MRI Physics 4 Flashcards
In which directions can PC MRA be flow sensitive
a. through plane
b. in plane
c. a and b
d. none of the above
c. a and b
Which of the following statements are true concerning venous flow imaging with bright blood TOF-MRA
I. slower than arterial flow
II. lower flow related enhancement than arterial flow
III. cannot be imaged with TOF
a. I only
b. I and II only
c. II and III only
d. I II and III
b. I and II only
If one desires to do a set of axial 2D-TOF MRA scans for the saphenous veins, where should sat pulses be placed in relation to the imaging region
a. inferior
b. superior
c. a and b
d. none of the above
b. superior
Pulsating motion is best described as
a. acceleration
b. stagnation
c. jerk
d. none of the above
c. jerk
Time of Flight (TOF) effects can lead to
a. MRI signal loss from flow
b. MRI signal gain from flow
c. a and b
d. none of the above
c. a and b
In order to make every slice and “entry slice”, the slice excitation wave should be performed
a. co current
b. counter current
c. inferior to the FOV
d. superior to the FOV
b. counter current
Which of the following is not a mechanism for MRI signal loss in flow
a. turbulence
b. flow compensation
c. dephasing effects
d. none of the above - all cause signal loss
b. flow compensation
Which timing parameter is critical for “black blood” MRA
a. TR
b. TE
c. TI
d. none of the above
b. TE
The most common procedure for the Circle of Willis is _____, while the most common procedure for the carotids is _____.
a. 2D-TOF, 2D-TOF
b. 2D TOF, 3D TOF
c. 3D TOF, 2D TOF
d. 3D TOF, 3D TOF
c. 3D TOF, 2D TOF
Application of pre-sat pulses during a flow imaging sequence will ____ SAR and ____ the number of slices per TR period.
a. decrease, decrease
b. decrease, increase
c. increase, decrease
d. increase, increase
c. increase, decrease
The usual MRI picture displayed on the console is the
a. phase image
b. magnitude image
c. a and b
d. none of the above
b. magnitude image
If the slice thickness is increased, then high velocity signal loss in “black blood” TOF-MRA tends to
a. decrease
b. stay the same
c. increase
d. none of the above
a. decrease
Magnetization Transfer directly affects which spins
a. free water
b. fat
c. protein bound water
d. protein bound fat
c. protein bound water
Intra voxel dephasing occurs for which kind of flow
a. turbulent
b. laminar
c. a and b
d. none of the above
c. a and b
In PC MRA flow velocity is mapped into the
a. frequency
b. phase
c. a and b
d. none of the above
b. phase
For SE imaging of flow, odd echo dephasing will occur for which kind of flow
a. turbulent
b. laminar
c. a and b
d. none of the above
c a and b
Which of the following techniques will be useful for reducing intra voxel dephasing
I. increase voxel size
II. increase TE
III. use gradient moment nulling (GMN)
a. I only
b. I and II only
c. III only
d. I II and III
c. III only
Bends in the ICA can mimic stenosis in “bright blood” MRA because of
a. turbulent flow
b. vortex flow
c. plug flow
d. accelerated flow
d. accelerated flow
Even Echo Rephasing works for SE sequences with
a. symmetric echoes
b. asymmetric echoes
c. a and b
d. none of the above
a. symmetric echoes
If the following orders of gradient lobes are turned on for the same amount of time,which set of relative amplitudes will compensate for accelerated fluid motion
a. 1 neg, 1 pos
b. 1 pos, 2 neg, 1 pos
c. 1 neg, 3 pos, 3 neg, 1 pos
d. 1 neg, 3 pos, 1 neg, 3 pos
c. 1 neg, 3 pos, 3 neg, 1 pos
In order to image flow in the jugular veings using 2D TOF MRA slices should be acquired in what order
a. I to S
b. S to I
c. A to P,
d. P to A
a. I to S
If A0 is the vessel radius, r is the cylindrical radial coordinate, and V0 is a constant, then the laminar flow velocity V(r) is given by
a. V(r) = V0
b. V(r) = V0(1-(r/A0))
c. V(r) = V0(1-(r/A0)^2)
d. none of the above
c. V(r) = V0(1-(r/A0)^2)
Sensitivity to flow near the edge of a vessel could best be accomplished with ___, while flow near the lumen center is best determined with ______.
