EXAM #3 — MODULE 3 Flashcards
_____ off: antiparallel vectors flip back to parallel (one-by-one): protons hand over heat energy to surrounding molecules)
and then
_____ net magnetic vector NMV (Mz) regenerates
90° RF pulse off: antiparallel vectors flip back to parallel (one-by-one): protons hand over heat energy to surrounding molecules)
and then
Longitudinal net magnetic vector NMV (Mz) regenerates
T1 = relaxation along the __-axis
T1 = relaxation along the Z-axis
Overall magnetization of nuclei = sum of vectors from individual _____
Overall magnetization of nuclei = sum of vectors from individual nuclei
[T2 (Transverse) Relaxation]
RF pulse caused H+ protons to precess in phase in __ plane
RF pulse off:
- H+ protons affected by external magnetic _____ and internal magnetic variations (_____ interactions + _____ susceptibility)
- H+ protons precess _____ out of phase
- XY NMV _____ and _____
[T2 (Transverse) Relaxation]
RF pulse caused H+ protons to precess in phase in XY plane
RF pulse off:
- H+ protons affected by external magnetic inhomogeneities and internal magnetic variations (spin-spin interactions + magnetic susceptibility)
- H+ protons precess increasingly out of phase
- XY NMV degenerates and disappears
T2 = relaxation in __-axis
When is the MR signal strongest?
T2 = relaxation in XY axis
Strongest signal = everything in phase but superimposed
[T2 (Transverse) Relaxation ]
90° RF pulse _____: in-phase transverse magnetic vectors increasingly precess out of phase
Transverse NMV (MXY) _____
- external magnetic field inhomogeneities
- internal spin-spin interactions and magnetic susceptibility
[T2 (Transverse) Relaxation]
90° RF pulse off: in-phase transverse magnetic vectors increasingly precess out of phase
Transverse NMV (MXY) degenerates
- external magnetic field inhomogeneities
- internal spin-spin interactions and magnetic susceptibility
[Excitation + Relaxation ]
_____: RF pulse on (transmitted)
• Z net magnetic vector (NMV) spins (flips) to _____ NMV
_____: RF pulse off:
• XY NMV spins back to _____ NMV
[Excitation + Relaxation]
Excitation: RF pulse on (transmitted)
• Z net magnetic vector (NMV) spins (flips) to XY NMV
Relaxation: RF pulse off:
• XY NMV spins back to Z NMV
[Magnetic Relaxation ]
Occurs when transmitted RF pulse is turned _____
_____ Relaxation: longitudinal (z) regeneration
_____ Relaxation: transverse (x,y) degeneration
[Magnetic Relaxation]
Occurs when transmitted RF pulse is turned off
T1 Relaxation: longitudinal (z) regeneration
T2 Relaxation: transverse (x,y) degeneration
[T1 + T2 Relaxation]
Different tissues (fat, water) have different _____
T1 and T2 relaxation
[T1 + T2 Relaxation]
Different tissues (fat, water) have different rates
T1 and T2 relaxation
[Long + Short T1 Relaxation Times]
Degree of longitudinal (Z magn) relaxation that occurs is determined by _____
[Long + Short T1 Relaxation Times]
Degree of longitudinal (Z magn) relaxation that occurs is determined by TR length
[Long + Short T2 Relaxation Times ]
Degree of transverse (XY magn) relaxation that occurs is determined by _____
[Long + Short T2 Relaxation Times]
Degree of transverse (XY magn) relaxation that occurs is determined by TE length
CSF = _____ relaxation rate
Adipose = _____ relaxation rate
Determined by how _____ the hydrogen protons are (_____ per volume)
And the _____
And the _____ of the protons
And how _____ it is
CSF = slower relaxation rate
Adipose = quicker relaxation rate
Determined by how packed the hydrogen protons are (density per volume)
And the precession rate
And the energy content of the protons
And how homogenized it is
- RF pulse switched off causing:
a. _____ relaxation - _____ magnetization grows back to original size - Protons lifted to higher energy level (on hands) by RF pulse go back to _____ energy level (on feet) one by one.
- Energy which protons picked up from RF pulse is now given up as _____ _____ to surroundings (lattice) -
∴ longitudinal relaxation = _____ relaxation
- RF pulse switched off causing:
a. Longitudinal relaxation - longitudinal magnetization grows back to original size - Protons lifted to higher energy level (on hands) by RF pulse go back to lower energy level (on feet) one by one.
