MRI 2

Question 1

Field homogeneity

Answer 1

In context of MRI, it is the uniformity of the static magnetic field over space and time.

Question 2

Field strength

Answer 2

The magnitude of the static magnetic field generated by a scanner typically expressed in units of Tesla (T).

Question 3

Superconducting electromagnets

Answer 3

A set of wires made of metal alloys that have no resistance to electricity at very low temperatures. By cooling the electromagnets near absolute zero, a strong magnetic field can be generated with minimal electrical power requirements.

Question 4

Cryogens

Answer 4

Cooling agents used to reduce the temperature of the electromagnetic coils in an MRI scanner.

Question 5

Radiofrequency (RF) coils

Answer 5

Electromagnetic coils used to generate and receive energy at the samples resonant frequency, which for field strengths typical to MRI is in the radiofrequency range (MHz).

Question 6

Excitation

Answer 6

The process of sending electromagnetic energy to a sample at its resonant frequency (also called transmission).

Question 7

Reception

Answer 7

The process of receiving electromagnetic energy emitted by a sample at its resonant frequency (also called detection).

Question 8

MR signal

Answer 8

The current measured in a detector coil following excitation and reception.

Question 9

surface coil

Answer 9

An RF coil that is placed on the surface, very close to the location of interest and has excellent sensitivity to close regions, but poor sensitivity to distant regions.

Question 10

Volume coil

Answer 10

An RF coil that surrounds the entire sample, with roughly similar sensitivity throughout.

Question 11

Phased array coil

Answer 11

A method for arranging multiple surface detector coils to improve spatial coverage while maintaining high sensitivity.

Question 12

Gradient coils

Answer 12

Electromagnetic coils that create controlled spatial variation in the strength of the magnetic field. The cause the MR signal to become spatially dependent in a controlled fashion.

Question 13

Shimming coils

Answer 13

Electromagnetic coils that compensate for inhomogeneities in the static magnetic field.

Question 14

Pulse sequence

Answer 14

A series of changing magnetic field gradients and oscillating electromagnetic fields that allows the MRI scanner to create images sensitive to a particular physical property.

Question 15

Projectile effect

Answer 15

The movement of an untethered (unrestrained) ferromagnetic object through the air toward the bore of the MRI scanner.

Question 16

Ferromagnetic

Answer 16

A description of any material or substance that is attracted to a magnet (i.e. material or substance containing: iron, nickel, cobalt and their alloys).

Question 17

Translation

Answer 17

The movement of an object along an axis in space (in the absence of rotation).

Question 18

Torsion

Answer 18

A rotation (twisting) of an object.

Question 19

Specific absorption rate (SAR)

Answer 19

A quantity that describes how much electromagnetic energy is absorbed by the body over time.

Question 20

Claustrophobia

Answer 20

Fear of confined spaces. Roughly 10% of all patients experience claustrophobia during clinical MRI scans.