MRI Safety aspects for the anaesthesiologist
Magnet Safety Outline Understanding MRI Magnets,magnetic fields and safety issues Your role in MR Safety Metallic parts Screening Screening Subjects / Colleagues Other Safety Considerations What to do in case of Emergencies
Magnetism / Magnets All substances possess some form of magnetism. The degree of magnetism exhibited depends on the atoms that make-up the substance. Magnetic susceptibility is the ability of a substance to become magnetized. There exist: diamagnetic, paramagnetic, superparamagnetic and ferromagnetic substances Ferromagnetic substances which interfere most with the magnetic field, such as iron have a large magnetic susceptibility, it is easily magnetized permanently becoming a magnet itself. All magnets have a fringe magnetic field which exists in the vicinity surrounding the magnet.
Magnetic Fringe Fields The magnetic fringe field is the magnetic field which exists in the vicinity surrounding the magnet. This field may extend many meters from the magnet itself. Magnetic fields are measured in units of Gauss or Tesla. (1T = 10,000G) Magnetic field force lines
Magnetic Fringe Fields The fringe field of the 1.5 T Siemens Aera scanner 1m 1m 3m 3m
Magnetic Fringe Fields The fringe field of the 3T Siemens Trio Scanner
MRI Safety The STATIC MAGNETIC FIELD IS ALWAYS PRESENT 24hrs/day, 365 days/yr. EVEN WHEN THE MAGNET IS NOT IN USE.
What is wrong?
Who should know MR Safety issues? All personnel (hospital/university) that have a reason to enter the MR suite area should be trained in MR safety procedures at a certain level: MR technologists, students, researchers, transporters and other medical personnel Maintenance and janitorial personnel All personnel must be thoroughly briefed about the potential risks involved and reminded not to bring any ferromagnetic items into the magnetic field.
Common unsafe items MR technologists, students, researchers, transporters & other medical personnel Screwdrivers, Dect phones Scissors, Hemostats Scalpels, Syringes, Needles Stethoscopes Oxygen Cylinders Wheelchairs Clipboards, Metal Pens,
MRI Safety - Projectiles Projectile effects of metal objects seriously compromises safety. The potential harm cannot be over emphasized. Paper clips, hair pins accelerate to a velocity of 60 km/h @ 1.5T. Larger objects (scissors, etc.) can have higher velocities and may be fatal. Many types of clinical equipment are ferromagnetic and should never be brought into the scan room.
Metal Objects Becoming Projectiles
Metal Objects Becoming Projectiles
Fatal Accidents CAN Happen!
Controlled Access Area This area is labeled with the use of warning signs on every access door and markings to prevent the entry of any ferromagnetic object into this area to limit the access of unauthorized individuals and persons with metal implants.
Equipment The main magnetic field can damage equipment or personal items such as: Cameras Watches Bank cards / Credit cards / Access cards Hearing Aids Hairpins, Belts, Shoes Change
Chair removal
Screening Procedures At least one MR certified person must screen the subject for possible contraindications that could affect the MR scan or endanger the subject. Questions about implants should be discussed with a licensed MRI technologist or a radiologist before allowing the patient/subject to be scanned.
Screening Procedures
High risk Contraindications Cardiac Pacemakers (except in rare, controlled environments) Cochlear (inner ear) implants Ferromagnetic or unidentifiable aneurysm clips of the brain Implanted neuro stimulators (except in rare, controlled environments) Metal or unidentifiable foreign bodies in the eyes Any ferromagnetic material in the body
Bioeffects There is up till now no conclusive evidence for irreversible or harmful bioeffects in humans at and below 3.0T, but there do exist some reversible effects Localized tissue heating (caused by RF irradiation energy absorption in the tissue) Cutaneous sensations, dizziness, metallic taste (induced by gradient magnetic field switching, or fast movement in the magnetic field) Peripheral nerve stimulation, involuntary muscle contractions (induced by gradient magnetic field switching) Burn hazards (by electrical currents produced in conductive loops of material)
Acoustic Noise The MR scanner can produce very high acoustic noise levels. (Up till 120 db) Some subjects may experience discomfort from the associated noise of the scanner. Prior to scanning, it is necessary and obligatory that earplugs and/or headphones are provided to the subject to reduce the noise level.
Magnetic Field / Scan Room Emergencies If an emergency situation arises, you may need to quickly evacuate the subject from the scanner and remove power from the MR system. The type of the emergency will dictate which procedure you follow.
Magnetic Field / Scan Room Emergencies Each magnet is equipped with 3 different types of emergency buttons: 1 Emergency Stop / Shut Off Turns off all electrical power to the magnet 2 Emergency table release button 3 Quench button Causes immediate collapse of the superconductive magnetic field within minutes
1. Emergency Stop / Shut Off Shutting power to scanner required for life threatening situations such as: Fire, sparks, loud noises in the scan room or in the computer room Catastrophic equipment failure ***Keep in mind that when this button is pushed, it does not initiate a quench, the magnet remains at field. All ferromagnetic material should remain outside of the scan room***
2. Emergency table release Release of the patient table to manually pull it out of the magnet. This may be used in case of emergencies: When the emergency stop button (1) cutting the electricity to the scanner has been pushed When the subject has to be evacuated rapidly from the magnet In case of a general or local power shutdown
3. Quench Button THE ONLY TIME when quenching the magnet is required/allowed is when : A large magnetic object (e.g. oxygen tank, floor cleaner, ) traps a person against the magnet and a large risk of injury exists and no other method can prevent further injury or free the person. Do not touch a quenched magnet. It can contain an electrical potential of >1,000 volts on the surface and can be extremely cold. Do not attempt to pull large magnetic objects (oxygen tanks) from a magnet field by yourself (even when no subject is in the scanner). The object may become a projectile, causing a serious or fatal injury.
What is a Quench? A loss of superconductivity of the main magnet coil due to an induced local temperature increase in the magnet resulting in a rapid reduction of the current on the coil, a heat up of the magnet coil resulting in evaporation of the liquid helium. A quench may happen spontaneously or can be manually instigated by pushing the quench button. Quenching may cause severe and irreparable damage to the magnet. A magnet quench will result in several days downtime and total cost can run op to several ten thousands of euro s (If the magnet has irreparable damage costs are even higher up to a million euro). So never press the quench button except in a true emergency. Never attempt to test this button! It is sealed
Emergency Buttons @ TRIO QUENCH BUTTON 1 Button is located on the right wall next to the console QUENCH Console room 2 Button is located on the wall of the scanner room next to the door on the left side if you enter the room Scanner room QUENCH
Emergency Buttons @ Aera Emergency table top release button Red button, located on left and right side of magnet (also stops the magnet scanning) Table release Button on top of patient interface Table release
Emergency Buttons @ Aera Quench BUTTON Quench button
QUENCH BUTTON 1 Button is located on the right wall next to the console Emergency Buttons @ Philips Achieva 3T QUENCH 2 Button is located on the wall of the scanner room next to the door on the left side if you enter the room QUENCH
Emergency Buttons @ Philips Achieva 3T Emergency table top release button Red Button is located on left and right side of magnet on the side of the table Table release