mr safety iu nov2013 v2 - indiana university …mri/seminars/slides/mr safety.pdf radio frequency b...
TRANSCRIPT
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