MRI SafetyWm. Faulkner, B.S.,R.T.(R)(MR)(CT), FSMRT

RF

3 Powerful Magnetic Fields

Static

Gradient

RF

3 Powerful Magnetic Fields

Static

Gradient

Magnetize the Tissues

RF

3 Powerful Magnetic Fields

Static

Gradient

Excite the Protons / Detect Signals

RF

3 Powerful Magnetic Fields

Static

Gradient

Localize the Signals

Static Magnetic Field

Vertical Field

Horizontal Field

SuperconductivityThe electrical resistivity of a metallic conductor decreases gradually as temperature is lowered. In ordinary conductors, such as copper or silver, this decrease is limited by impurities and other defects. Even near absolute zero, a real sample of a normal conductor shows some resistance. In a superconductor, the resistance drops abruptly to zero when the material is cooled below its critical temperature. An electric current flowing through a loop of superconducting wire can persist indefinitely with no power source

Field Strength

TeslaGauss

1 Tesla = 10,00 Gauss

The earth’s magnetic field is approximately!0.5 Gauss

Small bar magnet is approximately!100 Gauss

Powerful Persistent Magnetic Field1.5 Tesla MRI system is !

15,000 Gauss!30,000 x the earth’s magnetic field

Powerful Persistent Magnetic Field3.0 Tesla MRI system is !

30,000 Gauss!60,000 x the earth’s magnetic field

July 2001

JMRI 2013, Pg 3 JMRI 2013, Pg 3

Radio Frequency RF Burns

3rd Degree from Pulse Ox

www.simplyphysics.com

Initial Injury

Few days later

All too common injury

Always use proper insulating pads

Skin-to-Skin Contact

Street Clothes Can !Be Dangerous

Blouse catches fire during 1st sequence of a shoulder exam. 3rd degree burns to forearm.

- FDA MAUDE database

www.lululemon.com

Radio Frequency B1

Heating

Tissue Device

Radio Frequency B1

Heating

Tissue Device

Power In Cooling

Power InHeat

Cooling

If input is greater than output, heating occurs

Currently clinical systems cannot exceed!4 W/kg whole body

Normal Mode: No physiologic stress is expected

1st Level Mode: Physiologic stress can occur

From a GE system

Cooling Influenced By

Bore Temperature!Ambient Temperature!Relative Humidity!Air Flow Rate!Perspiration!Blood Flow

“Various underlying health conditions may affect an individual’s ability to tolerate a thermal challenge including cardiovascular disease, hypertension, diabetes, fever, old age, and obesity. In addition, medications including diuretics, beta-blockers, calcium blockers, amphetamines, and sedatives can alter thermoregulatory responses to a heat load. Importantly, certain medications have a synergistic effect with RF radiation with respect to tissue heating. The environmental conditions (i.e., ambient temperature, relative humidity, and airflow) that exist in the MR system will also affect tissue temperature changes associated with RF energy-induced heating.”

www.mrisafety.com

“Various underlying health conditions may affect an individual’s ability to tolerate a thermal challenge including cardiovascular disease, hypertension, diabetes, fever, old age, and obesity. In addition, medications including diuretics, beta-blockers, calcium blockers, amphetamines, and sedatives can alter thermoregulatory responses to a heat load. Importantly, certain medications have a synergistic effect with RF radiation with respect to tissue heating. The environmental conditions (i.e., ambient temperature, relative humidity, and airflow) that exist in the MR system will also affect tissue temperature changes associated with RF energy-induced heating.”

www.mrisafety.com Radio Frequency B1

Heating

Tissue Device

Radio Frequency B1

Heating

Tissue Device

Scalp burn from halo

wavelength @ 3 T is approx 2.4 meters!20 - 25 cm “worse case”

Field Strength, Frequency, Wavelength

Courtesy Frank Shellock, Ph.D.

Cervical Fixation Device at 3.0 T

For elongated or closed loop implant or device implant, heating can differ!significantly at different field strengths

Skull Pin 3-Tesla

Tem

pera

ture

(˚C)

18.00

20.00

22.00

24.00

26.00

28.00

30.00

32.00

Time (sec)

0 143 286 429 571 714 857 1000

Courtesy Frank Shellock, Ph.D.

MRI-Related Lead Heating: Pacing Lead, No IPG

1.5 (1.4-W/kg) vs. 3-T (3-W/kg)

Tem

pera

ture

(˚C)

18.00

26.00

34.00

42.00

50.00

Time (sec)

0 350 700 1050 1400

For certain lead lengths, less heating at 3-T/128MHz vs. 1.5-T/64MHz due to differences in resonant wavelength.

1.5 T

3.0 T

Courtesy Frank Shellock, Ph.D.

T/R Head Coil vs. Transmit Body/Receive-only Head Coil

T/R

Philips

Receive-only

GE

Transmit/Receive

Two Serious Injuries @ 1.0 TGuidelines not followed

1.5 T ONLY!T/R Head coil ONLY!Head SAR 0.1 W/kg

Courtesy Frank Shellock, Ph.D.

Time-Varying Magnetic FieldsGradient fields used for imaging

Used for spatial encoding

Strong magnetic fields that switch rapidly during imaging

Time-Varying Magnetic Fields

Current induction in conductive loops

Faraday’s Law of Induction

Changing field

time

Time-Varying Magnetic Fields

Current induction in conductive loopsSize and shapeConductive propertiesPosition / LocationGradient slew rate

Peripheral Nerve Stimulation VibrationDevice / component damage

Time-Varying Magnetic Fields

Eddy Current Induction

“Decisions based on published MR safety and com- patibility claims should recognize that all such claims apply only to specifically tested conditions, such as static magnetic field strengths, static gradient magnetic field strengths and spatial distributions, and the strengths and rates of change of gradient and radiofrequency (RF) magnetic fields.”

Labeling

MR Safe

MR Conditional

MR Unsafe

*ASTM standard F2503: Standard Practice for Marking Medical Devices and Other Items for Safety in the!

Magnetic Resonance Environment

ASTM Standard F2503* Defines Three Terms:

MR Safe

An item that poses no known hazards in all MR environments

MR Unsafe

An item that is known to pose hazards in all MR environments

MR Conditional

An item that has been demonstrated to pose no known hazards in a specified MR environment with specified conditions of use

Gadolinium

chelate, any of a class of coordination or complex compounds consisting of a central metal atom

attached to a large molecule, called a ligand

http://www.britannica.com/EBchecked/topic/108427/chelate

Gd+3

Non-Ionic

Non-Ionic

“...recently emerged among patient with renal disease”

Published 2001

“...recent emergence of this condition”“...suggested a possible infections and/or toxic agent”

Sadowski, E. A. et al. Radiology 2007;0:2431062144

Broome DR et al. AJR:188, Feb 2007 586-92

NSF

Non-Ionic

Non-Ionic

Fundam Clin Pharmacol. 2006 Dec;20(6):563-76

Published data: frequency of NSF not equal among all agents (Radiology 2008, 10.1148/radiol.2483072093)

ACR Grouping StabilityNo Unconfounded Cases of NSF

DotaremProHance

MultiHance

Contraindicated with eGFR < 30MagnevistOmniscanOptiMARK

Understand the risks

Provide the best outcome while minimizing risks

William Faulkner & Associates, LLC www.t2star.com