EXAM #6 — MODULE 6

Question 1

V. Pulse sequences

A. Saturation Recovery Pulse sequence/Partial Saturation sequence

1. use _____ pulses only: consist of _____ _____ pulses
2. difference is time interval between pulses: _____

Answer 1

V. Pulse sequences

A. Saturation Recovery Pulse sequence/Partial Saturation sequence

1. use 90° pulses only: consist of two 90° pulses
2. difference is time interval between pulses: TR

Question 2

V. Pulse sequences

• Saturation Recovery Pulse sequence
  1. _____ TR
  2. _____ magnetizations of 2 different tissues have both fully _____ (_____, have fully _____, are _____)
  3. contrast not due to _____ relaxation differences: image is _____ weighted

Answer 2

V. Pulse sequences

• Saturation Recovery Pulse sequence
  1. long TR
  2. longitudinal magnetizations of 2 different tissues have both fully regrown (recovered, have fully relaxed, are saturated)
  3. contrast not due to T1 relaxation differences: image is proton density weighted

Question 3

V. Pulse sequences

• Partial Saturation sequence
  1. _____ TR
  2. _____ magnetizations of 2 different tissues have not fully _____ (have not fully _____, are _____ saturated)
  3. contrast is due to _____ relaxation differences: image is _____ weighted

Answer 3

V. Pulse sequences

• Partial Saturation sequence
  1. short TR
  2. longitudinal magnetizations of 2 different tissues have not fully regrown (have not fully relaxed, are partially saturated)
  3. contrast is due to T1 relaxation differences: image is T1 weighted

Question 4

V. Pulse sequences

B. Spin Echo Pulse sequence: (Fig 55, pg 80)

1. _____ pulse @ start of _____ (_____: time between _____ pulses)
2. _____ also starts @ _____ pulse (_____: time between _____ pulse and _____)
3. _____ pulse @ _____, record signal (echo) at _____
4. repeat cycle @ time _____; repeated multiple times to generate many signals needed for an image - signals become progressively _____
5. Images: _____, _____, _____ weighted

• T1 weighted: _____ TR, _____ TE
• T2 weighted: _____ TR, _____ TE
• proton density weighted: _____ TR, _____ TE
  6. Spin echoes collected after _____ and _____ RF pulses (see dual contrast spin echo)

Answer 4

V. Pulse sequences

B. Spin Echo Pulse sequence: (Fig 55, pg 80)

1. 90° RF pulse @ start of TR (TR: time between 90° pulses)
2. TE also starts @ 90° pulse (TE: time between 90° pulse and echo)
3. 180° RF pulse @ TE/2, record signal (echo) at TE
4. repeat cycle @ time TR; repeated multiple times to generate many signals needed for an image - signals become progressively weaker
5. Images: T1, T2, proton density weighted

• T1 weighted: short TR, short TE
• T2 weighted: long TR, long TE
• proton density weighted: long TR, short TE
  6. Spin echoes collected after 2nd and 3rd RF pulses (see dual contrast spin echo)

Question 5

V. Pulse sequences

C. Dual Contrast Spin Echo sequence: _____ - _____ - _____ - record signal at _____…repeat

1. Images: echo 1: _____ weighted;
   echo 2: _____ weighted

Answer 5

V. Pulse sequences

C. Dual Contrast Spin Echo sequence: 90° - 180° - 180° - record signal at TE…repeat

1. Images: echo 1: proton density weighted;
   echo 2: T2 weighted

Question 6

V. Pulse sequences

D. Rapid Spin Echo Pulse sequence: _____ - _____ - _____ - _____ - _____

1. Separate _____ after each _____ pulse
2. Images: each echo has unique _____ weight

Since each 180 rephasing RF pulse doesn’t completed rephase protons in the xy plane, each echo’s amplitude (signal) is _____ than the previous that of the previous echo.

Answer 6

V. Pulse sequences

D. Rapid Spin Echo Pulse sequence: 90° - 180° - 180° - 180° - 180°

1. Separate TE after each 180 RF pulse
2. Images: each echo has unique T2 weight

Since each 180 rephasing RF pulse doesn’t completed rephase protons in the xy plane, each echo’s amplitude (signal) is less than the previous that of the previous echo.

