Chapter 30 Equipment for the Magnetic Resonance Imaging Environment P.872

Magnetic resonance imaging1 (MRI) is a noninvasive diagnost ic procedure tha t can

produce superior images wi thout us ing ionizing radiat ion. MRI s tudies are not

painful but do require patient immobili ty. Patien ts who are unab le to hold sti l l of ten

require sedation or genera l anesthesia. Med ically uns table patients such as those

f rom in tensive care may need scann ing. A more recent development is the use of

MRI to guide and moni tor inte rventional procedures (1 ,2,3,4,5,6). MRI-guided

procedures may resul t in smaller inc is ions as wel l as more accurate local ization

and t issue retrieval .

Administering anesthesia in the MRI un it poses a number of technical dif f icult ies.

Knowledge of this envi ronment as wel l as i ts r isks and problems are essential for

safe anesthesia pract ice. The prac tice guide lines for anesthesia care and

moni toring developed by the American Soc iety of Anesthes iolog ists and the

American Associat ion of Nurse Anesthetis ts apply to the MRI env ironment just as in

other parts of the hea lth care fac il i ty (8). In some states, these guidel ines are

codif ied in to law (9).

Definitions A device is considered to be MR safe if i t presents no addi tional risk to the patient

or operator. The presence of such a device may affect the quali ty of the diagnost ic

info rmation when i t is p laced in the MR environment (10,11,12,13,14).

A device is MR compatible i f i t is MR safe, its use in the MR environment does not

s ignif icant ly affect imaging quali ty, and there is no s ignif icant effect on its

operations. A device may be MR compatible or safe fo r certain MR environments

but not o thers. Therefore , using the terms MR compatib le and MR safe wi thout

specif ica tion of the MR environment to which the device was tested should be

avoided. The term MR environment is used to desc ribe the area wi th in the 5-gauss

l ine around the scanner (the perimeter around an MR scanner wi thin wh ich the

stat ic magnet f ie ld is higher than 5 gauss).

Basic Principles

There is a s tat ic magnetic fie ld ins ide the MRI scanner bore

(7,13,15,16,17,18,19,20,21,22,23). Once the magnetic f ield is establ ished, it is

usual ly no t tu rned OFF. If the magnet is deactivated, i t can take up to 96 hours to

reestabl ish the magnetic f ie ld. The un it of measurement of magnetic f ie ld s trength

is the Tesla. A field of 1 Tesla is roughly 10,000 times the magnetic field at the

earth's surface. One Tesla equals 10,000 gauss. The strength of a magnet is

quant if ied in the midd le of the magnet. However, the f ie ld ex tends beyond the

margins of the magnet (the fr inge f ield), dec reasing in strength with distance f rom

the bore.

Atomic nuclei wi th an odd number of protons and/or neutrons have a spin that

produces a weak loca l magnetic f ie ld. In the absence of a strong magnetic f ie ld,

these nuclei are randomly aligned. A strong magnetic f ie ld causes approximately

half of them to rotate and al ign para llel to th is appl ied f ie ld (the low-energy, or

ground, state). The remain ing nuclei align against the appl ied f ield (the high-

energy, or exci ted, s tate).

Resonance describes the process of inducing a change in energy s tates of the

nucle i caused by absorpt ion of a specif ic radio frequency (RF) radiation . Adding

energy wi th a short, control led burst of RF energy causes some low-energy

(parallel ) sp ins to jump to the exci ted (ant i -paral lel ) energy level . Immediately after

the RF pulse, the nuc le i ro tate back into al ignment wi th the static magnetic f ie ld. As

they re turn to their orig inal orienta tion, energy is released. A receiver coi l detects

this weak electrical s ignal and ampl if ies i t fo r processing and eventual image

formation. Re laxat ion rates vary fo r specif ic body t issues , al lowing d if fe rentiat ion of

body structures.

Facility Design A member of the anesthesia department should be involved in p lanning the MRI uni t

(24,25). An anes thesia induction room that adjoins the scanning area is useful . The

anesthet ic can be in it ia ted at this locat ion, where ferromagnetic objects can be

safely used. The anesthet ized patient can then be moved into the scanning area.

Consideration should be given to plac ing a postanes thesia care room near the MRI

unit .

Wave gu ides, special ly designed condu its in the wal ls , can be used to pass pipes ,

cables, ducts, tubings, and electrica l wires through the wal l whi le maintaining RF

sh ielding (26,27) (Fig. 30.1). They are commonly p laced low in the room at the

farthes t point f rom the magnet and RF coils.

Fluorescent l ight ing emits RF energy that inte rferes with imaging (21). Therefore,

incandescent l ight ing a t a low wattage is used. Isola ted e lec trical power is used to

reduce the problem of leakage currents (10). I t is important that there are an

adequate number of elec trical plugs a t convenient locat ions for portab le mon itors

and o ther equipment.

There are four bas ic op tions for locating moni to ring and other equipment tha t is

used to administer anesthes ia or sedation and the person attending the monitors

and patient:

P.873

View Figure

Figure 30.1 Wave guides are used to pass cables, tubings, sires, and the like through the wall while maintaining radio frequency shielding.

• Both the monitors and the attendant a re ins ide the magnet room. This allows

di rect observat ion of the pat ien t. The attendant can both see and hear the

moni tors , but the attendant is subject to possible hazards (loud sounds,

magnetic forces, and possibly trace anes thetic gases or hypoxia). I t may be

necessary for the attendant to be in the room when there is an inabi l ity to

see the pat ient, particula rly if the pat ient has entered the scanner headfi rs t

and/or the patient is a child (28).

• The monitors are ins ide the room wi th the attendant outs ide. The pat ien t and

moni tors can be v iewed through a window or by us ing a telev ision camera.

Light-emitting diode (LED) d isp lays are usual ly easier to read from a

distance than l iquid c rystal displays (21). Remote auscul tation using

special ly designed equipment can be used to moni to r heart and respiratory

sounds (29). A drawback is that moni tor sounds and a la rm s ignals may not

be heard wel l by the attendant.

• The thi rd op tion is to have the moni tors ou ts ide and the attendant ins ide the

room. Mos t equipment can be kept ou ts ide the scanner room wi th cables and

such running through wave guides (30,31). The a ttendant can observe the

moni tor through a window or a te lev is ion screen but cannot hear moni to r and

alarm sounds we ll .

• The last opt ion is to have both the monitors and the attendant outs ide the

room. The a ttendant can see the monitors and can hear the alarms and

sounds but cannot observe the patient wel l.

I f the a ttendant is outs ide the room, he may fai l to detect dangerous s ituat ions in a

t imely manner (32). There is a report of a pat ient dying during an MRI procedure

when the pneumatically-driven venti la tor ran out of oxygen (33). MRI auditory alarm

s igna ls need to be much louder than those used in the operat ing room due to the

s ignif icant scanner noise .

Problems I t is important to note that some dev ices tha t are s ta ted to be MR compatib le have

l imi ta tions or res tric tions to the ir use in the MR environment, and if they are not

used in accordance with these restric t ions/ l imitat ions, they can pose the same

types of hazards as devices that are no t MR compatible (14,34).

Ferromagnetic Materials All materials can be c lassif ied as ei ther paramagnetic o r diamagnetic

(7,15,16,17,18,21,22,27,35,36,37,38,39,40,41,42). Paramagnetic materials a re

weakly a ttracted and diamagnetic materials are weakly repel led by magnetic f ields.

Ferromagnetism is an extreme form of paramagnetism exhibited by a small g roup of

materials that are powerfully attracted to magnetic f ie lds. Ferromagnetism is shown

by devices conta in ing i ron, i ron oxide, i ron-containing a lloys , nickel, and cobalt

(43).

Depending on the conf igurat ion of the magnetic f ie ld and the shape and mass of the

object and i ts posi tion wi thin the magnetic fie ld, these forces can result in

rota tiona l (torque) and/or translationa l (a ttractive) motion of the object.

