Magnetic resonance imaging (MRI) uses strong magnetic fields and radio waves to generate images of the body's internal structures. While MRI is generally safe, certain safety considerations must be addressed regarding the static magnetic field, time-varying gradient magnetic fields, and radiofrequency fields used. Key risks include attraction of ferromagnetic objects, acoustic injury from loud noises, and heating of tissues from radiofrequency exposure. Guidelines limit exposure levels and recommend screening patients for implants to ensure safe MRI examinations.

1. Presenter : Sujan Karki
B.Sc. MIT 2nd year
National Academy of Medical Sciences(NAMS)
BIR HOSPITAL
Safety And Bioeffects of MRI

2. Topics Included..
•Static Field Considerations
•Gradient Field Considerations
•RF Field Considerations
•Common MR Contrast Agents

3. Introduction
• Magnetic Resonance Imaging (MRI) has a superior soft-tissue contrast
compared to other radiological imaging modalities and its physiological and
functional applications have led to a significant increase in MRI scans
worldwide.
• Protection of patients and other healthcare workers from potential bio-effects
and risks of the magnetic fields in an MRI suite is therefore essential.

4. Main Magnet
• The MR imaging magnet is essentially a large coil of
wire wound around the axis of the bore, when an
electric current is applied to this wire, a magnetic
field is produced.
• Modern clinical MR imaging field strengths range
from 1.0 to 3.0 T, with field strengths for research
systems of up to 9.4 T.
• These fields are approximately 10,000– 100,000
times the magnitude of the earth’s surface magnetic
field.
• For imaging purposes, the magnetic field strength
must be uniform across the imaging field of view
(typically 30–60 cm); hence, the most common
systems are cylindric

5. Fringe field
• The stray of magnetic field that can
be felt outside the bore of magnet.
• Distance from the isocenter at
which the magnetic field strength
falls of to 5gauss.
• For the safety reasons the person
with implants are askes to stay
outside the 5gauss field.
• 10 G may affect computers while
fields of 30 G may magnetize your
watch and erase your credit cards.

6. Magnetic Shielding
• Passive shielding OR
Active shielding.
• Magnetic Shielding are used
to reduce the fringe field.

7. As you approach the magnet, the
fringe magnetic field gets
STRONGER

8. • There are two major safety issues regarding the static magnetic fields
used in MR:
• attraction of ferromagnetic material towards the magnet
• biological changes.

9. Translational Force and Torque
• When a magnetic object is placed in the field of an MR imaging unit,
it is subject to translational force and/or torque.
• Translational and rotational forces can result when any metallic
object interacts with static or changing magnetic fields.
• The force on a magnetic object increases with ferromagnetic
composition, total mass, and the gradient of the magnetic field
strength at its location.
• Although the strongest magnetic field is at the isocenter of the
magnet, the strongest forces are present where the gradient is
largest.
• The largest gradients occur well away from the isocenter and in
some cases may be near the ends of the magnet bore.

10. Projectile Injury
• This is a major safety concern to patients and medical personnel who enter
the MRI room.
• Any ferromagnetic objects (earrings, scissors, hairpins, pagers, clamps,
tie-pins or screwdrivers) may become airborne and accelerate towards the
center of the bore of the magnet.
• Anyone coming between the airborne object and the magnet may become
impaled by it.
• Ferromagnetic objects may reach velocities in excess of 66 km/h or 40
m.p.h. in the presence of a 1.5T magnet.
• Newer magnets are built to minimize the field strength outside the bore of
the magnet, a technique termed shielding
• It should be noted that the 5-G line does not safeguard against a
projectile incident, nor was it defined for that purpose.

11. Results of Projectile /Missile
Effect

12. Two hospital workers spend FOUR HOURS pinned to
MRI machine by metal oxygen tank that was catapulted
across room when device's giant magnet was turned on

15. No loose metallic objects should be taken into the
Scan room

16. Contd…
• Those that do contain some ferromagnetic materials may be deemed MR safe if
the amount of material is too small to cause any substantial force or if the
device is anchored securely (eg, most dental implants and orthopedic screws).

