磁共振安全信息简介(1)

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Projectile Accidents
• The fringe magnetic field can be deadly • Valhalla, N.Y. • Westchester County Medical Center • July 27, 2001 • Six year old Michael Colombini was fatally
• An anesthesiologist was in the scan room with the patient
• The built-in oxygen delivery system failed • A nurse heard the anesthesiologist calling
for oxygen
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Signage
• FDA Guidance for the Submission Of Premarket Notifications for Magnetic Resonance Diagnostic Devices states:
• "The controlled access area should be labeled "Danger High Magnetic Field" at all entries."
-At least two deaths have resulted from MRI Scans on patients with pacemakers.
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Foreign Materials in the Body
• Heating of metals and implants has not been significant (even for large prostheses)
Other Stuff
பைடு நூலகம்
Projectile Accidents
• The MRI magnets are ALWAYS on (24 hours/day, 365 days/year)
• There is a STRONG fringe magnetic field around the magnets
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M R I Physics Course
Other Safety Issues
Static Magnetic Fields Time Varying Magnetic Fields
RF Magnetic Fields Auditory Safety
FDA Safety Guidelines Contrast Agents
• The presence of certain foreign materials in the body can be fatal in an MRI magnet
• Deaths have occurred due to the presence of aneurysm clips and cardiac pacemakers in patients undergoing MRI
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Foreign Materials in the Body
• Foreign material in the body is a concern in MRI
• Foreign material is any material in the body other than the flesh and bones that we are born with
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Fatal Accident Details
• The nurse delivered a STEEL oxygen cylinder to the anesthesiologist thinking it was safe (ALUMINUM)
• Within 3 to 6 feet of the magnet, the STEEL cylinder flew into the bore, fatally injuring the patient
• The term "warning" does not convey the importance of a situation that may not only be potentially hazardous, but has been responsible for serious injuries and deaths.
injured “when an oxygen canister was turned into a guided missile by the powerful MRI magnet”
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Fatal Accident Details
• Michael Colombini was in the bore of a GE Signa
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M R I Physics Course
Other Safety Issues
Psychological Distress Cryogen Safety
Experiences at Higher Magnetic Fields Pregnancy
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Safety
Why worry about biological and safety issues? -The patient is exposed to: Static magnetic field B0: < 3.0 T Time varying magnetic fields (gradients) RF magnetic fields (B1) Acoustical noise Psychological distress (claustrophobia) Contrast
• Wide variety of foreign material is intentionally and unintentionally present in patients, health care providers and others
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Foreign Materials in the Body
• Sight has been lost by movement of ferrous metal in the eye resulting in vitreous hemorrhage (2.0 mm x 3.5 mm iron fragment @ 0.35 T)
• Prostheses are usually securely anchored to bone and are usually non-ferrous.
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Foreign Materials in the Body
• Fringe magnetic fields stronger than 5 Gauss can affect cardiac pacemakers.
• To protect patients and others having pacemakers there is a 5 Gauss Exclusion Zone around MRI magnets.
• The fringe magnetic field is confined to the scan room
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Projectile Accidents
• The fringe magnetic field can cause ferrous metal objects to fly into the bore of the magnet with great force and speed
• At MCGHI, the Exclusion Zones are the MRI scan rooms
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Fringe Diagram of Active Shield 1.5 T*
5 Gauss
26’ 4”
16’ 6”
*Siemens Symphony 17
Safety (continued)
Caveat
• This lecture emphasizes MRI safety for high field (1.5T and 3.0T) superconducting magnets such as those used at MCGHI.
MRI Safety
Projectile Accidents Foreign Materials in the Body
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Safety (continued)
-The patient is also exposed to: Metal implant accident (foreign materials in the body) Cryogen accident Projectile acident
• There are resources for assessing safety of foreign materials in MRI
• F.G. Shellock. Reference manual for Magnetic Resonance Safety: 2003 Edition Salt Lake City: Amirsys Inc. 2003.
• Ferrous metal objects contain iron (steel) • The closer you are to the bore of the magnet,
the stronger the fringe field
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As you approach the magnet, the fringe magnetic field gets STRONGER
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My Favorite Horror Story
Here's one I heard from an Oxford Magnets engineer which was later independently verified by a technologist who had been hired to work at this site. A brand new magnet had just finished being installed into a brand new building. All of the acceptance testing had been completed and the magnet was to be turned over to the customer the very next day. There was only one minor problem to be dealt with first. One of the sprinklers in the scan room had a tiny leak. A welder was brought in to fix the leak, but somebody forgot to tell him that the magnet was at field. So..... in walks this welder with his acetylene torch system. His tank flies into the magnet, the valve breaks off, sparks and catches fire. Since he was in there to fix a leak in the sprinkler system, it had been turned off first. The brand new building burned to the ground!