State Emanuel

Kanal,

Frank

MD

Patient

G. Shellock,

#{149}

magnetic has been advances acutely ill this

diag-

however, of vital

tion of most MR imaging systems makes direct visualization of the patient difficult, if not impossible. Furthermore, the static and time-varying magnetic (and electric) fields associated with MR imaging systems may be incompatible with most physiomonitoring

devices,

either

of safety or function. The review herein the data represently available monitor-

devices

for various

physiologic

parameters and provide recommendations regarding what-and whom-to monitor during clinical MR examinations. Index terms: logical effects

Magnetic resonance Magnetic resonance #{149}State-of-art reviews

safety

Radiology

during

M

the num-

functions during the examination. Unfortunately, the present construc-

ing

PhD

Monitoring

The impressive growth in ber of patients imaged with resonance (MR) technology accompanied by technical that have permitted more patients to be studied with nostic tool. Such patients, might require monitoring

logic

Clinical

.

1992;

(MR), bio(MR),

185:623-629

resonance (MR) imaging and angiographic techniques have proliferated during the past decade to a point where it is now difficult to find a hospital that does not provide this service. With such proliferation of imaging systems there has been a concomitant increase in the number of patients being studied

iologic

with this modality. Other factorssuch as the development of more rapid MR imaging techniques and technical advances in what can be examined-have resulted in more examinations with MR imaging of

issue of monitoring the ambient environment in the imaging room. For all

seriously ill, or even critically ill, patients than ever before. Along with these developments, the importance must be stressed of adequate monitoring of patient vital signs and other physiologic parameters during MR examinations of such ill, sedated, pediatric, and possibly unresponsive or

magnet

uncommunicative There seems large variation

specifications

AGNETIC

1

From

the Department

of Pittsburgh

(EK.);

Tower

School

Imaging,

electrocardiogram,

of Radiology, of Medicine,

Los Angeles

UniverPittsburgh

(FG.S.);

and

of California, Los Angeles, School of Medicine, Los Angeles (F.G.S.). Received May 26, 1992; revision requested July 7; revision received August 5; accepted August 10. Address reprint requests to E.K., Pittsburgh NMR Institute, 3260 Fifth Ave. Pittsburgh, PA 15213. F, RSNA, 1992 University

we

It should also are referring

monitoring

be stressed specifically

time

to bring

up

superconductive a functional

at all times

when

mend that it be mounted of 5 ft [150 cm] or more ground and be placed tolerated to the imaging as determined on the facturer.) Since

cryogenic

clinical

MR

imaging

IS “MONITORING”?

the

sake

of clarification,

patient

“monitoring” during refers to any activity

MR imaging that permits

the

health care provider tus of any physiologic

to follow the parameter(s)

staof

choice. This ranges from simply speaking with the patient to assess the level of consciousness to intraarterial

pressure

arterial cludes

recording

pressure everything

monitoring

bedside

be performed

(“magnet-side,”

or remotely

or automated

and

can

as closely

as

magnet

itself,

these

magnets

and

gases

function of the rooms in are

located

constantly Similarly,

for mon-

itors should be present in rooms used for moderateor long-term storage of such cryogenic dewars, or storage containers, and ideally the rooms should be well ventilated to the outside environment. Thus, in the unlikely event of a venting of cryogenic gases into monitor’s about the

the imaging alarm will decreasing

room, the alert the operator oxygen concen-

tration in the room. Appropriate steps can then be taken in a timely manner to evacuate the room and ensure the safety of those in the area.

for continuous

mapping, and inin between. Patient

can

which

at a height from the

liquids

concentration.

mon-

patients,

basis of the provided by the manu-

oxygen

during

oxygen

volunteers, health care providers, or others are in the room. (We recom-

be monitored

of physiologic

to patient it is an opthe related

in this review,

portune

that while

monitor should be operating within the imaging room that houses the

patients. to be, however, a very in what is considered

practice

of

be-

ing examined.

should

propriate

if any,

entirely on the basis history of the patient

review is to address these topics and to present our opinion about the ap-

For

=

is determined the specific

be monitored;

to follow,

are used in the routine these imaging systems,

WHAT

ECG frequency.

can

of which

MR imagers with magnet systems,

examinations.

Abbreviations: RF = radio

parameters

the choice

the standard as to whom, what, and even why to monitor during clinical MR examinations. The purpose of this

itoring

sity

Art

Imaging’

MR

because authors garding

ofthe

at the

in this case) include

techniques.

manual

Many

phys-

II 1II 1111 III 11111 11111 I11111111 II 111111111 III

WHY

MONITOR

DURING During

relatively

MR

PATIENTS

MR imaging

isolated

IMAGING? the

patient

in an imaging

is

room

that

is somewhat

remote

care

practitioners;

the

from

examinations to be visually and/or verbally monitored (2-23). All patients who are sedated, anesthe-

health

closest

person

is generally in an adjacent control room. Some degree of direct visualization of the patient within the mag-

net

is often

have

video systems that permit the

try

possible.

tam visual throughout ally

built into the ganoperator to main-

intercom

have

system

that

commu-

between the patient and opSome MR systems have been with a “panic bulb,” which

nation. All these the

patient Virtu-

permits

they

measures

if he or she the exami-

inadequate

with will

for

medical care of cerpopulations. Patients voices-or weak hearinghave difficulty communicat-

weak often

ing over the noises produced imager itself. The presently

lion, nized

below).

