Transcript Dangers in MRI environment

Dangers in MRI environment
Sources of dangers in MRI
environment
Components of MRI
Strong Static Magnetic Field
Time varying magnetic field
Radiofrequency energy source
Effects of the Fringe Magnetic Field-Static SMF
The magnet produces forces that interact with
susceptible materials. The effect of the SMF may
reach a distance far away from the magnet.
The effects of the fringe field depend on many factors:
The strength of the magnet
The distance away from the magnet
Shielding
The degree of susceptibility of the objects
The location in accordance to the center of the
isocenter
The strength of the magnet
FDA approves 3 T for clinical use while in
research there are strong magnets up to 10 T
FDA:MRI
Safety
The boy, Michael
Colombini of
Croton-onHudson, N.Y.
A six year old boy
undergoing an MRI
(Magnetic Resonance
Imaging) scan was
killed by a
ferromagnetic oxygen
tank that was pulled
into the MR scanner.
Stronger magnetic field
stronger effects
The effects of magnetic field on loose
objects
Attraction of ferromagnetic susceptible objects
by the translational force
The magnet attracts loose objects within the
fringe field
Small objects such as paper clips and hairpins have a terminal
velocity of 40 mph when pulled into a 1.5 T magnet
Only MRI compatible safe equipments can be brought
into the scanner in CTI
electronic devices and implants
The effects of magnetic field on electronic devices
Physiological interaction with electronic devices:
Magnetic force may interfere with Electronic
and physiologic devices by inducing voltage or
interfere with the function of the device, for
example neuorostimulator and cardiac
pacemaker, may change their functionality
sequence or stop working.
Spine stimulator
Deep Brain Stimulator
The effects of magnetic field on secured
objects
Rotation of the secured objects by the rotational force
secured objects :Ferromagnetic inside the body such as
implants
Vascular stent
Absolute contraindications to MRI
Cardiac pacemakers/pacemaker wires
Electronically, magnetically, or mechanically
activated implanted devices
Metallic orbital foreign bodies
Tissue expanders
Ocular prostheses
Dental implants
Relative contraindications include:
Intracranial vascular clips
Extra-cranial vascular clips
Intravascular coils, filters, and stents
Heart valves
Middle ear prostheses
Penile prostheses
Shrapnel/foreign bodies
Halo vests
Devices that are relatively safe to
study include
Surgical hemostasis clips (after a 2-3 month post
surgery delay)
Orthopedic prostheses, pins, rods, and plates
Dental fillings and orthodontic braces
Intrauterine devices (IUDs) and contraceptive
diaphragms
Metal Implanted devices artifacts.
Metal Implanted devices may
distort the images due to its
susceptibility causing artifacts.
artifacts
Biological effects
As yet, no long term adverse biological effects of extended
exposure to the magnetic field associated with MRI have been
documented injuries, or even death.
Pregnant Patient safety
1-Magnetic Field
Data currently available about hazards of
magnetic field on fetus/embryo does not
show any contraindication to scan
pregnant patient, however, this current
information does not exclude future
discovery of potential hazards of magnetic
field on pregnancy.
Pregnant MRI
Dangers in MRI environment
Sources of dangers in MRI
environment
Components of MRI
Time varying magnetic field
Radiofrequency energy
source
Part 2 Gradients
Components of MRI
Time varying magnetic
field (Gradients)
Effects of rapidly changing magnetic filed
According to Faraday’s law of induction, changing magnetic fields
may cause induced electrical current in conductors within the body.
The gradient magnetic force strength increases away from the
isocenter.
conductors in the body, blood vessels,
induced electrical
muscles and nerves,
current
electrical current
EPI MRI
Rapidly changing magnetic field
especially in EPI sequence may cause
nerve stimulation or muscle tissue to
excite.
Faraday’s Law of induction equation
db/dt =dV, where db is the magnetic
field change (which is caused by the
gradients), dt is the change
overtime, and dV is the change in
voltage that result from altering the
magnetic field over time.
Applications of the equation
Db/dt=dv
20T/1sec=20v
Db/dt=dv
20T/5sec=4v
Db/dt=dv
10T/5sec=2v
Effects of rapidly changing magnetic
filed
Tingling or
Tapping sensations
Avoid Gradients effects
Increase time between scans
Do not use fast sequences
Avoid Gradients effects
Do not allow patients to make
circuits: separate hands and feet
Noahs MRI accident.
