SECTION
5
MAGNET
SAFETY AND EQUIPMENT SHUTDOWN
version
2
7-17-07
Chief
of CAMRIS Technical Staff:
Norman Butler 215-349-5298
mr5research@uphs.upenn.edu
Scope &Application
Overview
Definitions
Static Field
Safety
Radio frequency
Field
gradient
fields
MR Personnel Qualifications
Intercom
and Call Bell
Scanner Interrupt
Electrical
Shutdown
Quench Button
Main System
Switch
Screening
Contraindications
Log Book Data
Entry
Registration
Fields
1.0
Scope &Application
1.1 This standard operating procedure is a basic introduction
to MR instrumentation shutdown procedures and equioment
safety standards on the Trio (Hup6) and Sonata (Hup5)
MR systems at the Hospital of the University of Pennsylvania.
Pictures shown (PDF version) and locations discussed
in this SOP deal with these scanners only. The patient
screening information at the end of this SOP is general
and not intended as a complete screening procedure
for the MR Environment.
2.0
Overview
2.1 This SOP is intended to provide the approved user
information about operating and shutting down the
scanners safely
3.0
Definitions
3.1 Magnet - Super conducting source of the static
field. This field strength 1.5 Tesla for the Sonata
and 3 Tesla for the Trio.
3.2 Static Field - This is the field generated by
Superconducting magnet. This field is never turned
off.
3.3 Radio frequency- frequencies in the range within
which radio waves may be transmitted, from about 3
kilohertz to about 300,000 megahertz. These RF fields
are generates by the transmitting coil used for imaging.
3.4 Gauss -The centimeter-gram-second unit of magnetic
flux density, equal to one Maxwell per square centimeter.
10,000 Gauss are equal to 1 Tesla.
3.5 Gauss Lines - demarcation lines of specific field
strengths
3.6 EPO Switch- Emergency Power Off switch controls
electrical power to all systems from the Power Distribution
Unit.
3.7 Quench - Rapid elimination of the Static Magnetic
field generated by the
Superconducting Magnet. Quenching can happen due to
several conditions:
3.7.1 Request for a quench made by operator by using
Quench Switch
3.7.2 The abrupt change in the field due to a large
magnetic object drawn into or removed from the magnet
3.7.3 Conditions arising from inadequate cryogen levels
to maintain the
superconducting properties of the magnet.
3.8 Quench Switch - Operator switch for quenching
magnet
3.9 Oxygen monitor- Sensor inside magnet room that
monitors the oxygen level.
3.10 Contraindication- A factor that renders the administration
of a drug or the carrying out of a medical procedure
inadvisable.
3.11 MR Suite - The MR scanning room which contains
the magnet.
CAMRIS - Operational Operational Safety 6/13/2005
4.0 Static Field Safety
4.1 The static magnetic field is the foundation upon
which the MR image is built. This field strength can
range from as low as 150 gauss (.15T) to as high as
90,000 gauss (9T). Some systems operate at even higher
strengths. The University of Pennsylvania operates
two full body scanners for human research. The TRIO
system in the Rhodes building basement operates at
3 Tesla (30,000 gauss) and the Sonata system in basement
Founders operates at 1.5 Tesla (15,000 gauss).Both
are self shielding, superconducting Siemens magnets.
4.2 Safety concerns of the static field are:
4.2.1 Attraction or rotation of Ferromagnetic Materials.
These objects can
become airborne and have catastrophic results.
4.2.2 Torsion or motion of implanted devices or materials
inside the human
body.
4.2.3 Interruption or corruption of devices susceptible
to Electromagnetic
fields.
4.3 Magnet design of the TRIO is the OR64.
| field
strength |
.5mT
Fringe field |
magnet
weight |
magnet
bore |
current |
| 2.895T |
z
direction 6.0m |
9970kg |
.9
m |
489Amps |
| |
x,y
direction |
|
|
|
4.4
Magnet design of the SONATA is the OR70.
| field
strength |
.5mT
Fringe field |
magnet
weight |
magnet
bore |
current |
| 1.494T |
z
direction 4.0m |
3900
kg |
.9
m |
585
Amps |
| |
x,y
direction 2.5m |
|
|
|
4.5 No ferromagnetic material may be brought into
the scanning room. There is a small permanent magnet
available for test questionable items before entering
the scanning room. All instruments, equipment, and
personnel must be cleared by a Technologist or approved
user before entering the magnet room.