There

least

reported

case

one

has

been

of death

monitoring

examinations

this

statement

It is good

reads practice

undergoing

The

not

at

text

clearance

letter

from

the

manufac-

Such information can also be obtained from the Freedom of Information Office of the Center for Devices and Radiological Health, Food and Drug Administration. 624

Radiology

#{149}

history and the parameters

WHOM

MONITOR

During

TO

a lengthy

nature be-

MR examination, for visual

the technolocontact with

the patient. Even if the magnet signed to allow for direct visual

is decon-

tact, the physician, technologist, nurse, nurse anesthetist, respiratory technician, or other health care pro-

to set it is to state that

vider infrequently remains in the room during imaging. Physiologic monitoring of the patient is, however, indicated in multiple circumstances. For example, increasing numbers of clinical MR examinations are being

(9,10,24-30).

For these

to be safely

complished

at current

standards

MR

or even

examinations.

several

facets

training. For must be well

of moni-

example, versed

the with

with

the

under

patient

patient

general

care,

the

sedated

anesthesia

patient

acof

should

be

the operation of the monitoring devices and should be able to recognize

appropriately monitored for possible adverse reactions to the anesthetic medications used. Monitoring of the

malfunctions entiate them

patient’s physiologic

and from

the

artifacts and true abnormal

Further,

appropriately normal from each monitored

person

at a very

the

person

differ-

must

be

trained to distinguish abnormal readings for parameter. Ideally,

would

appropriately

resonance

ing on the medical of the patient and ing monitored.

it is not uncommon gist to lose direct

in this regard,

during

includes

readings.

for all patients

radidepend-

patients tor-related individual

of

of various

gists, nurses, nurse anesthetists, ologists, or anesthesiologists,

MR

appropriate

monitoring

performed

This

2 For a manufacturer to market a device as “MR compatible” in the United States, the Food and Drug Administration has stated that the device should have undergone the scrutiny of a premarket notification (510k). To determine that a 510(k) has been cleared, the user can request a

of the

At our sites,

MONITOR

to attempt

mdi-

is

performed.

only those with appropriate training should be responsible for monitoring

be able

should

minimum,

to intervene

a problem

however,

arise;

the

in-

dividual should be aware of whom to call in the event that such an abnorma! parameter reading is exhibited by the patient. The person also should be well versed in treating and attempting to correct any significant abnormality of any of the monitored func-

vital

signs parameters

and/or

other is thus

such

mdi-

cated in multiple circumstances, cluding the following: 1. When

the

patient

in-

requires

moni-

toring

as a part of their health (eg, the patient is being monitored to undergoing

the

MR

care prior

examination).

2. When the patient is unable, for whatever reason, to respond to or alert the health care practitioners performing

the

MR

examination

about

pain, respiratory or cardiac distress, or other difficulty that might arise during the examination. Such cases would thetized

include

sedated

and/or

anes-

patient undergoing an MR study suddenly exhibits a rapid decline in oxygen saturation, the monitoring mdividual should not only be able to recognize the problem but also be able to deal with any of its potential

patients; patients cations

patients; certain psychiatric certain pediatric patients; with language or communidifficulties, especially if inter-

preters

are

causes,

ten

lions.

copy turer.

intention

monitoring

or being

physiologic parameters thus becomes the responsibility of either technolo-

as the

DURING IMAGING?

for others

nevertheless

as follows:

magnetic

our

policy

during

main

body such Administration.2

or control room with to detect and respond Indeed, we believe that

physiologic

cated

Although there are very broad standards of practice in this area, and it is

(Di!-

of patients (1).

no

by a recog-

SHOULD

PATIENTS

underwent an unmonitored MR examination and who was subsequently found to have expired during the examination from probable respiratory obstruction of a tracheotomy tube. The likelihood of such disastrous events might be decreased as we become more sensitive to the needs of the patient and limitations inherent to the normal environment of many MR imaging systems. Finally, the Safety Committee of the Society for Magnetic Resonance Imaging has put forth guidelines reMR

by appropriate

clearance

should a alone in the

this is appropriate medical practice for all MR examinations, even when

is to be

authorizing and Drug

WHO

lon W, oral communication, May 1992), a postoperative patient who

garding

and/or

Food

by the available

video systems are insufficient to observe fine respiratory motion, skin coloration, and other such health status indicators. For some patients, such as those who are sedated or anesthetized, it is simply good medicine to perform monitoring (see Whom to

Monitor,

accombe physi-

achieved by electrical and/or mechanical devices, it is important that MR compatibility (patient safety and performance of the device and the MR system) be demonstrated by prior testing, manufacturer declara-

appropriate

tam patient

monitored

ically indicated. If this monitoring

notwithstand-

are simply

and/or should

means. The specific type(s) of monitoring should be determined by the site. Suggestions include physiologic monitoring of respiration, heart rate, blood pressure, and/or electrocardiographic output, as cm-

a functional

the patient may squeeze requires assistance during

ing,

ologically

imaging room no one present to a problem.