17. Displacement of these implants may cause life threatening
situation

18. Cochlear Implants
SYNCHRONY’s unique rotatable magnet self-aligns to
the magnetic field of the MRI scanner. This neutralizes
any adverse effects of magnetic torque—enabling
comfortable scans.

19. Pacemakers and Defibrillators
• Until recently, most devices were not FDA-approved for
MRI. They had been considered risky because it was
feared that the high-strength magnetic fields used for
the scanning could disrupt a pacemaker's or
defibrillator's circuits.
• Yet, when researchers reviewed 212 MRI examinations
involving 178 patients with these nonapproved devices,
they did not find a single problem with how they
functioned.
• The researchers concluded that MRI is safe for someone
with a device implanted after 2000, as long as the
device is checked before and after the procedure and its
pacing function is monitored during the scan.
• In the last seven years, the FDA has approved newer and
more expensive devices that are designed to be safe for
MRI; these are labeled "MRI conditional."

20. Contd..
• Several types of implants may require a waiting period before an MR imaging
examination can be performed.
• Many cardiac and vascular stents, do not become securely embedded into
the vessels until 6 weeks after implantation,these stents are considered MR
safe afterward.
• Some gastrointestinal endoclips, typically used for hemostasis, can translate
or rotate within a magnetic field, but the majority are sloughed off and
passed at 2 weeks. Delaying a nonemergent MR imaging examination in this
case would bypass any potential safety issues and could eliminate imaging
artifacts.

21. Biologic effect of Static Magnetic Feild
• No known biological long
term effect on human below
2.5T(1Tesla is equal to 10000
gauss)
• Some biological effects are
noticed when exposed to a
field strength of 4.0 T.

22. Gradient System
• magnetic field gradient spatially encode the MR imaging signal.
• Modern gradient systems can carry electrical currents of hundreds of
amperes.
• Rapid fluctuations in current result in microscopic movements of the coils,
which lie within an audible frequency range; this is the source of the
knocking and buzzing noises.
• They require dedicated cooling systems to counteract the heat induced by the
large and changing currents.

23. Gradient coil

24. Acoustic Injury
• The FDA sets a maximum of 140 dB for an MR imaging
system and a maximum of 99 dB for a patient with hearing
protection.
• The majority of MR imaging unit noise originates from
gradient coils because they are subject to rapid changes in
current.
• Echo-planar sequences are typically the loudest, producing
sound pressures in the range of 110-120 dB.
• Typically disposable earplugs or headphones which can
reduce noise levels by 10–30 dB.
• major MR vendors have released low-noise imaging software
package known as SilentScan (GE), QuietX (Siemens),
and ComforTone(Philips).

25. PERIPHERAL NERVE STIMULATION
• Rate of change of the magnetic field over time, termed dB/dt and expressed in
teslas per second.
• Induced electrical currents can produce painful neurostimulation in patients.
• This stimulation is most often felt in the arms and legs, where the gradient
magnetic field is changing most rapidly, and is referred to as peripheral
neurostimulation.
• Sensitivity to peripheral neurostimulation varies widely among individuals, and it
is possible that an imaging examination that is well tolerated by one patient will
be uncomfortable for another.
• MR imaging studies that pose the greatest risk of peripheral neurostimulation are
those that involve high-bandwidth readouts and/or rapid gradient switching, such
as echo-planar imaging.

26. Radiofrequency coils
• MR imaging units require transmission coils to excite nuclear magnetization
inside the patient’s body for imaging and receive coils to acquire the nuclear
MR signal after transmission.
• These coils are tuned to the proton resonance frequency of the subject, which,
at typical clinical magnetic field strengths, happens to lie within the
radiofrequency range of the electromagnetic spectrum, hence the termed as
radiofrequency coils.
• Coils of different sizes and shapes are available to accommodate different
anatomic areas.(volume coil, surface coil, phased array coil, Quadrature Coils )

27. Different types of RF Coils
• Volume coils Surface coils
Phased array coils

28. Contd..
• Radiofrequency coils need to be very sensitive to acquire MR signal,
which unfortunately makes them sensitive to unintentional background
electronic noise.
• Magnet room is encased by a thin metallic shield to block all external
electromagnetic signals that might fall within the operating frequency.

