Chapter 1: Basic Principles

Question 1

There are essentially 2 ways of explaining the fundamentals of MRI. What are these 2 ways?

Answer 1

Classical theory and Quantum theory.

Question 2

What is the most abundant atom in the human body?

Answer 2

Hydrogen

Question 3

In what 2 ways are atoms characterized?

Answer 3

Atomic number
Mass number/atomic weight

Question 4

What is the sum of the protons in the nucleus called?

Answer 4

Atomic number

Question 5

What is the sum of the protons and neutrons in the nucleus?

Answer 5

Mass number/atomic weight

Question 6

Atoms of elements with the same number of protons but a different number of neutrons are called?

Answer 6

Isotopes

Question 7

What 3 types of motion are present within the atom?

Answer 7

Electrons spinning on their own axis
Electrons orbiting the nucleus
The nucleus itself spinning about its own axis.

Question 8

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?

Answer 8

Angular momentum

Question 9

In MRI, in general, only nuclei with an odd mass number or atomic weight are used. These are known as what?

Answer 9

MR-active nuclei

Question 10

What is the isotope of hydrogen called?

Answer 10

Protium

Question 11

What is the most commonly used MR-active nucleus in MRI?

Answer 11

Hydrogen (Protium)

Question 12

What states that a magnetic field is created by a charged moving particle (that creates an electric field)?

Answer 12

Faraday’s Law of electomagnetic induction.

Question 13

In the absence of an applied magnetic field, the magnetic moments of hydrogen nuclei are what?

Answer 13

Randomly oriented and produce no overall magnetic effect.

Question 14

Which theory used the direction of the magnetic moments of spins to illustrate alignment?

Answer 14

Classical theory

Question 15

Which theory uses the energy level of the spins to illustrate alignment?

Answer 15

Quantum theory

Question 16

Protons of hydrogen nuclei couple with the external magnetic field. What is this referred to as?

Answer 16

Zeeman Interaction

Question 17

What equation predicts the number of spins in each energy level?

Answer 17

Boltzmann equation

Question 18

Boltzmann’s equation also shows that the _________ is an important factor that determines whether a spin is in the high or low energy population.

Answer 18

Patient’s temperature

Question 19

What reflects the relative balance between spin-up and spin-down nuclei? What is this termed as?

Answer 19

NMV

Question 20

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.

Answer 20

Avogadro’s Law

Question 21

In a 1.5 T scanner, what is the number of excess spins?

Answer 21

4.5 for every million protons

Question 22

The precessional frequency is often call what?

Answer 22

Larmor frequency

Question 23

1 megahertz is how many cycles or rotations per second?

Answer 23

1 million

Question 24

______ expresses the relationship between angular momentum and the magnetic moment of each MR-active nucleus.

Answer 24

Gyromagnetic ratio

Question 25

What is the gyromagnetic ratio of hydrogen at 1T?

Answer 25

42.58 MHz/T

Question 26

When the only influence is Bo, what happens to the magnetic moments?

Answer 26

They are out of phase with each other, and therefore the NMV does not precess.

Question 27

________ refers to the position of magnetic moments on their precessional path at any moment in time.

Answer 27

Phase

Question 28

What is the unit of phase?

Answer 28

Radian

Question 29

_______ 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.

Answer 29

Resonance

Question 30

How is resonance achieved?

Answer 30

By transmitting an RF pulse at the Larmor frequency. This is called an RF excitation pulse.

Question 31

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?

Answer 31

Nutation

Question 32

In what 2 ways is the RF excitation pulse characterized by?

Answer 32

It's amplitude and it's frequency

Question 33

What is defined as the energy available from a unit of charge traveling once around a loop of wire?

Answer 33

Electromotive Force (emf)

Question 34

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?

Answer 34

Signal

Question 35

The process by which hydrogen loses its energy is called?

Answer 35

Relaxation

Question 36

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?

Answer 36

TR

Question 37

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?

Answer 37

TE

Question 38

What determines the amount of T1 relaxation that has occured when the signal is read?

Answer 38

TR

Question 39

What controls the amount of T2 relaxation that has occured when the signal is read?

Answer 39

TE