Question 7

V. Pulse sequences

E. Gradient Echo Pulse sequence: _____ - magnetic gradient (_____ direction)

1. _____ mag gradient rephases precessing protons without changing precessing direction
2. Images: _____, _____ weighted

Can use shorter TR than _____

<90° RF excitation pulse: allows for _____ T1 relaxation

Gradient rephasers are generated in less time than 180° pulses in Spin Echo sequences

Allows for _____ scan time

Answer 7

V. Pulse sequences

E. Gradient Echo Pulse sequence: < 90° - magnetic gradient (opposite direction)

1. Opposite mag gradient rephases precessing protons without changing precessing direction
2. Images: T1, T2 weighted

Can use shorter TR than spin echo

<90° RF excitation pulse: allows for faster T1 relaxation

Gradient rephasers are generated in less time than 180° pulses in Spin Echo sequences

Allows for shorter scan time

Question 8

V. Pulse sequences

F. Spoiled Gradient Echo Pulse sequence: _____ - _____ mag gradient - _____ mag gradient

1. _____ mag gradient rephases precessing protons without changing precessing direction
2. _____ mag gradient dephases precessing protons without changing precessing direction
3. Images: _____, _____ weighted

Answer 8

V. Pulse sequences

F. Spoiled Gradient Echo Pulse sequence:< 90 - opposite mag gradient - same mag gradient

1. Opposite mag gradient rephases precessing protons without changing precessing direction
2. Same mag gradient dephases precessing protons without changing precessing direction
3. Images: T1, T2 weighted

Question 9

V. Pulse sequences

G. Inversion Recovery sequence: _____ - _____ - _____ - _____ (figs 53, 54, pg 78)

1. _____ pulse inverts upright magnetism first; then _____ pulse flips inverted magnetism into _____ plane;
2. tissues with shorter T1 relaxation time will begin to relax back to the upright position _____ before the _____ pulse & will have _____ inverted longitudinal magnetization to be flipped into transverse plane by _____ pulse
   - short T1 tissues generate a _____ signal with inversion recovery
3. tissues with longer T1 relaxation time will begin to relax back to the upright position _____ before the _____ pulse & will have _____ inverted longitudinal magnetization to be flipped into transverse plane by _____ pulse
   - long T1 tissues generate a _____ signal with inversion recovery

Answer 9

V. Pulse sequences

G. Inversion Recovery sequence: 180° - 90° - 180° - 90° (figs 53, 54, pg 78)

1. 180° pulse inverts upright magnetism first; then 90° pulse flips inverted magnetism into transverse plane;
2. tissues with shorter T1 relaxation time will begin to relax back to the upright position quickly before the 90° pulse & will have shorter inverted longitudinal magnetization to be flipped into transverse plane by 90° pulse
   - short T1 tissues generate a weak signal with inversion recovery
3. tissues with longer T1 relaxation time will begin to relax back to the upright position slowly before the 90° pulse & will have longer inverted longitudinal magnetization to be flipped into transverse plane by 90° pulse
   - long T1 tissues generate a stronger signal with inversion recovery

Question 10

V. Pulse sequences

G. Inversion Recovery sequence: _____ - _____ - _____ - _____ (figs 53, 54, pg 78)

4. Signal intensity depends on time span between _____ & _____ pulses, the time after the inversion by the _____ pulse
   - thus is called inversion time = _____
5. TR = time between sequences (between _____ pulses)
6. Signal intensity depends on _____ of each tissue: determines how fast longitudinal magnetization goes back to original value
   - _____ weighted images are obtained with inversion recovery sequence

Answer 10

V. Pulse sequences

G. Inversion Recovery sequence: 180° - 90° - 180° - 90° (figs 53, 54, pg 78)

4. Signal intensity depends on time span between 180° & 90° pulses, the time after the inversion by the 180° pulse
   - thus is called inversion time = TI
5. TR = time between sequences (between 180° pulses)
6. Signal intensity depends on T1 of each tissue: determines how fast longitudinal magnetization goes back to original value
   - T1 weighted images are obtained with inversion recovery sequence

