MRI Flashcards
How does an MRI scanner work?
The MRI scanner makes use of a physics concept called the
dipole moment. This refers to the ability of the nucleus of a
hydrogen atom to act as a magnet. When placed within a
powerful magnetic field, the spin of the hydrogen’s lone electron
will align itself parallel to the magnetic field. The patient’s watercontaining
tissues are then subjected to radiofrequency
impulses. When the proton in the hydrogen is stimulated by this
impulse it emits radiofrequency signals that can be interpreted
as three-dimensional spatial information.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1280.
How do the strong magnetic fields in an MRI scanner
affect the patient?
Because of its iron content, the patient’s blood flow will be
altered and the blood pressure will exhibit a compensatory
increase. Some patients report dizziness, headache, nausea,
and visual sensations.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1282.
The American College of Radiology divides the MRI
area into four zones. What are they?
Zone 1 is the area with public access and requires no
supervision. The waiting room and hallway outside the MRI
suite are an example of Zone 1. Zone 2 has public access but
limited supervision. The entrance into the MRI suite is an
example of Zone 2. Zone 3 has limited access and stringent
supervision. The area immediately outside the MRI room is an
example of Zone 3. Zone 4 is the room where the MRI scanner
is located and is under constant supervision.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1280.
Why might sedation or anesthesia be required for an
MRI scan?
The patient must remain completely still for an hour or more
during an MRI. Patients that cannot remain still or suffer from
claustrophobia may require sedation, or in exceptional cases,
require a general anesthetic.
Nagelhout JJ, Zaglaniczny KL. Nurse Anesthesia. 4th ed.
Philadelphia, PA: WB Saunders Company; 2010: 1293.
Why is the presence of ferromagnetic (ironcontaining)
objects contraindicated in the MRI suite?
Because of the strength of the magnet used, iron-containing
objects such as pens, cell phones, pagers, jewelry, some
anesthesia equipment, and even credit cards can become
missiles that could strike the patient or damage the machine.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1282-1283.
How can a pacemaker be affected by an MRI scan?
The pacemaker can be reset or reprogrammed, it may revert to
asynchronous mode, become hot, or even become dislodged.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1283.
What is the composition of MRI contrast dye and
what are the side effects of its administration?
MRI contrast is a chelated form of gadolinium that is
administered intravenously. A common side effect is nausea.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1283.
You are performing a general anesthetic for a patient
undergoing an MRI. You are using an endotracheal
tube with an extra-long circuit and extension tubing
for the end-tidal CO2 sampling line. How would this
affect the capnograph waveform?
Lengthening the ETCO2 sampling cable will result in a
prolonged upslope of the capnography waveform.
Can a pregnant anesthetist be present in an MRI
suite?
Pregnant anesthesia can be in the MRI room during all of the
required anesthesia preparations, but the American College of
Radiology recommends that personnel should not be in the MRI
scanner with the patient during the actual scan. Pregnant
anesthesia personnel should discuss this with their obstetrician
prior to MRI exposure.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1283.
How does the anesthetic equipment and monitoring
setup differ in an MRI suite versus the operating
room?
All of the standard equipment necessary to deliver anesthesia in
any other environment is still mandatory for delivery of an
anesthetic in an MRI suite, including all monitoring and
emergency equipment. An oxygen supply is necessary, but is
usually provided by a non-ferrous wall oxygen flowmeter.
Pressurized oxygen tanks may be composed of ferrous material
that is not allowed in the MRI suite itself.
Magnetic Resonance Imaging. [Online] August 17, 2008
.
What are the most important preparations to make
prior to beginning IV sedation for an MRI?
As in all sedation procedures, there is a risk that the patient
may need some form of emergency airway management. An
emergency plan should be developed for this procedure
because the patient is secluded in the MRI machine making
observation more difficult. Should an emergency arise, it is
necessary to be able to communicate the issue with the
technician who can then, immediately stop the procedure and
remove the patient from the MRI. If intubation is necessary and
MRI safe laryngoscope blades are not available, it may be
necessary to have a stretcher ready to remove the patient from
the suite entirely.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1283-1284.
Why should monitor leads be maintained in a
straight line when placed on a patient undergoing
anesthesia for an MRI? What other anesthesia
items may be precluded by this fact?
Loops in the monitor leads can cause thermal injury during the
MRI. The magnetic field can induce the flow of current in coiled
leads or tubing, causing them to become hot enough to burn the
patient. For this reason, flexible LMAs and anode endotracheal
tubes that contain wire winding should not be used. Even
tissue loops, such as the curve caused by the patient’s hand
touching his/her hip can induce current flow and result in injury.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1283.
