nuclear physical principles Flashcards
- refers to intrinsic angular momentum of an atomic nucleus much like how electrons have spin. concept comes from quantum mechanics and describes a property of nucleons inside the nucleus
- determines the energy levels of the nucleus in an external magnetic field, which can be detected and used to gather information about the environment around the nucleus
nuclear spin
influences the behavior of nuclei in magnetic fields
nuclear spin
nuclei with an even number of nucleons usually have ___ nuclear spin
zero nuclear spin
nuclei with an odd number of nucleons often have ___ nuclear spin
non-zero nuclear spin
fundamental law of physics states that a spinning, charged mass induces a magnetic field about itself. earth is one such example.
magnetic moment
nucleus is a spinning, charged particle and therefor has an associated ____
magnetic field
magnetic field is given the special name of _____, and its intensity is related to ___,___,___
magnetic moment. mass, charge, and rate of spin of the nucleus
ratio of the magnetic moment to the angular momentum of particle; this is a constant for a given nucleus
gyromagnetic ratio (γ)), (MHz/T)
when a magnetic field is applied, nuclei with non-zero spin will precess (or “wobble”) around the direction of the magnetic field, and the frequency of this precession is ___ proportional to the gyromagnetic ratio
directly
formula of γ
γ = μ/J
μ - magnetic moment of a particle
J - angular momentum or spin of the particle
a single, isolated 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
ensemble of spins
measuring the action of individual 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 10 ^26 nuclei
net magnetization
process by which an atomic nuclei are exposed to a strong magnetic field and then to a pulse of RF energy. this causes the nuclei to absorb the energy and ____ at a a specific frequency
resonance
specific frequency at which this energy is absorbed by the nuclei is called the _____, which depends on the strength of the magnetic field and the type of nucleus
resonance frequency
electromagnetic radiation produced by the oscillator is called a
radiofrequency (RD) emission
composed of an oscillating electric field positioned 90 degrees to an oscillating magnetic field
RF
this rotation follows a pulse of RF tuned to the nuclei’s Larmor frequency. if RF is not at this frequency, the nuclei
do not absorb energy and net magnetization is not rotated
Larmor equation
f = γB0
cartesian coordinate system is used by mathematicians to diagram phenomena in space (x, y, z) drawn perpendicular to one another to describe a coordinate system
vector diagrams
quantity that has direction
vector
reasonable to expect that one of the parameters that affects the amplitude of the magnetic resonance (MR signal) might be the number of hydrogen nuclei within the volume of the sample
spin density
after the RF pulse excites the hydrogen nuclei, the nuclei release energy as they return to their original, lower energy state (a process called____)
relaxation
as they relax, they emit RF signals at the same frequency they absorbed when they were flipped. this is called
signal emission
also called the longitudinal or spin-lattice relaxation time
T1
is called the transverse relaxation time
T2
refers to events occurring along the axis of the net magnetization vector, which is parallel to B0
longitudinal
represents a loss of net XY magnetization, represents the loss of phase coherence in a plane perpendicular to or transverse to M0
T2 relaxation
