Magnetism

Atomic mass

Sum of an atom’s protons and neutrons

Ions

When the protons and neutrons

What are the four main categories of magnetism?

Diamagnetism, Paramagnetism, Superparamagnetism, Ferromagnetism

Diamagnetic

demonstrates no magnetic moment on their own

What can Diamagnetic slightly also be?

Repelling

Is diamagnetic MRI safe, unsafe, or conditional?

MRI safe

What are some examples of Diamagnetic?

Lead, Carbon, and copper

Paramagnetic

demonstrates a small magnetic moment

What can Paramagnetic slightly be?

Attracted to the main field

What are some Paramagnetic examples?

Tungsten, magnesium, and gadolinium

What does it mean if materials posses both paramagnetic and diamagnetic?

The substance will be Paramagnetic

Superparamagnetic

materials have a greater magnetic moment than paramagnetic substances, but less than ferromagnetic substances

What are some examples of Supraparamagnetic?

Iron oxide particles and Some MRI contrast medias

Ferromagnetic

Materials with half-filled electron shells, creating an object strong attraction and alignment with an external magnetic field

Is Ferromagnetic materials MRI safe, unsafe, or conditional?

MRI UNsafe

With Ferromagnetic materials, they may______, _____, or____

become projectiles, torque, or maintain their magnetism after removal

What are some examples of Ferromagnetic materials?

iron, steel, and nickel

Magnets have …..

a north and south pole

Magnets can be described as:

Dipolar and bipolar

Gauss

Used to measure low field strengths

Permanent Magnets

created using actual ferromagnetic substances stacked together with magnetic fields going vertically-no electricity

Permanent magnets can also be described as:

open magnet

What are some electromagnetic subdivisions?

Resistive and superconductivity

Resistive magnets

Use electric copper-wound solenoids

When using the word “Resistive” what does it mean?

known for the heat produced during their use due to electrical “resistance.”

How do Resistive magnets cool down?

The use of water or air

Ohm’s Law

the degree of resistance along a wire

Can resistive magnets be turned off?

Yes, this causes less safety concerns

Is a resistive magnet strong?

No, can only get up to 0.3T

What temp can cryogen get to?

4 Kelvin/-269C or -450F

Superconducting magnets

The popular magnets for research and clinical

Are superconducting magnets strong?

Yes, range from 0.5T to 3T

Do superconducting magnets need a constant power source to maintain its magnetic field?

Once ramped up to the appropriate field strength do not.

How are superconducting magnets able to maintain high field strength without electrical boil off?

Surrounding the electromagnet with Cryogens

Can a superconducting magnet be turned off?

NO! MAGNET IS ALWAYS ON! Exception: have to quench in order to stop it but takes time

What does a NICHE magnet mean?

can only scan one extremity part at a time

What is the FDA limit for clinical scanning for infants?

4T

What is the FDA limit for clinical scanning for adults?

8T

Magnetic shielding

Necessary to restricts the fringe field if the static magnetic field

Passive Shielding

The use of steel plates either in the magnet casing or lining the walls of the magnet room

Active Shielding

The use of electromagnets located within the main magnet

How do the magnets work with active shielding?

gradient coils are put at both ends of the superconducting magnet to keep the RF secluded

Stainless steel walls do what and is under what category?

Redirect the gauss line- Passive shielding

Magnet Homogeneity

Important for MRI scanners to have a homogenous field

Homogeneity is measured in

Parts per million (ppm)

Sweet spot for homogeneity

4 ppm but 1-10 is ideal

What ppm does the magnet come with

100ppm

How do you get a magnet down from 100ppm?

Shimming

What is Passive shimming?

A process that a engineer comes into make sure the magnet is homogeneity by placing metal disks

What is active shimming?

The electromagnet, when putting a patient in the scanner, will level out the unwanted field making it a homogeneity