MRI safety

The purpose of this document is to provide an easy reference for MRI safety issues, included in the safety course. For more details please also refer to Siemens Safety manual that is available on site, to ACR White Paper on MR Safety, AJR:178, 1335-1352, 2002, and to the Reference Manual for Magnetic Resonance Safety, Implants and Devices: 2007 Edition; By Frank Shellock. - Available on site.

Although not detectable by the human senses, a magnetic field can be dangerous to equipment and to people. Since the magnet is always "at field" , always on 24 hrs/day, 365 days /year safety procedures must be followed to prevent accidents. Due to the high magnetic field, ferromagnetic materials or tools introduced into the proximity of the scanner become projectiles which may present a lethal risk to personnel working in the vicinity of the magnet and to subjects participating in the experiments.

Warning signs are posted on all entrances to the facility and on the door of the scanner, stating that a strong magnetic field is in use. 
No one may enter the MRI scan room without authorization from the Current responsible person.
The 0.5 mT zone is labeled with a red line on the floor at the entrance to the scanner room - Never leave the door of the scan room open.

When entering the room, entrance to the room should be restricted by the plastic chain that is attached to the two entrance poles.

Below are links to our safety rules and regulations and to the screening from.

-> Do not carry or move ferromagnetic objects into the examination room. Objects such as buckets, oxygen tanks, toolboxes, fire extinguishers, chairs, cameras, etc.
-> Do not move objects in the scanner room, while a subject is in the scanner.
-> Small metal objects (such as: pens, pins, hair clips, scissors, flashlight, phones) are prohibited in the scan room. Do not wear or carry any magnetizable object.

The high magnetic field in and around the magnet may disturb the function magnetic implants such as cardiac pacemakers and other implanted electronic devices. Persons with pacemakers or other implanted electronic devices must remain outside the 0.5 mT zone.

Due to risk of injury for personal with metallic implants in their bodies, persons with metallic parts or mechanical implants in their bodies (such as clips, screws, and plates) are prohibited from entering the marked zone - the scanner room.

Make sure that your subjects are escorted, while attending the facility.

Screening Procedures

The researcher screens the prospective MRI subjects for contraindications at the time an appointment is made (mri-screening-form.pdf). Absolute contraindications for scanning include: cardiac pacemakers, cochlear (inner ear) implants, ferromagnetic or unidentifiable aneurysm clips, implanted stimulators, metal or unidentifiable foreign bodies in the eyes. Occupational exposure to metal lathe or welding. Participants are asked during the screening process if there is any chance they may be pregnant. If there is such a chance, they are excluded from the study.
If there is any question regarding a possible risk to the subject, due to his medical history, the Weizmann Imaging Center (WIC) staff are to be consulted.
Before entering the scan room, the current responsible person (CRP) reviews the subject screening form, item by item, to ensure that there is no contraindication for scanning. The CRP then witness the subject signing the MRI screening form. Screening will be conducted each time a participant is scanned, regardless of being a repeat participant.
Some minor contraindications are allowable for MRI scanning. These include most permanent dental retainers, and tattoos, not in the scanned region.
In any experiment that involves a human subject who is currently a patient, defined as a member of a non-healthy subject population in the Helsinki-approved research, the physician from the medical center that is a partner to the Helsinki must review the subjects screening form and satisfy himself/herself that there is no contraindication for scanning, the physician will also witness the subject signing the MRI screening form.
It is the WIC policy to defer scanning if there is any possibility of causing injury to a subject or staff.

Noise protection

The MR scanner produces very high acoustic noise levels. The acoustic noise is caused by operating the gradients in conjugation with the static magnetic field.
Prior to scanning, provide ear protection to the subject to reduce the noise level. Researchers that stay in the scan room while the gradient system is on, must also wear hearing protection.