29. Specific Absorption Rate (SAR)
• The radiofrequency power delivered to tissue during an MRI examination is
referred to as the SAR.
• Expressed as watts per kg (W/kg).
• Radiofrequency power deposition results in heating of patient tissues.
• Current FDA guidance limits SAR whole-body exposure in patients with
“normal thermoregulatory function” to 4.0 W/ kg in the body and 3 W/kg
for head.
• The electric fields increase approximately linearly with the main magnetic
field strength. Therefore, if the magnetic field strength is doubled—for
example, from 1.5 T to 3.0 T—the SAR will increase by a factor of
approximately four if other parameters are kept equal.
• As field strengths increase, techniques for estimating and managing the
SAR will become more critical for patient safety.

30. contd
•Most MR imaging units can provide an estimate of SAR by
using the total radiofrequency power that is transmitted
per unit time with the patient’s weight and data on the
transmit coil coverage to compute the global average SAR.
•With most modern clinical imaging units, if any one of the
FDA limits is going to be exceeded within an examination, the
user is notified automatically, and the parameters must be
changed so that the SAR limits are not exceeded.

31. • The concern for a rise in tissue temperature is greater in certain
patients:
• Patients with reduced thermoregulatory capacity
• Cardiac impairment
• Hypertension
• Diabetes
• Old age
• Fever
• Impaired ability to perspire
• Pregnancy (risk for fetal heating)
• Drug regimes that may affect thermoregulatory capabilities
(diuretics, tranquillizers, vasodilators)

32. Contd..
• Because patient tissues can conduct electrical current, exposure of tissue to
radiofrequency pulses results in electrical currents that produce heating.
• Spin-echo MRI techniques use large radiofrequency pulses for the 90° and 180°
manipulation of tissue magnetization.
• Fast spin-echo (FSE) techniques apply large radiofrequency pulses very rapidly.
• As a result, spin-echo techniques, particularly FSE, deliver more radiofrequency
power, resulting in higher SAR and relatively more tissue heating.
• Gradient-echo techniques use much smaller radiofrequency pulses. Even though
gradient-echo techniques apply radiofrequency pulses very rapidly, the net
deposition of power is lower, resulting in lower SAR and less tissue heating.
• However, certain gradient-echo sequences, e.g., time-of-flight MR angiography,
apply radiofrequency pulses at such a high speed that they also result in high SAR.

33. Most SAR reduction approaches have associated
imaging consequences.
• Increase the TR, which can lead to longer scanning times.
• Reduce flip angles (for FSE sequences, use 60–130° refocusing pulses rather
than 180° refocusing pulses), which can alter image contrast-to-noise ratio or
signal-to-noise ratio.
• Reduce the number of slices in an acquisition, which can lead to longer
scanning times.
• Reduce the number of echoes in multiecho sequences, which can lead to longer
scanning times.
• Control the scanning room temperature and humidity.
• Take breaks between high SAR acquisitions or interleave high SAR and low
SAR acquisitions to allow patient cooling, which can lead to longer scanning times.

34. Burns
• The majority of MR imaging–related burns
occurred during routine examinations that
involved typical pulse sequences.
• Skin contact against radiofrequency transmit and
receive coils and cables can result in direct burns.
• modern coils and cables are typically insulated
and sealed within a thicker plastic protective
sleeve to provide a maximum safe distance.
• Even when coils and cables are appropriately
insulated, if they are pressed tightly against bare
skin, a direct burn can potentially occur as a
result of arcing through the insulation.

35. Contd..
• Gradient or radiofrequency coils provide the
source of the fluctuating magnetic fields, but the
current can be produced within any conducting
material, either internal or external to the body.
• Wires and leads—for example,
electrocardiography cables or jewelry (eg,
piercings)—can form an inductive circuit if they
are accidentally coiled.
• Some transdermal medicinal patches containing
trace aluminum have caused superficial burns.
• A cutaneous burn from a shirt that contained silver
particles was recently reported.