a. low VENC, low VENC
b. low VENC, high VENC
c. high VENC, low VENC
d. high VENC, high VENC
b. low VENC, high VENC
Shaded surface Display is
a. an RF artifact
b. an MRA display method
c. a and b
d. none of the above
b. an MRA display method
Using cardiac gating, which parameter is set by the patient heart rate
a. TR
b. TE
c. TI
d. a and c
a. TR
For “bright blood” MRA, which pulse sequence is more likely to be used.
a. Incoherent GRE
b. Coherent GRE
c. SE
d. EPI
a. incoherent GRE
The most common artifact associated with MOTSA is
a. ghosting
b. aliasing
c. venetian blind
d. all of the above
c. venetian blind
Which is the critical time parameter for flow related enhancement
a. TR
b. TE
c. TI
d. none of the above
a. TR
“Flow Encoding” in PC MRA refers to
a. readout
b. spoilers
c. reqinders
d. gradient sensitizing directions
d. gradient sensitizing directions
Which of the following effects reduce flow saturation in MRA scans
I. increasing the FA
II. decreasing TR
III. using gadolinium contrast
a. I and II only
b. I and III only
c. III only
d. I II and III
c III only
“Black Blood” MRA uses
a. minimum intensity perception
b. maximum intensity perception
c. minimum intensity projection
d. maximum intensity projection
c. minimum intensity projection
The tau time is given by which expression
a. TE
b. TE/2
c. TR/2
d. .693 T1
b. TE/2
the “in flow effect” in GRE flow sequences decreases with
a. thin slices and slow flow velocities
b. thin slices and fast flow velocities
c. thick slices and slow flow velocities
d. thick slices and fast flow velocities
c. thick slices and slow flow velocities
If the MRI signal is greater than some threshold, then MIP plots the brightest signal in
a. each slice
b. each pixel channel
c. the imaging volume
d. none of the above
b. each pixel channel
In PC MRA flow contrast with stationary tissue occurs because different phases arise from turning on
a. RF
b. gradients
c. a and b
d. none of the above
b. gradients
Another name for Laminar flow is
a. plug flow
b. vortex flow
c. parabolic flow
d. stagnation point
c. parabolic flow
A large slice thickness is ____ for FRE
a. good
b. bad
c. indifferent
d. none of the above
b. bad
What will the effect of a very low flow velocity V be on “bright blood” MRA
a. increase signal
b. no effect
c. decrease signal
d. none of the above
c. decrease signal
For 2D TOF MRA the MRI signal will be largest if the flow is directed
a. parallel to the slice
b. perpendicular to the slice
c. a or b
d. none of the above
b. perpendicular to the slice
For SE sequence with high velocity loss, what is the critical velocity above which no signal is produced by flowing spins in a slice with thickness z
a. (2z)/TE
b. (2z)/TR
c. TE/2z
d. TR/2z
a. 2z/TE
In bright blood 2D MRA sequences, how are the slices acquired
A. Multiplanar
B. sequential
C. A and B
D. None of the above
B. sequential
In bright blood MRA sequences, TE is kept short principally because A. Emphasizes T2W B. minimizes high velocity loss C. Minimizes dephasing effects D. None of the above
C. Minimizes dephasing effects
Flow saturation is a greater problem for A. 2D TOF MRA B. 3D TOF MRA c. A and B D. None of the above
B. 3D TOF MRA
Supposing one uses ECG gating. If the heart rate is for 45 bpm, what is the period T between heart beats A. .75s B. 1.0s C. 1.33s D. 1.50s
C. 1.33s
In MRA applications, fluid velocities are typically given in which set of units A. Mile/hr B. meter/sec C. Cm/sec D. Mm/sec
C. cm/sec
First order flow compensation cannot compensate for which of the following flows? A. Laminar B. accelerated C. Turbulent D. B and C
D. B and C
How many different directions can be flow compensated in an MRI scan
I. Readout
II. Phase encoding
III. Slice
A. I only
B. I and II only
C. III only
D. I II and III
D. I II and III
Suppose that 2D MRI scan is prescribed. now one wishes to add flow compensation. which of the folowing parameters must increase
a. T1
b. T2
c. min. TE
d. none of the above
c. min TE
In order to reduce phase errors, how many acquisitions are typically acquired for PC MRA
a. 1
b. 2
c. 4
d. none of the above
b. 2
Constant velocity is an example of _____ motion
a. 0 order
b. 1st order
c. 2nd order
d. 3rd order
b. 1st order
Which scan acquisition time would usually be the longest for MRA of the COW
a. 2D TOF
b. 3D TOF
c. 2D PC
d. 3D PC
d. 3D PC