Ferromagnetic Materials External to the Patient

The attrac tive force exerted on a ferromagnetic object depends on the distance

between the object and the center of the magnet, the mass and geometry of the

object, the strength of the magnet, and fac tors that modify the f ie ld configurat ion

such as magnetic shielding.

The attrac tive force inc reases rapidly as one nears the magnet and can be several

t imes that of the earth's gravi ta tiona l f ie ld by the t ime i t reaches the center of the

magnet. When free, ferromagnetic objects can move toward the magnet center wi th

dangerous speed (“missi le ” or “pro jec ti le” effect). Th is can resu lt in equ ipment

damage as wel l as serious injury to pat ients and/or workers trying to restrain the

equipment or trapped between the equipment and the magnet (14 ,44,45). Since the

magnet is cont inuously ON, it can attract ferromagnetic devices even when no

imaging is occurring . In addit ion,

P.874

s ignif icant masses of ferromagnetic material in proximi ty to the magnet can disturb

the homogenei ty of the s ta tic magnetic fie ld, resul t ing in dis torted images .

Ferromagnetic parts may work loose over t ime, so precautions should be taken

during product design to prevent the inclusion of components that could be pulled

loose and attracted to the magnet bore (10). Removable equ ipment covers should

use capt ive hardware (e.g., screws and fasteners ).

There are hundreds of fe rromagnetic objec ts that must be kept out of the MRI room.

These inc lude personal i tems (watches, sc issors, keys, paper c lips , nai l cl ippers,

hairpins, calculators, ident if icat ion badges , c igarette l ighters, s teel-t ipped/hee led

shoes, pens , jewelry, c lipboards, pagers, cell phones, f irearms, e tc.); pat ient i tems

(strap buckles, safety pins , jewelry, zippers, metal gown fasteners, contracept ive

diaphragms, cosmetics containing metall ic part icles (such as eye makeup), sk in

staples , superf ic ia l metall ic sutures, RF tagging brace lets, metall ic handcuffs or

ankle cuffs , e tc .), and medical dev ices (s tandard gas cylinders, hemostats,

needles, v ia ls , s te thoscopes, chest tube stands , in travenous po les, s tre tchers,

wheelchairs , mobi le s tands, carts, anes thesia machines , vaporizers, monitors,

defibri l la tors, sandbags, tract ion weights, etc.) as wel l as mop buckets, vacuum

cleaners , laundry carts, chairs, ladders, l ight f ix tures, f loor buffers, and parts of a

fork lif t (12 ,38,39,40,46,47,48,49,50,51). Non-l ithium batteries are strongly

magnetic .

The presence or absence of ferromagnetism in a given object depends on a number

of fac tors, including i ts composit ion and manufac ture. Some objects tha t are

ferromagnetic may sti l l be safe because their mass is too small for the forces

involved to be s ignif icant and/or because they are fi rmly anchored in posi tion at a

safe distance f rom the scanner. One method is to anchor a ll devices that have

ferrous material to a movable cei l ing pendant system with a predetermined l imited

range of motion (24). Even wi th a reduced ferrous load, some delicate instruments

are sti l l ferromagnetic and subject to to rque tha t can cause serious damage.

Therefore, al l equipment that is no t required should be removed f rom the s ite.

Equipment may be posi tioned away from the magnet, in a room adjacent to the MRI

room with tub ings and wires used to connect to the patient. The safe distance from

the center of the magnet depends on field strength and shielding. I t is usually

considered to be greater than the 5-gauss l ine (12). Equipment containing

ferromagnetic components should not be a llowed past the 5-gauss l ine unless i t has

been labeled MR safe for that specif ic MR environment.

All persons entering the scan room must be rigorously sc reened for inte rnal and

ex ternal ferromagnetic material . Prominent warning s igns should be pos ted. MRI

centers should keep registers of commonly used devices and whether they are safe

to bring in to the magnet room. The use of metal de tec tors in MR env ironments may

help, but is not recommended by the American Col lege of Rad io logy (49).

Nonambulatory patients should be brought into the MR uni t by using a nonmagnetic

wheelchair or wheeled stretcher and transport equipment checked fo r magnetic

objects (12).

Materials considered safe in the MRI scanner sui te inc lude aluminum, brass, nickel ,

plast ic , t itanium, copper, bery ll ium, s i lver, and gold (43,52). Certain types of

s tainless steels are considered safe, but others are strongly a ttracted in the

magnetic f ie ld (11,38).

Battery-powered equipment shou ld be tested at i ts intended locat ion and maximum

f ield strength to ensure that there is no s ignif icant attract ion . A magnet can be used

to tes t equipment going into the MRI room (53). Mos t inst itut ions have a cardiac

pacemaker ring magnet, and this can be used.

Ferromagnetic screening does not evaluate the potent ial for RF-related pat ien t

injury (53). Nonferromagnetic metals (e .g., aluminum or copper) that would y ield a

negat ive magnetic screen can absorb RF energy, resu lt ing in MR image art ifact or

thermal inju ry to the patient.

Implanted or Inserted Ferromagnetic Objects

Ferromagnetic objects wi thin the patien t are subject to fo rces tha t try to bring them

into alignment wi th the magnetic field. The extent of injury wil l be affected by the

magnetic f ie ld strength, ferromagnetism of the objec t, the objec t's geometry and

orienta tion, the loca tion of the objec t in s i tu, and the length of t ime the object has

been indwel l ing (f ibrosis or granulat ion t issue can serve to s tab il ize the object).

There are documented cases of death and blindness resul t ing f rom MR imaging of

patients with fe rromagnetic in tracerebral aneurysm clips, cardiac pacemakers, and

c linical ly occul t metal l ic in traocular (39,54,55,56). MRI is contraind ica ted for a

patient wi th shrapnel located in a biologically sens it ive area. I t cou ld move and

injure the pat ient (10). People in certain occupations, such as sheet metal workers,

are at risk of having magnetic f ragments in their bod ies and in many cases are not

aware of thei r presence (39). Now tha t MR imaging is a f i rmly establ ished

diagnost ic modality, efforts are being made to use magnetical ly compatible

subst itutes fo r previously uti l ized ferromagnetic implants (39). For example , most

new cerebral aneurysm clips are made of nonferrous material (52).

The Food and Drug Adminis trat ion (FDA) requires that MR imagers be labeled to

indicate that the device is contraindicated fo r pat ients who have electrica l,

magnetic , or mechanical implants because the energies produced by MRI systems

may interfere wi th the opera tion of these devices (57). The composi t ion of the

device and i ts magn itude of magnetic def lection should be determined before these

patients are scanned. These

P.875

devices inc lude pacemakers , cardioverter-def ibri l lators, elec tromechanical infus ion

pumps, cochlear implants, neurostimu lators, bone-growth st imula tors, dental

implants, bul lets, magnetic sphincters , magnetic stoma plugs, magnetic ocular

implants, t issue expanders wi th magnetic posts , and magnetic pros thetic appl iances

(57). Problems may also occur with magnetic objects that are attached to the

patient 's body (e .g ., body pierc ing) (12).

Equipment Malfunction Magnetic inte rference can cause computer o r oscil lometric images to be distorted

(7,21,27,58,59). Devices wi th rechargeable batteries may swi tch off and blank their

sc reens. MRI interference also causes transformers to become saturated and burn

out. RF pulses are also capable of inducing electrical eddy currents and short

ci rcui ting electrical equ ipment. The magnetic f ie ld may cause damage or erase data

on magnetic media such as digi tal tapes or f loppy disks.

Equipment may conta in pumps, e lec tric motors, elec tronic ci rcuitry , or analog

gauges that a re affected by the magnetic f ie ld (10). The magnets in motors may

become saturated. This can result in lack or s lowing of motor operation or

increased operat ing current, which could u ltimately burn the motor out.

There are two general methods to solve this p rob lem: locate the equipment ou t of

the magnetic f ie ld or make the equipment compatible wi th the magnetic f ie lds.