reason, unreadily with

the imager operator panying personnel

imagers

contact with the the examination.

all imagers

nication erator. equipped

A few

tized, or, for whatever able to communicate

to the patient. At no time monitored patient be left

For example,

whether

if an anesthetized

they

are related

to

the ventilation equipment or endotracheal tube placement or are intrinsic

ing with

the

weak

have

not

readily

imaging voices

the

ager;

patients

noises

dur-

patients

or hearing,

difficulty

over

available

procedure;

who

of-

communicating produced

who

by

the

im-

are unresponsive December

1992

and/or

uncommunicative

son;

and

tential

patients

for any

with

or predisposition

and

po-

MR imaging claustrophobic

patients

pro-

receiving

con-

trast material, especially if there is a history of asthma or other allergic res-

piratory

condition

or a history

respiratory sirable oxide,

to a change

of status during the cess, such as acutely

patients

rea-

a greater

of sen-

depression,

saturation.

As another

tients

have

who

examination to watch opment of potentially

age insert; Magnevist [gadopentetate dimeglumine]; Berlex Laboratories, Wayne, Nil; revised August 1991).

need to be continued examination. Patients anesthesia will require

Patients

with

of MR

undergoing

sequences contrast

MR

being evaluated trical induction,

and

in which

the

elec-

heat deposition, audisuch imaging sequelae are understood and/or approved by the Food and Drug Administration either in general or specifically for that population or application. tory, or other not yet clearly

This list is not meant

to represent

an exhaustive compilation, to provide key examples of patient and/or volunteer

but rather of the type for whom

physiologic monitoring would be indicated. Although it may not seem practical, at sites with ready access to such vices

MR-compatible as electrocardiographs,

mographs,

amount provided.

even

deplethys-

oximeters, it might be prudent to monitor all patients undergoing an MR examination. The extra amount of effort required to hook up these devices is minimal, especially considering the extra safety

and

monitoring

pulse

of patient care and And while the pa-

general monitored

tions.

Such

include

rate,

ality

of such

equipment

starting

a patient

verbal

The

or vol-

be tested

each MR study

PHYSIOLOGIC

further

consideration

risk-to-benefit

regarding

ratio

performing monitored

to the

might

The question often arises as to what are the parameters that should be monitored during an MR imaging procedure. This question, unfortunately, cannot be answered by a sim-

in question. The vary depending tory

and

patient

what

during

the

if the

an agent

with 185

answer, on the

rather, patient

is being

example,

Volume

response, the specific

done has

a known #{149} Number

abcase

will his-

to the

MR procedure.

patient

side 3

For

be available, with might

equipment

similar

the

or ex-

another imnot require

yet might

diagnostic

pro-

information.

it is safe

to assume

standards all sedated

study,

to preclude

cer-

must be met. patients

of thermal be unable

of

any electrion the paduring the

the development

injury to which they to respond (4,5,7,21).

Much

has

been

written

the availability of numerous ing devices and the issues MR

compatibility

of such

the purpose

of this

review

regarding

monitorconcerning devices It is not

to re-

data,

so the

to note,

however,

that

multiple monitoring devices are currently available that have already been tested and found to be both appropriate and safe for use in and around high-magnetic-field-strength environments, as well as compatible with the MR imaging process itself. These include heart rate and blood pressure monitors, respiratory moni-

capnometers skin blood

and pulse flow monitors,

probes

and

oximeand

monitors.

It

is also important to recognize that some of these devices may be functional in the environment of the MR imager but should not be brought

close

to the

imager

due

to potential

ferromagnetic attractive device. Thus, while the labeled MR compatible,

that

the

device

forces on the device may be it might be

is functional

only

when operated remotely with appropriate leads (see Note to Table). It is the responsibility of the site to ensure the safety and the accuracy of the de-

vices prior to their the MR environment. sites should ensure

introduction into All clinical MR that the appropri-

ate equipment is available at their site before using MR imaging to examine a patient who might require monitor-

ing

with

such

a device.

Most monitoring equipment may be set up in such a manner that the patient can be monitored remotely, with the monitor located, for example, in the imager control (operator’s) room. This greatly assists in the efficiency of monitoring multiple functions at a single console. For sites with multiple imagers, efficiency might

also

be increased

monitoring

central using

by allowing

of multiple

for

patients

at a

console, valuable

thus more optimally personnel resources.

WHEN

TO MONITOR

PATIENTS

DURING

MR

IMAGING

may

HOW TO MONITOR PATIENTS: EQUIPMENT AVAILABILITY

(2,5,8-16,18-20,22,29,30-33).

received

effect

same

of

in an Unsuch

referring where the

In unresponsive patients, cal lead attachment sites tient should be examined

MONITOR

ple generic or absolute stractly isolated from

the vide

the

patient

the examination fashion, acquiring

monitoring equipment, patient to another site

site, for

should be monitored for, at the very least, respiratory status in light of the respiratory suppressant potential of the commonly used sedative agents.

before

on each patient.

