module 3 - mri
MAGNETIC FIELD
A spinning charged particle will induce a magnetic field along the axis of spin. Protons act like a tiny magnets Nuclear Magnetic Resonance
What is MRI?
Magnetic resonance imaging. Images based on the magnetic properties of chemical elements within the body, rather than ionizing radiation such as X-rays.
proton
Normally ________ are aligned in a random fashion.
MR active nuclei
a nucleus has an odd mass number
42.57 MHz/T
gyromagnetic ratio ___________
What is MRI?
magnetic resonance imaging
MAGNETIC FIELD
motion plus a charged particle will produce this
Protons and neutrons
spin about their own axes within the nucleus. The direction of spin is random so that some particles spin clockwise, and others anticlockwise.
Negatively charged electrons
spin on their own axis.
The nucleus
spins on its own axis.
B0
strength of the external magnetic field (T) -
Quantum Theory
the study of the structure and behavior of the atom and of subatomic particles from the view that all energy comes in tiny, indivisible bundles
Quantum Theory
the theory that describes matter and energy at very small (atomic) sizes
proton
A _________ has a spin. The ___________ has its own magnetic field and it can be seen as a little bar magnet
Nuclear Magnetic Resonance (NMR)
- Certain atomic nuclei have magnetic moments that are oriented at random. Their magnetic moments tend to align either with or against the direction of this applied field. - Aligned with the field = Alpha state = low energy - using radio frequency pulses, excite some lower energy nuclei into the Beta state (Higher Energy) - Ex) Magnetic Roesonance imaging (MRI)
Precession
A slow motion of Earth's axis that traces out a cone over a period of 26,000 years
MAGNETIC FIELD
A spinning charged particle will induce a ______________ along the axis of spin.
spin
A proton has a _________
C
10.7
Na
11.3
P
17.2
K
2.0
F
40.1
H
42.6
O
5.8
H
6.5
Proton + Neutron
= Mass Number
Hydrogen
= Proton = Spin
# Proton ≠ # Neutron
> net spin > spin angular momentum (MR active)
# Proton = # Neutron
> no net spin
more nuclei with their magnetic moments aligned parallel
At room temperature there are always ____________________ to the main field than aligned antiparallel. The net magnetism of the patient (termed the net magnetization vector or NMV), which reflects the balance between the parallel and antiparallel magnetic moments, is therefore aligned parallel to the main field at room temperature (thermal equilibrium).
than aligned antiparallel
At room temperature there are always more nuclei with their magnetic moments aligned parallel to the main field _______________. The net magnetism of the patient (termed the net magnetization vector or NMV), which reflects the balance between the parallel and antiparallel magnetic moments, is therefore aligned parallel to the main field at room temperature (thermal equilibrium).
net magnetization vector or NMV
At room temperature there are always more nuclei with their magnetic moments aligned parallel to the main field than aligned antiparallel. The net magnetism of the patient (termed the _______________________), which reflects the balance between the parallel and antiparallel magnetic moments, is therefore aligned parallel to the main field at room temperature (thermal equilibrium).
Classical Theory
At room temperature there are always more nuclei with their magnetic moments aligned parallel to the main field than aligned antiparallel. The net magnetism of the patient (termed the net magnetization vector or NMV), which reflects the balance between the parallel and antiparallel magnetic moments, is therefore aligned parallel to the main field at room temperature (thermal equilibrium).
thermal equilibrium
At room temperature there are always more nuclei with their magnetic moments aligned parallel to the main field than aligned antiparallel. The net magnetism of the patient (termed the net magnetization vector or NMV), which reflects the balance between the parallel and antiparallel magnetic moments, is therefore aligned parallel to the main field at room temperature ______________.
Spin up nuclei
Low energy nuclei that align their magnetic moments parallel to the external magnetic field
Any charged particle in motion creates what?
MAGNETIC FIELD
Alignment can be described using two theories:
Classical Theory Quantum Theory
Larmor equation
Describes the resonant frequency of a nucleus, the precession frequency of a nuclear magnetic moment, and the dependence of resonant frequency on magnetic field strength. w = yB w = resonant (and precessional) frequency of nucleus. y = gyromagnetic ratio (intrinsic, constant property of a nuclear species). B = magnetic field where nuclear moment is located. If B varies in space, so does w
Precession
Every MR active nucleus is spinning on its own axis. Owing to the influence of the external magnetic field these nuclei produce a secondary spin or spin wobble.
Spin down nuclei
High energy nuclei that align their magnetic moments in the anti-parallel direction
high or low
Hydrogen can only have two energy states - ____________. Therefore the magnetic moments of hydrogen can only align in the parallel or antiparallel directions. The magnetic moments of hydrogen cannot orientate themselves in any other direction.
parallel or antiparallel directions
Hydrogen can only have two energy states - high or low. Therefore the magnetic moments of hydrogen can only align in the ___________________. The magnetic moments of hydrogen cannot orientate themselves in any other direction.
cannot orientate themselves in any other direction.
Hydrogen can only have two energy states - high or low. Therefore the magnetic moments of hydrogen can only align in the parallel or antiparallel directions. The magnetic moments of hydrogen ___________________
What do the quantum and classical theories tell us?
Hydrogen can only have two energy states - high or low. Therefore the magnetic moments of hydrogen can only align in the parallel or antiparallel directions. The magnetic moments of hydrogen cannot orientate themselves in any other direction.
MR active nuclei
Li F H
tiny magnets
Protons act like a _______________
thermal equilibrium
Refers to the property of a thermodynamic system in which all parts of the system have attained a uniform temperature which is the same as that of the system's surroundings.