One way to make equipment MRI compatib le is to shield moni to rs and cables f rom

RF currents . Cables can be wrapped wi th a th in layer of aluminum fo il , and small

copper boxes can be used to house electrical equipment. Using appropriate RF

f il te rs in the magnet shie lding and iso la ted f i l tered a lternat ing-current power

c i rcui ts may permit effec tive monitoring (58).

Moni tors special ly designed for use in the MRI uni t combine low ferromagnetic

content, shielding, and f i l ters to min imize magnetic f ie ld inte rference. These

devices may have some limi tat ions to their use in the uni t. It is important tha t prior

to use, manufacturer dec laration and/or clearance by a recognized body such as

the FDA demons trates MR compatibil i ty .

Image Degradation Equipment can degrade the qual i ty of imag ing in two ways (7,10,17,27,30,58,60).

Fi rs t, ferrous meta l in mon itors and other equipment can cause distu rbances in the

magnetic f ie ld. Second, the equipment may genera te s ignals that interfere with the

MRI s ignals .

Any RF energy within the bandwidth of the rece iver, inc luding stray radiation f rom

outside RF sources, is amplif ied. Sources of RF noise include electrical machinery,

motors, computer hardware, disp lays, telev is ion transmitters , beeper-paging

systems, two-way rad ios, commercial rad io stat ions, and other electrical equ ipment.

I t is common practice, therefore, to enclose the scann ing area in an RF shield.

Nonconduct ive devices can safely be passed th rough the shield , but wires that

transgress the shield can ac t as aeria ls and feed noise from the ex ternal

environment into the examination area. This can be overcome by f i l tering wires that

run in and out of the sh ield. Care mus t be taken to match f i l ters to specif ic

moni tors .

To prevent RF in terference from degrading the MR image, appropriate measures to

provide sh ielding, such as housing the display in a RF-t igh t enclosure or locat ing

the uni t outside the room, shou ld be used. In ei ther case, the connect ions between

the display uni t and the patient should pass through f i l ters tha t attenuate

f requenc ies around the imaging f requency. All electrically conduc tive material tha t

is not required shou ld be removed f rom the MRI system bore .

The distance from the magnetic core necessary to prevent RF interference varies

wi th the strength of the magnet. Severa l meters be tween the scanner and other

equipment are usually necessary. This dis tance can make it dif f icult to read and

inte rac t wi th the equipment. Long spl iced l ines and tubings may disconnect, impose

high resistance, or become obs tructed.

Another solut ion is to adjust the frequency of the noise source so that i t is outs ide

the MRI-receiver system bandwidth. This can of ten be accomplished by adjust ing

the block that controls the operation of the microprocessor in the monitor.

Once the examination has started, the pos ition of the moni to ring equipment should

not be changed, because reposit ioning of a la rge metal l ic mass may degrade

magnetic f ie ld homogeneity.

Burns Apply ing intermit ten t RF f ields to metal lic objec ts wi th in the imaging area can

cause heating and resu lt in burns (7 ,10,16,26,48,57,59,61,62,63,64,65,66).

Equipment of p rimary concern is tha t which may be posit ioned di rect ly in the RF

transmission f ield. Th is includes electrocard iogram (ECG) electrodes and leads,

pulse pickup and pu lse oximetry sensors and cables , halo dev ices, and surface

co ils as wel l as metal lic components, connectors, and surface coils . These can

provide a path fo r curren t f low th rough the patien t or along the cab le sh ie ld to

ground. If this current is not l imi ted, patient burns can resul t at the loca tion of

equipment or at body parts located next to an insuff icient ly insulated RF shield.

Other devices that uti l ize a wire such as thermodilut ion Swan-Ganz ca theters or

epidural catheters can also sub jec t the patient to electric shocks or dangerous

heating (43).

Burns may also occur f rom contact wi th the scanner bore. High duty cyc le

sequences cause heat to bu ild up

P.876

on the ins ide of the bore. Burns can be minimized by using the fo llowing measures:

• Electrica lly-conduct ive leads should be replaced with nonconduct ing paths

(e.g ., f iberopt ic cable or plast ic tubing) o r high-res is tance paths (e.g ., carbon

ECG leads).

• Electrica lly-conduct ive material (ECG leads, cables, e tc .) that must remain

wi th in the MR system bore should be pos it ioned to prevent “cross po ints.” A

cross poin t is where a cable c rosses another cab le , loops ac ross i tself , or

touches ei ther the patien t or s ides o f the magnetic bore more than once.

When the patient is moved, wires may coil and fo rm a loop, so i t is important

to check a ll wires each t ime the pat ient is moved.

• Cables and sensors should be kept away f rom the bore (e.g., by plac ing a

pulse oximeter sensor on the pat ient's toe when the head is being

examined).

• All sensors, wires, and cables should be checked to ensure that the electrical

insulat ion around them is intact. A small towel should be placed between the

patient and the wires or cab le to avoid contac t wi th the skin.

• All unnecessary conduct ive materials such as unused wires, leads, sensors,

cables, and surface coi ls should be removed f rom the MRI envi ronment.

• All electrica lly-conductive material that must remain in the MR system bore

should be kept from direct ly contacting the patient by placing thermal and/or

electrical insulat ion (inc luding ai r) between the conductive material and the

patient. Wires should not cross metall ic prostheses.

• Cables should be pos itioned so that they exi t as c lose as possible to the

center of the pat ient table of the MR system (63). I t is a lso important to avoid

cable contact wi th the sk in or the MRI scanner.

• Conscious patients should be ins tructed to call out if they experience

uncomfortable heat levels so that the procedure can be immediately

discont inued.

• Any monitor that does not appear to be operating properly during the MR

procedure should be removed.

• A cold compress/ice pack should be placed along skin stap les , superf ic ial

metall ic sutures, and lead attachment s ites, if this can be safely

accomplished (49).

Hypothermia

Hypothermia can be a problem, especial ly with smal l children (27). Ai r is often

c i rculated over the patient during the imaging sequence. Covering the patien t,

warming f luids, and using non-electrical heating pads and humidif ied inspired gases

can help to prevent hypothermia (52). Heating blankets and radiant l ights cannot be

used because they inte rfere wi th imaging.

Other Patient Problems Loud sounds in the MR environment may obscure cries for help from a patient in

dis tress (9). The patien t should be given a squeeze bal l to sound a distress signa l,

but this is of l imi ted usefulness in the sedated patient.

A major problem for anesthesia personnel is the relative inaccessibi l i ty of the

patient. This creates problems with moni to ring, airway management, intravenous

access , patient v isual ization, and moni tor applicat ion. Patients can only be di rectly

observed from ei ther end of the tunne l and can only be extricated by sl iding them

out.

Specific Equipment A number of devices special ly designed to be used in the MRI unit are avai lable . It

is important to demonstrate MR compatib il i ty by preuse tes ting, manufacturer

declarat ion, and/or c learance by a recognized body such as the FDA. For devices

that do not carry such credentials , i t is advisable to consul t the manufacturer or

biomedical personnel with expert ise in MRI before introduc ing them in to the MRI

room. I t is important to read all of the ins truct ions accompanying a p iece of

equipment, because some equipment may be MR safe or compatible only if

instal led a certain dis tance from the magnet (67).

MR is an evolv ing technology, and specif ications and perfo rmance characteris tics

of specif ic MR sys tems cont inual ly change. Products should be tes ted under

s imulated or ac tual use condi tions. Because upgrades to the MR sys tem to achieve

higher perfo rmance levels may affect the characteris t ics of the equ ipment,

yesterday's device tests may not be suf fic ient to ensure the safety and

ef fectiveness of a device wi th today's MR system (10). Since new equipment is

continually being introduced, it is on ly possible to make general iza tions about

which equipment is MRI compatible. I t is recommended tha t equipment intended for

use wi thin the magnet room be c learly labeled wi th the maximum field level wi th in

which i t can opera te effect ively (10).

Monitors wi th mul tiple funct ions decrease the amount of equipment that must be

transported, decreasing the risk of equipment damage and injury to the personnel

responsible for transport.

Any equipment that has an alarm should have a v isual alarm s ignal , because

auditory s ignals may not be heard (5).