Question 11

V. Pulse sequences

H. Fast Imaging sequences (Gradient Echo sequences)

1. Attempt to shorten TR to make imaging _____
2. Problems w/ reduced TR:
   a. very short TR: not enough time to deliver _____ pulse (these take time)
   b. lower TR: less and less _____ magnetization regenerated between _____ pulses, shrinking amount of longitudinal magnetization gets tilted with each _____ pulse yielding very _____ signal
3. Solution to problems:
   a. instead of using 180° pulse to refocus spins, superimpose a _____ _____ _____ over static magnetic field causing _____ magnetic field inhomogeneities in the examined slice
   * inhomogeneities cause protons in slice to dephase even _____: lose signal _____ (ordered _____)

Answer 11

V. Pulse sequences

H. Fast Imaging sequences (Gradient Echo sequences)

1. Attempt to shorten TR to make imaging faster
2. Problems w/ reduced TR:
   a. very short TR: not enough time to deliver 180° pulse (these take time)
   b. lower TR: less and less longitudinal magnetization regenerated between 90° pulses, shrinking amount of longitudinal magnetization gets tilted with each 90° pulse yielding very little signal
3. Solution to problems:
   a. instead of using 180° pulse to refocus spins, superimpose a gradient magnetic field over static magnetic field causing larger magnetic field inhomogeneities in the examined slice
   * inhomogeneities cause protons in slice to dephase even faster: lose signal faster (ordered dephasing)

Question 12

V. Pulse sequences

H. Fast Imaging sequences (Gradient Echo sequences)

• turn off 1st magnetic _____, turn on 2nd magnetic field _____ in _____ orientation: protons precess in same direction, but at new _____ (fast become _____, slow become _____) and _____
• signal recreated: called a gradient echo signal (generated by magnetic _____ instead of 180° RF pulse), signal then fades
  b. to prevent small amount of longitudinal magnetization w/ short TR, use RF pulses that cause less than 90° flip angles: _____-_____ flip angles
• 90° RF pulse totally _____ longitudinal magnetization
• lesser flip angle leaves _____ longitudinal magnetization which can be flipped by the next RF pulse even after a very _____ TR

Answer 12

V. Pulse sequences

H. Fast Imaging sequences (Gradient Echo sequences)

• turn off 1st magnetic gradient, turn on 2nd magnetic field gradient in opposite orientation: protons precess in same direction, but at new frequencies (fast become slow, slow become fast) and rephase
• signal recreated: called a gradient echo signal (generated by magnetic gradient instead of 180° RF pulse), signal then fades
  b. to prevent small amount of longitudinal magnetization w/ short TR, use RF pulses that cause less than 90° flip angles: 10°-35° flip angles
• 90° RF pulse totally abolishes longitudinal magnetization
• lesser flip angle leaves substantial longitudinal magnetization which can be flipped by the next RF pulse even after a very short TR

Question 13

V. Pulse sequences

H. Fast Imaging sequences (Gradient Echo sequences)

4. _____ pulse neutralizes dephasing effects of external magnetic field inhomogeneities
   - transversal decay thus caused by local lattice (internal) magnetic field inhomogeneities called _____
5. if no 180° pulse used protons experience both _____ & _____ magnetic field _____
   - get out of phase much faster: signal intensity decays faster due to these _____ effects (_____): internal and external magnetic field dephasers

Answer 13

V. Pulse sequences

H. Fast Imaging sequences (Gradient Echo sequences)

4. 180° pulse neutralizes dephasing effects of external magnetic field inhomogeneities
   - transversal decay thus caused by local lattice (internal) magnetic field inhomogeneities called T2 effects
5. if no 180° pulse used protons experience both external & internal magnetic field inhomogeneities
   - get out of phase much faster: signal intensity decays faster due to these T2* effects (T2 star): internal and external magnetic field dephasers

Question 14

V. Pulse sequences

H. Fast Imaging sequences (Gradient Echo sequences)

6. gradient echo imaging guidelines:
   a. larger flip angles yield more _____ weighting (diff tissues regrow diff amounts)
   b. longer TEs yield more _____ weighting
   c. w/ fast scans: intense signals from _____
   d. imaging time saved due to:
   - _____ flip angles requires a short duration RF pulse
   - _____ pulse not used: takes time to generate and exert its effects
   - no need to wait for long _____ for enough longitudinal magnetization to reappear: w/ _____ flip angles substantial longitudinal magnetization left after RF pulses

