CMR Flashcards
(36 cards)
how does Gd work?
proton electron dipole interaction (PEDI) –> occurs only at less than 3 angstroms. Energy is exchanged from protons to Gd 3 UNPAIRED electrons ( inc spin lattice interaction = shortens T1)
B0, B1
B0 = main magnetic field, B1 = RF magnetic field
what are different types and values for susceptibility in tissue?
susceptibility (Chi, X) is the ability of an object to be magnetized (negative opposes, positive augments). biological is diamagnetic X = -10, ferritin is paramagnetic augments at +5000.
TR, TE
repetition time, echo time (time when you sample)
spin is shorthand for
spin angular momentum
shorthand for spin angular momentum
spin
what does spin interact with?
magnetic field in the same way angular momentum (a top) interacts with a gravitational field
value of hydrogen spin
+1/2 or -1/2
larmor equation
frequency = gyromagnetic ratio x Bo
what is torque have to do with MR?
Bo causes a force that is perpendicular to the orientation of angular momentum
what is the chemical shift?
minor differences in local magnetic field of biological tissue, caused by electron cloud
what is net magnetization?
M, average angular momentum, aligned with B0 before precession, dependent on proton density
ways to deal with respiratory motion artifact
1) better breathing
2) free breathing (inc scan time)
3) dec duration of acquisition
- decrease views per segment
- dec FOV
- single shot imaging (only for LGE)
- parallel imaging (dec SNR)
4) real time imaging (dec spatial AND temporal resolution)
how to deal with motion artifact 2/2 high HR
trigger at end-systole rather than end-diastole
what are drawbacks of increasing FOV
inc scan time, dec spatial resolution
what are the drawbacks of signal oversampling?
inc scan time
what are the drawbacks of real time imaging?
dec temporal and spatial resolution
how to deal with wrap artifact?
1) Inc FOV (inc scan time, dec spatial resolution)
2) Signal oversampling (inc scan time)
3) Inc # phase encoding steps (No change in spatial resolution)
4) Decrease parallel imaging factor
what to do with wrap artifact, poor spatial resolution to begin with?
can use signal oversampling (will inc scan time), can increase # of phase encoding steps (no decrease in spatial resolution
DON’t increase field of view (this will further worsen spatial resolution
what to do with wrap artifcact with good spatial resolution
try increasing FOV, then try decreasing parallel imaging factor
what VENC to shoot for?
most recent echo peak velocity (cm/s) x 100
ghost lines along phase enc direction
respiratory (or other) motion artifact
bands or dark spot near heart/lung interface
inhomogeneity artifact -> shim box over area of interest
Sequences that work with metal artifact
BB or TFE (not ssfp - gradient echo)