Anesthesia Machines Standard anesthetic machines conta in varying amounts of fe rromagnetic

substances and electronically control led components, making them unsui table for

use in

P.877

proximity to an MRI magnet (68 ,69). Non-MRI compatible anesthes ia machines

have been used wi thout problems by keeping them 20 to 30 feet away f rom the core

of the magnet (26). Some anesthesia pract itioners have used long tubings fed into

the scanning room f rom an anesthesia mach ine p laced outs ide the scanning room

or a standard anesthesia machine bol ted to the wa ll (31 ,52). Replacing

ferromagnetic components (e.g., support s tructures, castors, cy linders, and parts of

cylinder supports) with nonferromagnetic materia ls and aluminum cylinders can

make an anesthesia machine MRI compatible. A few ounces of magnetic material

may prove negl igible. MRI-compatible anesthesia machines are available (Fig.

30.2). Aluminum cyl inders have been avai lable for some time. Unfortunately,

confusion about cylinder composit ion can arise (70).

Vaporizers Most standard vaporizers perform accura tely when used in the scanning room

(36,68,69,71). However, a portable vaporizer may be dangerous due to

ferromagnetism (51).

Anesthesia Breathing Systems A number of breathing sys tems have been used successful ly in the MRI

environment. These inc lude the c i rc le and Mapleson systems (20,35,52,58,72,73).

Long corrugated or fresh gas tub ing wi l l be required if the anesthesia machine is

remote f rom the pat ient. Fortunate ly, most components of ci rc le breathing systems

used today are nonmetall ic .

View Figure

Figure 30.2 MRI-compatible anesthesia machine. (Picture courtesy of Ohmeda.)

P.878

Anesthesia Ventilators Standard anesthesia venti lato rs usual ly contain ferromagnetic materia ls , pumps ,

electric motors, and analog gauges that can be affected by the magnetic field

unless specif ically adapted fo r the MRI. These may not function properly in a

magnetic f ie ld or may degrade the image. A remote venti lato r in the control room

wi th c i rcui t tubing fed into the scann ing room can be used, o r an incompatible

venti lato r can be attached to the wall (31 ,52).

Specially engineered MRI-compatible venti lators (bo th anesthesia and c ri tical care)

that have no electronic components are avai lab le (27,35,74,75,76,77). Fluidic

venti lato rs work wel l in the MRI envi ronment (75). Cur-rent ly avai lab le MRI-

compatible anesthesia machines are equipped wi th venti lators . An MR-compatible

posit ive end-expiratory pressure (PEEP) device is available (78).

Pulse Oximetry Most of the early pu lse oximeters were both suscept ible to interference from the RF

pulses and a source of interfe rence to the MRI s ignal (10 ,15,17,21,79,80). Burns

have been reported at both the sensor s i te and along the cable

(17,22,61,62,81,82). Heavy insulat ion and shielding can be used to isolate the

moni tor signa l (17,21). The moni to r should be p laced as far from the magnet as

possible.

Components, inc luding the probe, with a low ferromagnetic content are useful , as is

minimizing the number of electrica l connec tions and computer chips within the

moni tor. Most consoles have f i l te rs in the circui try and some models have f i l te rs in

the cable to help eliminate ex traneous s igna ls . These help to separa te the s ignal

f rom background noise (21).

A convenient method to eliminate ferromagnetic wire is to use a f iber-opt ic cable

(79,83). If a s tandard ferromagnetic cable is used, i t should be wrapped wi th

aluminum or copper foi l to shield the metal and decrease RF interference

(22,80,84).

A varie ty of MRI-compatible sensors , cables, and consoles are available. The

sensor can be shielded to prevent noise from reaching the MR system. The digi ts

can be protec ted wi th c lear plast ic coverings (27).

The sensor should be placed as fa r from the scan si te as possible. This may

require that i t be placed on the foo t or head, depend ing on the area to be imaged.

The cable should be extended in a s traight l ine away from the patien t. The length of

the cable should a llow the oximeter to be far enough f rom the magnet to prevent

image degradation .

Respiratory Gas Monitoring There are a number of di fferent technologies to measure respiratory gases. They

are discussed in Chapter 22 . Mainstream capnometry sys tems cause image

interference. The sensor requires shielding f rom RF rad iat ion. Sidestream moni tors

may be used during imaging as long as the moni toring device is ou ts ide the

magnetic f ie ld (19,58,85). Mult iple lengths of tubing may be connected to a llow the

moni tor to be outs ide the magnetic f ie ld. The extra length of tubing between the

patient and the monitor may degrade the capnogram and decrease the accuracy of

the end-tidal reading, especially with smal l pa tients (22). However, even if end-tidal

measurements are no t accura te, the trends and resp iratory pa ttern may s ti l l g ive

useful info rmation. If enough tubings are connected together, the resistance can

become so high that the alarm for blocked tubing is activated (83).

MRI-compatible mul tigas monitors are avai lable . This techno logy can be combined

wi th other modal it ies such as pulse oximetry, electrocardiography, and non invasive

blood pressure monitoring (52). Such equipment can be posi tioned either ins ide or

outside the magnet room.

Chemica l detectors (Chapter 22) tha t change color in the presence of carbon

dioxide are made of plas tic and contain no metal parts. They mus t be placed c lose

to the patient and may be diff icul t to see. They are qual itat ive devices and are on ly

generally quanti tative . This makes them more sui ted for checking tracheal tube

placement than for long cases. Electrochemical oxygen analyzers are usua lly safe

for use in the MRI sui te as long as they are outside the magnetic f ie ld (20,22).

Noninvasive Blood Pressure Monitors Automated blood pressure monitors are discussed in Chapter 27. The MRI does not

af fect monitors that use the osci l lometric method as long as the elec tronic uni t is

ei ther sh ielded or wel l away f rom the magnet core (18 ,19,20,26,27,36,85,86,87,88).

I t may be necessary to use extended tubings. Ferrous connections on the cuff

should be replaced wi th plast ic ones (83).

Manual sphygmomanometers have been adapted for use during MRI by rep lacing all

ferromagnetic components wi th brass, aluminum, or plast ic pieces (36). A plast ic

s tethoscope can be used to moni tor Koro tkoff sounds. The magnetic f ie ld may

af fect the accuracy of analog gauges since the movement mechanism in some

gauges uses a smal l magnet and a co il for operation . Blood pressure can be

moni tored outside the scanner by lengthen ing the tubing connected to the cuff (89).

Ul trasonic Doppler units have been used to moni to r sys tolic blood pressure (89,90).

Invasive Blood Pressure Monitors Most intravascular l ines are nonmagnetic and are not affec ted by the magnetic f ie ld

(36). Direct pressure readings can be obtained if the lead f rom the pressure

P.879

transducer is passed th rough a RF f il ter or posi tioned away from the magnet

(30,58). Fiber-op tic MRI-compatible transducers are avai lable (18,91).

Electrocardiographic Monitors The ECG can cause patient burns and image degradation as we ll as funct ion

inaccurate ly in the MRI envi ronment (15,17,21,27,35,52,58). ST-segment

moni toring is impossible in the presence of the magnetic f ie ld using current

technology (92).

The amount o f RF interfe rence tha t is coupled into the leads can be controlled by

appropriate design measures (e.g., by se lecting appropriate materials for the ECG

leads and by fi l tering the amplifier c ircui try input) (10). Special MRI-compatible

electrocardiographic leads may be constructed by using high-resistance conduc tors

that minimize induced RF currents (23).

A number of measures wil l minimize effects (7,21 ,27 ,35 ,58,93). Non-ferromagnetic

fasteners, e lectrodes, leads , and cables are avai lable. A f i l ter can reduce artifacts

in most leads (68,94). Good skin prepara tion is important to opt imize the ECG

signa l. The skin should be shaved and cleansed wi th alcohol before the e lec trodes

are placed (15). For best resul ts , the sk in should be dried or l ightly abraded (27).

