performed at 0.5-Tesla. A
survey of reproductive health among 280 pregnant MR healthcare professionals performed by Kanal et al. showed
no substantial increase in common adverse reproductive outcomes.
There has been on-going concern that acoustic noise associated with MRI may impact the fetus. Reeves et al.
(2010) conducted an investigation to establish whether fetal exposure to the operating noise of 1.5-T MR imaging
causes cochlear injury and subsequent hearing loss in neonates. The findings in this study provide some evidence
that exposure of the fetus to 1.5-T MR imaging during the second and third trimesters is not associated with an
increased risk of substantial neonatal hearing impairment.
With regard to the publications to date, there are discrepancies with respect to the experimental findings of the
effects of electromagnetic fields used for MR procedures and the pertinent safety aspects of pregnancy. These
discrepancies may be explained by a variety of factors, including the differences in the scientific methodology used,
the type of organism examined, and the variance in exposure duration, as well as the conditions of the exposure to
the electromagnetic fields. Additional investigations are warranted before the risks associated with exposure to MR
procedures can be absolutely known and properly characterized.
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ANNEXURE C
GUIDELINES FOR THE USE OF MR PROCEDURES IN PREGNANT PATIENTS
As stated in the Policies, Guidelines, and Recommendations for MR Imaging Safety and Patient Management
issued by the Safety Committee of the Society for Magnetic Resonance Imaging in 1991, “MR imaging may be used
in pregnant women if other nonionizing forms of diagnostic imaging are inadequate or if the examination provides
important information that would otherwise require exposure to ionizing radiation (e.g., fluoroscopy, CT, etc.).
Pregnant patients should be informed that, to date, there has been no indication that the use of clinical MR imaging
during pregnancy has produced deleterious effects.”
This policy has been adopted by the American College of Radiology and is considered to be the “standard of care”
with respect to the use of MR procedures in pregnant patients. Importantly, this information applies to MR systems
operating up to and including 3-Tesla.
Thus, MR procedures may be used in pregnant patients to address important clinical problems or to manage
potential complications for the patient or fetus. The overall decision to utilize an MR procedure in a pregnant patient
involves answering a series of important questions including, the following:
-Is sonography satisfactory for diagnosis?
-Is the MR procedure appropriate to address the clinical question?
-Is obstetrical intervention prior to the MR procedure a possibility? That is, is termination of pregnancy a
consideration? Is early delivery a consideration?
With regard to the use of MR procedures in pregnant patients, this diagnostic technique should not be withheld for
the following cases:
-Patients with active brain or spine signs and symptoms requiring imaging.
-Patients with cancer requiring imaging.
-Patients with chest, abdomen, and pelvic signs and symptoms of active disease when sonography is nondiagnostic.
-In specific cases of suspected fetal anomaly or complex fetal disorder.
Studies of low-molecular weight water-soluble extracellular substances such as iodinated diagnostic X-ray and
computed tomography (CT) and gadolinium-based magnetic resonance imaging (MRI) contrast media in pregnancy
have been limited, and their effects on the human embryo or fetus are incompletely understood. Iodinated diagnostic
contrast media have been shown to cross the human placenta and enter the fetus in measurable quantities (1, 2). A
standard gadolinium-based MRI contrast medium has been shown to cross the placenta in primates and appear within
the fetal bladder within 11 minutes after intravenous administration (3). It must be assumed that all iodinated and
gadolinium-based contrast media behave in a similar fashion and cross the blood-placental barrier into the fetus.
After entering the fetal blood stream, these agents will be excreted via the urine into the amniotic fluid and be
subsequently swallowed by the fetus (4). It is then possible that a small amount will be absorbed from the gut of the
fetus with the additional swallowed gadolinium-based contrast agents eliminated back into the amniotic fluid.
In the study in primates, placental enhancement could be detected up to 2 hours following the intravenous (IV)
administration of gadopentetate dimeglumine. When gadopentetate dimeglumine was injected directly into the
amniotic cavity, it was still conspicuous at 1 hour after administration (3). There are no data available to assess the
rate of clearance of contrast media from the amniotic fluid.
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ANNEXURE C
Iodinated Low Osmolality Contrast Media
Mutagenic effect of LOCM
Diagnostic iodinated contrast media have been shown to cross the human placenta and enter the fetus when given in
usual clinical doses. In-vivo tests in animals have shown no evidence of either mutagenic or teratogenic effects with
low-osmolality contrast media (LOCM). No adequate and well-controlled teratogenic studies of the effects of these
media in pregnant women have been performed.
Effect of iodinated contrast media on fetal thyroid function
The fetal thyroid plays an important role in the development of the central nervous system. There have been rare
reports of hypothyroidism developing in the newborn infant after the administration of iodinated contrast medium
during pregnancy; however, this occurred only following amniofetography using fat soluble iodinated contrast medium
which was performed in the past to detect congenital malformations.
Intravenous administration of iodinated contrast medium does not affect short-term neonatal TSH, likely because the
overall amount of excess iodide in the fetal circulation is small and transient. However, the long term effects are
unknown. To date, there has been no documented case of neonatal hypothyroidis from the maternal intravascular
injection of water-soluble iodinated contrast agents (5,6). Given the current available data and routine evaluation of all
newborns for congenital hypothyroidism by measurement of thyroid stimulating hormone levels at the time of their
birth, no extra attention is felt to be necessary (7, 8, 9).