- Energy which protons picked up from RF pulse is now given up as thermal energy to surroundings (lattice) -
∴ longitudinal relaxation = spin-lattice relaxation
- RF pulse switched off causing:
a. _____ relaxation - longitudinal magnetization grows back to original size - When these protons flip from pointing downward to upward, they no longer _____ magnetic vectors pointing upward, but _____ to them, causing the regrowth of the _____ magnetic sum vector to its value before the RF pulse
- T1 = time taken for longitudinal magnetization to _____ to _____ of its original value starting from time _____ is switched off (not actual time, but time constant describing how fast the longitudinal magnetization regrows)
- RF pulse switched off causing:
a. Longitudinal relaxation - longitudinal magnetization grows back to original size - When these protons flip from pointing downward to upward, they no longer cancel magnetic vectors pointing upward, but add to them, causing the regrowth of the longitudinal magnetic sum vector to its value before the RF pulse
- T1 = time taken for longitudinal magnetization to regrow to 63% of its original value starting from time RF pulse is switched off (not actual time, but time constant describing how fast the longitudinal magnetization regrows)
- RF pulse switched off causing:
a. _____ relaxation - longitudinal magnetization grows back to original size
** T1 ≈ ___ to ___ msec (dependent on magnetic field strength)
- T1 = _____ relaxation time
- T1 = _____ relaxation time
- 1/T1 = _____ relaxation rate
- RF pulse switched off causing:
a. Longitudinal relaxation - longitudinal magnetization grows back to original size
** T1 ≈ 300 to 2000 msec (dependent on magnetic field strength)
- T1 = longitudinal relaxation time
- T1 = spin-lattice relaxation time
- 1/T1 = longitudinal relaxation rate
- RF pulse switched off causing:
a. _____ relaxation - longitudinal magnetization grows back to original size - Brain white matter: _____ T1 time
- Brain gray matter: _____ T1 time
- CSF: _____ T1 time
- RF pulse switched off causing:
a. Longitudinal relaxation - longitudinal magnetization grows back to original size - Brain white matter: short T1 time
- Brain gray matter: intermediate T1 time
- CSF: long T1 time
Transversal relaxation - transverse magnetization starts to _____
- Protons precess more and more out of phase (out of step) after _____ is turned off
a. MR magnet’s magnetic field not _____ in strength, ∴causing different precessing _____ of protons at differing points within slice
b. Each proton influenced by differing magnetic field strengths of neighboring nuclei, causing different _____ _____ which dephase protons
Transversal relaxation - transverse magnetization starts to disappear
- Protons precess more and more out of phase (out of step) after RF pulse is turned off
a. MR magnet’s magnetic field not homogenous in strength, ∴causing different precessing frequencies of protons at differing points within slice
b. Each proton influenced by differing magnetic field strengths of neighboring nuclei, causing different precessional frequencies which dephase protons
Transversal relaxation - transverse magnetization starts to _____
- Magnetic vector components on the x,y plane soon point in opposite directions and increasingly cancel each other out, causing transverse magnetic sum vector to grow _____ and eventually _____ (fig 20)
- T2 = time taken for transverse magnetization to _____ to _____ of its maximum value from the time RF pulse is switched off due to spin-spin interactions (not actual time, but time constant describing how fast the transverse magnetization decreases)
** T2 ≈ ___ to ___ msec
Transversal relaxation - transverse magnetization starts to disappear
- Magnetic vector components on the x,y plane soon point in opposite directions and increasingly cancel each other out, causing transverse magnetic sum vector to grow shorter and eventually disappear (fig 20)
- T2 = time taken for transverse magnetization to decrease to 37% of its maximum value from the time RF pulse is switched off due to spin-spin interactions (not actual time, but time constant describing how fast the transverse magnetization decreases)
** T2 ≈ 30 to 150 msec
Transversal relaxation - transverse magnetization starts to _____
- T2 = _____ relaxation time
- T2 = _____ relaxation time
- 1/T2 = _____ relaxation rate
Transversal relaxation - transverse magnetization starts to disappear
- T2 = transversal relaxation time
- T2 = spin-spin relaxation time
- 1/T2 = transversal relaxation rate
Transversal relaxation - transverse magnetization starts to _____
- CSF: _____ T2 time
- Brain gray matter: _____ T2 time
- Brain white matter: _____ T2 time (fig 1-16 mic)
Transversal relaxation - transverse magnetization starts to disappear
- CSF: long T2 time
- Brain gray matter: intermediate T2 time
- Brain white matter: short T2 time (fig 1-16 mic)
Transversal relaxation - transverse magnetization starts to _____
c. Longitudinal and Transversal relaxation are 2 _____ processes which occur _____ of one another
Transversal relaxation - transverse magnetization starts to disappear
c. Longitudinal and Transversal relaxation are 2 different processes which occur independently of one another
Relaxation times: influenced by _____ of precessional frequencies of protons (precess with Larmor frequency) and molecules of surrounding lattice
- If protons and lattice molecules both precess with Larmor frequency (ie: precess at similar speeds), then protons can give _____ _____ (after RF pulse cessation) to lattice molecules quickly, causing _____ T1
Relaxation times: influenced by similarity of precessional frequencies of protons (precess with Larmor frequency) and molecules of surrounding lattice