Electrodes should be placed as c lose to the center of the magnet as poss ible

because the RF power is chang ing least at this point. The l imb electrodes should

be as c lose together as possible and in the same plane. Using chest leads, V5 and

V6 minimizes art ifac ts (95). Liquid crystal sc reens do not undergo distortion as do

ca thode ray tubes (58). The relat ive length of ECG leads may be cri t ical in

preventing gradient-induced art ifact; therefore, many manufac turers advise against

modifying ECG leads supp lied wi th MR sys tems (58).

Telemetry may sound appea ling because i t reduces the wiring and cables needed,

but it may interfere wi th the RF used for imaging. Th is interference is not seen wi th

ul trahigh f requency uni ts . These telemetry uni ts are l imited to QRS complex

detec tion (27,88).

Temperature Monitors Standard thermistor temperature probes can distort the magnetic f ie ld, causing

localized image distort ion if placed near the area of in terest (96). They could also

cause a localized concentration of RF power that would result in increased heat ing.

Smal l wire probes have been used in the MRI without excessive heating (96).

Al though temperature probes with f i l tered cables are availab le, they carry the same

risks of s ignal inte rference and burns as other electronic moni tors (97,98). A burn

associated wi th temperature monitoring us ing a probe specially designed for use

during MRI has been reported (98). A burn may be caused by inadvertent formation

of a cable loop during patient movement.

Fluoropt ic temperature probes that contain material that has temperature-

dependent op tical properties are not affected by high magnetic field strength and

RF pulses and are therefore more sui table for use in the MRI env ironment (96).

These probes are more expensive and more f ragi le than wire thermistors.

Liquid crystal temperature s tr ips work we ll in the MRI room but may not be easy to

observe (15).

Laryngoscopes The s tandard laryngoscope (Chapter 18) is no t fe rromagnetic but can undergo a

degree of to rque in a magnetic f ie ld (58). Plast ic laryngoscopes are available, but

most batteries are magnetic . One solution is to modify the hand le to operate f rom a

non-battery-based power source (36 ,52). A remote f iberopt ic l ight source can be

used. MRI-compatible laryngoscopes are avai lable. Most are powered by l i th ium

batteries . A paper- or p las tic-covered l i th ium battery can be used wi th a plas tic

laryngoscope (17,18,19,58,99).

I f an MRI-compatible la ryngoscope is not avai lable , anesthesia can be induced and

the ai rway intubated outs ide the magnet room using a conventional laryngoscope

before the patient is moved in to the scanner (19). If inadvertent ex tubat ion occurs

whi le the patient is in the scanner, an MRI-safe laryngoscope wil l be needed.

Tracheal Tubes Tracheal tubes (Chapter 19) are most commonly made of polyv inyl chloride and are

safe to use in the MRI env ironment. There are reports of signal interfe rence from

the spring in the cuff inf lat ion check valve (60 ,100,101). A tracheal tube wi th a wire

sp iral cannot be used in the MRI room (35,102). Connectors shou ld be plast ic .

Supraglottic Airway Devices The laryngeal mask (Chapter 17) is sui table for the MRI envi ronment. It a llows the

l ight level of anesthesia that is possib le, as there are no painful s t imuli involved in

the MRI process. Because some la ryngeal inf lation valves masks contain metall ic

material , i t may be necessary to remove the valve and knot the pilot tube (103).

Special laryngeal mask a irways (LMAs) wi th valves that do not conta in ferrous

material are availab le (104). I f the LMA-Flex ible or LMA-ProSeal is used, the metal

co il p roduces a large black hole in the image in the area surrounding the airway as

wel l as deteriora tion of the image fu rther out (105).

P.880

The LMA may not be sui table if magnetic resonance spec troscopy is performed

because the resonance of some s i l icone-containing materials compromises

inte rpretat ion of the scans (106).

Other supraglott ic devices are for the most part made of polyv iny l chloride or

s il icone, wh ich does not cause problems with the MRI. There are no reports of

problems at the t ime of this wri ting .

Other MRI-safe and -compatible suc tion regulators and nonmetall ic precordial

s tethoscopes are availab le and should be used.

Some infusion pumps need to be located away from the magnet o r shielded or they

may perform inaccura tely (17,36). MRI-safe infus ion pumps are avai lable.

Extension tubing may be required. There is a report of a pat ient-control led

analgesia device that malfunc tioned a fter exposure to the magnetic f ie ld (107,108).

Some infusion pumps func tion correct ly in the MRI envi ronment (52,109,110,111).

I t is possible to moni tor intrac ran ial pressure in this setting by using a

nonferromagnetic subdural bo lt o r plast ic catheter and a f iberoptic cable

(21,53,112,113).

Electroencephalography and evoked potential monitoring, both of wh ich use long

conduc ting wires , wil l requ ire technologica l advances before they can be used in

magnetic f ie lds (92).

Personnel Hazards I t is no t possible a t th is time to determine wi thout question if there are hazards to

personnel who work in the MRI envi ronment. Th is is largely due to the relatively

short t ime for wh ich this method of imaging has been in exis tence and the fact that

this work is occasional for most pract i tioners. Future ep idemiologic ev idence may

or may not demonstra te harmfu l effects of long-term exposure . Female staff should

consider avoiding th is area during the f irs t 3 months of a pregnancy.

Noise Noise is due to v ibrat ion of the swi tched gradient coils and is enhanced wi th h igher

strength gradient coils , shorter gradient duty cycles, and fas ter pulse repetit ion

f requenc ies in the magnet (114). The trend toward upgraded imaging systems and

stronger magnets would suggest tha t noise levels are likely to increase (31). No ise

levels up to 106 ±4 decibe ls wi th an average around 92 decibels have been

demonstra ted (31). These are potentially damaging levels, and care must be taken

to reduce these levels of exposure as much as possible . Ear plugs shou ld be

considered, a lthough they may interfe re wi th hearing aud itory ala rm signals (43,52).

Exposure to the Magnetic Field

With the inc reased use o f MRI and magnets of increasing strength, anesthesia

providers are experiencing increased exposure to stat ic magnetic f ie lds wi thin MRI

units . The s ta tic magnetic f ie ld extends beyond the conf ines of the magnet. The

strength of this f ringe f ield depends on the magnet conf igura tion and sh ie lding . It

decreases rapidly as the dis tance from the magnet increases. The biologic effect of

s tat ic magnetic f ie lds is a controvers ial topic (38). There are no demonstra ted

oncogenic or teratogenic e ffects (52). I t wou ld seem prudent to take reasonable

precautions against repeti tive and avoidable exposure to intense magnetic f ie lds.

Risks include danger from unrestrained ferromagnetic objects and from movement

or malfunct ion of MR-incompatible implants wi thin their bodies (31).

Trace Anesthetic Gases Trace anesthet ic gases and the ir r isks to anesthesia personnel are discussed in

Chapter 13. Scavenging sys tems and good venti lat ion wi th f requent ai r exchanges

are not always available in the MRI uni t (31). Some breathing systems such as the

Mapleson sys tems (Chapter 8 ) are often used for pediatrics, and many of these are

not scavenged.

Hypoxia I f l iquid helium that surrounds the superconducting so lenoid in the magnet escapes ,

i t is possible that a hypoxic envi ronment may be created (31). Oxygen sensors can

be placed in the cei ling to warn of this problem. 1Most physicians refer to this type of imaging as MRI, wh ile most physic is ts refer to

i t as nuclear magnetic resonance (NMR) (7). Both are accepted terms and refer to

the same technology.

References 1. Berkenstadt H, Perel A, Ram Z, e t al . Anesthesia for magnetic resonance guided

neurosurgery. Initial experience wi th a new open magnetic resonance imag ing

system. J Neurosurg Anesthesiol 2001;13:158–162.

[Fu ll text Link]

[CrossRef]

[Med line Link]

2. Black P, Moriarty T, Alexander EI, et a l. Development and implementat ion of

intraopera tive magnetic resonance imaging and i ts neurosurgical appl icat ions.

Neurosurgery 1997;41:831–845.

[Fu ll text Link]

[CrossRef]

[Med line Link]

3. Hinks RS, Bronskil l MJ, Kucharczyk W, et al . MR sys tem for image-guided

therapy. JMRI 1998;8:19–25.