On November 22, 2009 we handed Noah
off to the MRI staff (for his first MRI since
the discovery of his brain tumor) so he
could be put to sleep for his scan. After
he awoke from the scan, we were
questioned about the injury to his arm.
The staff quickly realized that he had
been somehow burned during his MRI
scan.
Part 3 RF(B1)
Components of MRI
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Radiofrequency energy
sources
Effects and safety of Radio Frequency Pulses
RF is an energy sent to the body..
The Transmitter coil produces the RF which enters the
body
The range of frequencies is from 10
to 200 MHz.
The Electromagnetic Spectrum
RF transformation into heat
Some of the RF will be absorbed by
the body tissues and transformed
into heat. The amount of heat that is
absorbed by the body is measured
by Specific Absorption Rate (SAR).
The unit of SAR
Specific Absorption Rate (SAR).
Watt/Kg is the unit of SAR
Effects and safety of Radio Frequency Pulses
RF may induce electrical current in the body,
this result in the generation of heat .
The presence of any conductor inside the
body may concentrate the electrical current
and produce heat due to resistance of the
tissues heat may cause local burns
Specific Absorption Rate (SAR)
The ability of patient to dissipate heat during MRI depends on many
factors such
ambient room temperature
,
coil type,
RF pulse amplitude,
sequence type,
number of slices,
TR,TE, Saturation pulses
air flow through the bore
,
volume of tissue being scanned
.
Some parts of the body have very limited ability to dissipate heat
that may include the cornea and the testicles
Effects and safety of Radio Frequency Pulses
Heat deposition is increases with higher magnetic field.
The FDA guidelines for maximum Specific Absorption Rate (SAR)
exposure
4 Watt/kg averaged over 15 minutes for the whole
body
3 Watt/kg averaged over 10 minutes for the
head
12 Watt/kg per gram of tissue over five minutes for the extremities
Part 4 Other sources of danger
Sources of dangers in MRI environment
Acoustic hazards.
Fast switching of the gradients during scanning produce noise
that may exceed 99 db in the bore, this high level of sound may
cause hearing impairment. The noise level is higher with EPI
sequences.
Psychological hazards
People may develop claustrophobia, feel irritable, and may panic
during the exam. These hazards may be caused by confining into
small space and noise
Laser light
Used by the technologist to set the center point; laser
light may have negative effects on the eyes
Contrast Media
MRI Contrast medium Side effects…
Renal disease
Nausea and/or vomiting
Slight transitory increase in bilirubin and blood iron
Mild transitory headaches
Hypotension
Gastrointestinal upset or rash
Anaphylaxis and/or respiratory problems
Death (2/500,000 injections
Contrast medium Contraindication
When scanning pregnant women .
Contrast medium may cross blood barrier into placenta.
In women choosing to breast feed
In patients with hemoglobinopathies, hemolytic anemia, sickle cell anemia, hematological
disorders
In patients with renal disease (CrCl < 20 ml/min)
In patients with an allergic history or diabetics
sthma
A
Patients with unstable angina or New York Heart Association functional class IV heart failure
Zone number what?
The American College of Radiology (ACR) has developed a set of guidelines to be used in the
design of the MRI suite utilizing four zones:
Zone I. Any area freely accessible to the general public.
It should lie outside the MRI suite but lead to its entrance.
Zone II. Serves as a buffer zone. Includes the reception and waiting areas.
Zone III. Areas restricted to MRI personnel and other individuals and equipment that have
been properly screened. MRI personnel are in charge of supervision and safety of this room.
Zone III Includes the MRI control room. The fringe field in this area is .5mT (5 gauss). A clear
red line should be made visible.
Zone IV. This is the scan room itself. It should be marked with the necessary warnings and
cautions pertaining to the magnetic field and should always be observable by the MRI
personnel
MRI Safety Procedures
Comprehensive safety policies and
procedures must be in place to
ensure the safety of patients and
personnel and it is the
responsibility of a qualified person
to assure the practice of the MRI
safety procedures.
knowledgeable interviewer
Although MRI Screening
form is an important safety
procedure, the availability of
a qualified knowledgeable
interviewer is a must.