Other adverse effects
There have been no other adverse effects that have been reported in the fetus or neonate following administration of
LOCM. However, information in this area is sparse.
Recommendations prior to performing imaging studies requiring iodinated contrast material administration
We recommend that all imaging facilities should have policies and procedures in place to identify pregnant patients
prior to the performance of any examination involving administration of iodinated contrast media. If a patient is known
to be pregnant, the potential added risks of contrast media should be considered before proceeding with the study
(10).
There is insufficient evidence to conclude that LOCM are without any risk with respect to the fetus. Consequently, the
Committee on Drugs and Contrast Media recommends the following in patients in whom imaging studies are
requested that may require the use of iodinated contrast material:
A. The radiologist should confer with the referring physician and document in the radiology report or the patient’s
medical record the following:
1. That the information requested cannot be acquired without contrast administration.
2. That the information needed affects the care of the patient and fetus during the pregnancy.
3. That the referring physician is of the opinion that it is not prudent to wait to obtain this information until
after the patient is no longer pregnant.
B. It is recommended that pregnant patients undergoing a diagnostic imaging examination with iodinated
contrast media and their referring physicians should indicate that they understand the potential risks and
benefits of the procedure to be performed, the potential for risk to the fetus, and the alternative diagnostic
options available to them (if any), and that they indicate the desire to proceed.
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ANNEXURE C
Gadolinium-Based Contrast Agents (GBCAs)
Mutagenic effect of GBCAs
To date, there have been no known adverse effects to human fetuses reported when clinically recommended dosages
of GBCAs have been given to pregnant women. A single cohort study of 26 women exposed to gadolinium chelates
during the first trimester of pregnancy showed no evidence of teratogenesis or mutagenesis in their progeny (11).
However, no adequate and well-controlled teratogenic studies of the effects of these media in pregnant women have
been performed.
Risk of nephrogenic systemic fibrosis
There are no known cases of NSF linked to the use of GBCAs in pregnant patients to date. However, gadolinium
chelates may accumulate in the amniotic fluid. Therefore, there is the potential for dissociation of the toxic free
gadolinium ion, conferring a potential risk for the development of nephrogenic systemic fibrosis (NSF) in the child or
mother. Because the risk is unknown, it is generally recommended that gadolinium chelates not be used routinely in
pregnant patients.
Recommendations for the use of GBCA-enhanced MRI examinations in pregnant patients
Because it is unclear how GBCAs will affect the fetus, these agents should be administered only with caution. They
should only be used if their usage is considered critical and the potential benefits justify the potential risk to the unborn
fetus. If a GBCA is to be used in a pregnant patient, one of the agents believed to be at low risk for the development of
NSF (12) should be used at the lowest possible dose to achieve diagnostic results. In pregnant patients with severely
impaired renal function, the same precautions should be observed as in non-pregnant patients.
At the present time, the Committee on Drugs and Contrast Media recommends the following concerning the
performance of contrast-enhanced MRI examinations in pregnant patients.
Each case should be reviewed carefully and gadolinium-based contrast agent administered only when there is a
potential significant benefit to the patient or fetus that outweighs the possible risk of exposure of the fetus to free
gadolinium ions.
A. The radiologist should confer with the referring physician and document the following in the radiology report or
the patient’s medical record:
1. That information requested from the MRI study cannot be acquired without the use of IV contrast or by
using other imaging modalities.
2. That the information needed affects the care of the patient and/or fetus during the pregnancy.
3. That the referring physician is of the opinion that it is not prudent to wait to obtain this information until
after the patient is no longer pregnant.
B. It is recommended that both pregnant patients undergoing an MRI examination and their referring physicians
should indicate that they understand the potential risks and benefits of the MRI procedure to be performed,
and the alternative diagnostic options available (if any), and that they wish to proceed.
PREMEDICATION OF PREGNANT PATIENTS (WITH PRIOR ALLERGIC-LIKE REACTIONS TO IODINATED OR
GADOLINIUM-BASED CONTRAST MEDIA
Diphenhydramine and corticosteroids (most commonly prednisone and methyl-prednisolone) are commonly used for
prophylaxis in patients at risk for allergic-like contrast reactions to contrast media. Diphenhydramine is classified as
FDA category B. (FDA category B: Animal reproductive studies have failed to demonstrate a risk to the fetus and there
are no adequate well-controlled studies in pregnant women.) Prednisone (FDA category C) and dexamethasone (FDA
category C) traverse the placenta; however most of these agents are metabolized within the placenta before reaching
the fetus and therefore are not associated with teratogenicity in humans. (FDA category C: Animal reproduction
studies have shown an adverse effect on fetus and there are no adequate and well-controlled studies in humans, but
potential benefits may warrant use of the drug in pregnant women despite potential risks.) However, sporadic cases of
fetal adrenal suppression have been reported. Methylprednisolone also classified as a class C drug, carries a small
risk of cleft lip if used before 10 weeks of gestation (16, 17).