4. Manninen PH, Kucharczyk W. A new front ie r: magnetic resonance imaging-

operating room. J Neurol Anesth 2000;12:141–148.

5. Schmitz B, Nimsky C, Wendel G, et al . Anesthesia during high-f ield

intraopera tive magnetic resonance imaging experience with 80 consecutive cases . J

Neurosurg Anesth 2003;15:255–262.

6. Archer DP, McTaggart Cowan RA, Falkenstein RJ , et al. Intraoperative mobile

magnetic resonance imaging fo r craniotomy lengthens the procedure but does not

increase morbidi ty . Can J Anes th 2002;49:420–426.

7. Menon DK, Peden CJ, Ha ll AS, et al. Magnetic resonance for the anaesthet is t.

Part I : physical princ iples, appl icat ions, safety aspects. Anaesthesia 1992;47:240–

255.

[CrossRef]

[Med line Link]

8. American Society of Anesthesiologists . Guidel ines fo r nonoperat ing room

anesthet iz ing locations (approved by ASA House of Delegates on October, 19,

1994) (http://www.ASAhq.org). Park Ridge, IL: Author, 1994.

9. Schiebler M, Kaut-Watson C, Wi ll iams DL. Both sedated and crit ical ly i l l require

moni toring during MRI. MR 1994;4:41–45.

P.881

10. Keeler EK, Casey FX, Enge ls H, e t al . Accessory equ ipment considerations with

respect to MRI compatibil i ty . J Magn Reson Imag ing 1998;8:12–18.

[CrossRef]

[Med line Link]

11. Jolesz FA, Morrison PR, Koran SJ , et al. Compatible instrumentat ion fo r

intraopera tive MRI: expanding resources. JMRIS 1998;8:8–11.

12. Anonymous . Safety emphas ized in MR environment. Biomed Instrum Technol

2001;35:291–292.

[Med line Link]

13. Pool JL. The fundamentals of magnetic resonance imaging. Biomed Ins trum

Technol 2002;36:341–346.

[Med line Link]

14. Keens SJ, Laurence AS. Magnet-safe is not the same as magnet compatible in

the MR scanner. Anaes thesia 2004;59:516.

[Fu ll text Link]

[CrossRef]

[Med line Link]

15. Jorgensen NH, Messick JM, Gray J, et al. ASA monitoring standards and

magnetic resonance imaging. Anesth Analg 1994;79:1141–1147.

[Fu ll text Link]

[CrossRef]

[Med line Link]

16. Malhotra V. Successful anesthesia techniques outs ide the operating room (ASA

Ref resher Course #145). Atlanta, GA: 1995.

17. Patteson SK, Chesney JT. Anesthet ic management fo r magnetic resonance

imaging: p rob lems and solut ions. Anesth Analg 1992;74:121–128.

[CrossRef]

[Med line Link]

18. Nixon C, Hirsch NP, Ormerod IEC, et a l. Nuclear magnetic resonance. Its

implica tions for the anaesthetis t. Anaesthesia 1986;41:131–137.

[CrossRef]

[Med line Link]

19. Burk NS. Anes thesia for magnetic resonance imag ing, Anes th Cl in North Am

1989;7:707–721.

20. Sury MRJ, Johnstone G, Bingham RM. Anaes thesia for magnetic resonance

imaging of children. Paediatr Anaesth 1992;2:61–68.

[CrossRef]

21. Hal l SC. Moni toring in rad iology. In: Lake CL, ed . Clinical Moni to ring fo r

Anesthesia and Crit ical Care. Philadelphia: WB Saunders , 1994:395–411.

22. Bel l C, Conte AH. Mon itoring oxygenation and venti la tion during magnetic

resonance imaging: a pic toria l essay. J Cl in Moni t 1996;12:71–74.

[CrossRef]

[Med line Link]

23. Van Slyke MA, Wise SW, Spain JW. Computerized patient imag ing. In : Russel l

GB, ed. Al ternate-s i te Anesthesia. Boston: Butterworth-Heinemann, 1997:35–68.

24. Miyasaka K , Kondo Y, Tamura T, et al. Anesthes ia-compatible magnetic

resonance imaging. Anesthesio logy 2005;102:235.

[Fu ll text Link]

[CrossRef]

[Med line Link]

25. Li tt L. Anes thesia-compatible magnetic resonance imaging. Inv ited commentary.

Anesthesiology 2005;102:236.

[Fu ll text Link]

[CrossRef]

[Med line Link]

26. Hughes CW. Moni toring chi ld ren in remote locat ions. STA Interface

1994;5(4):43, 46.

27. Hughes CW, Bell C. Anesthesia equipment in remote hospital locations . In:

Ehrenwerth J, Eisenkraft JB, eds . Anes thesia Equipment. Principles and

Applicat ions. St. Louis: Mosby, 1993:565–587.

28. Leak JA. Endoscopy, diagnost ic imag ing and therapeutic radiat ion sui tes . ASA

News le tt 2003;67:6–7, 10.

29. Henneberg S, Hok B, Wik lund L, et al . Remote auscul tatory pat ien t moni to ring

during magnetic resonance imaging. J Cl in Mon it 1992;8:37–43.

[CrossRef]

[Med line Link]

30. Taber KH, Thompson J, Coveler LA, et a l. Invasive pressure moni toring of

patients during magnetic resonance imag ing. Can J Anaesth 1993;40:1092–1095.

[Med line Link]

31. McBrien ME, Winder J, Smyth L. Anaesthesia for magnetic resonance imaging:

a survey of current practice in the UK and Ireland. Anaes thesia 2000;55:737–743.

[Fu ll text Link]

[CrossRef]

[Med line Link]

32. Kempen PM. S tand near by in the MRI. APSF Newslett 2005;20:32, 36.

33. Anonymous . Vent ilators. Technol Anes th 2000;21:5–6.

34. Anonymous . Datex-Ohmeda—Aestiva /5 MR-compatible anesthesia machines:

must be used in accordance wi th safe ty instructions in MR environments. Heal th

Dev ices Alerts 2004;28:8 .

35. Rejger VS, Cohn BF, Vielvoye GJ, et a l. A s imple anaesthet ic and moni toring

system for magnetic resonance imaging. Eur J Anaesth 1989;6:373–378.

[Med line Link]

36. Karlik SJ, Heatherley T, Pavan F, e t al . Pat ient anesthesia and monitoring a t a

1.5-T MRI ins tal lat ion . Magn Reson Med 1988;7 :210–221.

[CrossRef]

[Med line Link]

37. Nixon C. Magnetic resonance imaging. Can Anaes th Soc J 1991;38:420.

38. Kanal E, Shellock F, Talagala L. Safety considerations in MR imaging.

Rad iology 1990;176:593–606.

[Med line Link]

39. Schenk JF. MRI safety a t high magnetic f ie lds. MRI Clin North Am 1998;6:715–

730.

40. Chaljub G, Kramer LA, Johnson RFI, et al . Project ile cyl inder accidents

resul ting f rom the presence of ferromagnetic ni trous oxide or oxygen tanks in the

MR sui te . AJR 2001;177:27–30.

[Med line Link]

41. Gooden CK, Dilos B. Anesthesia for magnetic resonance imaging. Int Anesth

Cl in 2003;41:29–37.

42. Anonymous . Projective inc idents involv ing oxygen cyl inders cont inue to occur in

the MR environment. Heal th Devices Alerts 2004;28:1–2.

43. Li tt L, Cauldwel l CB. Being extra safe when prov iding anesthesia for MRI

examinations. ASA News lett 2002;66:17–18, 29 .

44. Anonymous . Boy dies when MRI magnetics tu rn O2 tank in to a projecti le.

Biomed Safe Stand 2001; 31:137–138.

45. Agarval A, Singha l V, Dhiraaj S, e t al . Head injury f rom an MRI compatible

pulse oximeter. Anaesthesia 2005;60:1049.

