MRI: Protons in the Strong Magnetic Field Flashcards
Proton magnetic moments aligned parallel to the field tend to have a
Lower energy state
These tend to align with B0 and are energy dependent
Proton magnetic moments
This unit refers to the protons in a steady magnetic field
B0 unit (1 Testa or T = 10,000 Gauss or G)
When protons are placed in a strong magnetic field,
The magnetic moments tend to align _____ or ______ to the external magnetic field
Parallel or anti-parallel
The magnetic moment is induced to rotate around the axis of the magnetic field, also called as
Precession
- A vertically oriented gyroscope rotates without any wobbling
- Once tipped off its axis, gravity causes the spinning gyroscope to wobble
- The wobbling has its own frequency that can be considered independent of the spinning frequency
This device is analogous to the precession of a proton spin
Gyroscope
Spin excess is used to generate
MR signals
(only 10 out of 1 million protons contribute to spin excess)
When the number of protons parallel to B0 is slightly higher than the number of protons anti-parallel to B0, this is an instance of
Spin excess
Proton magnetic moments aligned anti-parallel to the field tend to have a
High energy state
The number of protons parallel and anti-parallel to B0 are
Similar
Overall, net magnetization (M->) is in the _______ direction
Longitudinal, z-direction
The component in net magnetization wherein phases of proton spins are random, so vector summation yields zero
Transverse component
The component in net magnetization wherein the majority of the parallel and anti-parallel spins cancel each other.
Some spin excess remains and can be used to generate MR signals
Longitudinal component
Each proton magnetization can be considered as a
Vector
Net magnetization of the precessing proton spins can be found using
Vector summation