Participant Safety during scanning

Participants should be monitored continuously through the radio frequency-shielded window between the MR scanning room and the control room or by using the IR camera that is located in the scanner room and projects the scanner to the screen above the console. The participant can hear the MRI operator through use of the intercom and can communicate with the operator. Throughout every scanning, an emergency buzzer is placed in the subject's hand, to be present if he/she experiences any pain, discomfort, claustrophobia, or has any other concern. In the event that the buzzer is pressed, scanning is aborted immediately and the subject is removed from the scanner upon his/her request or if needed.
To date, there is no scientific proof that MR examination are harmless for pregnant women or that RF exposure are harmless for pregnant operating personnel. Therefore, pregnant researchers and staff should not enter the scanning room, while scanning.

Participant Emergencies

Should a condition exist where the patient is having a medical emergency, all efforts must be made to quickly and safely remove the patient from the scan room. Once the patient is removed from the MR scan room, close the door to prevent re-entry. Under no circumstances entrance to the scan room without proper screening can be allowed!

In case of participant emergency immediately call

  1. Weizmann's emergency call 2999
  2. Natali for medical aid (1-800-800-666 or 6800, customer code: 62421)

Physiologic Effects

During an MR examination, the subject is exposed to three different types of electromagnetic fields: static main magnetic field, gradient fields and radio frequency fields. The effects of these fields vary including the immediate vicinity of the MR system. In addition to the subject, accompanying personnel or operating personnel are subject to these fields in the scanner room.

Static magnetic field effects

A known physical effect of static magnetic field is that they exert forces on moving particles that are electrically charged (e.g. ions). This results in induced electrical currents and directional changes in the way these particles move, which may cause noticeable physiological effects.
If the head is moved rapidly in the proximity of the magnet bore, forces are exerted on the ions in the fluid, causing nerve stimulations, which may result in feeling of dizziness, vertigo, drowsiness, or metallic taste. Therefore, it is recommended to avoid sudden movements when exposed to the strong magnetic field. Prior to moving into the magnetic field, inform the patient about the possible occurrence of these symptoms.

Time varying magnetic field effects

The low-frequency change of the magnetic flux (switching on and off gradients) induces an electrical field in the tissue of the subject that shifts the charge in the nerve fibers of the tissue. This shift in charge may lead to peripheral nerve stimulation and to muscle stimulation, depending on the strength, frequency, and duration of the shift in charge.
Large current loops caused by skin-to-skin contact for example by crossed hands, knee-knee contact, or ankle-to-ankle contact, may occur if the subject is not positioned correctly. These may enhance the nerve and muscle stimulation.
Therefore, Ensure that the subjects is positioned correctly and is not closing loops. Additionally, if the subject is wearing electrically-conducting material peripheral nerve stimulation may occur - Ensure that the subject is free of metallic rings, chains, or electrically-conducting materials worked into items of clothing (for example zippers or brassiere support wires).

Hazards related to radio frequency (RF) fields

The RF field emitted during MR examinations induce electrical fields analogous to gradient fields. However, due to their high frequency they do not lead to stimulation effects in the electrically conductive body tissue. The energy exchange of the RF field leads primarily to warming. Exposure to high RF fields may cause excessive heating of skin and body tissue. 

Instruct your subjects to press the squeeze ball in case of strong heat sensations. Use only covers (clothing, blankets, etc..) made of paper, cotton or linen.

An important value per body weight is the specific absorption rate or SAR, measured in watts/kg. The SAR limit is calculated for every subject by the subject's weight and the expected increase in body temperature for each imaging pulse sequence. The SAR values are monitored by an integrated SAR monitor on the MR console.
Subjects with poor thermo-regulatory systems must be carefully monitored.

Looped cables (for example in RF coils, EEG lines etc) function as antennas and may warm to levels leading to skin burns at the points of contact. Current loops are also generated when the subject's skin contacts the tunnel lining or RF coil cables. To avoid this source for injury, special care has to be taken in correctly positioning especially adipose subjects.

