Chapter 1: Basic Principles Flashcards
There are essentially 2 ways of explaining the fundamentals of MRI. What are these 2 ways?
Classical theory and Quantum theory.
What is the most abundant atom in the human body?
Hydrogen
In what 2 ways are atoms characterized?
Atomic number
Mass number/atomic weight
What is the sum of the protons in the nucleus called?
Atomic number
What is the sum of the protons and neutrons in the nucleus?
Mass number/atomic weight
Atoms of elements with the same number of protons but a different number of neutrons are called?
Isotopes
What 3 types of motion are present within the atom?
Electrons spinning on their own axis
Electrons orbiting the nucleus
The nucleus itself spinning about its own axis.
Nuclei need an odd number of protons, neutrons, or an odd number of both protons and neutrons, so that the spin directions are not equal and opposite, so the nucleus itself will have a net spin. What is this called?
Angular momentum
In MRI, in general, only nuclei with an odd mass number or atomic weight are used. These are known as what?
MR-active nuclei
What is the isotope of hydrogen called?
Protium
What is the most commonly used MR-active nucleus in MRI?
Hydrogen (Protium)
What states that a magnetic field is created by a charged moving particle (that creates an electric field)?
Faraday’s Law of electomagnetic induction.
In the absence of an applied magnetic field, the magnetic moments of hydrogen nuclei are what?
Randomly oriented and produce no overall magnetic effect.
Which theory used the direction of the magnetic moments of spins to illustrate alignment?
Classical theory
Which theory uses the energy level of the spins to illustrate alignment?
Quantum theory
Protons of hydrogen nuclei couple with the external magnetic field. What is this referred to as?
Zeeman Interaction
What equation predicts the number of spins in each energy level?
Boltzmann equation
Boltzmann’s equation also shows that the _________ is an important factor that determines whether a spin is in the high or low energy population.
Patient’s temperature
What reflects the relative balance between spin-up and spin-down nuclei? What is this termed as?
NMV
According to _________, there are about 6 x 10^23 molecules per gram of tissue, and the number of excess spins is in the order of 6 x 10^17 per gram of tissue.
Avogadro’s Law
In a 1.5 T scanner, what is the number of excess spins?
4.5 for every million protons
The precessional frequency is often call what?
Larmor frequency
1 megahertz is how many cycles or rotations per second?
1 million
______ expresses the relationship between angular momentum and the magnetic moment of each MR-active nucleus.
Gyromagnetic ratio
What is the gyromagnetic ratio of hydrogen at 1T?
42.58 MHz/T
When the only influence is Bo, what happens to the magnetic moments?
They are out of phase with each other, and therefore the NMV does not precess.
________ refers to the position of magnetic moments on their precessional path at any moment in time.
Phase
What is the unit of phase?
Radian
_______ is a phenomenon that occurs when an object is exposed to an oscillating perturbation that has a frequency close to its own natural frequency of oscillation.
Resonance
How is resonance achieved?
By transmitting an RF pulse at the Larmor frequency. This is called an RF excitation pulse.
The transition that the magnetic moments have in precessing at the higher rate in the longitudinal plane to decreasing the NMV into the transverse plane creates a spiraling motion downward of the NMV. This spiraling down is called what?
Nutation
In what 2 ways is the RF excitation pulse characterized by?
It’s amplitude and it’s frequency
What is defined as the energy available from a unit of charge traveling once around a loop of wire?
Electromotive Force (emf)
According to Faraday’s Law, a changing magnetic field causes movement of charged particles (electrons). This flow of electrons is a current, which generates a voltage induced in the receiver coil. This voltage is called?
Signal
The process by which hydrogen loses its energy is called?
Relaxation
What is the time from the application of one RF pulse to the application of the next RF pulse for each slice and is measured in milliseconds?
TR
What is the time from the application of the RF pulse to the peak of signal induced in the receiver coil and is also measured in milliseconds?
TE
What determines the amount of T1 relaxation that has occured when the signal is read?
TR
What controls the amount of T2 relaxation that has occured when the signal is read?
TE