4.6 No person should enter the magnet room without
prior screening for
contraindications to the MRI environment.
4.7 All equipment used inside the magnet room must
be tested for field interaction prior to actual use
in the scanning arena. This screening must be performed
in conjunction with a CAMRIS representative.
5.0
Radio frequency Fields
RF fields are present during active scanning of the
MR experiment. These RF fields interact with the static
field and are absorbed by tissue to allow image production.
The principal safety issue concerning these fields
is heat induced in tissue or on the surface of conductors.
High voltages and currents can be produced along lengths
of cable or conductors during the RF pulse. These
in turn can generate sources of intense heat. Care
not to loop coil transmission or reception lines is
crucial. All coils used in the MR environment must
have undergone the Coil Approval Process outlined
in the CAMRIS Policies and Procedures Manual.
6.0
Gradient Fields
These fields are generated in order to spatially encode
frequency information. The gradient coil operates
during the active phases of the MR experiment.
The primary safety issues of application of the gradients
are neuro-stimulation, torsion of magnetic material,
and eddy current generation. The Siemens scanner monitors
neuro-stimulus threshold levels. The system will prompt
the user to make modifications in the sequence to
avoid this effect. Patient position and orientation
play a role in the possibility of neuro-stimulation.
The subject must be advised not to cross their legs
or place their hands together while lying in the magnet
to avoid creating a continuous loop
6.1 Specifications of the gradients operating on our
systems
| system |
gradients |
gradmax
|
Gradmin |
1grad |
rise
time |
SR |
| trio |
quantum |
40mT/m |
69mTm |
500A |
200
us |
200 |
| TIM trio |
quantum |
40mT/m |
69mTm |
500A |
200
us |
200 |
| sonata |
quantum |
40mT/m |
69mTm |
500A |
200
us |
200 |
6.2 The gradient operational setting can be modified
between a normal and "First Level" fast
mode. The decision for the gradient performance is
chosen from part 2 of the Sequence tab of the prescription
pages or the decision may be forced upon sequence
download. In either case the operator must be aware
of which mode is in operation and make appropriate
adjustments. Operation near the limits of gradient
capability will often force the system to calculate
options for the operator and present the possibilities
to this operator on a pop up screen prior to scanning
the specific sequence.
6.3 The STIMO (Stimulation Monitor) will offer some
options for alleviating
stimulation threshold excesses.
6.3.1 Swap of Phase and Frequency encoding directions
6.3.2 Increase of Receiver Bandwidth
6.3.3 Increase of Echo Time or Echo Spacing
6.3.4 Increase of Field of View
6.3.5 Decrease in number of slices acquired
7.0
MR Personnel Qualifications
7.1 All individuals operating within the MRI environment
will be a trained Radiologic Technologists or approved
users recognized by CAMRIS.
7.2 All individuals responsible for screening and
handling patients will have an
understanding of MRI safety and have completed a course
in basic MR safety.
8.0
Intercom and Call Bell
The Trio and Sonata systems are equipped with an intercom
device to talk to MR subjects between and during scans.
The system should always be in a state with the Listen
Out Activation button in the on position. A call bell
is also available and should be given to every human
subject scanned. The ball should be tested for activation
prior to the session. Pushing the Speak-in activation
button resets the alarm for the call bell.
9.0
Scanning Interrupt
Scanning and table motion can be interrupted at any
time byusing the "Stop Scan" button on the
GUI interface of the scanners operator console or
the
"Stop" button on the magnet couch control
panel. The presence of the MAGNETIC FIELD is NOT TURNED
OFF by the use of this switch. The Stop scan button
is mouse click activated and is located in the lower
left hand corner of the screen. Use of this button
will stop the current scan and allow you to proceed
using the continue option. The emergency scanner table
interrupt switch is also available.<see pdf version
page 5>This switch shown in the picture (red plunger
type switch) allows for immediate scan interruption.