RF coils that are not correctly connected to the coil socket may warm considerably and cause burn hazards-> Ensure that all RF coils used are connected and remove disconnected RF coils from the patient table.

Equipments and Personal items

Only proven MR-compatible accessories should be used with the MR system. Accessory devices may be brought into the scanner room only after approval by the WIC staff.
Items may be tested for magnetic susceptibility with a hand-held magnet located at the MR facility.

Devices can be installed or brought into the MR room only after it has been approved in writing by the safety committee. Devices should be non-magnetic and should not introduce rf noise.

It is important to set up all the equipment in the scan room before the participant enters the room.

Devices that are approved for use in the magnet room should be labeled accordingly.
Note: devices compatible with 1.5T systems may be unsuitable for 3T systems.

Watches can not be brought into the MRI scan room since the magnetic field will render them inoperable. Devices with magnetically recorded information such as credit cards, cameras, phones, bank cards or data stored on magnetic tape will be erased if brought into the MRI scan room. Hearing aides may be damaged when exposed to the magnetic field.

Operating Safely

When operating the MR equipment, be attentive to the following abnormal conditions:

  • Louder-than-normal motor noises
  • Sparks
  • Components overheating
  • Smoke or odors coming from the electronic equipment or from within the scan room.

Magnetic Field / Scan Room Emergencies

The magnet is equipped with two emergency buttons:

  1. Quenching the magnet button- Causes immediate collapse of the superconductive magnetic field. The magnetic filed collapses within 20 s
  2. Emergency - electricity stop / Shut Off - Turns off all incoming electrical power to the magnet

The nature of the emergency will dictate which procedure you follow. Each procedure has a distinct and specific purpose.

FAMILIARIZE YOURSELF WITH THESE BUTTONS. KNOW THE DIFFERENCE!

Quench Button

Quenching is a loss of superconductivity of the magnet coil due to a local temperature increase in the magnet as it becomes resistive, resulting in rapid evaporation of liquid helium via the exhaust line and quickly reducing the magnetic field strength. The time from activation of the emergency field shut down unit to the moment when the field strength in the magnet center has dropped to 20mT is typically 20s.

  • A quench may happen spontaneously (for example when ramping up or filling the magnet, during an earthquake or fire or spontaneously without an obvious reason) or can be manually instigated in case of an emergency.

    Quenching may cause severe and irreparable damage to the superconducting coils (magnet).

  • A magnet quench will result in several days' downtime, so do not press the button except in a true emergency.

     

  • Do not attempt to test this button!

The following situation is THE ONLY TIME that may require quenching of the magnet: An accident involving large magnetic object pins or impales a person against the magnet and no other method can prevent further injury or free the person.
Do not attempt to pull large magnetic objects (oxygen tanks) from a magnet field. The object may change its magnetic polarity and re-align itself on the magnet and become a projectile, causing a serious or fatal injury.

Following a quench, due to Asphyxiation hazard, you must immediately remove the subject and all staff from the scan room.

Location of quench buttons at the WIC

  • One button is located in the alarm box, in the control room.
  • One button is located at the entrance inside the examination room.

Emergency Stop / Shut Off Electricity Button

Shutting power may be required for life threatening situations such as:
  • Fire in the computer room
  • Fire, sparks, smoke in the scan room
  • Flooding, water leaks

Keep in mind that when this button is pushed, it does not initiate a quench, the magnet remains "at fiel d." Make sure that all ferromagnetic materials remain outside of the scan room.

Location of electricity - stop buttons at the WIC

  • One button is in the control room
  • One button is located at the entrance to the examination room inside on the left side.
  • One button is in the electronics room.

Table Stop Button

The table stop button is used to stop the table movement. Push it immediately in case of accidents or risk of injury due to table movement, or if something gets caught. The table stop button disengages the table motor and allows a manual movement of the table

  • Two buttons are located on the magnet, on the control units, on both sides.
  • One button is located on the intercom

mri-safety-rules.pdf
mri-screening-form.pdf