Intro to MRI
Card Set Information
Intro to MRI
Intro to MRI
Some research shows what biologic change in MRI?
In MRI, what changes body temperature?
Projectiles can have a velocity of ___ mph when pulled by a 1.5 T.
MRI can cause what to implants and prosthesis?
Torque, heat, and unpredictable movement in the body
These cause death in MRI:
aneurysm clips (intracranial vascular clips)
RF can increase:
body temperature and specific absorption rasio (SAR)
RF power absorbed per unit of mass of an object; measured in W/kg.
SAR Specific Absorption Ratio
During excitation, nuclei ____. During relaxation, nuclei ____.
absorb energy; give off energy
Loss of absolute zero temperature of magnet:
What escapes during quenching?
If pressure builds inside the scan room:
break the glass partition
Purpose of magnet in MRI:
aligns nuclei into parallel (low energy) and anti-parallel (high energy)
The RF source in MRI does what?
excites nuclei and aligns nuclei away from Bo. Also receives magnetic property of a tissue.
Hardware required for MRI:
Magnet, RF source, Image receptor, computer system
The image receptor in MRI records:
magnetic property of a tissue as data
Magnetic dipole is also termed:
Classifications of magnet:
Diamagnetic, Paramagnetic, Ferromagnetic
Deliberate quenching should be done:
only in emergency; i.e. fire
Most widely used magnet:
Moving electrical charges induce magnetic fields around themselves:
Made of super conducting material; shows zero resistance after critical temperature and is super cooled by cryogen:
Hydrogen protons are used in routine MRI imaging because of:
it's abundance in the body
What is the precession frequency of H?
With the influence of a magnet, H protons want to:
line up with the magnet in the longitudinal direction
With the influence of a magnet, what happens to low energy and high energy protons?
Low energy protons spin up (parallel) while high energy protons spin down (anti-parallel).
The relative balance between spin up and spin down nuclei is called:
Net Magnetization Vector (NMV)
Large NMV results in:
high signal that will appear light
Small NMV results in:
low signal that will appear dark
A secondary spin caused by the magnet on a hydrogen atom which is spinning on it's own axis:
The speed at which an atom wobbles:
Precessional frequency is determined by:
Magnet strength and gyro-magnetic ratio
Phenomenon that occurs when an object is exposed to an oscillating perturbation that has a frequency close to it's own natural frequency:
The angle to which the NMV moves out of alignment:
Flip angle is usually set to reach
Process by which hydrogen loses it's energy:
T1 recovery is also called _____ and results in nuclei giving up their energy to ____.
spin lattice; the environment
T2 decay is also called _____ and is caused by nuclei exchanging their energy with ____.
spin-spin relaxation; neighboring nuclei
Intrinsic factors of MRI:
T1 recovery, T2 decay, proton density, flow apparent diffusion coefficient
Extrinsic factors of MRI:
TR, TE, Flip angle, T1, and Turbo fact
Time from the application of on RF pulse to the next; determines T1 relaxation and hence T1 weighting:
TR, or Repetition Time
Time from the application of RF pulse to the peak of echo measured in the coil:
TE, or Echo Time
Molecular motion of fat is ____ and fat molecules release energy in to their environment ____.
T1 time of fat is _____.
short, 200 ms
Molecular motion of water is ____ and it is ____ for water molecules to release energy to their environment.
The T1 and T2 time of water is ____.
long, 2500 ms
T2 weighted images have ____ fat and ____ water signals.
Long TE results in ____ fat while short TE results in ____ fat.
Series of RF and gradient pulses used to disturb and manipulate the orientation of the net magnetization of protons and to spatially encode the information contained within the MR echoes.
Two major groups of pulse sequences:
Spin echo and Gradient echo
Which pulse sequence is called the gold standard for most imaging?
Spin Echo Pulse Sequence; conventional
Which pulse sequence was introduced to cut time and how?
Gradient Echo; uses short TR
Which pulse sequence is mainly used for cardiac imaging?
GE pulse sequence
Which pulse sequence is used for diagnosing bone bruise?