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84 Cards in this Set

  • Front
  • Back
What is the mass weight of Hydrogen?
What type of charge do the atoms have that are used for MRI?
What is the Law More Frequency?
Does T1 stand for growth or decay?
T2 is growth or decay?
What is the transverse plane called?
Which gives off more energy fat or water?
What type of energy is given off by T1?
Spin Lattice
What kind of energy is given off by T2?
What is the time of repetition between one RF pulse to the next?
What is the T1 relaxation time?
the time it takes to recover 63 percent of the longitudinal magnetization?
What is T2 relaxation time?
The time it takes for 63 percent of the transverse magnetization to be lost
As the magnitude of of transverse magnetization decreases, so does the magnitude of the voltage induced in the receiver coil, what is this called?
Free Induction Decay
What is TE?
The time from the application of the RF pulse to the peak of the signal induced in the coil
Contrast parameters that can not be changed because they are inherent to the body's tissues.
Intrinsic contrast parameters
Contrast parameters that can be changed?
Extrinsic Contrast Parameters.
What are the 3 mechanisms you can get contrast by?
T1 recovery, T2 decay, Proton Density
the number of protons per unit of volume of that tissue
proton density
T1 and T2 recovery depend on what 3 factors?
1. the inherent energy of the tissue

2.How closely packed the molecules are.
3.How well the molecular rate matches the lawmore frequency of hydrogen.
Where is information stored in the computer, phase and frequency?
Time between RF pulse and regrowth
Free Induction Decay
number of protons in nucleus?
atomic #
number of protons and neutron in nucleus?
mass number
slightly magnetic
very magnetic
not magnetic
Time of RF pulse to peak of signal
If you have more spatial resolution what do you sacrifice?
Magnetic field that extends outside of the magnet?
fringe field
turns magnetic field back into itself?
passive shielding
Is active shielding better than passive
Either add power or decrease power to even out magnetic field?
shim coils
What coils does the gantry require?
Primary and Secnodary
Primary field in magnets?
B sub O or z axis
Table can move up to what speed?
10 cm a second
What strength do permanent magnets go up to?
.3 tesla
What strength do air core magnets go up to?
.1 tesla
What strength do Iron Core magnets go up to?
.6 tesla
What strength do spuerconductive magnets go up to?
8 tesla
How does magnet strength affect T1?
Higher magnet strength makes T1 longer
How do artifacts affect High Field Magnets?
They are more sensitive to motion artifcacts, but have less artifacts due to homogenity
Are most MR machines run by AC or DC current?
Waht are the 2 coolants we use?
helium and nitrogen
What is used to make primary coils?
Niopium Titanium
What gradient is used for axial slices?
what gradient coil do we use for coronal?
what gradient coil do we use for sagittal?
What can make coils better?
more channels
steep gradient equals what?
longer rise time
What are some intrinsic contrast parameters?
T1 recovery time
T2 Decay time
proton density
What are some extrinsic contrast paramters?
Flip Angle
Is the T1 of fat long or short?
The T1 time of water is short or long?
T2 time of fat is long or short?
T2 time of water is short or long?
Images where fat is bright and water is dark are called what?
T1 weighted images
Images where water is bright and fat is dark are called what?
T2 weighted images
Direction of a gradient?
receiver coil or any conducive loop is placed in moving magentic field a voltage is induced in this coil.
faraday law
the position of a magnetic moment on its precessional path at any given time
What is an elctromagnetic field surrounding individual atoms and groups of atoms possessing specificu characteristics?
What are the types of movement in an atom at all times?
the spin of each electron on its own axis
the orbiting of each electron
the spin of the nucleus on its own axis
the magetic field of each atom or groups of atoms
magnetic domain
force with direction
patients magnetic vector?
what is usually used to enhance the magetic properties of the solenoids?
Soft Iron
What are some examples of ferromagnetic materials?
iron, cobalt, nickel
108 lines of flux?
What is a faraday cage?
An unbroken copper surround, to shield room from outiside RF frequencies.
precessional frequency of the nuclear spins
flux density of the applied magnetic field
Mz + Mxy =
Is MR singal maximized by a 90 degree flip or a 180 degree flip
90 degree
Why is T2* decay faster than T2 decay?
It combines T2 decay with dephasing due to magnetic inhomogenities.
What are the 2 ways to compensate for T2* decay?
spin echo sequence and gradient echo sequence
When using one spin echo, how do you T1 weight the image?
Using a short TR and a short TE, with only one echo
How do you produce a proton denisty weighted image and a T2 weighted image using two echo with spin echo?
First echo is a short TE and a long TR producing a proton density weighted image, and the 2nd echo has a long TE and a long TR, producing a T2 weighted image
What kind of weighted images does spin echo pulse sequence create?
T1, T2 , or Proton Density
What controls the T1 weighting?
What maximizes T! weighting?
Short TR
What maximizes proton density weighting?
Long TR
What controls T2 weighting?
What maximizes T2 weighting?
Long TE
T1 time of water?
T2 time of water?
2500 ms
2500 ms