chap 1&10 review Flashcards
the static magnetic field is referred to as
B0
the signal/voltage is only induced if there is _______ magnetization in the transverse plane that is in-phase
coherent
high energy nuclei align their magnetic moments in the anti - parallel direction are ________ nuclei
spin-down
process by which hydrogen loses its energy
relaxation
application of an RF pulse that causes resonance, “energy giving”
excitation
relationship between angular momentum & the magnetic moment of each MR-active nucleus
gyromagnetic ratio
when an object is exposed to an oscillating perturbation that has a frequency close to its own natural frequency of oscillation
resonance
balance between spin-up and spin-down nuclei
NMV
what are 2 results of resonance
- NMV moves out of alignment with B0
- magnetic moments move into phase with each other
most abundant atom in the human body
hydrogen
the atomic number comes from
the sum of protons
the atomic mass comes from
the sum of protons & neutrons in the nucleus
the precessional frequencies of MR-active nuclei fall within which band of the electromagnetic spectrum
radio frequency
the time from the application of the RF excitation pulse to the peak of the signal
TE
the point in a pulse sequence from the excitation pulse to the echo of the signal
TE (time to echo)
the time from the application of one RF excitation pulse to the application of the next RF pulse for each slice
TR (time to repetition)
the position of the magnetic moment at any point of time is recorded as their
phase
what best refers to the position of the magnetic moment on their precessional path as it travels 360 degrees during one rotation
phase
protium has a atomic number & mass number of
1
even atomic number & mass number
forces cancel out , no spin
odd number of protons, neutrons, or both
has net spin, or angular momentum
unit of precessional frequency
Hertz
the three types of motion inherent within the atom with angular momentum
- electrons spinning on their own axis
- electrons orbiting the nucleus
- nucleus itself spinning about its own axis
T/F: the number of spin-up / spin-down is directly related to the strength of the magnetic field
true
T/F: high energy nuclei possess enough energy to oppose the magnetic field
true
most commonly used MR active nucleus in MRI
protium
the Larmor equation
precessional freq. = B0 strength (x) gyromagnetic ratio
unit of phase
radian
measure of how quickly the phase position of magnetic moments change over time
frequency
not in the same place on the precessional path, aka incoherent
out-of-phase
magnetic moments in the same place on the precessional path around B0 at any time, aka coherent
in-phase
current opposes the change in magnetic field , refers to which law
Lenz’s Law
governs precessional frequency
Larmor Equation
refers to 3 forces (motion, magnetism, & charge) and states that if two of these are present, then the 3rd is automatically induced
Faraday’s Law of Electromagnetic Induction
the gyrometric ratio of Hydrogen on 1T
42.58 MHz
the gyrometric ratio of Hydrogen on 3T
127.74 MHz
patient heating/burns, antenna effect, & adverse effects on implant function can all be attributed to
the RF field
the energy wavelength in MRI
RF
responsible for determining the amount of energy that is deposited and translated across our patients
RF
when a stationary object twists or rotates
rotational force
when an object moves from one point to another
translational force
translational force likelihood increases
closer to isocenter
translational force likelihood decreases
away from isocenter
the magnet’s static field is responsible for 4 main safety related effects
- transient biological effects
- projectile hazards
- torque on implants
- translational force on foreign bodies
magnetic field outside the bore, not confined to ceilings, floors, or walls
fringe field
reversible amplitude of the T-wave
hematodynamic effect
tips for reducing SAR
- increasing TR
- reducing flip angle
- using a different local receiver coil
- removing/reducing presaturation pulses
- scanning on lower field strength magnet