Answer 14

V. Pulse sequences

H. Fast Imaging sequences (Gradient Echo sequences)

6. gradient echo imaging guidelines:
   a. larger flip angles yield more T1 weighting (diff tissues regrow diff amounts)
   b. longer TEs yield more T2* weighting
   c. w/ fast scans: intense signals from vessels
   d. imaging time saved due to:
   - small flip angles requires a short duration RF pulse
   - 180° refocussing pulse not used: takes time to generate and exert its effects
   - no need to wait for long TRs for enough longitudinal magnetization to reappear: w/ small flip angles substantial longitudinal magnetization left after RF pulses

Question 15

VI. Flow Effects

A. Flow-Void Phenomenon (fig 47, pg 69)

1. _____ pulse flips magnetization of all protons in a chosen slice
2. _____ pulse turned _____: protons in blood have left the chosen slice
3. no signal from vessel: it appears _____ in the image

Answer 15

VI. Flow Effects

A. Flow-Void Phenomenon (fig 47, pg 69)

1. 90° RF pulse flips magnetization of all protons in a chosen slice
2. 90° RF pulse turned off: protons in blood have left the chosen slice
3. no signal from vessel: it appears black in the image

Question 16

VI. Flow Effects

B. Flow-Related Enhancement (fig 48, pg 70)

1. chosen slice includes _____ w/ surrounding _____
2. _____ pulse flips protons w/in slice
3. RF pulse turned _____: protons’ longitudinal magnetization begins to regrow
4. Protons w/ short longitudinal magnetization w/in vessel flow _____ of slice, protons in vessel adjacent to slice w/ full longitudinal magnetization flow _____ slice
5. 2nd 90° RF pulse flips full longitudinal magn vectors of protons in blood and partial longitudinal magn vectors of protons in surrounding tissue into _____ magn vectors: signal from blood is more _____, vessel appears _____

Answer 16

VI. Flow Effects

B. Flow-Related Enhancement (fig 48, pg 70)

1. chosen slice includes vessel w/ surrounding tissue
2. 90° RF pulse flips protons w/in slice
3. RF pulse turned off: protons’ longitudinal magnetization begins to regrow
4. Protons w/ short longitudinal magnetization w/in vessel flow out of slice, protons in vessel adjacent to slice w/ full longitudinal magnetization flow into slice
5. 2nd 90° RF pulse flips full longitudinal magn vectors of protons in blood and partial longitudinal magn vectors of protons in surrounding tissue into transverse magn vectors: signal from blood is more intense, vessel appears brighter

Question 17

VII. Contrast Media (fig 49, pg 72)

A. Proton Relaxation Enhancement: contrast media have small local _____ _____ which cause shortening of relaxation times

1. longitudinal relaxation shortening: protons precess w/ same frequency as surrounding _____ _____, can give up _____ energy more quickly to _____
2. transversal relaxation shortening: local magnetic field inhomogeneities cause protons to lose _____ _____ more quickly

Answer 17

VII. Contrast Media (fig 49, pg 72)

A. Proton Relaxation Enhancement: contrast media have small local magnetic fields which cause shortening of relaxation times

1. longitudinal relaxation shortening: protons precess w/ same frequency as surrounding lattice molecules, can give up thermal energy more quickly to lattice
2. transversal relaxation shortening: local magnetic field inhomogeneities cause protons to lose phase coherence more quickly

Question 18

VII. Contrast Media (fig 49, pg 72)

B. contrast media: paramagnetic substance which changes signal _____ by _____ T1 and T2 in its surroundings

1. T1 and T2 curves are shifted to the _____
   - for any chosen TR, there is _____ signal in the gadolinium enhanced tissue
   - for any chosen TE, there is _____ signal in the gadolinium enhanced tissue
2. @ any TR: T1 curve of Gad enhanced tissue moves _____ from T1 curve of adjacent tissue: much _____ difference in signal _____ (tissue contrast) on T1 weighted images (fig 50, pg 74)
3. @ any TE: T2 curve of Gad enhanced tissue moves _____ from T2 curve of adjacent tissue: much _____ difference in signal _____ (contrast) on T2 weighted images
4. T1 weighted images predominantly obtained with Gad enhancement: _____ of signal w/ Gad on T1 weighted image is preferred to _____ of signal w/ Gad on T2 weighted image