PARAMETER(S)

TO

as

site. Conversely, if the appropriate equipment is not available at that multiple options are still available the site and patient. These include

tam minimal For example,

communications

should

and

well, of course, as on what type of equipment might be available at the

equipment

function-

rate,

being examined being performed,

recent

temperature

oxygen saturation, level of consciousness, and/or skin or body temperature. The type of monitoring that is most appropriate is dependent on the

type of patient the examination

these

reader is instead referred to the Table and to other articles for further, more specific information regarding specific makes and models of various types of monitoring equipment (9,10,29,30,33).

tors, ters,

parameters

respiratory

Nevertheless,

when

studied.

signs.

anesthesia-can be during MR examina-

erly

is being

vital

physiologic paneed to be monithose monitored

amining the patient aging modality that

at all times

the MR receiving general yet more inten-

physiologic

heart

may

during

of multiple

during safely

electro-

monitoring

Nowadays, every rameter that might tored-for example,

tient intercom and other such verbal communication devices are not often thought of as monitoring devices, it is essential that they be operating propunteer

patients,

(ECG)

present

It is important

for the devellife-threatening

In such

cardiographic

sive monitoring

imag-

(or administration agents) that are still

pamyocar-

dial infarction may already be undergoing monitoring prior to the MR

arrhythmias.

3.

example,

experienced

sitivity to the drug but the decision is still made to administer the agent (pack-

ing

it may be de-

expired carbon dirate, and/or oxygen

to monitor respiratory

Although at first glance this would seem to be a somewhat unusual question to ask-as the answer may seem to be “during imaging, obviously!” In actuality the responsibility does not necessarily end there. For cases in which sedation and/or anesthesia is needed, for example, monitoring of

respiratory

and

need to continue recovery criteria

circulatory until have

status

predetermined been met. Radiology

may

Al625

#{149}

though might

be handled

of the

department

that such recovery adequately outside

it is true

of radiology,

example,

until

the

patient

predetermined

has

recovery.

This

level

level

will

absence

or to an inpatient

is

of active

arrive

to have

these

before

the

It is also have

at the

site;

criteria

electric

voltages

established

is administered.

generally

a backup

good

plan

practice

in place

of induction,

to

before

may

more

than

electrical

tracing,

common

manifestations

arise

in whatever

monitored,

it is possible

be a sudden

from, for example, secretions. Therefore,

be available ognize

the

that

obstruction the

there

should to respond who could recproblem and perform tra-

protocols

and

indeed

this

country,

formed only

they

in the

medication.

ment

for such should

on

correct it. the issue While suggested

throughout

all must

be

Appropriate

such

Se-

possible result from

therapeutic it become

not

of the

equip-

intervennecessary,

also be available beto perform MR impatients.

DIFFICULTIES MONITORING

WITH PATIENT DURING MR

EXAMINATIONS Several

drawbacks

are

associated

with the performance of patient itoring during MR examinations. 626

#{149} Radiology

in

monFor

such

various

flow potentials

effects

on the one

of the

the

rectly of the

patient

proportional observed

need

subsequent

and

may most

to

is di-

to a worsening

T-wave elevation canso severe as to induce

conductive

should loops increase

likelihood of such an adis one reason why it suggested to coil the leads each other rather than let

(This

effect.

is often around

them lie loosely free, loops may inadvertently the bore.) rity

of each

lead,

form

or other

induced

coil,

such

current

false

should

be

on a patient the patient’s conductive

may

also

result

to the patient. conductive material

in the bore of the magnet should be kept from direct contact with the patient being studied, if at all possible. Place

thermal

including

or electrical

air, between

material and the 5. Only devices

(20) (Table)

be severe

enough to render the reading entirely useless. This is especially true during active imaging, when the RF and gra-

use

integ-

monitoring

device

loop

in thermal injury 4. Electrically

such within

insulation

surface

ECG

can

where

checked before each or volunteer. Involving tissue in an electrically

of

large might

the

verse

tested and found ble, both electrically

that

if

material

be kept from forming within the bore, which

triggering of the excitatory radio-frequency (RF) pulse. Furthermore, the gradient, RF, and static magnetic fields of the MR imager can also be associated with other distortions

con-

are followed:

3. The electrical of

the quality of a study obtained with the repetition time interval gated to the cardiac cycle (or a multiple thereof), as the rarely-be

the

(surface coil wires, ECG leads, etc) that must remain within the bore of the imaging system during imaging

before removal

is that the flow potentials so are not believed to be di-

contribute

electrically

may be diminished

guidelines

2. Electrically strength

rectly harmful to the patient, a!though they may result in the ECG aberrations noted above. Similarly, may

might into

rial

the patient from the static field, and results should be compared to assess accurately the patient’s cardiac status.

this

the

1. All electrically conductive matewithin the bore of the imaging system that is not required for the study being performed should be removed from the bore before imaging.