[Fu ll text Link]

[CrossRef]

[Med line Link]

46. Anonymous . Discharge of a f irearm in the MR environment. Heal th Devices

Alerts 2002;26:1.

47. Anonymous . ECRI hazard report: pat ient death i l lus trates the importance of

adhering to safety precautions in magnetic resonance environments. Health

Dev ices 2001;30:311–314.

[Med line Link]

48. Bout in , RD, Briggs JE, Wi ll iamson MR. Injuries associa ted wi th MR imaging:

survey of safety records and methods used to screen pat ients for metal l ic fore ign

bodies before imaging. AJR 1994;162:189–194.

[Med line Link]

49. Kanal E, Borgstede JP, Barkov ich AJ , et a l. American Col lege of Radiology

White Paper on MR safety. AJR 2002;178:1335–1347.

[Med line Link]

50. Anonymous . Ferromagnetic sandbags are hazardous in magnetic resonance

imaging (MRI) env ironments . Heal th Devices 1998;27:266–267.

[Med line Link]

51. Zimmer C, Janssen MN, Treschan TA, et al . Near-miss accident during

magnetic resonance imaging by a “f lying Sevoflurane vaporizer” due to

ferromagnetism undetectable by handheld magnet. Anesthes iology 2004;100:1329–

1330.

[Fu ll text Link]

[CrossRef]

[Med line Link]

52. Russell GB, Taekman JM, Cronin AJC. Anesthes ia and magnetic resonance

imaging. In: Russel l GB, ed. Al ternate-s i te Anesthes ia : Clinical Practice outs ide the

Operat ing Room. Bos ton: Butte rworth-He inemann, 1997:69–81.

53. Grady RE, Wass T, Maus TP, et al. Fiberoptic intracranial pressure moni to ring

during magnetic resonance imaging. Anesthesiology 1997;87:1001–1002.

[Fu ll text Link]

[CrossRef]

[Med line Link]

54. Klucznik RP, Carrie r DA, Pyka R, et al . Placement of a ferromagnetic

intracerebra l aneurysm c lip in a magnetic f ie ld wi th a fa tal outcome. Radiology

1993;187:855–856.

[Med line Link]

55. Kel ly WM, Pag len PG, Pearson JA, et al. Ferromagnetism of intraocular foreign

body causes uni late ral bl indness after MR study. AJNR 1986;7:243–245.

[Med line Link]

56. Schenk JF. MRI safety a t high magnetic f ie lds. MRI Clin North Am 1998; 6:715–

730.

57. Shel lock FG, Kanal E. SMRI safety committee, pol ic ies , guidel ines , and

recommendations fo r MR imaging safety and patient management. JMRI 1991;1:97–

101.

58. Peden CJ , Menon DK, Hal l AS, et al. Magnetic resonance for the anaesthetis t .

Part I I: anaes thesia and moni to ring in MR uni ts . Anaesthesia 1992;47:508–517.

[CrossRef]

[Med line Link]

59. Kanal E, Shellock FG. SMRI safety committee, pol ic ies , guidel ines , and

recommendations fo r MR imaging safety and patient management. JMRI

1992;2:247–248.

60. Brenn BR, Saldutt i G, MRI image degradation f rom an endotracheal tube p ilot

balloon. Anes th Analg 1994;79:586–587.

[Fu ll text Link]

[CrossRef]

[Med line Link]

61. Shel lock FG, Dimp GL. Severe burn of the f inger caused by using a pulse

ox imeter during MR imaging. AJR 1989;153:1105.

[Med line Link]

62. Kanal E, Shellock FG. Burns associated with cl inica l MR examinat ions.

Rad iology 1990;175:585.

[Med line Link]

63. Shel lock FG, Kanal E. Burns associated with the use of moni toring equipment

during MR procedures. J Magn Reson Imaging 1996;6:271–272.

[CrossRef]

[Med line Link]

64. Anonymous . Thermal injuries and pat ient moni toring during MRI studies. Heal th

Dev ices 1991;20:362–363.

[Med line Link]

65. Anonymous . MRI sys tem recalled due to patien t burns. B iomed Safe Stand

1999;28:59.

66. Anonymous . Jerome Medical—MR-compatib le cerv ical halo tract ion devices:

may not be MR compatib le . Heal th Devices Alerts 2004;28:5.

67. Farling PA, McBrien ME, Winder RJ . Magnetic resonance compatible

equipment: read the small print! Anaesthesia 2003;58:86–87.

68. Rao CC, McNiece WL, Emhardt J , e t al . Modifica tion of an anesthesia machine

for use during magnetic resonance imaging. Anesthes io logy 1988;68:640–641.

[Fu ll text Link]

[CrossRef]

[Med line Link]

69. Rao CC, Krishna G, Emhardt J . Anesthesia machine for use during magnetic

resonance imaging. Anesthes io logy 1990;73:1054–1055.

[Fu ll text Link]

[CrossRef]

[Med line Link]

70. Anonymous . Steel oxygen cylinders : can become ki l ler projec ti les in magnetic

resonance environments. Hea lth Devices Alerts 2002;26:3.

71. Rao CC, Brandl R, Mashak JN. Mod if ication of Ohmeda® Excel 210 anes thesia

machine for use during magnetic resonance imaging. Anesthesiology

1989;71:A365.

[Fu ll text Link]

[CrossRef]

72. Liao J, Belan i K, Mikhai l S, e t al . Use of new anes thesia c ircui t for remote

venti lation during magnetic resonance imaging. Anesth Analg 1986;65:S88.

73. Boutros A , Pavlicek W. Anesthesia fo r magnetic resonance imaging. Anesth

Analg 1987;66:367.

[Fu ll text Link]

[CrossRef]

[Med line Link]

74. McGowan JE, Erenberg A. Mechanical venti lat ion of the neonate during

magnetic resonance imaging. Magn Reson Imaging 1989;7:145–148.

[CrossRef]

[Med line Link]

75. Dunn V, Coffman CE, McGowan JE, et al. Mechanical vent i lat ion during

magnetic resonance imaging. Magn Reson Imaging 1985;3:169–172.

[CrossRef]

[Med line Link]

76. Wil l iams EJ, Jones NS, Carpenter TA, et al . Testing of adul t and paediatric

venti lato rs for use in a magnetic resonance imaging uni t. Anaes thesia

1999;54:969–974.

[Fu ll text Link]

[CrossRef]

[Med line Link]

77. Wil l iams EJ, Jones NS, Carpenter TA, et al . Testing of adul t and paediatric

venti lato rs for use in a magnetic resonance imaging uni t. Anaes thesia

1999;54:969–974.

[Fu ll text Link]

[CrossRef]

[Med line Link]

78. Ste iner LA, Chatf ield DA, Donovan T, et al. Assessment of the Caradyne

WhisperFlow for administrat ion of continuous posi t ive a irway pressure in a 3 Tesla

magnetic resonance scanner. Anaes thesia 2002;57:470–474.

[Fu ll text Link]

[CrossRef]

[Med line Link]

79. Shel lock FG, Myers SM, Kimble KJ. Mon itoring heart rate and oxygen saturat ion

wi th a f iberoptic pulse oximeter during MR imaging. AJR 1992;158:663–664.

[Med line Link]

80. Salvo I, Colombo S, Capocasa T, et al . Pulse oximetry in MRI un its . Cl in Anesth

1990;2:65–66.

81. Bashein G, Syrovy G. Burns associated wi th pulse ox imetry during magnetic

resonance imaging. Anesthesio logy 1991;75:382–383.

[Fu ll text Link]

[CrossRef]

[Med line Link]

82. Farling PA. Anaesthesia in the magnetic resonance uni t: a hazardous

environment. Anaes thesia 2002;57:421–423.

[Fu ll text Link]

[CrossRef]

[Med line Link]

83. Zorab JSM. A general anaesthesia serv ice for magnetic resonance imaging. Eur

J Anaesth 1995;12:387–395.

[Med line Link]

84. Wagle WA. Technique for RF isolat ion of a pulse ox imeter in a 1.5-T MR uni t.

AJNR 1989;10:208.

