* Electromagnetism/RF & Gradient Field Quiz *

What is purpose of the static magnetic field?

To magnetize tissues.

What is the gyromagnetic ratio of hydrogen?

42.6 mHz/T

What is the precessional frequency of hydrogen in a 1.5 T MRI machine?

63.9 mHz

What is the larmour frequency of hydrogen in a 3.0 T MRI machine?

128 MHz

Name three types of primary magnets?

Permanent, Resistive, superconducting

What type of primary magnet can never be turned off?

permanent

What type of primary magnet produces the largest fringe field?

superconducting

What is the term for when the net magnetization has been rotated at an angle from the z-axis after application of an RF pulse?

flip angle

What is the primary MRI signal?

Free induction decay FID

What are we imaging in MRI?

Hydrogen protons as they exist in fat and water

What is it called when the Net magnetization vector is aligned with B0?

equilibrium

What is the liquid cryogen used in a superconducting magnet?

helium

What will hydrogen protons do when placed in a static magnet field?

Align with the magnetic field or against it.

Name two types of electromagnets?

Resistive, superconducting

Name the secondary magnets used in the MRI system?

Shim coils, RF system, Gradient system

What is it called when two local coils are used at the same time for imaging?

Helmholtz pair

What is the purpose of shimming?

homogeneity

What gradient is used for slice select in an axial image?

Z gradient

What gradient is used for the phase encoding in a sagittal image?

y gradient

What is B1?

RF field

When a receive only coil is being used, what transmits the RF?

main body coil

What is the name for the center of the bore of the MR system?

isocenter

Name an example of a paramagnetic substance?

Gadolinium, aluminum, manganese, platinum, tungsten, titanium

What is an example of a ferromagnetic substance?

Iron, steel, nickel, cobalt

True or False: To achieve thin slices you need to use a steep gradient.

true

What gradient coil alters the magnetic field in the head to foot direction?

Z gradient

What does SNR stand for

Signal to noise ratio

Name three properties of magnetism.

Ferromagnetic, Paramagnetic, diamagnetic

What happens to the precession of hydrogen when the magnetic field strength goes up?

increases

As a technologist, what patient care concerns should you have with placing patients on high magnetic field strength (think about biological concerns)?

Increase in heating of patient