cardiac

to be performed to the

such

this occurring

especially for sedated or patients, ECG monitor-

MR

or other

several

to the magnitude effect; ECG lead posi-

ing may

Alternatively,

magnetic fields of the system may harm the

ductive material used in monitoring equipment while the patient is in the bore of the MR imager. The risk of

tioning can also affect the severity of the observed tracing perturbation. Such ECG tracing aberrations can also be associated with true pathologic conditions, such as myocardial ischemia, infarction, and potassium toxicity. Thus, unresponsive

in a trans-

For example, burns from power deposition

leads

ampli-

is exposed

result

patient from the RF oscillating magnetic fields used during MR imaging. This power can be concentrated in

is an eleva-

lion of the T-wave segment tude of the ECG. The static magnetic field

which

patient. result

potenon alone

Of note produced

per-

qualified

in treating that may

should of course fore a site agrees aging

been

administration

but also effects

such lion,

have

are followed

by personnel

dation adverse

own

patient’s someone

cheal suction to address and This indirectly addresses of sedation in MR imaging.

many

might

of the tube

flow

as an

may

harm.

time-varying MR imaging

of detected

induced

system

The static and fields of the may also incapac-

or torque force on the monidevice, which may itself result

in patient

the voltage, or tracing, expected the basis of cardiac physiology have

is

if a tube is status

movement in the presfield may

alteration

(34). While

to the

system

these

tials are detected

It is also reasonable to ensure that monitoring be performed when appropnately qualified and trained staff are available to respond to a problem might

lational toring

a recording

poses should be prepared initiation of anesthesia

that

imaging

whereby

voltages,

being monitored. For example, patient with an endotracheal studied and his/her respiratory

be gener-

from flow pofrom Faraday’s

conductor magnetic

the sedation is given. For example, if the patient may not sufficiently recover by the time the site is scheduled to close, the availability of overtime staffing for that site or of an inpatient site to which the patient can be readily transported for recovery purprior sedation.

as long

magnetic

produce an electric potential, or voltage, within this conductor. This is indeed the case with especially bulk blood flow, particularly as blood courses around the aortic arch. Because ECG tracing is actually nothing

it is important well

sedation

imaging,

is in a static

of an electrical ence of a static

driving from the facility or being transported by others. The time to create such protocols is before the pa-

tients

acti-

the field,

patient

also

as the patient

be deter-

the

are

a

law

to home

fields

of

discharged

whether

magnetic

itate or adversely affect the function and reliability of the measurements being reported. The static magnetic field of the MR

is particularly challengreasons. First, even in

ated within the body tentials. This results

and

dient

re-

MR suite for several

mined on the basis of multiple factors, such as whether the patient is being status

may

the ing

the

attained

satisfactory

difficulties

vated intermittently. time-varying magnetic MR imaging system

key point is not where the monitoring occurs but rather that the monitoring continue by qualified personnel

several

sult from the monitoring process itself and its interactions with the MR imaging equipment. ECG monitoring in

should advent leads this

insulation,

the

patient. that

have

conductive been

to be MR compatiand magnetically,

be used. The relatively recent and proliferation of fiberoptic on many monitoring devices

should

eliminate

much

of

concern.

The monitoring interfere with the

device(s) imaging

also may process

December

1992

Examples

of MR-compatible

MOnitOrs

and

it was believed the gradients

Ventilators

and Manufacturer

Device

Function

process

saturation

though this might yield monitoring equipment,

Heart

rate, oxygen

Omega 1400 In Vivo Research, Inc Winter Park, Florida

Blood

pressure,

Omni-Trak 3100 MR vital signs monitor In Vivo Research, Inc Winter Park, Florida MR fiber-optic pulse oximeter Nonin Medical, Inc Plymouth, Minnesota Laserfiow blood perfusion monitor Vasomed, Inc St Paul, Minnesota

Heart rate, ECG, oxygen rate, temperature

Medpacific LD 5000 laser-Doppler perfusion monitor Medpacific Corporation Beanie, Washington Respiratory rate monitor, models

Skin blood

Model

1040 pulse

oximeter International

Biochem

Waukesha,

heart

rate

brain, saturation,

capnometer

Fluoroptic model

8800

flow

Respiratory

Respiratory

thermometery 3000

Luxtron Mountain

and monitoring and/or volunteers

series

Madison,

carbon

dioxide

rate

result in image artifact At this date, however,

Percentage

of carbon

dioxide

sounds

MR

CONTROVERSIES

Several dressed

and

FUTURE areas

as areas

for

consideration

Volume

185

#{149} Number

further

regarding 3

monitoring during MR exFor example, with echoimaging

stronger

systems,

magnetic

field

a much

gradient

sub-

system is used in the MR imager, with much higher rates of change (rise and fall times) of the magnetic fields used in the imaging procedure. Such high

within

ISSUES

still need

of patient aminations.

rates of magnetic field change, by Faraday’s law, may yield electric voltage and possibly current induction

MONITORING:

AND

effects.

ductors

to be addiscussion

the

issue

there

room itself

and dur-

ventilating a pediatric with a ventilation

brings up the issue of the effects on the health care In addition to those menabove

regarding

thermal

in-

magnetic

imaging tremely

that are modulated at exlow frequency (ELF) rates.

issue

fields

the

patient

or electrical

on or in the

patient.

have

been

several

reports

con-

Indeed, of

muscle twitching associated with the use of such imaging equipment, and

is highly appear

The

used

of extremely

electromagnetic

planar

is

its

cillating

This

physiologic monitors for various parameters have been shown to function without interfering with imaging and do not degrade the quality of the images obtained while the patient is being monitored.