- If protons and lattice molecules both precess with Larmor frequency (ie: precess at similar speeds), then protons can give thermal energy (after RF pulse cessation) to lattice molecules quickly, causing short T1
Relaxation times: influenced by similarity of _____ _____
- If protons and lattice molecules precess at dissimilar frequencies, then protons give energy to lattice molecules more slowly, causing _____ T1
Relaxation times: influenced by similarity of precessional frequencies
- If protons and lattice molecules precess at dissimilar frequencies, then protons give energy to lattice molecules more slowly, causing long T1
Relaxation times: influenced by similarity of _____ _____
- Water/liquids: _____ T1; _____ T2
(_____ drink: T1 - _____ to get it; T2 - _____ to consume it)
a. _____ tissues
b. Pathologic / diseased tissues: high _____ content
c. Small _____ molecules in lattice precess more rapidly than protons; protons have difficulty giving thermal energy to more rapidly precessing _____ lattice molecules; thus _____ T1 for _____/_____
Relaxation times: influenced by similarity of precessional frequencies
- Water/liquids: long T1; long T2
(Long drink: T1 - long to get it; T2 - long to consume it)
a. Watery tissues
b. Pathologic / diseased tissues: high water content
c. Small water molecules in lattice precess more rapidly than protons; protons have difficulty giving thermal energy to more rapidly precessing H2O lattice molecules; thus long T1 for water/liquids
Relaxation times: influenced by similarity of _____ _____
Fat: _____ T1; _____ T2
(Fast food: T1 - _____ to get it; T2 - _____ to consume it)
a. Fat (lattice) molecules precess at frequency close to protons’ frequency (Larmor frequency); protons can more easily give thermal energy to lattice fat molecules; thus _____ T1 for fat
Relaxation times: influenced by similarity of precessional frequencies
Fat: short T1; short T2
(Fast food: T1 - short to get it; T2 - short to consume it)
a. Fat (lattice) molecules precess at frequency close to protons’ frequency (Larmor frequency); protons can more easily give thermal energy to lattice fat molecules; thus short T1 for fat
Relaxation times: influenced by similarity of _____ _____
Typical body tissues
a. liquids containing various sized lattice molecules which precess with frequency _____ proton Larmor frequency
b. Exchange of thermal energy from protons to molecules of lattice can occur _____; thus _____ T1
Relaxation times: influenced by similarity of precessional frequencies
Typical body tissues
a. liquids containing various sized lattice molecules which precess with frequency near proton Larmor frequency
b. Exchange of thermal energy from protons to molecules of lattice can occur quickly; thus short T1
Relaxation times: influenced by similarity of _____ _____
Strong magnetic fields
a. Protons precess _____ in strong magnetic fields than do the lattice molecules; ∴ more difficult to for protons to hand energy over to molecules precessing at slower frequency; ∴ T1 is _____
Relaxation times: influenced by similarity of precessional frequencies
Strong magnetic fields
a. Protons precess faster in strong magnetic fields than do the lattice molecules; ∴ more difficult to for protons to hand energy over to molecules precessing at slower frequency; ∴ T1 is longer
Influences on T2 relaxation
- Inhomogeneities in _____ (causing differing precession frequencies of protons)
Influences on T2 relaxation
- Inhomogeneities in external magnetic field strength (causing differing precession frequencies of protons)
Influences on T2 relaxation
- Inhomogeneities of _____ due to varied precessing frequencies of molecules (causing differing precession frequencies of protons)
Influences on T2 relaxation
- Inhomogeneities of local magnetic fields within tissues due to varied precessing frequencies of molecules (causing differing precession frequencies of protons)
Influences on T2 relaxation
- _____ molecules (pg.37)
a. _____, precess _____, creating fairly _____ lattice local magnetic filed strength
b. Protons in fairly _____ magnetic field strength (no differences in proton precessing rates ∴ protons stay in phase for a _____ time ∴ _____ T2)
Influences on T2 relaxation
- Water molecules (pg.37)
a. Small, precess quickly, creating fairly homogeneous lattice local magnetic filed strength
b. Protons in fairly homogeneous magnetic field strength (no differences in proton precessing rates ∴ protons stay in phase for a long time ∴ longer T2)
Influences on T2 relaxation
- _____ liquids
a. Molecules in lattice are different _____, thus variations in precessing frequencies of molecules in lattice (larger - _____; smaller - _____)
b. Variations in molecule precessing frequencies cause local magnetic field strength variations in _____
c. Local magnetic field strength variations in lattice cause protons to precess out of phase _____ ∴ T2 is _____
(Protons fan out more quickly) (pg. 37)
Influences on T2 relaxation
- Impure liquids
a. Molecules in lattice are different sizes, thus variations in precessing frequencies of molecules in lattice (larger - slower; smaller - faster)
b. Variations in molecule precessing frequencies cause local magnetic field strength variations in lattice
c. Local magnetic field strength variations in lattice cause protons to precess out of phase faster ∴ T2 is shorter
(Protons fan out more quickly) (pg. 37)
NOTE: The differences in relaxation times among different tissues make these tissues _____ in the image (ie: create _____ in the image).
NOTE: The differences in relaxation times among different tissues make these tissues distinguishable in the image (ie: create contrast in the image).
