DR. WAN NAJWA ZAINI WAN MOHAMEDRADIOLOGIST AND HEAD

JPD, HQE I I24 t h JUNE 2015

MRI SAFETY – THE DOs AND DON’Ts

PREPARED FOR: HOSPITAL’S CME

CONTENTS

1. INTRODUCTION

2. SAFETY RULES

3. SCREENING GUIDELINES

4. HAZARDS, RISKS, SIDE EFFECTS

5. SAFETY GUIDANCE

INTRODUCTION

WHAT IS MRI?

Magnetic Resonance Imaging is a medical diagnostic tool to help doctors to diagnose diseases by scanning the insides of the human body.

a noninvasive NON-IONIZING imaging technique.

Basic components are the magnet, gradient coils, radio frequency coils and computer

BASIC COMPONENTS OF MRI

MRI uses very STRONG MAGNETIC FIELD and

Radio Frequency waves (RF)

In an MRI examination the patient is exposed to the following:

• Strong Magnetic Field.

• Radio Frequency Waves (RF).

• Audible noise.

WHAT IS MAGNETIC FIELD?

Magnetic field is an invisible force that can attract objects that have iron content (Fe).

The stronger the magnetic field the stronger the force of attraction.

Objects that are not ferrous (no iron content) will not be attracted to the magnet, eg. Wood, plastic, gold, silver, aluminum, brass, copper.

WHAT IS MAGNETIC FIELD?

Magnetic field is measured in Tesla.

Avanto (Toshiba) = 1.5 Tesla

Earth = 0.00005 Tesla.

MR is 30,000 X stronger than the EARTH’s magnetic field.

GENERAL MISCONCEPTIONS ABOUT THE MAGNETIC FIELD

If the system is switched OFF, then the magnetic field will also be off.

This is a big object. The magnet is not strong enough to pull it.

This is a small object. Not necessary to remove from patient or my pocket.

X

X

X

GENERAL KNOWLEDGE ABOUT THE MAGNETIC FIELD’S EFFECT

The Magnetic field is very strong. It can pull objects up to hundreds of kilograms.

A 1.0kg iron object will feel like almost 100kg inside a 1.5 TESLA magnetic field.

GENERAL KNOWLEDGE ABOUT THE MAGNETIC FIELD’S EFFECT

Big objects will cause serious injuries or even death to the people who are around or inside the Magnet.

Small sharp objects will also cause serious injuries or even death to the people around or inside the Magnet.

TYPES OF MRI MAGNETS

PERMANENT

SUPERCONDUCTIVE

PERMANENT MAGNETS

PERMANENT MAGNET CANNOT BE SWITCHED OFF

PERMANENT MAGNETS

Open system MRI.

Uses low magnetic field (0.2 – 0.7 T) – low strength but safety precautions must still be adhered to.

Do not use liquid helium as coolant.

Advantage: cheaper, no fear of claustrophobia.

PERMANENT MAGNETS

Disadvantage – poor resolution, longer scanning time.

SUPERCONDUCTING MAGNETS

Very strong magnetic fields, typically 1T and above – susceptible to flying objects

Uses cryogens such as liquid helium as coolant

Advantage – improved anatomic resolution, reduced scan time with preserved image quality

Under normal working condition, is never turned off

SUPERCONDUCTING MAGNETS

IMPORTANT KNOWLEDGE

The MAGNETIC field of a SUPERCONDUCTIVE magnet is permanently ON (24hours).

The MAGNETIC FIELD cannot be switched off by the user under NORMAL conditions.(We will discuss on the Emergency condition later).

SAFETY RULES

Safety first!

SAFETY RULES

Magnetic Fringe Fields5 Gauss Limit and LineACR Safety ZonesMR CompatibilitySpecific Absorption Rate (SAR)

MAGNETIC FRINGE FIELDS

The fringe field is the peripheral magnetic field outside of the magnet core.

Depending on the design of the magnet and the room, a moderately large fringe field may extend for several meters around, above, and below an MR scanner.

Can cause interference with electronic devices including pacemakers.

Fringe field around a 1.5T superconducting scanner

5 GAUSS LIMIT AND LINE

Threshold for access to MRI areas.

1 Gauss (G) = 1 x 10-4 Tesla (0.0001 T).

5 G = 0.0005 T @ 0.5 mT

Five gauss and below are considered 'safe' levels of static magnetic field exposure for the general public.

5 Gauss Line specifies the perimeter around a MR scanner within which the static magnetic fields are higher than 5 Gauss.

5 gauss safety limit is ten times higher than the average earth magnetic field, but lower than the magnetic field in electric trains such as subways (up to 7 gauss).

