1. Please Be Courteous To Others
Turn off all cell phones and pagers now.

2. Magnetism
Kyle Thornton
DMI 50B

3. Lecture Objectives Define magnetism Identify the magnetic properties
Define magnetic moment, magnetic domains
Explain how a magnet is able to exert force through space
List the three different types of magnets and give an example of each
Classify different materials with regard to their magnetic susceptibility

4. What Is Magnetism?
The ability of certain metallic substances to attract iron, cobalt, and nickel
Magnetism was discovered as early as the 6th century, BC
First artificial magnet was discovered in China around 1 AD by stroking certain materials with iron
The first technological application of magnetism is believed to be the compass
There are many similarities between magnetism and electricity

5. Application Of Magnetism In Radiology
Used to produce images in Magnetic Resonance Imaging (MRI)
Utilizes very strong magnetic fields
Used in the circuitry of the X-ray machine and other x-ray apparatus

6. Magnetic Properties All magnets have two poles North South
If cut in two - each half will develop north and south pole
Like magnetic poles repel, opposite poles attract
The force of attraction between two magnetic poles is directly related to the strength of the magnets and inversely related to the square of the distance between them

8. Magnetic Lines of Force

9. More Magnetic Properties
Some materials can be easily magnetized, others cannot
Magnetic fields exist around magnets
The strength of a magnet can be adversely affected by heating or mechanically jarring it
Materials can be magnetized by leaving them near a strong magnet or stroking them with another magnet

10. Atoms - The Smallest Magnet
Any charged particle in motion creates a magnetic field
Spinning electric charges such as electrons induce a magnetic field
Magnetic domains
A group of atoms
Each atom behaves like a tiny magnet
These atoms determine the overall magnetic properties of the magnet
Each atom has a north and south pole

11. Magnetic Domains Order of magnetic domains Unmagnetized bar
Domains in random order
Magnetized bar
Domains are aligned in the same direction
This can be accomplished by dragging a strong magnet over a steel or iron bar
Domains can be knocked out of alignment by physical force or heating
This will destroy a permanent magnet

13. How Does MRI Work?
In the nucleus of an atom, a proton spinning creates a nuclear magnetic dipole
This is called a magnetic moment
The magnetic moments of hydrogen atoms in the body is the basis for MRI

14. Magnetic Fields A magnet has the ability to exert force over distance
This is accomplished by magnetic fields
Direction of magnetic fields
Flow from north to south outside the magnet
Flow from south to north inside the magnet

15. Three Principal Types of Magnets
Naturally Occurring Magnets
Artificially Induced Permanent Magnets
Electromagnets

16. Unit of Magnetic Strength
The magnitude of magnetic force exerted on an object
Tesla
Gauss
10,000 Gauss = 1 Tesla
MRI units are generally around 1.5 Tesla

17. Classification of Magnetic Materials
Dimagnetic
Paramagnetic
Ferromagnetic
High magnetic susceptibility

18. Review questions What is magnetism?
Name two applications of magnetism in Radiology
What will occur if two magnetic poles that are positive are brought together?
If the distance between two magnets is doubled, what will happen to the strength of the magnetic field?
How are the magnetic domains aligned in an object that has been magnetized?
What is the term for a magnet that has been wrapped in a coil of wire?
How would the substance gadolinium be classified?