HYDROGEN ATOM
Single proton (no neutron) Very high abundance in the body (80% of all atoms found in the human body ) magnetic properties of the proton in a hydrogen atom (strong NMR effect)
stronger the magnetic field
The __________________, the faster the precession rate and the higher the precession frequency.
precessional frequency
The speed at which the magnetic moments wobble about the external magnetic field is called the ________________
thermal equilibrium
The state of two or more objects or substances in thermal contact when they have reached a common temperature
the faster the precession rate
The stronger the magnetic field, ________________- and the higher the precession frequency.
higher the precession frequency.
The stronger the magnetic field, the faster the precession rate and the _________________
either parallel or anti- parallel to the external magnetic field.
Then they are aligned in only two ways, _________________
Classical Theory
Theory of human behavior that emphasizes free will as a core concept.
80%
Very high abundance in the body (__________ of all atoms found in the human body)
a nucleus has an even mass number
When ________________________ the spins cancel each other out so the nucleus has no net spin.
external magnetic field
When nuclei are placed in an ______________ their magnetic moments line up with the magnetic field flux lines.
magnetic moments line up with the magnetic field flux lines.
When nuclei are placed in an external magnetic field their ___________________
What happens to the protons, when we put them into an external magnetic field?
When nuclei are placed in an external magnetic field their magnetic moments line up with the magnetic field flux lines. Then they are aligned in only two ways, either parallel or anti- parallel to the external magnetic field.
a nucleus has an odd mass number
When_________________________, the spins do not cancel each other out and the nucleus spins.
Precession
Wobble in Earth's rotational axis
Hydrogen
_____________ can only have two energy states - high or low. Therefore the magnetic moments of hydrogen can only align in the parallel or antiparallel directions. The magnetic moments of hydrogen cannot orientate themselves in any other direction.
At room temperature
_______________ there are always more nuclei with their magnetic moments aligned parallel to the main field than aligned antiparallel. The net magnetism of the patient (termed the net magnetization vector or NMV), which reflects the balance between the parallel and antiparallel magnetic moments, is therefore aligned parallel to the main field at room temperature (thermal equilibrium).
magnetic properties of the proton
___________________ in a hydrogen atom (strong NMR effect)
Classical Theory
an abstract generalization that systematically explains relationships among phenomena
Classical Theory
an approach to the study of formal organizations that views workers as being motivated almost entirely by economic rewards
Larmor equation
an equation stating that the frequency of precession of nuclear magnetic moment is directly proportional to the product of the magnetic field strength(B0) and the gyromagnetic ratio
Quantum Theory
based on energy
Certain atomic nuclei
demonstrate the ability to absorb and re-emit radiofrequency energy when placed in a MF.
Quantum Theory
describes mathematically the wave properties of electrons and other very small particles
Precession
direction of the Earth's axis of rotation
Spin down nuclei
have high energy and have enough energy to oppose the main field. These are the nuclei that align their magnetic moments antiparallel to the main field in the classical description.
Spin up nuclei
have low energy and do not have enough energy to oppose the main field. These are the nuclei that align their magnetic moments parallel to the main field in the classical description.
What is MRI?
imaging through strong magnetic fields (brain anatomy)
precessional frequency
is not constant.
Negatively charged electrons
orbit the nucleus.
w0
precessional frequency -
Classical Theory
temperature alignment
Classical Theory
temperature excess > net magnetization vector alignment to balance the protons
gyromagnetic ratio
the _________________ is the precessional frequency of a specific nucleus at 1 T and therefore has units of MHz/T - y
MHz/T - y
the gyromagnetic ratio is the precessional frequency of a specific nucleus at 1 T and therefore has units of ___________-
Quantum Theory
the magnetic moments of hydrogen nuclei align in the presence of an external magnetic field in the following two energy states or populations
The single steps of an MR examination can be described quite simply:
the patient is placed in a magnet, a radio wave is sent in, the radio wave is turned off, the patient emits a signal, which is received and used for reconstruction of the picture
Larmor equation
used to calculate the frequency or speed of precession for a specific nucleus in a specific magnetic field strength.
What is MRI?
uses a powerful magnetic field, radio waves and a computer to produce detailed pictures of the body's internal structures that are clearer, more detailed and more likely in some instances to identify and accurately characterize disease than other imaging methods.
Nuclear Magnetic Resonance (NMR)
uses magnetic fields to determine the arrangement of nuclei in a molecule. Typical NMR methods only work on nuclei that have nonzero spin, such as 1H and 13C—the nonzero spin means that the nuclei oscillate between two spin states in a phenomenon called Larmor precession. NMR measures the frequency at which each nucleus oscillates, whose deviation from a reference nucleus (such as tetramethylsilane) depends on the local electron density and is called the chemical shift. Nuclei that have more electron density (due to proximity to electron-donating groups like alkyl groups) are said to be "shielded" and have lower chemical shifts, while those that have less electron density (due to proximity to electron-withdrawing groups like halogens) are said to be "deshielded" and have higher chemical shifts. Peaks in NMR can be "split" into several peaks due to J-coupling if they are adjacent to identical nuclei, like the three hydrogens of a methyl group. NMR is the theoretical basis for magnetic resonance imaging (MRI) in medicine.
Nuclear Magnetic Resonance (NMR)
volumes of specific tissues
Larmor equation
w = yB = 42 MHz/T x B w = precession frequency y = gyromagnetic ratio (constant) = 42 MHz/T B = magnetic field strength
thermal equilibrium
when two objects are at the same temperature and no heat flows
