MRI Screening & safety

Zone 1

Open & freely accessible to general public

Zone 2

Supervised area; for patients & families

Zone 3

Control/computer area. Restricted o MRI personnel

Zone 4

Mri room; restricted to personnel and screened individuals

Which zone is outpatient entrance: public hallways?

Zone 1

What zone is changing area/patient interview space, bathroom

Zone 2

What zone is control room, transfer to mri safe wheelchairs, anesthesia

Zone 3

MR Medical Director (MRMD)

Physician responsible for the mri safety program of an MR department; defines MR safety educational requirements

MR Safety Officer (MRSO)

Used a specialized technologist; maintain safety policy and procedures in concert with mrmd

MRI personnel

Individuals that have successfully attended Mr safety educational program specific to their level of

Level 1 MRI safety personnel

Passed minimal safety educational efforts to ensure their own safety as they work within zone 3

Level 2 mri personnel

Those who have been more extensively trained and educated in the broader aspects of

The attraction of objects to the bore of the magnet

Translational forces (force increases as object approaches isocenter

The torque or twisting of devices

Rotational

ASTM terminology MR safe

Poses no known hazards in MRI environmenta

MR conditional (triangle!

Item has been demonstrated to pose no known hazards in a specified MR environment with specified conditions

MR unsafe (circle/cross)

Item poses a known hazard

Temperature & humidity for MR environment

65-70 degrees and humidity 60-60%

Passive shielding

Steel or concrete lined walls

Active shielding

Solenoid magnets to force the magnetic field lines to an acceptable location

RF shielding

Keeps RF from entering/leaving zone 4; faraday cage, room lined with copper

quench

The boiling off of liquid helium

Static Magnetic Field

The main field created by the MR magnet or B0 (expressed in Tesla)

1 Tesla =

10 kG or 10,000 G (gauss)

Biological effects

T-wave of ECG can become elevated; fatigue, headache, hypotension, irritability

FDA Guidelines: imaging can be performed up to:

8T

Magneto-hydrodynamic effect

Change in T wave of ECG because of flowing blood moving across a magnetic field

Faraday's Law

Changing a magnetic field will induce a voltage and current in a perpendicular orientated electrical conductor

Lenz's Law

The induced current will generate a secondary magnetic field that opposes the original magnetic field

Eddy's currents

Swirling magnetic currents that can produce heating in tissues or peripheral nerve stimulation

Radio frequency

The number of oscillations or cycles per unit time generated by radio waves

Specific Absorption Rate (SAR)

Rate of heat/energy dissipation in a patients tissues is expressed in w/kg

FDA guidelines for SAR:

4.0 W/kg whole body 3.2 head

Biological effects

Heating of tissues; heating of structures like the lens of the eye can cause cataracts

Time Varying Magnetic Field

The magnetic field is varied linearly over time by the application current to the gradient coils