Answer 18

VII. Contrast Media (fig 49, pg 72)

B. contrast media: paramagnetic substance which changes signal intensity by shortening T1 and T2 in its surroundings

1. T1 and T2 curves are shifted to the left
   - for any chosen TR, there is more signal in the gadolinium enhanced tissue
   - for any chosen TE, there is less signal in the gadolinium enhanced tissue
2. @ any TR: T1 curve of Gad enhanced tissue moves farther from T1 curve of adjacent tissue: much greater difference in signal intensities (tissue contrast) on T1 weighted images (fig 50, pg 74)
3. @ any TE: T2 curve of Gad enhanced tissue moves farther from T2 curve of adjacent tissue: much greater difference in signal intensities (contrast) on T2 weighted images
4. T1 weighted images predominantly obtained with Gad enhancement: gain of signal w/ Gad on T1 weighted image is preferred to loss of signal w/ Gad on T2 weighted image

Question 19

VII. Contrast Media (fig 49, pg 72)

C. Gadolinium

1. a metal ion (Gd 3+): toxic in its free state
2. non-toxic when bound to other molecules through “_____”
3. gadolinium chelates: commercial names:

_____, _____, _____, _____

Answer 19

VII. Contrast Media (fig 49, pg 72)

C. Gadolinium

1. a metal ion (Gd 3+): toxic in its free state
2. non-toxic when bound to other molecules through “chelation”
3. gadolinium chelates: commercial names:

Dotarem, ProHance, Magnevist, Omniscan

Question 20

VII. Contrast Media (fig 49, pg 72)

D. use of contrast media increases _____ detection and diagnostic accuracy of MRI

1. _____ tumor tissues enhanced w/ Gad
2. differentiation between _____ tissue and surrounding _____ facilitated
   - T1 of tumor tissue shortened: tumor _____ on image compared to surrounding edema

Answer 20

VII. Contrast Media (fig 49, pg 72)

D. use of contrast media increases lesion detection and diagnostic accuracy of MRI

1. vascularized tumor tissues enhanced w/ Gad
2. differentiation between tumor tissue and surrounding edema facilitated
   - T1 of tumor tissue shortened: tumor brighter on image compared to surrounding edema

Question 21

VII. Contrast Media (fig 49, pg 72)

E. gadolinium shortens T1: enables shorter TR and thus _____ imaging time

Answer 21

VII. Contrast Media (fig 49, pg 72)

E. gadolinium shortens T1: enables shorter TR and thus shorter imaging time

Question 22

VIII. Acquisition Time (a.t.) (Pg 83)

A. a.t. = TR • N • Nex where:

_____ = time between ”flip” angles

-longer TRs yield _____ acquisition times than shorter TRs

_____ = number of rows of pixels in an image matrix; higher # rows yields more detail

_____ = number of excitations (# repeats)

• need _____ signals from same slice, only 1 signal too weak for image
• higher # excitations: collect and add up more signals which yields _____ final signal and _____ signal-to-noise ratio

Answer 22

VIII. Acquisition Time (a.t.) (Pg 83)

A. a.t. = TR ⊗ N ⊗ Nex where:

TR = time between”flip” angles

-longer TRs yield longer acquisition times than shorter TRs

N = number of rows of pixels in an image matrix; higher # rows yields more detail

NEX = number of excitations (# repeats)

• need several signals from same slice, only 1 signal too weak for image
• higher # excitations: collect and add up more signals which yields stronger final signal and better signal-to-noise ratio

Question 23

VIII. Acquisition Time (a.t.) (Pg 83)

B. Multi Slice Imaging to shorten imaging time (fig 56, pg 85)

1. during the time span of TR for one tissue slice A, we can _____ multiple other slices B,C, D, … with _____ - _____ pulse sequences
2. can thus obtain signals from several slices during the _____ of slice A (many signals will form images of the slices)

