EXAM #12 — PHYSICS UNIT 05 Flashcards
RF pulse.
a burst of radio frequency energy
net magnetization relaxation.
the return of net magnetization to equilibrium as it releases absorbed RF (Tl) and loses energy (T2)
free induction decay.
the simple signal given off by the relaxation of net magnetization to equilibrium
spin density or proton density.
the relative number of protons (spins) in a sample
spin echo.
the signal given off by the relaxation of net magnetization to equilibrium after a refocusing pulse- is a mirror image of the FID
Tl relaxation.
regrowth of net magnetization along the Z axis
longitudinal recovery.
regrowth of net magnetization along the Z axis
spin-lattice relaxation?
longitudinal recovery and spin-lattice relaxation are terms for ___ _____
spin-lattice relaxation. the process of RF being dissipated into the lattice surrounding the proton
longitudinal recovery and spin-lattice relaxation are terms for Tl relaxation
T2 relaxation.
the decay of transverse magnetization
transverse decay.
the decay of transverse magnetization
spin-spin relaxation?
transverse decay and spin-spin relaxation are terms for ___ _____
spin-spin relaxation. the process of spins interacting with each other, which causes phase changes, and loss of transverse magnetization
transverse decay and spin-spin relaxation are terms for T2 relaxation
T2* relaxation.
transverse decay in the presence of magnetic field inhomogeneities- spin-spin interaction plus magnetic field inhomogeneity
phase.
the degree to which spins are precessing at the same position at a specific point in time- T2 relaxation is also known as phase coherence
explain why T2* relaxation is shorter than T2 relaxation.
magnetic field inhomogeneities increase de-phasing and increase decay of transverse magnetization
identify the type of relaxation most affected by magnetic field inhomogeneity. T2*
identify the type of relaxation most affected by magnetic field inhomogeneity.
T2*
identify the amount of longitudinal regrowth that defines true Tl relaxation time.
Tl relaxation is defined as the time it takes for 63% of longitudinal magnetization to regrow
identify the amount of transverse decay that defines true T2 relaxation time.
T2 relaxation is defined as the time it takes for 63% of transverse magnetization to decay
explain the state of phase of all spins immediately after RF excitation.
all spins are in phase immediately after RF excitation
recognize a diagram of longitudinal regrowth and the relative relaxation times of tissues on the diagram.
O.K.
recognize a diagram of transverse decay and the relative relaxation times of tissues on the diagram.
O.K.
describe the relative Tl and T2 relaxation times of fat and water.
fat has short Tl and short T2 relaxation times (relative to water) water has long Tl and T2 relaxation times (relative to fat)
describe the relative brightness of fat and water on Tl and T2 weighted MR images.
Tl weighted images- fat is bright and water is dark T2 weighted images- fat is dark and water is bright
describe the relative local magnet fields experienced by fat and water nuclei, and their resulting relative resonant frequencies.
nuclei of fat molecules experience a lower local magnetic field and therefore have a lower resonant frequency
describe the effect of long and short Tl times on MR signal intensity and appearance on Tl weighted images.
tissues with long Tl times have low signal intensity, and appear dark; tissues with short Tl times have high signal intensity, and appear bright on Tl weighted images
describe the effect of long and short T2 times on MR signal intensity and appearance on T2 weighted images.
tissues with long T2 times have high signal intensity and appear bright; tissues with short T2 times have low signal intensity and appear dark on T2 weighted images
describe the relationship between M0 to M2 at equilibrium.
at equilibrium, M0 = Mz
identify what flip angle RF pulse creates an FID.
90° or less
identify what flip angle RF pulse creates a spin echo.
180°
identify which type of relaxation is caused by spin-spin interaction and magnetic field inhomogeneity.
T2*
identify which type of relaxation is caused by spin-spin interaction only.
T2
