AMICentre Safety Course

Question 1

What is the magnet used in the AMICentre?

Answer 1

GE VH/I 3T

Question 2

How is the magnetic field created? What does this mean?

Answer 2

By a superconductive magnet. It does not need electricity to work and is always on until the end of its life (5-7 years)

Question 3

What are some examples of ferromagnetic materials?

Answer 3

Iron, nickel, and kobolt

Question 4

How do ferromagnetic items act in a magnetic field?

Answer 4

1) They move towards higher field strength

2) They align along the magnetic flux lines (creates torque effect)

Question 5

What are the two types of magnets (and magnet fields) based on force?

Answer 5

1) Weak magnetic field, changes slowly -> weak attractive force
2) Strong magnetic field, changes quickly -> strong attractive force. Also called “actively shielded magnets”.

Question 6

How does the strong magnetic field function in practice?

Answer 6

Due to research, the field does not extend very far. However, the side effect is that the effect starts very rapidly, once it does start.

Question 7

What is the torque effect that affects elongated objects in a magnetic field?

Answer 7

Elongated objects tend to orient themselves along the magnet’s flux lines. This effect also occurs in the static field.

Question 8

Can people with implants be near the MRI device?

Answer 8

Yes, if the implants are compatible at 3T magnetic field. THIS MUST BE KNOWN. This means they must not:

1) Move
2) Turn
3) Heat up (RF)

During the MR scan.

Question 9

What is deflection testing of materials?

Answer 9

The object is attached to a thin string, and a static magnet is put next to it. Then we see if the object is deflected from the magnet.

Question 10

What precaution must be taken with people with implants or surgical history?

Answer 10

They should NOT be allowed to enter the shielded room without further evaluation.

A questionnaire must be filled prior to entering the room.

Question 11

Is the magnetic field hazardous?

Answer 11

It is not known to be dangerous OR safe, but it has been extensively studied. A static magnetic field has not been found to have any cell-level effects on living animals.

Cell-level effects, if any, are assumed to be catalytic, not inducing.

Question 12

What does the static magnetic field affect in the human body?

Answer 12

The vestibular organs. They contain a liquid that has ions. This can cause dizziness and nausea during long term stay in a strong magnetic field (>= 3T).

Question 13

What is Lenz’s law?

Answer 13

Time-varying magnetic fields induce currents to a loop.

The current is also induced if a loop is moved in a static field.

Question 14

Why are vestibular organs affected by magnetic fields, according to Lenz’s law?

Answer 14

Because the vestibular system has three loops that are perpendicular to each other and contain a liquid that has ions, and is conducting.

The liquid moves, and the hairs in the organs bend, which causes a sensation of motion.

When moving in a magnetic field, the movement of the liquid is different than what is perceived.

Question 15

What does the electricity shutdown button do, why is it there?

Answer 15

It turns off the electricity in the lab (but not the magnet!). It is there due to safety regulations.

Question 16

What does the emergency magnet shutdown switch do?

Answer 16

1) Removes the magnetic field in about 90 seconds.

2) Boils about 1000L of liquid helium (10€/L)

Question 17

When should the emergency magnet shutdown be initiated? What should be done if this is activated?

Answer 17

Only if human life is at risk or the well-being of the victim can be improved through disabling it. Report to AMI and GE service immediately. Service time is about 2 weeks.

Question 18

Tell a little about the helium inside the magnet.

Answer 18

1) There is about 3000L of it.
2) When boiling, the volume will increase by a factor of 760.
3) Gaseous helium replaces oxygen in air and suffocates.
4) Boiling helium creates a white cloud and freezes air.
5) Immediate evacuation needs to be done if it enters the room. However, it should not: There is an exhaust pipe.
6) Liquid oxygen is flammable.

Question 19

What usually causes accidents in the lab? What should be done if they are encountered?

Answer 19

1) Static field causes most accidents.

2) Accidents and near-accidents should always be reported.

Question 20

What is a gradient with magnets?

Answer 20

A gradient is a magnetic field’s (linear) variation.

They are loops of wire or thin conductive sheets on a cylindrical shell lying just inside the bore of an MR scanner.

Question 21

How do gradients work with MRI scans?

Answer 21

1) Gradients are activated and deactivated tens of times during a scan.
2) Fast varying gradient fields have been found to cause neural excitation.
3) The gradient coils create a secondary magnetic field that slightly distorts the main magnetic field in a predictable pattern, which causes the resonance frequency of protons to vary in as a function of position.
4) The main job of the gradient coils is to allow spatial encoding of the MR signal.

Question 22

How can neurons be activated?

Answer 22

By bringing a charged electrode close to it. The charge generated an electric field around the electrode, and the field disturbs the charge distribution around a nerve cell. The potential across the neuron cell membrane will change and cause an action potential.