Answer 23

VIII. Acquisition Time (a.t.) (Pg 83)

B. Multi Slice Imaging to shorten imaging time (fig 56, pg 85)

1. during the time span of TR for one tissue slice A, we can excite multiple other slices B,C, D, … with 90° - 180° pulse sequences
2. can thus obtain signals from several slices during the TR of slice A (many signals will form images of the slices)

Question 24

VIII. Acquisition Time (a.t.) (Pg 83)

C. Gadolinium use to _____ imaging time

1. Gadolinium _____ T1 - _____ regeneration of longitudinal magnetization
2. _____ magnetization in Z axis to be flipped into X axis after a shorter TR yields no loss in signal intensity with a shorter TR

Answer 24

VIII. Acquisition Time (a.t.) (Pg 83)

C. Gadolinium use to shorten imaging time

1. Gadolinium shortens T1 - quicker regeneration of longitudinal magnetization
2. More magnetization in Z axis to be flipped into X axis after a shorter TR yields no loss in signal intensity with a shorter TR

Question 25

[Dual Echo Spin Echo Pulse Sequence ]

180° RF rephasing pulse: counter-acts _____

1. Effectively overrides external dephasers
   Does not effectively override _____ _____

The 180° rephasing pulse does not rephase each echo _____

The second echo’s amplitude (signal intensity) is _____ that the previous echo

Answer 25

[Dual Echo Spin Echo Pulse Sequence]

180° RF rephasing pulse: counter-acts dephasers

1. Effectively overrides external dephasers
   Does not effectively override internal dephasers

The 180° rephasing pulse does not rephase each echo 100%

The second echo’s amplitude (signal intensity) is less that the previous echo

Question 26

[Inversion Recovery]

The NMV of different tissues (fat, fluid) relax through the _____ plane at different rates

If TI selected that matches zero point relaxation time of fat, then fat is flipped to _____ with excitation pulse; no signal from fat: _____

If TI selected that matches zero point relaxation time of fluid, then fluid is flipped to is flipped to _____ with excitation pulse; no signal from fluid: _____

Answer 26

[Inversion Recovery]

The NMV of different tissues (fat, fluid) relax through the transverse plane at different rates

If TI selected that matches zero point relaxation time of fat, then fat is flipped to saturation with excitation pulse; no signal from fat: STIR

If TI selected that matches zero point relaxation time of fluid, then fluid is flipped to is flipped to saturation with excitation pulse; no signal from fluid: FLAIR

Question 27

[Inversion Recovery ]

STIR = _____…

Suppressing _____ signal with STIR

FLAIR = _____…

Suppressing _____ signal with FLAIR

Answer 27

[Inversion Recovery]

STIR = Short T1 Inversion Recovery

Suppressing fat signal with STIR

FLAIR = Long T1 Fluid attenuated inversion recovery

Suppressing fluid signal with FLAIR

Question 28

[Flow Void]

Anterior Communicating Artery Aneurysm:

MRI shows the aneurysm as a _____ _____.

Answer 28

[Flow Void]

Anterior Communicating Artery Aneurysm:

MRI shows the aneurysm as a flow void.

Question 29

[MRI Contrast Agents ]

T2 post injection of gad, vessels appear _____

T1 post injection of gad, vessels appear _____

Answer 29

[MRI Contrast Agents]

T2 post injection of gad, vessels appear darker

T1 post injection of gad, vessels appear brighter

Question 30

Nephrogenic Systemic Fibrosis (NSF):

or nephrogenic fibrosing dermopathy is a rare and serious syndrome that involves _____ of skin, joints, eyes, and internal organs. Its cause is not fully understood, but it seems to be associated with exposure to _____ (which is frequently used as a contrast substance for MRIs) in patients with severe _____ _____. Most patients with NSF have undergone _____ for renal failure, some have never undergone dialysis and others have received only peritoneal dialysis.

Answer 30

Nephrogenic Systemic Fibrosis (NSF):

or nephrogenic fibrosing dermopathy is a rare and serious syndrome that involves fibrosis of skin, joints, eyes, and internal organs. Its cause is not fully understood, but it seems to be associated with exposure to gadolinium (which is frequently used as a contrast substance for MRIs) in patients with severe kidney failure. Most patients with NSF have undergone hemodialysis for renal failure, some have never undergone dialysis and others have received only peritoneal dialysis.