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Flashcards in MRI 3 Deck (35)
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1

Magnetic moment (μ)

The torque exerted on a magnet, moving electrical charge, or current-carrying coil when it is placed in a magnetic field.

2

Torque

Force that induces rotational motion.

3

Angular momentum (J)

A quantity given by multiplying the mass of a spinning body by its angular velocity.

4

Right-hand rule

A method used to determine the direction of a magnetic field generated by a moving electrical charge or electrical current.

5

Spin system

A collection of atomic nuclei that possess the NMR property within a spatial location.

6

Net magnetization (M)

The sum of the magnetic moments of all spins within a spin system.

7

Flux

A measure of the strength of a magnetic field over an area of space.

8

B (magnetic field)

The strong static magnetic field generated by an MRI scanner.

9

Precession

The gyroscopic motion of a spinning object in which the axis of the spin itself rotates around a central axis, like a gyroscope.

10

Larmor frequency

The resonant frequency of a spin within a magnetic field of a given strength.

11

Resonant frequency

The frequency of oscillation that provides maximum energy transfer to the system.

12

Parallel state

The low-energy state in which an atomic spin processes around an axis that is parallel to that of the main magnetic field.

13

Antiparallel state

The high-energy state in which an atomic spin processes around an axis that is antiparallel (opposite) to that of the main magnetic field.

14

Longitudinal

Parallel to the main magnetic field, or the z-direction of the scanner (i.e. into the bore).

15

Transverse

Perpendicular to the main magnetic field of the scanner, in the x-y plane.

16

The Zeeman effect

The energy difference (△E) between the parallel and antiparallel states increases linearly with the strength of the static magnetic field.

17

90-degree excitation pulse

A quantity of electromagnetic energy that when applied to a spin system during MR excitation, results in equal numbers of nuclei in the low- and high- energy states.

18

180-degree excitation pulse

A quantity of electromagnetic energy that when applied to a spin system during MR excitation, results in a flipping of the usual net magnetization such that there are now more nuclei in the high-energy state than the low-energy state.

19

Reception

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

20

MR signal

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

21

Relaxation

A change in the net magnetization over time.

22

Transverse relaxation (spin-spin relaxation)

The loss of net magnetization within the transverse plane due to the loss of phase coherence of the spins.

23

Longitudinal relaxation (spin-lattice relaxation)

The recovery of the net magnetization along the longitudinal direction as spins return to the parallel state.

24

T2 (decay)

The time constant that describes the decay of the transverse component of net magnetization due to accumulated phased differences caused by spin-spin interactions.

25

T2* (decay)

The time constant that describes the decay of the transverse component of net magnetization due to both accumulated phase differences and local magnetic field inhomogeneities. T2* is always shorter than T2.

26

T1 (recovery)

The time constant that describes the recovery of the longitudinal component of net magnetization.

27

Scalar

A quantity that has magnitude but not direction (i.e. mass, charge, length).

28

Vector

A quantity with both magnitude and direction (i.e. velocity, force, electromagnetic fields).

29

Dot product

The scalar product of two vectors. Summing the products along each dimension creates it (A! .B).

30

Cross product

The vector product of two vectors. It’s direction is perpendicular to the plane defined by those vectors and its magnitude is given by multiplying their product times the sin of the angle between them (AxB).