A volume acquistion in MRI requires what kind of data processing methods
a. 1D FT
b. 2D FT
c. 3D FT
d. none of the above
c. 3D FT
which pulse sequences are typically used for PC MRA
a. incoherent GRE
b. coherent GRE
c. incoherent SE
d. coherent SE
a. incoherent GRE
Gadolinium is primarily what kind of contrast agent
a. T1 shortening
b. T2 shortening
c. T1 lengthening
d. T2 lengthening
a. T1 shortening
The saturation of flowing spins in “bright blood” MRA increases if which of the following is performed
I. TR is decreased
II. FA is decreased
III. Gadolinium contrast is used
a. I only
b. I and III only
c. II only
d. II and III only
a. I only
Choose the proper order for 3D TOF MRA pulse sequence events from earliest to latest
a. rewinder, alpha pulse, presat pulse
b. alpha pulse, presat pulse, rewinder
c. presat pulse, rewinder, alpha pulse
d. presat pulse alpha pulse, rewinder
d. presat puilse, alpha pulse, rewinder
For which “bright blood” TOF MRA sequence would the FA typically be lower
a. 1D
b. 2D
c. 3D
d. 4D
c. 3D
If r is a radial coordinate acros the vessel lumen, then the flow velocity v(r) being independant of r best describes
a. laminar flow
b. plug flow
c. turbulent flow
d. vortex flow
b. plug flow
Even echo rephasing is most useful for which kind of imaging
a. T1W
b. PD
c. T2W
d. a and b
c. T2W
Which of the following MRA scans typically equire 3D methods
I. carotids
II. AVM
III.lower extremity vasculature
a. I only
b. II only
c. II and III only
d. I II and III
b. II only
In and MRA of the COW, Magnetization Transfer is uded to suppress signal from which tissues
a. White matter
b. Gray matter
c. flowing protons
d. a and b
d. a and b
the TOF MRA method with higher SNR is ___ and with shorter scan time is ____
a. 2D, 2D
b. 2D, 3D
c. 3D, 2D
d. 3D, 3D
c. 3D, 2D
for a “run off” MRA which scan method would normally be used
a. 2D TOF
b. 3D TOF
c. 2D PC
d. 3D PC
a. 2D TOF
Gadolinium contrast will have what effect on TOF MRA scans
a. decrease flow contrast
b. no efect
c. increase flow contrast
d. none of the above
c. increase flow contrast
“co curent” refers to
a. GRE
b. GREW
c. SE
d. SEW
d. SEW
Hich velocity signal loss is the dominant process when using which kinds of pulse sequences in flow imaging
a. gradient echo
b. spin echo
c. echo planar
d. none of the above
b. spin echo
The critical factor that determines the kind of flow in a vessel is
a. fluid velocity
b. fluid viscosity
c. reynolds number
d. none of the above
c. reynolds number
Advantages of 3D TOF MRA compared to 2D TOF MRA typically include which of the following?
I. higher spatial resolution
II. sensitivity to slower flow
III. larger coverage
a. I only
b. I and III only
c. II and III only
d. I II and III
a. I only
suppose that the flow in a vessel is laminar and that the maximum velocity in the lumen is Vmax. then the average velocity in the vessel is
a. 0
b. Vmax/4
c. Vmax/2
d. Vmax
c. Vmax/2
Which of the following are typically advantages of PC MRA compared to TOF MRA
I. sensitivity to in plane flow
II. lower scan time
III. measurement of flow velocity
a. I only
b. I and III only
c. II and III only
d. I II and III
b. I and III only
The gradient lobes used for flow encoding in PC MRA
a. can null higher order flow
b. are used for flow compensation
c. are bipolar
d. all of the above
c. are bipolar
Which of the following cannot appear in a PC MRA pulse sequence
a. flow encoding gradients
b. flow compensation gradients
c. spoiler gradients
d. none of the above - all can appear
d. none of the above - all can appear
MRI data is stored as
a. real numbers
b. imaginary numbers
c. complex numbers
d. none of the above
c. complex numbers
If one desires to image the vertebral arteries, where are saturation pulses placed in relation to the imaging region
a. inferior
b. superior
c. a and b
d. none of the above
b. superior
In order to extract flow speed V or direction from an MRA scan, one requires
a. magnitude image
b. phase image
c. a and b
d. none of the above
b. phase image
Choosing a VENC is requires for
a. TOF MRA
b. PC MRA
c. GMN
d. b and c
b. PC MRA
in an area of flow turbulence, the MRI picture will look
a. dark
b. bright
c. a or b depending on the imaging sequence
d. none of the above
a. dark
if the flow proton spins are saturated in a 3D acquisition, the saturation will be greatest where?