MRI Safety Procedures
Limit and monitor access to the magnet. No one should pass the 5 Gauss
line without being checked for Magnetic safety.
Use a detailed screening sheet for all subjects, patients, caretaker and
personnel before entering the magnet room.
The screening sheet must be reviewed by a qualified and authorized
interviewer who can approve or deny access to the magnet room and or
have access for resources to clear any ambiguous condition.
checking the safety of devices include, manufacturer documentation and
contact information, Implant card, peer-reviewed published information,
web searches and consultation with designated safety experts such as MRI
physicist, MRI Radiologist or licensed MRI technologist.
MRI Safety Procedures
Know what you dealing with
MRI Safety Procedures
It is important to recognize the strength of the magnet when
checking for the safety of implants. For Example, 1.5TMRI safe
materials or implants may be not safe for 3T.
A second brief interview must be performed just before entering
the magnet room to remind the subject of any unsafe implants
or materials.
For a safe and diagnostic MRI exam, participants could be
required to remove all clothes and jewelry and wear a gown
clear of any metallic parts or contrast residues.
The screening form must be documented in writing with the
participant and interviewer’s signature and date.
Never scan a patient
known to have a ferrous
or electronic device,
implant, or prosthesis
contra-indicated for MR.
MRI Safety Procedures
All items and devices that need to be entered to the
magnet room should pass the Magnetic safety check.
A sensitive ferromagnetic-detector may be installed at the
door of the magnet room or a hand held device may be
used to check for any ferromagnetic material.
In case of patient emergency, the scan may be aborted,
patient must be pulled out of the magnet, provide medical
help outside the magnet room as needed and call for help.
ferromagnetic-detectors
Hand held ferromagnetic Detector
quench
A quench is a process whereby there is a sudden loss of absolute
zero of temperature in the magnet coils, so that they cease to be
superconducting and become resistive. Magnetic field is reduced
to 0.02T within 20-30secs.
This is accompanied by a loud bang, as the energy in the
magnetic field is converted to heat and rapid boil-off of liquid
helium.
If a large magnet undergoes a quench, the inert vapor formed by
the evaporating liquid helium can present a significant
asphyxiation hazard to operators, by displacing breathable air.
MRI Safety Procedures
In case of quench, the helium gas
may fill the magnet room and
raise the pressure to a degree
that makes it hard to open the
door, this may be accompanied by
a loud noise, the oxygen level
may decrease, and cryogens may
cause frostbite and asphyxiation.
Liquid helium is at -450 F – hypothermia & frostbite
What should you do during a Quench?
Helium is lighter than oxygen
Oxygen may be Compressed down
What should you do during a Quench?
Technologist should calm the patient
Open scan room door immediately
Evacuate all personnel from room
If door does not open, break glass between scan
room and control room
MRI Safety Procedures
Avoid Burns of the Patient’s Skin and internal tissues.
The technologist must ensure the presence of
adequate insulation between the skin of the patient
and the cables and the sides of the magnet gantry.
The cable should be placed straight, and loops must
be avoided. Metal tattoos may be insulated by using
an aluminum foil to cover the tattoos.
MRI Safety Procedures
Avoid Burns of the Patient’s Skin and internal tissues.
To avoid metal implant heating, the technologist may use
time separation between the sequences that may
increase the temperature to give time for heat to
dissipate.
The technologist must monitor the SAR
reading especially with the fast imaging
sequences such as echo planner.
Protect your patient from RF hazards
• Use padding every time! No exceptions!
• Use only manufacturer (GE) approved padding to protect your
patient from RF heating.
• Place padding to prevent the patient’s skin from coming in
contact with the scanner bore AND to prevent the patient’s
body from creating “loops” such as between the patient’s
knees, hands, and thighs
• Never use surface coils, such as the extremity knee and head
coil, without the proper padding inserts.
MRI Safety Procedures
Noise Reduction
Avoid acoustic hazard to patient and personnel.
Loud noise may trigger claustrophobia, and it may be harmful to the
patient’s hearing.
Ear plugs must be provided to the patient, and the technologist may
encourage patients to use them as patients are not familiar with the
strength of noise.