5 GAUSS LIMIT AND LINE

5 GAUSS LIMIT AND LINE

Smaller fields (1-3 G) may affect nearby CT and MRI scanners.

Older generation pacemakers may be affected by magnetic fields exceeding 5 G.

Fringe fields of 10 G may affect computers.

Fringe fields of 30 G may magnetize your watch and erase your credit cards!

ACR SAFETY ZONES

The American College of Radiology has defined four safety zones within MRI facilities.

Zone I, II, III, IV.

Correspond to levels of increasing magnetic field exposure (and hence potential safety concern).

ZONE IAll areas freely accessible to the general public without supervision. Magnetic fringe fields in this area are less than 5 Gauss (0.5 mT). 

ZONE IIStill a public area, but the interface between unregulated Zone I and the strictly controlled Zones III and IV. MR safety screening typically occurs here under technologist supervision.

ZONE IIIAn area near the magnet room where the fringe, gradient, or RF magnetic fields are sufficiently strong to present a physical hazard to unscreened patients and personnel.

ZONE IVSynonymous with the MR magnet room itself. Has the highest field (and greatest risk) and from which all ferromagnetic objects must be excluded. 

MRI COMPATIBILITY

MR SafeThe potential for injury of the individual.

“When the device is introduced or used in the MRI environment it does not pose an increased safety risk to the patient or other personnel”

MRI COMPATIBILITY

MR CompatibleThe potential for damage to the device and its

associated components, the function of the device that will be affected during the MR procedure, and/or the potential source of image artifacts.

“When the device is introduced or used in the MRI environment, it is MR safe that it performs its intended function without performance degradation, and that it does not adversely affect the function of the MRI scanner (e.g. no significant image artifacts or noise)”

SCREENING GUIDELINES

SCREENING GUIDELINES

Absolute ContraindicationsRelative ContraindicationsPost-op periodContrast media and NSFPregnancy

ABSOLUTE CONTRAINDICATIONS

Electronically, magnetically, and mechanically activated implants.

Ferromagnetic or electronically operated active devices like automatic cardioverter defibrillators.

Cardiac pacemakers.

Metallic splinters in the eye. Ferromagnetic haemostatic clips in the

central nervous system.

ABSOLUTE CONTRAINDICATIONS

RELATIVE CONTRAINDICATIONS

Cochlear implants.

Other pacemakers, e.g. for the carotid sinus.

Insulin pumps and nerve stimulators.

Lead wires or similar wires.

Prosthetic heart valves (in high fields, if dehiscence is suspected).

Haemostatic clips (body). Non-ferromagnetic stapedial implants.

RELATIVE CONTRAINDICATIONS

POST OP PERIOD

If the metallic object is a “passive implant” (i.e. there is no electronically- or magnetically-activated component associated with the operation of the device) and it is made from nonferromagnetic material, the patient may undergo an MR procedure immediately after implantation.

POST OP PERIOD

For an implant or device that exhibits “weakly magnetic” qualities, it may be necessary to wait a period of six weeks after implantation before performing an MR procedure.

However, patients with implants or devices that are “weakly magnetic” but rigidly fixed in the body (e.g., bone screws, other orthopedic implants, or other devices) may be studied immediately after implantation.

CONTRAST MEDIA AND NSF

Nephrogenic Systemic Fibrosis (NSF)NSF has been observed in patients with

severe kidney disease or dysfunction receiving GBCA.

Characterized by extensive thickening and hardening of the skin with fibrotic nodules and plaques.

CONTRAST MEDIA AND NSF

The disease is progressive and can be associated with a fatal outcome with still no definitive cure.

Should not use if GFR < 30 mL/min/1.73m2.

Some GBCAs [gadodiamide (Omniscan); gadopentetate dimeglumine (Magnevist); gadoversetamide (OptiMARK) ] are specifically contraindicated for use in patients at risk of NSF.

CONTRAST MEDIA AND NSF

Other approved agents (Ablavar, Eovist, MultiHance,ProHance) should be used in patients at risk of NSF only if the diagnostic information is essential and not available with non-contrast enhanced MRI or other imaging modalities.

Post MRI – advice for several days haemodialysis with increased rate and volume to enhance elimination of GBCA.

PREGNANCY

Safety Committee of the Society for Magnetic Resonance Imaging in 1991:“MR imaging may be used in pregnant women if

other non-ionizing forms of diagnostic imaging are inadequate or if the examination provides important information that would otherwise require exposure to ionizing radiation (e.g., fluoroscopy, CT, etc.).

Pregnant patients should be informed that, to date, there has been no indication that the use of clinical MR imaging during pregnancy has produced deleterious effects.” 