a. entry side of imaging region
b. middle of imaging region
c. exit side of imaging region
d. none of the above
c. exit side of imaging region
because of the short TR used for GRE sequences, stationary tissue surrounding vessel walls tends to have ____ magnetization. This creates ____.
a. unsaturated, low contrast
b. unsaturated, high contrast
c. saturated, low contrast
d. saturated, high contrast
d. saturated, high contrast
Comparatively ____ VENC values are used for arteries, while _____ VENC values are used for veins.
a. small, small
b. small, large
c. large, small
d. large, large
c. large, small
MIP means
a. minimum intensity perception
b. maximum intensity perception
c. minimum intensity projection
d. maximum intensity projection
d. maximum intensity projection
Choosing to small a VENC will lead to which effect
I. ghosting
II. velocity aliasing
III. odd echo dephasing
a. I only
b. I and II only
c. II only
d. I II and III
c. II only
If the eye vascular system is imaged, a problem with MIP might be
a. eye motion
b. high retro orbital fat signal
c. low spatial resolution
d. low SNR
b. high retro orbital fat signal
TOF MRA is sensitive to flow
a. in the direction of the sensitizing gradients
b. in plane
c. through plane
d. all of the above
c. through plane
MOTSA is used to combat
a. TOF MRA saturation
b. flow dephasing due to gradients
c. a and b
d. none of the above
a. TOF MRA saturation
Which technique uses a ramped flip angle
a. GRE
b. TONE
c. MOTSA
d. all of the above
b. TONE
Flow with erratic velocity values occurs in
a. laminar flow
b. plug flow
c. turbulent flow
d. b and c
c. turbulent flow
Choose the correct ordering of the following maximum arterial flow velocities from slowest to fastest
a. aorta, femoral, vertebral
b. aorta, vertebral, femoral
c. vertebral, femoral, aorta
d. femoral, vertebral, aorta
c. vertebral, femoral, aorta
The main problem with “bright blood” MRA techniques is
a. underestimation of stenosis
b. overestimation of stenosis
c. long scan time
d. low SNR
b. overestimation of stenosis
If the TE = 50ms for a spin echo type of sequence, this suggests that an image of a flow signal could be acquired at the echo time
a. 50ms
b. 100 ms
c. 200 ms.
d. b and c
d. b and c
Swirling motion distal to a stenosis could be described best as
a. vortex flow
b. eddy motion
c. a whirlpool
d. all of the above
d. all of the above
The “entry phenomenon” relies on which kind of flowing proton spins entering a slice
a. saturated
b. unsaturated
c. a and b
d. none of the above
b. unsaturated
Dephasing effects in “bright blood” MRA can best be minimized by
a. decreasing TE
b. increasing TE
c. decreasing TR
d. increasing TR
a. decreasing TE
The MRI signal from calcified plaque in a vessel wall is
a. bright
b. gray
c. dark
d. depends on whether TOF of PC MRA is used
c. dark
Magnetization transfer RF pulse frequencies are nearest
a. the free water resonance
b. 15 kHz from the free water resonance
c. 1500 kHz from the free water resonance
d. 1500 Hz from the free water resonance
d. 1500 Hz from the free water resonance
“Black blood” MRA tends to ____ stenosis
a. underestimate
b. overestimate
c. a and b
d. none of the above
a. underestimate
The units for VENC are
a. mm/s
b. cm/s
c. m/s
d. mi/hr
b. cm/s
“venetian blind” is a
a. pulse sequence
b. MRA technique
c. artifact
d. b and c
c. artifact
In a vessel with normal blood flow, the flow is best described as
a. laminar flow
b. plug flow
c. turbulent flow
d. a and b
a. laminar flow
To increase the signal from flowing spins in a vessel lumen, it is best to prescribe slices
a. co-current
b. counter curent
c. a or b depending on TR
d. none of the above
b. counter curent