Lesson 3 (PRELIM) Flashcards by Justine RRT

_____ refers to the intrinsic angular momentum of an atomic nucleus, much like how electrons have spin.

Nuclear Spin

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_____, the concept comes from ____ and describes a property of _____ (protons and neutrons) inside the nucleus.

Nuclear spin
Quantum mechanics
Nucleons

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The _____ determines the energy levels of the nucleus in an _____ magnetic field, which can be _____ and used to gather information about the environment around the nucleus.

Nuclear spin
External
Detected

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_____ is important because it influences the behavior of _____ in magnetic fields. The value of the nuclear spin depends on the _____ and _____ in the nucleus.

Nuclear spin
Nuclei
Number and types of nucleons

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Nuclei with an even number of nucleons (like _____ or _____) usually have _____ nuclear spin.

carbon- 12 or oxygen-16
zero

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Nuclei with an odd number of nucleons (like _____ or _____) often have _____ nuclear spin, which can take values like _____, ______, ______, etc.

hydrogen-1 or nitrogen-15
non-zero
1/2, 1, 3/2

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A fundamental law of physics states that a spinning, charged mass induces a magnetic field about itself. _____ is one such example. The _____ is a spinning, charged particle and therefore has an associated _____. This field is given the special name of _____, and its intensity is related to the _____, ______ and _____ of the nucleus.

Magnetic Moment
Earth
Nucleus
Magnetic field
Nuclear Magnetic Moment
Mass, charge, and rate of spin

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Ratio of the magnetic moment to the angular momentum of a particle; this is a _______ for a given nucleus (_____).

Gyromagnetic Ratio (y)
Constant
MHz/T

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When a magnetic field is applied, nuclei with non-zero spin will _____ around the direction of the magnetic field, and the frequency of this precession is _____ proportional to the gyromagnetic ratio.

Precess (or “wobble”)
Directly

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Formula of Gyromagnetic Ratio

y=u/j
u = magnetic moment of a particle
j = angular momentum or spin of the particle

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Nuclei of Medical Interest and their Gyromagnetic Ratios
Nucleus
1 H
19 F
31 P
23 Na
13 C
2 H
17 O
39 K

Gyromagnetic Ratio (MHz/T)
Nucleus
1 H = 42.6
19 F = 40.1
31 P = 17.2
23 Na = 11.3
13 C = 10.7
2 H = 6.5
17 O = 5.8
39 K = 2.0

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Measuring the action of _____ nuclei is impossible, any signals received or data collected during the MRI process are the result of a bulk phenomenon from perhaps as many as _____ nuclei.

Net Magnetization
Individual
10^26

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A _____, _____ nucleus is never observed, just collections of similar nuclei as an aggregate. This aggregate of spins is sometimes called an _____ to emphasize the bulk of the signal-producing nuclear spins.

Net Magnetization
Single, isolated
Ensemble of spins

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Fortunately, the signal from a _____ accurately reflects the behavior of each of the individual nuclei, and therefore the _____ can be used.

Spin ensemble
Net Magnetization

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Net Magnetization

M=Eu

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The process by which atomic nuclei are exposed to a strong _____ and then to a pulse of _____ energy. This causes the nuclei to absorb the energy and “_____” at a specific frequency.

Resonance
Magnetic field
Radiofrequency
Resonate

The specific frequency at which this energy is absorbed by the nuclei is called the _____, which depends on the strength of the _____ and the type of _____.

Resonance frequency
Magnetic field
Nucleus

The electromagnetic radiation produced by the oscillator is called a _____.

Radiofrequency Field
Radiofrequency (RF) emission

An electromagnetic emission such as a radiofrequency (RF) is composed of an ______ positioned _____ to an oscillating magnetic field.

Radiofrequency Field
Oscillating electric field
90°

This rotation follows a pulse of radiofrequency (RF) tuned to the nuclei’s ______. If the RF is not at this frequency, the nuclei do not _____, and the net magnetization is _____.

Radiofrequency Field
Larmor frequency
Absorb energy
Not rotated

When a nuclear magnetic moment is placed in the presence of an intense static magnetic field, B0 , its axis of rotation precesses about the magnetic field. The exact frequency of precession by such a nucleus can be calculated with the _____.

Larmor Frequency
Larmor equation

Larmor Frequency Formula

f=yBo
f = frequency of precession (MHz)
y = gyromagnetic ratio (MHz/T)
Bo = strength of external magnetic field (T)

_____ is used by mathematicians to diagram phenomena in space (X, Y, and Z) drawn perpendicular to one another to describe a coordinate system.

Vector Diagrams
Cartesian coordinate system

Quantify that has direction

Vector

It is reasonable to expect that one of the parameters that affects the amplitude of the magnetic resonance (MR signal) might be the number of ______ within the volume of the sample.

Spin Density Hydrogen nuclei

Approximate Values of Mobile Hydrogen Nuclei Spin Density for Various Tissues Tissue Muscle White matter Fat Cerebrospinal fluid Kidney Gray matter Spleen Liver Blood Cortical bone Lung Air

Relative Spin Density Muscle = 90 White matter = 60 Fat = 95 Cerebrospinal fluid = 100 Kidney = 95 Gray matter = 70 Spleen = 90 Liver = 90 Blood = 85 Cortical bone = 1-10 Lung = 1-5 Air = <1

After the RF pulse excites the hydrogen nuclei, the nuclei release energy as they return to their original, lower energy state (a process called _____). As they relax, they emit radiofrequency signals at the same frequency they absorbed when they were flipped. This is called _____.

Relaxation Signal emission

Relaxation

T1 longitudinal or spin-lattice relaxation time T2 transverse relaxation time

The term _____ refers to events occurring along the axis of the net magnetization vector, which is parallel to B0.

T1 Longitudinal

Because _____ relaxation represents a loss of net XY magnetization, it represents the loss of phase coherence in a plane perpendicular to or transverse to M0.

When a patient is in the magnet at equilibrium, the _____ is constant and of maximum _____ . If the nuclei become disturbed by directing an RF pulse at the Larmor frequency into the patient, the nuclei absorb energy, and the net magnetization is _____ and changed in _____.

Signal Emission Net magnetization Amplitude, M0 Rotated Magnitude

This new magnetization state of the patient is _____ because the nuclei want to realign with the external magnetic field and return to equilibrium. The regrowth of MZ is the _____ and represents the spin’s return to _____.

Unstable T1 process Equilibrium

Analogous to T1, T2 is called the_____. Because T2 relaxation represents a loss of net _____ magnetization, it represents the loss of phase coherence in a plane _____ or _____ M0 . M0 lies along the _____.

Transverse relaxation time XY Perpendicular to or transverse to Z-axis

To summarize, _____ characterizes the amount of time for the transverse magnetization to reach equilibrium. ______ does not affect the magnitude of individual components of the MXY vector, but produces a net reduction due to _____ of MXY (loss of coherence).

T1 T2 Dephasing