What is a mass number?
Total number of nucleons in a nucleus
Why is mass number important to MRI?
Determines weather a nucleus has a net magnetic moment or not.
What conditions are necessary for resonance?
Energy must be applied at the precessional frequency of the nucleus
And at right angles to the main field.
What is phase?
Position of the magnetic moment at any point in time
What is frequency?
Number of revolutions per second
The speed of the precession
What is the most common atom in the body?
Atoms of elements with the same number of protons but different number of neutrons
The process of knocking out electrons
Net spin of a nucleus because of an odd number of protons and neutrons
MR Active Nuclei
Nuclei with an odd mass number or atomic weight
Law of electromagnetic induction (Faraday 1833)
Connection between electric and magnetic fields and motion.
A moving electric field produces a magnetic field and vise versa
Each nucleus in a magnetic field has vector properties
(Size and direction)
MR active Nuclei (list)
Mass number of hydrogen
Mass number of carbon
Mass number of nitrogen
Mass number of oxygen
Mass number of fluorine
Mass number of sodium
Name the isotope of hydrogen
What is the most common MR active nucleus
Protium (the isotope of hydrogen)
When placed in a strong static external magnetic field, the magnetic moments of H1 Nuclei orientate with the magnetic field.
Magnetic moments in the same direction as the main B0 field
Spin up is also known as:
Magnetic moments in the opposite direction to the main B0 field.
Spin-down is also known as:
Net magnetic vector
After alignment there are alway more spin-ups than spin-down.
Protons of H1 couple with the external magnetic field B0 and cause a discreet number of energy states
Not enough energy to oppose B0
Enough energy to oppose B0
What is B0
The large magnetic field of an MRI scanner.
How is B0 measured?
6 x 10 (to the 23rd power) molecules per gram of tissue, and the number of excess spins is in the order of 6 x 10(to the 17th power) per gram of tissue.
Secondary spin, causes magnetic moments to circle around B0
Course magnetic moments take around B0
The speed magnetic moments precess around B0
Precessional Frequency. Is determined by the Larmor Equation
Unit that precessional Frequency is measured
Expresses the relationship between angular momentum and the magnetic moments of each MR active nucleus
How is gyromagnetic ratio expressed
What is the gyromagnetic ratio for hydrogen
What is the Larmor Frequency of Hydrogen at 1.5T
Position of magnetic moments on their precessional Path
What is the unit of Phase?
Out of phase
Occurs when an object is exposed to an oscillating perturbation that has a frequency close to its own.
RF excitation pulse
Produced by a transmit coil.
How resonance is achieved.
How is the RF excitation pulse different from B0
B1 (RF excitation) produces an oscillating magnetic field 90 degrees to B0.
What axis is the transverse plane on?
X - y axis
Which axis is the longitudinal plane
The spiral motion cause by 2 precessional motions that happened simultaneously.
When spins are unable to absorb more energy or to be stimulated and release more energy
Electromotive force (emf)
Energy available from a unit of charge traveling once around a loop
MRI in practice ch 1