[Med line Link]

85. Davis P, Gi llen C, Kretchman E, e t al . Experience with anes thesia for chi ldren

requiring nuclear magnetic resonance imaging. Anesthesiol Rev 1990;17:35–40.

86. Sel lden H, De Chateau P, Erman G, et a l. Circulatory monitoring of chi ldren

during anaesthesia in low-f ield magnetic resonance imaging. Ac ta Anaesthesiol

Scand 1990;34:41–43.

[Med line Link]

87. Shel lock F. Monitoring during MRI: an evaluation of the effect of high-f ield MRI

on various patient moni tors. Med Elec tron 1986;100:93–97.

[Med line Link]

88. Selden H, De Chateau P , Ekman G, et al . Circulatory moni toring of children

during anaesthesia in lo-field magnetic resonance imaging. Acta Anaesthesiol

Scand 1990;34:41–43.

[Med line Link]

89. Roth J , Nugent M, Gray J, et a l. Patien t moni to ring during magnetic resonance

imaging. Anesthes iology 1985;62:80–83.

[Fu ll text Link]

[CrossRef]

[Med line Link]

90. McArdle CB, Nicholas DA, Richardson CJ, et al. Moni toring of the neonate

undergoing MR imaging: technical considera tions . Radiology 1986;159:223–226.

[Med line Link]

91. Roos CF, Carrol l FE Jr. Fiberopt ic pressure transducer for use near MR

magnetic f ie lds . Radiology 1985;156:548.

[Med line Link]

92. Archer DP, Manninen PH, McTaggart-Cowan RA. Anesthetic considerations fo r

neurosurgery using in traoperat ive magnetic resonance imaging. Tech Neurosurg

2002;4:308–312.

93. Keens SJ, Laurence AS. Burns caused by ECG monitoring during MRI imaging.

Anaesthesia 1996;51:1188–1189.

[Fu ll text Link]

[CrossRef]

[Med line Link]

94. Rokey R, Wendt RE, Johnston DL. Monitoring acute ly i l l pat ients during nuclear

magnetic resonance imaging: use of a t ime-varying f il te r electrocardiographic

gating dev ice to reduce gradient art ifac ts . Magn Reson Med 1988;6:240–245.

[CrossRef]

[Med line Link]

95. Dimick R, Hedlund LW, Herfkens RJ, et al . Opt imizing electrocardiographic

electrode placement for cardiac-gated magnetic resonance imaging. Invest Radiol

1987;22: 17–22.

[CrossRef]

[Med line Link]

96. Taber KH, Hayman LA. Tempera ture moni to ring during MR imaging: comparison

of f luoropt ic and s tandard thermistors . JMRI 1992;2:99–101.

97. Karlik SJ, Heatherley T, Pavan F, et al . Pat ient anesthes ia and monitoring a t a

1,5-T MRI ins tal lat ion . Magn Reson Med 1988;7 :210–221.

[CrossRef]

[Med line Link]

P.882

98. Hal l SC, Stevenson GW, Suresh S. Burn assoc ia ted wi th temperature

moni toring during magnetic resonance imaging. Anesthesiology 1992;76:152.

[Fu ll text Link]

[CrossRef]

[Med line Link]

99. Geiger RS, Cascorbi HF. Anesthesia in an NMR scanner. Anesth Analg

1984;63:622–623.

[Fu ll text Link]

[CrossRef]

[Med line Link]

100. Grady RE, Perkins WJ. An unexpected cause of magnetic resonance image

distortion: the endotracheal tube p ilot balloon. Anesthesiology 1997;86:993–994.

[Fu ll text Link]

[CrossRef]

[Med line Link]

101. Cro fts S, Campbell A. A source of art ifac t during general anaes thesia for

magnetic resonance imaging. Anaes thesia 1993;48:643.

[CrossRef]

[Med line Link]

102. Carrol l M, El jamel M, Cumnningham AJ . Ferrous disto rt ion during MRI. Br J

Anaesth 1994;72:727–728.

[CrossRef]

[Med line Link]

103. Langton JA, Wilson I, Fell D. Use of the laryngea l mask ai rway during

magnetic resonance imaging. Anaes thesia 1992;47:532.

[CrossRef]

[Med line Link]

104. Asa i T, Morris S. The laryngeal mask airway: its features , effects and role.

Can J Anaesth 1994;41:930–960.

[Med line Link]

105. Stevens JE, Burden G. Re inforced laryngeal mask airway and magnetic

resonance imaging. Anaes thesia 1994;49:79–80.

[CrossRef]

[Med line Link]

106. Fairf ie ld JE. Laryngeal mask and magnetic resonance imaging—a caution.

Anaesthesia 1990;45:995.

[CrossRef]

[Med line Link]

107. Leeson-Payne CG, Towell T . Magnetic mayhem. Anaesthesia 1996;51:1081–

1082.

[Fu ll text Link]

[CrossRef]

[Med line Link]

108. Englishby VL. Magnetic mayhem a reply. Anaesthesia 1996;51:1082.

[Fu ll text Link]

[CrossRef]

109. Kovac A, Swanson B, El l io tt C, e t al . Effect of dis tance and infusion rate on

operation of Medfus ion 2010 infusion pump during magnetic resonance imaging

(MRI). Anes th Ana lg 1999;88:S186.

110. Pathy S, Story D, Chandrashekara D, e t al . The ef fect of radiof requency

sh ielding on the perfo rmance of the Gemin i PC-1 infusion pump in the MRI sui te.

Anaesth Intens Care 1998;26:703–704.

111. Will iams EJ , Tam YC, Kendal l IV, et al. Infusion pump performance in an MR

environment. Eur J Anaesth 1999;16:468–472.

[CrossRef]

[Med line Link]

112. Will iams EJ , Bunch CS, Carpenter TA, et al . Magnetic resonance imaging

compatibi l i ty testing of intracranial pressure probes. Techn ica l note. J Neurosurg

1999;91:706–709.

[Med line Link]

113. Prall JA, Levy AS, Nicho ls JS. The use o f magnetic resonance imaging in

patients with fiberopt ic intracranial pressure monitors. Anesthesiology

1999;90:319.

[Fu ll text Link]

[CrossRef]

[Med line Link]

114. Shellock FG, Kanal E. SMRI safety committee . J Magn Reson Imaging

1991;1:97–101.

[CrossRef]

[Med line Link]

P.883

Questions For the fol lowing quest ion, select the correct answer

1. The distance from the center of the magnet that is usually considered to be safe for ferromagnetic objects is A. The 2-gauss l ine

B. The 3-gauss l ine

C. The 4-gauss l ine

D. The 5-gauss l ine

E. Beyond the 5-gauss l ine

View AnswerFor the following quest ions, answer

• i f A, B, and C are correct

• i f A and C are correct

• i f B and D are correct

• i f D is correct

• i f A, B, C, and D are correct.

2. Which factors determine the attractive force on a ferromagnetic object in the MRI unit? A. The strength of the magnet

B. The mass and geometry of the ob jec t

C. Magnetic shie ld ing

D. The d is tance of the objec t from the outer f ie ld of the magnet

View Answer3. Which of the following are considered to be safe in the MRI scanner?

A. Aluminum

B. Beryll ium

C. Gold and s ilver

D. All types of s tainless steel

View Answer4. Which metals can cause a negative magnetic screen and absorb radio frequency energy that can result in an MRI artifact or thermal injury to the patient?

A. Aluminum

B. Gold

C. Copper

D. Silver

View Answer5. Sources of radio frequency noise that can degrade the MRI image include

A. Commercial rad io stat ions

B. Beepers

C. Motors

D. Liqu id crystal d isplays

View Answer6. Which items may cause a burn from radio frequency fields? A. ECG electrodes

B. Epidural catheters

C. Pu lse oximetry cables

D. Swan-Ganz catheters

View Answer7. Methods to keep pediatric patients from developing hypothermia in the MRI unit include A. Warm f luids

B. Radiant l ights

C. Covering the pat ient

D. Electrical heating pads

View Answer