Headphones are very helpful to communicate with the patient during
scanning especially while using Flouro triggering in which the noise is
very loud during scanning, and to provide music for patients
Protect your patient from thermal hazards
• Always enter the patient’s correct
weight. The RF power monitor and SAR
limitations prevent excessive RF exposure
to the patient and are calculated based
upon the patient’s weight. Entering the
patient’s correct weight sets operating
limits that prevent excessive RF exposure.
Protect your patient from eye injury
• Protect every patient’s eyes from laser
radiation.
• Instruct patients to close their eyes when
the land-marking laser light is turned on.
• Never leave the laser light on after
positioning the patient.
Consult for pregnant patient
Consult MD for pregnant patient
to get the MRI exam, and for
nursing mother for having
contrast media.
MRI Safety Procedures
Avoid Peripheral Nerve Stimulation
When using the ultrafast sequences such as Echo
Planner Imaging (EPI), and due to the rapidly time
varying magnetic fields, some patients may feel muscle
twitching and tingling, and may see flashing lights in
their eyes.
The technologist can help reduce these effects by
swapping the frequency encoding right to left,
instructing patients to avoid loops by avoid crossing
their hands and ankles, and to ask the patient to use the
alarm to warn the technologist of any inconvenience
MRI Safety Procedures
Usage of Oxygen Supply for Patient in the Magnet Room.
The supply of oxygen for the patient in the magnet room should
be through an outside source, oxygen tube connection may be
used to supply the patient with oxygen during the exam.
In cases where oxygen outlet is not available, an MRI compatible
certified oxygen cylinder may be used.
The oxygen cylinder must be tested and verified for magnetic
safety before it can be taken to the magnet room.
MRI conditional safe fire extinguisher.
MRI Safety Procedures
Monitor the Helium range.
Monitor the SAR range.
Monitor the patient during scanning.
Maintain the MR scanner room below 21°C and
60% relative humidity.
Communicate with the subject during scanning.
Communicate with the subject during scanning
Ensure that you can communicate with your patient
• Provide all cooperative patients with the “Patient Alert”
squeeze bulb.
• Test the system by having the patient squeeze the bulb
before beginning procedure.
• Test verbal communication with the system intercom
before beginning procedure.
Terminology and signs.
It is fundamental to understand the terminology
and definitions approved and use in MRI safety.
Emergency Procedures
The participant needs to be taken out of the scan room
immediately!!! This is very important!
Dial 911
Inform the emergency operator what type of code team is
needed CARDIAC ARREST, FIRE OR …
Give the location of the code
The caller will hang up last
Emergency Procedures
Close and lock the scanner room
Direct the code team to the emergency.
Another person needs to make sure nobody enters
the scan room. NO WTH YOU! REMOVE THE KEY
Emergency Procedures
Use the MR safe Gurnee to bring the patient safely out of the
room in the event of a code
START Cardiopulmonary Resuscitation if need
Are you certified For CPR?
The crash cart and defibrillator are NOT MRI safe! Therefore a
code should NEVER occur in the MRI scanner room.
CARDIAC OR RESPIRATORY ARREST IS NOT A
REASON TO QUENCH THE MAGNET
References
Brown, Jeffrey J, Thomas Schrack, Alan H. Stolpen and Daniel Thedens, MRI for
Technologists – Technical Considerations of MRI, 2006
Magnetic Resonance Technology IP - MRI Patient Information, www.mrtip.com/serv1.php?type=pin&sub=1 - 78k -, Received November 24, 2007.
MRI Safety Patient Questionnaire, www.mr-tip.com/serv1.php?type=pin&sub=1
- 78k -, received November 24, 2007.
Parkside Magnetic Resonance Center - Preparing Your Patients for MRI,
www3.americanradiology.com/library/CLINICAL/mriclinical.pdf www.mrtip.com/serv1.php?type=pin&sub=1 - 78k -, received November 24, 2007.
Safety in Medical Imaging Procedures,
www.radiologyinfo.org/en/safety/index.cfm?pg=sfty_mr - 23k, received
November 24, 2007.
The ACR created a multidisciplinary blue ribbon panel to address
critical issues in MR safety. Initially published in the American Journal
of Roentgenology in June 2002, updated in May 2004, March 2007,
and then markedly expanded and updated in 2012 (for 2013
publication in the JMRI), the ACR Guidance Document for Safe MR
Practices: 2013 addresses numerous MR safety related topics,