36. contd
•Tattoos are known to cause
susceptibility artifacts, but thermal
injuries rarely happen and are
suspected to occur only with very dark
inks which are richer in iron oxide.
•Transient discomfort and first-degree
burns have rarely occurred with
permanent eyeliners, which do not
necessarily contain ferrous materials

37. MR Imaging of Pregnant Patients
• there is no definitive evidence of harmful effects
from performing routine (nonenhanced) MR
imaging examinations in pregnant patients.
• lack of unanimity regarding teratogenic effects
and acoustic damage.
• A recently published retrospective case-control
study on the safety of MR imaging at 1.5 T in
751 human fetuses showed no adverse effects of
MR imaging exposure in utero on neonatal
hearing function or birth weight percentiles.
• Reeves et al looked at this issue in 2010 ‘No
significant excess risk of neonatal hearing
impairment after exposure of the fetus to 1.5 T
MR imaging during the second and third
trimesters of pregnancy’.
•

38. MR Imaging Contrast Agents
• Gadolinium is toxic but is caged by a chelate (DTPA).
• The chelate may be dissolved by the kidneys, releasing the
gadolinium.
• They are filtered in the fetal kidneys and then excreted into the
amniotic fluid. In this location the gadolinium-chelate
molecules are in a relatively protected space and may remain in
this amniotic fluid for an indeterminate amount of time before
finally being reabsorbed and eliminated.
• It is unclear what impact such free gadolinium ions might have
if they were to be released in any quantity in the amniotic fluid.
• The risk to the fetus of gadolinium based MR contrast agent
administration remains unknown and may be harmful.

39. Nephrogenic Systemic Fibrosis (NSF)
• Nephrogenic systemic fibrosis (NSF) is a rare, progressive, usually fatal
disease characterized by skin thickening, painful joint contractures, and
fibrosis of multiple organs including the lungs, liver, muscles, and heart.

40. EFFECTS SEEN AFTER NSF

41. Pathophysiology of NSF
• The strong association with renal insufficiency most likely relates to the prolonged
biological half-life due to prolonged excretion of gadolinium.
• However, other factors have been imputed, including metabolic acidosis, elevated iron
and phosphate levels, erythropoietin therapy, vasculopathy, and infectious/inflammatory
mediators.
• The pathogenesis of NSF is believed to begin with the displacement of the Gd ion from
its chelate by another metallic cation (Fe+3, Zn+2, or Ca+2) through a so-called trans
metalation reaction.
(Metal ion) + Gd-Chelate ↔ Metal-Chelate + Gd+3
• The free Gd ion is then deposited in the skin and other soft tissues.
• There it is engulfed by CD163+ iron-recycling and other macrophages creating an
inflammatory response and cytokine release.
• Circulating fibrocytes (immunologically unique CD-34 positive cells derived from bone
marrow) deposit in tissue, transforming into spindle cells that proliferate and
become the hallmark of the disease.

42. Tumor Contrast Enhancement and Whole-Body
Elimination of the Manganese-Based Magnetic
Resonance Imaging Contrast Agent Mn-PyC3A.

43. Magnetohydrodynamic (MHD) effect.
• When a conductive fluid travels through a magnetic
field, there is a voltage induced in the direction
orthogonal to both the magnetic field lines and the
direction of flow of the fluid,this phenomenon is
called the magnetohydrodynamic (MHD) effect.
• moving blood can induce electric potential on the
order of millivolts within a static magnetic field.
• magnetohydrodynamic effect is not considered
hazardous at the magnetic field strengths that are
approved for clinical use.
• However, at higher field strengths, the probability
exists that induced potential might exceed 40 mV,
the threshold for depolarization of cardiac muscle

44. Pediatric MR Imaging
• Pediatric MR Imaging MR imaging is especially appealing in the pediatric
setting because it eliminates risks associated with ionizing radiation.
• Pediatric patient is more vulnerable to anxiety, and younger patients may
not have sufficient language skills to follow commands to minimize image
motion artifacts.
• To alleviate patient anxiety, family members may be allowed to accompany
patients during examinations, but they must undergo the same complete MR
imaging safety screening process.
• Use of sedation or general anesthesia to ensure that images of diagnostic
quality
• Cution be used in administering GBCAs to neonates and infants because of
their potentially low glomerular filtration rates and renal immaturity.

