All Flashcards
(22 cards)
- It is the element abundant in the
body and the molecule that comprises water and fat. - It also has only a single proton. Now, in its nucleus, only the proton is inside. And it rotates on its axis, which we call the “SPIN”
HYDROGEN
If a Subatomic particle is spinning? What happens?
It will have a magnetic moment
Before the Human Body is
Introduced to the MRI Machine which
has an Static Magnetic Field, the
orientation of the proton of the
Hydrogen Atoms inside the Body is
Random
When Introduced inside the MRI
Machine, The Protons of Hydrogen now
becomes Parallel and Antiparallel to
The External Magnetic Field of the
Magnet. This Situation is what we call
as
Equilibrium
Now, in Orienting in the Direction Parallel and Anti-Parallel, remember this Proton is now spinning, they are also now doing what?
Precession
- It describes the precessional motion of charged particles in a magnetic field.
- It shows the Angular Larmor Frequency.
- It also demonstrates that there is a
linear relationship between the
Frequency of Precession and the
Strength of the External Magnetic Field
LARMOR EQUATION
- It is a fundamental physical constant that describes the relationship between the magnetic moment and the angular momentum of a particle or nucleus.
- It is unique for each type of nucleus and must be measured for each.
GYROMAGNETIC RATIO
The symbol for External Magnetic field is
B0
the symbol for Net Magnetization i
M
is a quantity that has a direction
Vector
- By convention, the external magnetic field is parallel to the Z-axis of the Cartesian coordinate system; therefore, this Magnetization can also be referred to as MZ or the Z component of the net magnetization.
- At equilibrium, the X and Y components of net magnetization are zero.
VECTOR DIAGRAM
This component of the MRI system has no
moving parts, (except for the patient couch)
it is mainly composed of many subsystems
and several different electromagnetic coils
Gantry
*Magnetic Field of this type is
produced by two assemblies of
bricklike magnets which is attached
to a massive iron yoke.
*There are no shim coils in the
permanent magnet
Permanent Magnet
Type of magnetic imaging system
wherein the coils of wire are wound in
four to six rings, each containing a coil of wire conducting large electrical current, that ranges from 30 to 50 amperes.
Resistive Magnet
- Its size is approximately 3m across by 3 m high, with a length that ranges from 1.4 to 1.6 m
- This massive size is due principally to the need to have the primary magnetic coils at a super
cooled temperature or cryogenic state. - The magnetic coils are submerged in a cryogen usually liquid helium for it to attain super cold temperatures near absolute zero.
Superconducting Magnet
are liquefied gases that produce
super cold temperatures near absolute zero.
Cryogens
is a large insulating container in
which liquid helium and the superconducting
magnet coils reside.
Cryostat
- This subassembly performs two functions:
1) Support and
2) Position - Its basic specification is that it must be able to accept patients who weigh up to 150 kg at near floor level and raise the patient with a power assist to level on the gantry patient aperture.
- Also, it must be able to move the patient from home position to the isocenter position. (This is the same for your Central Ray in Xray). Localizing laser is used to find this isocenter.
Patient Couch
- This is not visible from the outside
because it is covered in a decorative
plastic housing. - Even if we remove the covering, we still cannot see the magnet because it is
housed in the cryostat. - The innermost chamber of the cryostat houses an aluminum cylinder around
which the superconducting wire is
found
Primary Electromagnetic Assembly