and

jury potential and electrical current induction, there is also the possible interactions and effects of the RF os-

Ventilator

generation numerous

technique

physiologic

bag) and potential provider. tioned

Heart

this

while manually or infant patient

Note.-Adapted from reference 29. Note that these devices may require modifications to make them MR compatible, and none of them should be positioned closer than 8 ft (240 cm) from the entrance of the bore ofa 1.5.1 MR imager. Also, moulton with metallic cables, leads, or probes may cause mild to moderate imaging artifacts if placed near the imaging area of interest Consult manufacturers to determine compatibility with specific MR imagers.

and (29).

about

ing the imaging process. Such an mdividual could be exposed to the timevarying magnetic fields used during the MR imaging process. Although this situation would be highly unusual, it is theoretically possible (eg,

Wisconsin

Los Angeles, California precordlal stethoscope Anesthesia Medical Supplies Santa Fe Springs, California

of such patients continue as more

main within the imaging indeed within the magnet

Ventilator

Wenger

or neuregions

rate, end-tidal

Ventilator

Infant ventilator MVP-10 Bio-Med Devices, Inc Madison, Connecticut Datex carbon dioxide monitor Puritan-Bennett Corporation

is

Another case to consider is when a health care provider (eg, nurse anesthetist or anesthesiologist) must re-

Ventilator

D

Columbia Medical Marketing Topeka, Kansas Ventilator, models 225 and 2500 Monaghan Medical Corporation Plattsburgh, Pennsylvania Anesthesia ventilator Ohio Medical

When

material

potential

Temperature

system,

function.

rate

View, California

0mm-Vent,

cardiac

also nerve,

within the patient, such as pacing leads, the potential

learned

Biochem International Waukesha, WiscOnsin Aneuroid chest bellows Coulbourn Instruments Allentown, Pennsylvania

in

it might effects on

and structures with as yet unknown sequelae. It is recommended that, as this is an area of intense development and growth, appropriate screening

Skin blOod flow

Respiratory

Al-

artifacts

exists for electrical excitation ral stimulation of physiologic

Oxy gen saturation

from

(35,36).

conductive

present epicardial

respiratory

devices

physiologic

and/or

electrically

and 525 Biochem International Waukesha, Wisconsin MicroSpan

of such

produce

Wisconsin

515

to result directly used in the imaging

low

radiation

reader

frequency

and

controversial to have

and

been

in MR

safety

does

resolved

is referred

not yet.

to several

re-

view articles on this matter for further information (37-39). Suffice it to say at this point that a case in which the health care provider moni-

toring the patient is not only room but within the magnet during imaging for extended of time

is extremely

majority

of cases,

should

be safely

rare.

in the itself amounts

In the

vast

patient

monitoring

achievable

from

ei-

ther outside of the imaging room remotely or from within the imaging room and outside of the imager itself, where

the

time-varying

magnetic

field exposure is an exceedingly small fraction of that in the magnet bore during imaging. Finally, there is the rather controversial issue of whether all patients receiving intravenous contrast agents Radiology

#{149} 627

should be monitored for possible verse reaction. While it is indeed that there have been some serious and even one fatal reaction to the administration of gadopentetate dimeglumine,

the

present

data

adtrue

appropriate

adverse

reactions

fects of the appropriate

sug-

of any

to ensure

that

at are be

adequate

function

be reserved

known

asthma

ratory whom other

condition, monitoring reasons.

MR

for those

or other

allergic

us that

for

we are al-

ways responsible, both ethically as well as legally, for all controlled examinations (eg, MR examinations) that we perform or prescription medications (such as MR contrast agents) that we administer. Thus, because there is always the potential for adverse reactions during or after an MR

examination

(eg, RF burns,

noise-related

injury,

untoward

auditory ferro-

interactions, drug reactions), a physician responsible for that study and its contrast material orders should be available for rapid response should any difficulty arise during the study. Further, especially as a very significant percentage of all examinamagnetic

Note that not all gating electrocardiographs provided by the manufacturers of the MR equipment may be adequate for use as a heart rate monitor. Indeed, some manufacturers of MR equipment specifically exclude such patient monitoring objectives from the listed capabilities and appropriate uses of that piece of equipment. It may be necessary to purchase an MRcompatible plethysmographic or other such heart rate monitoring device that has been shown to function reliably and safely within the MR environment. 3

628

Radiology

#{149}

the

particular may

is the

first

Fur-

with

the

moni-

and

their

appropri-

step

to determining

which may be most appropriate each patient or application. Because a potential side effect

thetic sion,

used

agents patients

regardless amount),

sure

sedatives

for of all

or anes-

is respiratory depresreceiving such agents,

of type or route (or should be monitored

an adequate

ventilatory,

for pulse oximetry, a de facto standard of anesthetized

even to en-

respiratory, not just Thus, equipment which has become for the monitoring

status.