45. Magnetic phosphenes
• Flashes of light that can sometimes be perceived with
eyes closed
• Caused by the electric stimulation of the sensory
receptors of retina
• None at 2 T
• Reported at 4T

46. MRI SAFEY ZONE
• patients and MR imaging personnel are the focus of
many safety policies, greater hazards may be
associated with individuals who are not patients and
who do not regularly work in the MR imaging
environment may bring ferromagnetic materials
accidentally bypass screening checkpoints .
• Specific examples of the latter include physicians,
nurses, and nonimaging technologists who enter
the MR imaging suite in urgent situations; security
and cleaning personnel who are responding to
emergencies or are unaware of MR imaging safety
hazards; and patients’ family members and friends.

47. MRI EQUIPMENT ZONING

48. Claustrophobia
• Affects 5-10% of patients
Causes
• Restrictive dimension of the interior of the
magnet
•Duration of the examination
• Gradient coil induced noises
• The ambient condition within the imaging bore

49. Factors to reduce Anxiety
• Education and Explanation
• Trial visit to the department
• Presence of the relatives and friends
• Use of the mirror,prism or glass
• Good communication system
• Good light and ventilation
• Music
• Plesent thoughts

51. Quenching
• MRI magnets are cooled with the inert gas
helium (cryogen gas)
• When the gas is boiled off either intentionally
or unintentionally a quench will occur.
• Quenching shuts off the magnetic field in a
minute.
• Quenching can cause severe damage to the
MRI and therefore should be performed in the
extreme cases.
When to perform QUENCHING ???
• For every MRI there is a button to manually
quench the magnet which may be in the
control room or in the room with MRI.

52. QUENCH HAZARDS -ASPHYXIATION
•“New York Times Article: Worker at Hospital Dies; Gas
Leak Suspected, September 21, 2000. A worker was
asphyxiated by liquid nitrogen while installing an MRI. Six
other people were injured.”
•Individuals in the room can be asphyxiated if a quench
occurs. Remove patients and personnel as quickly and safely
as possible.

53. Screening Form
• Example of questions in radiology
assessment
• Level II personnel will ask all of
the questions to the right
•If any answers are yes, they will
seek more information

54. Ensuring Safe Practice
• Safety Checklists
• Establishing and maintaining consistent MRI safety education
among healthcare practitioners.
• Adequate MRI site access restriction and supervision by MRI
healthcare professionals over patients and other non-MR
personnel.
• Training for nonmedical personnel, such as maintenance staff,
housekeeping staff, and security officers.

55. Remember…
THE MAGNET
IS ALWAYS
ON!!!

56. References
• Safe Considerations in Magnetic Resonance Imaging (MRI) BJ J Abdullah, FRCR, SI Bux,
MRad & D Chien*, PhD, Department of Radiology, University of Malaya Medical Center,
50603 Knala Lnmpm and *Siemens, Ltd. Medical Division, Hong Kong
• A Practical Guide to MR Imaging Safety: What Radiologists Need to KnowLeo L. Tsai,
MD, PhD, MSc Aaron K. Grant, PhD Koenraad J. Mortele, MD Justin W. Kung, MD Martin
P. Smith, MD
• https://www.ajronline.org/doi/full/10.2214/AJR.14.14173 American Journal of
Roentgenology, Jerry Allison1 and Nathan Yanasak1
• Magnetic Resonance Imaging: Health Effects and Safety
• Questions and Answers in MRI
• Kwan-Hoong Ng, Azlan C Ahmad, MS Nizam, BJJ Abdullah Department of Radiology
University of Malaya Kuala Lumpur Malaysia
• MR Artifacts, Safety, and Quality Control1,Jiachen Zhuo, MS Rao P. Gullapalli, PhD
• Characterization of the Magnetohydrodynamic Effect as a Signal from the Surface
Electrocardiogram during Cardiac Magnetic Resonance Imaging ,GM Nijm1, S
Swiryn1,2,3, AC Larson1, AV Sahakian1,

57. questions
What do you think can a pregnant women perform MRI scan ?
What do you understand by fringe feild?
What you think could be done to perform MRI scans of Claustrophobic
Patients?
Whom do you think should be included while giving training to MRI safety?
Is it necessary to have RFT test before the administration of contrast media?