A similarly functioning button is present on the couch
control console. The reset for these buttons is accomplished
by toggling the couch control stick.
10.0
Electrical Shutdown
The electrical portion of the MR Systems can be shut
down using the EPO (Emergency Power Off) breakers
available at the scanners. The MAGNETIC FIELD is NOT
AFFECTED. The need to cut all power to the system
is necessary in the case of electrical fire or electrocution.
Each scanner has an EPO switch in the following locations.
A picture of the switch is shown.<
see pdf version
page 6 > Note the protective cover over
the switch. To operate this switch you lift the cover
and press firmly on the red button. The activation
of this switch will cut all power to systems inside
the magnet room, systems cabinets, and the operator's
console. The system will need to be booted from the
main power distribution box located at the operator
console. Minimum reset time is 10-30 minutes.
11.0
Quench Button
This switch allows for rapid elimination of the magnetic
field generated by the super-conducting magnet. Use
of this button is a grave decision and carries many
ramifications. The button should be used in situations
where potential for catastrophic injury is possible.
Your first concern and responsibility is to the subjects
and colleagues operating with you in the MR environment.
A comprehensive quench action plan is outlined in
the SOP for Quench Procedure. A picture of each switch
is shown.<see pdf version page 7> One switch
is located at the operator console and the other is
in the MR Suite. To activate a quench lift the cover,
press the button firmly and hold for a count of 3.
12.0
Main System Switch
The following image shows the main system switch.
<see pdf version page 7> The panel has 4 buttons
and a key lock out. The system on and off buttons
shutdown and boot the entire system. The standby mode
is used primarily for service. The alarm silence is
used for interruption of the alarm while resets to
the system are made. The key lock out will allow use
of the buttons only when in the unlocked position.
13.0 Subject
Screening
All individuals that enter the MRI Environment must
be screened for possible contraindications to being
in magnetic or RF fields. For more detailed information
about patient screening and preparation please review
the SOP for Patient Screening and Safety in the MR
Environment as the full scope of this issue is beyond
the descriptions given in this SOP. Screening consists
of three phases:
13.1 Subject Screening Form -Forms can be picked up
from the Technologists at the Research Scanners. The
format of the form is specific to clinical and surgical
history. These questionnaires are to be completed
outside the scanning area. Questions about the presence
of specific prosthesis, surgical implants, and other
contraindications are addressed.
13.2 Subject Interview - Upon completion of the screening
form the information given is to be reviewed for completion
by the MR personnel for accuracy and
completion.
13.3 Subject preparation - subject will be requested
to remove all metal from their person. It may be necessary
for the subject to gown prior to session.Any persions
scanned in the Tim Trio ( Devon Center) must be gowned.
14.0
Contraindications
Any type of metallic implant, jewelry, or foreign
body is to be considered a contraindication until
MR personnel have evaluated all issues about the metallic
object and deemed it safe. No subject having a contraindication
may enter the MR Suite.
15.0
Log Book Data Entry
All approved users of the Trio and Sonata systems
must enter their usage into the logbook. The logbooks
are stored at the operator consoles of each scanner.
The following information is entered into the book
for each session.
15.1 Name of investigator
15.2 Type of "subject" scanned - (Phantom,
specimen, animal, volunteer)
15.3 All information pertaining to the subject as
required by any overseeing groups.The MR personnel
must be able to contact the investigator and track
the subject that is scanned content goes here
16.0
Registration Fields
All new sessions will require information in registration
fields.This information varies based on the type of
subject being scanned. All human subjects will have
necessary medical record numbers and demographics
as outlined in the SOP for Patient Information Entry.
Animal and specimen scanning may not enter names or
characters that resemble a human subject's medical
information in any way. This is in order to avoid
any mix-up of images that are sent to central archive
(PACS). A thorough discussion of acceptable registration
field information is given in the SOP for Animal Research
in the Hup5 and Hup6 Environments