patients,

would

be

of oxyhemoof deoxyhe-

moglobin present in the circulating blood. It is possible, however, for adequate blood oxygenation to continue for a limited amount of time in the absence of continued good respiration. An expired, or end-tidal, carbon dioxide monitor, measuring via nasal prongs the

amount

pired sitive

of carbon

air, would for detecting

tion than would Indeed, a pulse oxygen saturation

dioxide

oximeter. measuring not demon-

per se until if the patient

cold,

peripheral

secondary

constriction,

or if the

nificant peripheral poor peripheral

patient

vascular flow, the

late is vaso-

has

sig-

disease accuracy

or

and performance of the pulse oximeter might be deleteriously affected. Thus, ideally, if money to purchase the

necessary

ject, carbon

monitoring dioxide

complement

equipment

were

end-tidal would

to pulse

no

ob-

measur-

output of oxy-

measurements monitor are

of all.

gross feasible

Essentially,

chest that

airway

prothe these

wall motion. It is, a patient with an may

be making

great respiratory efforts and moving the chest wall substantially while in actuality failing to ventilate or oxygenate at all. An adequate heart rate monitor-s should also be available at MR sites, in our opinion. Not only would heart rate be a useful vital sign to monitor in patients receiving any type of sedative or anesthetic agent, but it would also be most useful for general monitoring of anxious or more clinically unstable patients or patients for whom it might be advisable to closely follow their vital functions. Ideal situations would also provide for the ability to monitor and measure patient’s

blood

pressure,

be a superb

as the

may be specific

as well

to

legal

re-

for any given site regardstandards of care and re-

sponsibility

for

adverse

or even

incidental reactions or problems that may occur while the patient is in the MR imager. This is especially true for “routine,” stable, nonsedated outpatients.

Each

site

should

with these requirements ting individual policies ble, nonsedated, adult 3. For requirements

sedated are

be familiar

before regarding outpatients.

patients, markedly

setsta-

however, different.

At a minimum, pulse oximetry should be considered the appropriate monitoring technique of choice for such patients. In fact, our recommendation is to use workhorse

(expired)

oximetry,

helpful

for

of adequacy

genation. Finally, vided by an apnea

2. There

in ex-

strate hypoventilation in its course. Further, with

a measure

quirements ing local

actually be more sendepressed ventilaa pulse oximeter may

is more

the

(ie, gas lungs) by

monitoring the amount globin versus the amount

sensitive

ensure that blood pressure is neither precipitously decreasing, due to vasovagal responses or true hypotensive episodes (drug related or otherwise), nor dangerously increasing (from anxiety, pain, drug reaction, etc). The following, therefore, are our own opinions about what equipment and procedures might be considered appropriate for patient monitoring in MR imaging environments: 1. Visual and verbal or auditory contact with the patient should be maintained throughout the examinalion. At all times it should be possible for a patient experiencing distress to signal and notify a supervising health care practitioner about the difficulty being experienced.

ideal to have at any site where such sedation and monitoring may be done. Not only does it provide very coarse data regarding the heart rate, but it provides information regarding the adequacy of respiration exchanges in the patient’s

adequacy of ventilation, the pulse oximeter’s

obstructed

be significant.

about

is more

ing the whereas

measure in fact,

associated

more

equipment

former

least

even

site.

expense

selection(s)

commonly

The question of what may constitute appropriate monitoring of outpatients in an exclusively outpatient imaging center is a rather difficult one to resolve definitively. One argument is that stable patients whose condition is not acute should not require monitoring with special equipment. Nevertheless, a perhaps equally convincing

reminds

for any

thermore,

ate use

MONITORING: PRACTICAL RECOMMENDATIONS

argument

needed

toring

respi-

or for those for was requested

to site and

large selection of MRmonitoring equipment

Understanding

with

constitutes however,

presently available, it can be confusing to determine what equipment is

the

medical personnel are readily available to handle any potential adverse reaction that might occur, but that monitoring of respiratory or cardiac

performed for the serious side ef-

from site to case.

With the compatible

the use agent,

monitoring

agent. What monitoring,

may vary from case

sever-

ity to gadopentetate dimeglumine, approved doses, are rare, averaging less than 2% (40). Severe reactions even more rare. It might therefore appropriate

patient

should be routinely rare but potentially

gest that this drug is as safe as-or safer than-many of the iodinated agents that we have been using for years in diagnostic radiologic practice. In fact,

tions are now performed with of an intravenous MR contrast

a day-to-day

the

pulse oximeter as the of sedation monitoring

basis.

Expired

on

carbon

December

1992

dioxide

monitoring

technique,

is the

and

an

should

be considered

of such should

monitoring not be used

patients

ing

as the

the

status

best

the lowest

only

by-case

monitor

and, alone

level

frankly, in sedated

means

ventilatory

and

of sedated

next

apnea

of ensur-

respiratory

or anesthetized

pa-

tients. In addition, heart rate monitoring equipment should also be required. To reiterate, we believe that it is not unreasonable to perform MR examinations with routine and mild sedation with the basic equipment of an MR-compatible pulse oximeter and

heart priate ment).

rate monitor emergency

(as well as approresuscitation equip-

4. In an ideal should

be able

bon

dioxide

addition

and

blood

to heart

of respiration try), while

and

configuration,

a site

to monitor

expired

car-

pressure,

rate

and

in

adequacy

(ie, with pulse oximekeeping in constant visual

auditory

contact

Of incidental note, found it necessary

with

the patient.

we have

not

to monitor either flow or heart sounds per se for routine clinical patient care. 5. For truly anesthetized patients, we choose to leave all choice of sedation agents, MR-compatible monitoring devices, and postsedation orders to the anesthesiologist. We communi-

skin blood

cate

prospectively

such

issues

as the

anticipated length of the study anesthesiologist to assist in the tion of an appropriate anesthetic sedation agent and dose.