PREGNANCY

Relatively few studies performed in pregnant human subjects exposed to MR imaging or the MR environment.

No published reports on persons exposed to magnetic fields, including staff at MR departments, have a higher incidence of genetic damage to their children than found in the average population.

PREGNANCY

Should only be used if their usage is considered critical and the potential benefits justify the potential risk to the unborn fetus.

Should use agents believed to be at low risk for the development of NSF at the lowest possible dose to achieve diagnostic results.

Therefore, their use should not be limited, particularly given the important clinical reasons for MRI examinations during pregnancy.

HAZARDS, RISKS AND SIDE EFFECTS

HAZARDS, RISKS AND SIDE EFFECTS

Magnetic ForcesMagnetic ShieldingAcoustic NoiseClaustrophobiaQuenchingContrast media Absorbed DoseCardiac RisksMagnetohydrodynamic EffectsNerve Conductivity

MAGNETIC FORCES

The “MISSILE EFFECT”: Very dramatic and dangerous phenomenon.

Occurs when a metal object is pulled into the magnet with great force ( >20 mph).

Can be a lethal danger if one is hit by an unrestrained object in flight.

Could also be trapped in between.

MAGNETIC FORCES

The “MISSILE EFFECT”:

Many objects including wrenches, hammers, IV poles, oxygen bottles, crash carts, floor buffers, wheelchairs, tool boxes, stretchers, mop buckets … even a policeman’s handgun, have been involved in accidents.

Could damage the MRI machine.

Boy, 6, Killed in Freak MRI AccidentJuly 31, 2001A 6-year-old boy died after undergoing an MRI exam at a New York-area hospital when the machine's powerful magnetic field jerked a metal oxygen tank across the room, crushing the child's head.

The force of the device's 10-ton magnet is about 30,000 times as powerful as Earth's magnetic field, and 200 times stronger than a common refrigerator magnet.

The canister fractured the skull and injured the brain of the young patient, Michael Colombini, of Croton-On-Hudson, N.Y., during the procedure Friday. He died of the injuries on Sunday, the hospital said.

The routine imaging procedure was performed after Colombini underwent surgery for a benign brain tumor last week. Westchester Medical Center officials said he was under sedation at the time of the deadly accident.

Hospital Takes ‘Full Responsibility’

FIRST FATAL MRI ACCIDENT

MRI EATS BED….

MAGNETIC FORCES

Torque

Twisting and pulling force on objects.

Objects may be pulled or twisted out of position and will tend to align along the magnet’s field lines.

Internal injuries can result if this involves an implant, prosthesis, surgical staples, aneurysm clips, etc.

ACOUSTIC NOISE

Caused by the interactions of the magnetic field created by pulses of the current through the gradient coil with the main magnetic field.

Loudest noise range between 110-120dB.

Noise levels increase with field strength.

ACOUSTIC NOISE

May create discomfort, anxiety, and even temporary hearing loss.

Disposable earplugs and/or headphones are recommended in high-field systems.

Ear protection sign.Earplugs or headphone required - for patients especially infant and children.

CLAUSTROPHOBIA

A psychological reaction to being confined in a relatively small area.

Reported in about 1-4% of cases as a reason to interrupt the MRI examination.

Short and wide open MRI are advantageous.

Can be overcome by detailed explanation, careful attention, special equipment, sedatives.

QUENCHING

Quenching the magnet is DEACTIVATING THE MAGNETIC FIELD OF THE MAGNET.

A quench is an escalating reaction to heat.

It causes the cryogens (helium) to boil off rapidly, which in turn causes the loss of the static magnetic field.

May occur unexpectedly or from pressing the EMERGENCY button.

QUENCHING

As the superconductive magnet becomes resistive, heat will be released.

To protect patients and operators, the evaporated helium requires emergency venting systems – quench pipe through the roof or the wall.

If large amounts of helium gas escapes into the examination room – risk of frostbites, asphyxiation and injury due to panic.

QUENCHING

Large quantities can completely displace oxygen from the entire room and if inhaled may cause loss of consciousness within 10 seconds with the possibility of asphyxia and death.

Patients and staff must therefore be evacuated immediately from the scanner room if a quench occurs.

CONTRAST MEDIA

Gadolinium based contrast agents (GBCA) are extremely well tolerated by the vast majority of patients.

Reactions resembling an “allergic” response are very unusual and vary in frequency from 0.004% to 0.7%.

Severe, life-threatening anaphylactoid or nonallergic anaphylactic reactions are exceedingly rare (0.001% to 0.01%).

CONTRAST MEDIA

The frequency of acute adverse reactions is about 8 times higher in patients with a previous reaction to gadolinium-based contrast media.