Question 23

How can gradients excite neurons?

Answer 23

Gradient field is magnetic by nature. Lenz’s Law: Time-varying magnetic fields can induce currents to a loop.

The gradient field is indeed time-varying during slopes.

Question 24

What do gradient slopes cause?

Answer 24

They induce eddy currents to a body. These currents generate the necessary electric field to activate neurons.

Large loops cause large electric fields. The frequency direction can be right or left.

Question 25

What are eddy currents?

Answer 25

Eddy currents / Foucault currents are loops of electrical current induced within conductors by a changing magnetic field in the conductor, due to Faraday’s law of induction.

Question 26

What kind of nerve stimulation is possible in the AMI scanner?

Answer 26

Peripheral nerve stimulation (this can cause tingling / sense of electric shock).

Cardiac, respiratory or pain stimulation is not possible.

Question 27

What is important to know in a practical sense about peripheral nerve stimulation?

Answer 27

It is important to tell volunteers that this may happen; they may sense a tickling sensation or electric shock. It is not known to be dangerous but it is to be expected.

Question 28

What is important to know about body loops?

Answer 28

Body loops should be minimized. For instance, spreading legs in a loop, or standing with hands on your sides.

Question 29

Can there be acoustic noise in the MRI machine?

Answer 29

Yes. This is caused by the gradient coils trying to move when activated or deactivated. They are not able to move, since they are firmly molded in the bore. This causes a hammering noise that is very loud, that can cause permanent hearing defect.

Hearing protection that covers the whole ear is MANDATORY, with additional plugs recommended.

Question 30

How and why is radiofrequency (RF) irradiation used in MRI?

Answer 30

1) It is used to excite spins.
2) It is given in short (1 ms) consecutive pulses.
3) Use of intense RF irradiation is in many ways beneficial in MR imaging.

Question 31

What are side effects of radiofrequency (RF) irradiation?

Answer 31

1) RF irradiation heats tissue.
2) Very intensive RF irradiation can cause internal tissue burns.
3) RF monitoring is of special concern in MRI.

Question 32

What method and unit is used for evaluating tissue heating from RF power (in W) and the object’s weight (in kg)?

Answer 32

• SAR (Specific Absorption Rate).
• W / kg = SAR.
• Irradiating the object 1 hour at a rate of 1 SAR will raise the temperature by 1 degree.

Question 33

What should be noted about SAR?

Answer 33

It is strongly dependent on sequence type. E.g., FSE : GRE ~ 100 : 2.

Question 34

How is SAR monitoring implemented in the AMI scanner?

Answer 34

There is real time RF monitoring: 6 minutes RF average, and 10 seconds RF average.

Question 35

What happens if the RF limit is reached?

Answer 35

The scanner will stop. However, the subject does not need to be taken out of the scanner: they must just be let cool down a little before restarting the scanner.

Question 36

When can SAR monitoring fail and cause excessive tissue heating?

Answer 36

1) Body weight is not given correctly
2) Additional heat sources are near the body
3) The person has fever
4) The person cannot regulate their body temperature (newborns or people with a rare disease)
5) The RF field is focused

Question 37

How can RF focusing be caused by RF coils?

Answer 37

If a RF coil is damaged. All the coils contain electrically activated switches, which are opened and closed several times depending on whether the system is transmitting RF energy or receiving RF signals.

Question 38

What can happen if the RF coil is damaged or not connected?

Answer 38

The coil will be in an uncontrolled state, which can focus RF. This means that tissue temperature can rise excessively in the vicinity of the coil.

Question 39

How can RF focusing be caused by cables?

Answer 39

If there is a RF cable loop.

In case there are any looped cables near the body, they may cause severe tissue burns.

Question 40

How can other components acting as conductors cause RF focusing?

Answer 40

Straight conductors can also focus RF in the ends. They can draw the RF current.

Things such as implants or wires attached to the body can act as straight conductors.

Question 41

What further complications can straight conductors cause if they are of certain length?

Answer 41

If the wire length is 1/4 of the wavelength of the RF radiation, resonance can occur, which can magnify this effect. (from 1.5 to tens)

If the conductor is about 6.5 cm long, resonance inside the body can occur. There are wire implants of that size.

If the subject has any implants, DO NOT scan them without further evaluation.

Question 42

How is the security organized in the magnet building?

Answer 42

The level 1 floor has limited access: the door is always locked.

Access to the shielded room is strongly restricted. Senior personnel is required to access this area, and they are responsible for what happens when the door is opened.

The person opening the door/traffic bar to the shielded room can ask everyone to leave the laboratory: they have full control of the area.