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84 Cards in this Set
- Front
- Back
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What is the mass weight of Hydrogen?
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1
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What type of charge do the atoms have that are used for MRI?
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Negative
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What is the Law More Frequency?
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42.57
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Does T1 stand for growth or decay?
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growth
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T2 is growth or decay?
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decay
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What is the transverse plane called?
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xy
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Which gives off more energy fat or water?
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Water
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What type of energy is given off by T1?
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Spin Lattice
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What kind of energy is given off by T2?
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spin-spin
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What is the time of repetition between one RF pulse to the next?
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TR
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What is the T1 relaxation time?
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the time it takes to recover 63 percent of the longitudinal magnetization?
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What is T2 relaxation time?
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The time it takes for 63 percent of the transverse magnetization to be lost
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As the magnitude of of transverse magnetization decreases, so does the magnitude of the voltage induced in the receiver coil, what is this called?
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Free Induction Decay
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What is TE?
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The time from the application of the RF pulse to the peak of the signal induced in the coil
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Contrast parameters that can not be changed because they are inherent to the body's tissues.
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Intrinsic contrast parameters
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Contrast parameters that can be changed?
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Extrinsic Contrast Parameters.
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What are the 3 mechanisms you can get contrast by?
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T1 recovery, T2 decay, Proton Density
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the number of protons per unit of volume of that tissue
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proton density
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T1 and T2 recovery depend on what 3 factors?
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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. |
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Where is information stored in the computer, phase and frequency?
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Kspace
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Time between RF pulse and regrowth
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Free Induction Decay
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number of protons in nucleus?
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atomic #
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number of protons and neutron in nucleus?
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mass number
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slightly magnetic
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paramagnetic
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very magnetic
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ferromagnetic
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not magnetic
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diamagnetic
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Time of RF pulse to peak of signal
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TE
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If you have more spatial resolution what do you sacrifice?
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SNR
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Magnetic field that extends outside of the magnet?
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fringe field
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turns magnetic field back into itself?
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passive shielding
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Is active shielding better than passive
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Yes
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Either add power or decrease power to even out magnetic field?
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shim coils
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What coils does the gantry require?
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Primary and Secnodary
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Primary field in magnets?
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B sub O or z axis
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Table can move up to what speed?
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10 cm a second
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What strength do permanent magnets go up to?
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.3 tesla
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What strength do air core magnets go up to?
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.1 tesla
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What strength do Iron Core magnets go up to?
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.6 tesla
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What strength do spuerconductive magnets go up to?
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8 tesla
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How does magnet strength affect T1?
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Higher magnet strength makes T1 longer
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How do artifacts affect High Field Magnets?
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They are more sensitive to motion artifcacts, but have less artifacts due to homogenity
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Are most MR machines run by AC or DC current?
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AC
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Waht are the 2 coolants we use?
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helium and nitrogen
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What is used to make primary coils?
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Niopium Titanium
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What gradient is used for axial slices?
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z
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what gradient coil do we use for coronal?
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y
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what gradient coil do we use for sagittal?
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x
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What can make coils better?
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more channels
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steep gradient equals what?
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longer rise time
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What are some intrinsic contrast parameters?
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T1 recovery time
T2 Decay time Flow proton density ADC |
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What are some extrinsic contrast paramters?
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TR
TE Flip Angle TI |
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Is the T1 of fat long or short?
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short
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The T1 time of water is short or long?
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long
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T2 time of fat is long or short?
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short
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T2 time of water is short or long?
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long
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Images where fat is bright and water is dark are called what?
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T1 weighted images
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Images where water is bright and fat is dark are called what?
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T2 weighted images
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Direction of a gradient?
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polarity
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receiver coil or any conducive loop is placed in moving magentic field a voltage is induced in this coil.
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faraday law
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the position of a magnetic moment on its precessional path at any given time
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phase
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What is an elctromagnetic field surrounding individual atoms and groups of atoms possessing specificu characteristics?
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magnetism
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What are the types of movement in an atom at all times?
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the spin of each electron on its own axis
the orbiting of each electron the spin of the nucleus on its own axis |
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the magetic field of each atom or groups of atoms
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magnetic domain
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force with direction
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vector
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patients magnetic vector?
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MO
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what is usually used to enhance the magetic properties of the solenoids?
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Soft Iron
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What are some examples of ferromagnetic materials?
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iron, cobalt, nickel
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108 lines of flux?
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Wb
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What is a faraday cage?
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An unbroken copper surround, to shield room from outiside RF frequencies.
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precessional frequency of the nuclear spins
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fO
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flux density of the applied magnetic field
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B0
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Mz + Mxy =
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M0
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Is MR singal maximized by a 90 degree flip or a 180 degree flip
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90 degree
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Why is T2* decay faster than T2 decay?
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It combines T2 decay with dephasing due to magnetic inhomogenities.
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What are the 2 ways to compensate for T2* decay?
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spin echo sequence and gradient echo sequence
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When using one spin echo, how do you T1 weight the image?
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Using a short TR and a short TE, with only one echo
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How do you produce a proton denisty weighted image and a T2 weighted image using two echo with spin echo?
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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
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What kind of weighted images does spin echo pulse sequence create?
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T1, T2 , or Proton Density
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What controls the T1 weighting?
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TR
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What maximizes T! weighting?
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Short TR
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What maximizes proton density weighting?
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Long TR
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What controls T2 weighting?
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TE
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What maximizes T2 weighting?
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Long TE
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T1 time of water?
T2 time of water? |
2500 ms
2500 ms |