Persons with asthma and various other allergies to food or medications are at greater risk, with reports of adverse reaction rates as high as 3.7%.

CONTRAST MEDIA

At risk patients should be covered with oral prednisolone.

Breast-feeding mothersLess than 0.04% of the iv dose is excreted

into the breast milk in the first 24 hours.

Expected systemic dose absorbed by the infant from the breast milk is less than 0.0004%.

CONTRAST MEDIA

The available data suggest that it is safe for the mother and infant to continue breast-feeding after receiving such an agent.

If the mother remains concerned about any potential ill effects to the infant, she may abstain from breast-feeding from the time of contrast administration for a period of 12 to 24 hours.

CONTRAST MEDIA

Gadolinium-based contrast agent in pregnancy

Current radiology practices and recommendations discourage the use of gadolinium-based contrast agents during pregnancy because their safety for the fetus has not been proven.

Because it is unclear how GBCAs will affect the fetus, these agents should be administered only with caution.

SAFETY GUIDELINES

GENERAL SAFETY INFORMATION

Ensure system is operated by qualified personnel only.

Provide safety training for medical and non-medical staff.

Warning signs must be clear in MR area.

Report accidents to proper authorities.

GENERAL SAFETY INFORMATION

Keep MR door closed at all times.

MR area must be a restricted zone.

Create EMERGENCY plan for evacuation.

Call service to notify incident of emergency.

Do not use unapproved accessories or software.

SAFETY GUIDELINES

SAFETY INFORMATION FOR NON-MEDICAL STAFF – Engineers, Cleaners, Rescue Workers:

Warning signs must be observed.

DO NOT enter MR room unless given permission.

Use non-magnetic tools, equipment in MR room.

SAFETY GUIDELINES

SAFETY INFORMATION FOR MEDICAL STAFF – Doctors, MR Technologists, Nurses:

Observe warning signs.

Do not enter MR room unless authorized by person on duty.

All equipment must be checked for MR compatibility.

SAFETY GUIDELINES

Patients must be screened.

Personnel must be screened if they are not familiar with the MR environment before.

Record patients’ data, eg weight, age, correctly.

SAFETY GUIDELINES

Proceed with extra caution:Claustrophobic patients.Children.Elderly patients.Persons that have less sensation.Persons that cannot communicate.Unconscious, sedated or intensive care

patients.Pregnant women.

SAFETY GUIDELINES

DO NOT PERFORM MR EXAMINATION IF PATIENT HAS METALLIC AND ELECTRICALLY CONDUCTIVE DEVICES OR IMPLANTS THAT MAY BE AFFECTED BY ELECTROMAGNETIC FIELDS. Eg Pacemakers, aneurysm clips, implanted defibrillators.

SAFETY GUIDELINES

EMERGENCY PLANEmergency plans should be devised and

discussed with emergency staff.

Emergency phone numbers must be available.

Location maps for :Emergency buttons.Emergency exits.

SAFETY GUIDELINES

In the event of an EMERGENCY or ACCIDENT:

Remove patients and personnel from MR Room.

Notify emergency staff.

DO NOT PRESS QUENCH BUTTON if no one is stuck inside the Magnet.

(No immediate danger to patients or staff)

SAFETY GUIDELINES

EMERGENCY RUN DOWN UNIT (ERDU) or ‘QUENCH’ BUTTON can only be pressed if:

Life threatening to patient or staff – stuck by magnetic objects inside magnet and cannot be removed.

Safety personnel such as a fireman needs to put out a fire in the MRI room.

SAFETY GUIDELINES

DO NOT PRESS QUENCH button if:

an object is stuck but not life threatening.

Inform the hospital authorities for next course of action.

SAFETY GUIDELINES

Other EMERGENCY Buttons that can be activated anytime if required are:

ELECTRICAL STOP button – to shutdown the MR in an emergency situation e.g. Fire, flood.

Patient TABLE STOP button – to remove patient from magnet by pulling table manually.

Incident Injury or Death

Damage to MR

Damage to personal belonging

Person resposible e

Quench

O2 tank NO YES NO Doctor No.Ramp down

O2 tank NO YES NO Nurse No. Ramp down

Wheelchair NO YES NO Ragiographer NO

Video camera NO YES YES Camera-manRadiographer

NO

Helium tank YES YES YES Engineer NO. Ramp down.

Hearing aid NO NO YES Radiographer NO

Magneticsandbags

NO YES YES Doctor NO

O2 tank holder

NO YES NO Radiographer YES (not necessary)

REPORTED INCIDENTS IN M’SIA:

THANK YOU FOR YOUR ATTENTION