6. In the recovery tion has ended, the

should

to the selecor

room, after sedasame equipment

be available

as noted above. In addition, a resuscitation cart should also be available to ensure adequate coverage for incidental problems in the site’s patient population (eg, arrhythmias, myocardial infarction), as

well as possible, albeit rare, adverse reactions to MR contrast agents. CONCLUSIONS Different levels

ing

patients

of monitoring

procedures.

servation surances rameters closely The

level

MR

imag-

simple

ob-

intermittent all is fine

multiple

verbal will suffice.

physiologic

will need to alert the

ble deterioration

varying

during

For some,

and that

For others,

require

must

Volume

185

by

of any

that

be determined

#{149} Number

vital

cally

indicated.

3

on

the

18.

his-

safety

when

their

afforded

use

19.

20.

Shellock FG, Myers S. Kimble K. Monitorin heart rate and oxygen saturation during MR with a fiber-optic pulse oximeter. AIR 1991;

21.

Shellock FG, Slimp C. Severe burn of the finger caused by using a pulse oxiineter during MR imaging (letter). AIR 1989; 153:1105. Wendt RE, Rokey R, Vick GW,Johnston DL. Electrocardioaphic gating and monitoring durinNMR imaging. Magn Reson Imaging

158:663-664.

from

is medi-

22.

#{149}

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Smith D, Askey P. Young M, Kressel H. Anesthetic management of acutely ill patients during magnetic resonance imaging. Anesthesiology 1986; 65:710-711. Rokey R, Wendt R,Johnston D. Monitoring of acutely ill patients during nuclear magnetic resonance imaging: use of a time-varying filter electrocardiographic gating device to reduce gradient artifacts. Magn Reson Med 1988;

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Kanal E, Shellock FG, SMRI Safety Committee. Policies, uidelines, and recommendations for MR imaging safety and patient management. JMRI 192; :247-48. 2. Barnett C, Ropper A,Johnson K. Physiological support and monitoring of critically ill patients during magnetic resonance imaging. Neurosurg 1988; 68:246-250. 3. Dimick R, Hedlund L, Herfkens R, Fram E, Utz J. Optimizing electrocardiographic electrode placement for cardiac-gated magnetic resonance imaging. Invest Radiol 1987; 22:17-22. 4. ECRI. A new MRI complication? Health Devices Alert 1988; May 27(1). 5. ECRI. Thermal injuries and patient monitoring during MRI studies. Health Devices Alert 191; 20:362-363. 6. Edelman R, Shellock FG, AhladisJ. Practical MRI for the technologist and imaging specialist. In: Edelman R, Hesselink J, eds. Magnetic resonance clinical applications/advanced techniques. Philadelphia: Saunders, 1990; 39-73. 7. Kanal E, Shellock FG. Bums associated with clinical MR examinations (letter). Radiology 1990; 176:593-606. 8. Legrendre J, Misner R, Frester GV, Geoffrion Y. A simple fiber-optic monitor of cardiac and respiratory activity for biomedical magnetic resonance applications. Magn Reson Med 1986; 3:953-57. 9. McArdle C, Nicholas DA, Richardson CJ, Amparo EG. Monitoring of the neonate undergoing MR imaging: technical considerations. Radiology 1986; 159:223-226. 10. Karlik SJ, Heatherley T, Pavan F, et al. Patient anesthesia and monitoring at a 1.5 T MRI installation. Magn Reson Med 1988; 7:210-221. 11. Rejger VS, Cohn BF, Vielvoye GJ, de-Raadt FB. A simple anesthetic and monitoring system for magnetic resonance imaging. Eur J Anesthesiol 1989; 6:373-378. 12. Roos CF. Carol FE. Fiber-optic pressure transducer for use near MR magnetic fields. Radiology 1985; 156:548. 13. Roth JL, Nugent M, GrayJE, et al. Patient monitoring during magnetic resonance imaging. Anesthesiology 1985; 62:80-83. 14. Selden H, De Chateau P, Ekman C, Linder B, SaafJ, Wahlund LO. Circulatory monitoring of children during anesthesia in low-field magnetic resonance imaging. Acta Anesthesiol Scand 1990; 34:41-43. 15. Shellock FG. Monitoring sedated patients during MR imaging (letter). Radiology 1990;

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Acknowledgment: The authors thank Carolyn Gillen, RN, for her invaluable assistance in the compilation of some of the data used in the preparation of this article.

pa-

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depending

additional

devices

16.

on a case-

the

such

to be monitored physician to possi-

of monitoring

quired

as-

basis,

tory and situation at hand. All levels of patient monitoring during MR examinations, however, can be readily accomplished with equipment that has been tested and found to be cornpatible with such environments. The additional expense, training, and efforts necessary to achieve quality patient monitoring is more than offset

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Radiology

#{149} 629