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Flashcards in MRI Physics 2 Deck (100)
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1

Which of the following variables controls the MRI signal sampling rate?
a. frequency encoding matrix
b. phase encoding matrix
c. transmit bandwidth
d. receiver bandwidth

d. receiver bandwidth

2

The faraday cage is usually made out of which substance?
a. niobium-titanium
b. steel
c. copper
d. silver

c. copper

3

A 3.0T superconducting MR magnet has high performance gradients with a maximum amplitude of 100 mT/m. this is equivalent to a maximum gradient amplitude of
a. .1G/cm
b. 1G/cm
c. 10G/cm
d. 1000G/cm

c. 10G/cm

4

The center of K space contains data with
a. the highest signal amplitude along both phase and frequency directions
b. the lowest signal amplitude along both phase and frequency directions
c. the highest signal amplitude along the phase direction only.
d. the highest signal amplitude along the frequency direction only.

a. the highest signal amplitude along both phase and frequency directions

5

filling only half of k space along the frequency axis is called
a. partial echo
b. 1/2 NEX
c. a and b
d. none of the above

a. Partial echo

6

the time of the phase encoding gradient to achieve its proper amplitude is the
a. sample time
b. TE
c. rise time
d. tau time

c. rise time

7

Suppose that the FOV = 25cm on a side and the matrix = 512x512. which value below is the closest to the area of a single pixel
a..25mm
b..25 mm^2
c. .50 cm
d. .50 cm^2

b. .25mm^2

8

which value below is closest to the scan time fora CSE pulse sequence with 15 slices, TR = 500ms, FOV = 12cm, matrix of 256x256 and 1 NEX. Assuming only 10 slices can be acquired in one acquisition with the paramaters above
a. 2 min 8 sec
b. 21 min 20 sec
c. 4 min 16 sec
d. 42 min 40 sec

c. 4 min 16 sec

9

the direction of current through the gradient coil controls
a. the value of the static magnetic field
b. the polarity of the gradient
c. the gradient rise time
d. none of the above

b. the polarity of the gradient

10

if the FOV is 16cm, matrix is 256x256 and the slice thickness is 8mm with 2mm slice gaps then the total size of a single voxel is closest to
a. .625 mm^3
b. 3.13 mm^3
c. 3.91 mm^3
d. 6.25 mm^3

b. 3.13mm^3

11

the best strategy to increase both snr and spatial resolution is to
a. increase voxel volume size
b. decrease voxel volume size
c. increase NEX
d. decrease NEX

c. increase NEX

12

A large TR leads to
a. higher SNR
b. lower SNR
c. chemical shift artifacts
d. aliasing

a. higher SNR

13

if the readout gradient amplitude is Gx, then
a. FOVx is proportional to (Gx)
b. FOVx is proportional to (Gx^2)
c. FOVx is inversely proportional to (Gx)
d. FOVx is inversely proportional to (Gx^2)

c. FOVx is inversely proportional to (Gx)

14

consider how SNR depends on the number of phase encoding steps (NPE). first increasing NPE has the effect of increasing the total scan time. second, for a given fixed FOV, increasing NPE decreases the voxel volume. In this case, SNR is proportional to
a. NPE
b. 1/NPE
c. (NPE) ^1/2
d. 1/(NPE)^1/2

d. 1/NPE^1/2

15

during a CSE acquisition, the pase endoding gradient for any particular slice is
a. turned on before the frequency encoding gradient
b. turned on after the frequency encoding gradient
c. turned on both before and after the frequency encoding gradient
d. not turned on

a. turned on before the frequency encoding gradient

16

Image contrast setting on the console is related to _____ and image brightness is related to _____
a. window, level
b. level, window
c. resolution, SNR
d. SNR, resolution

a. window, level

17

an RF excitation pulse that is ____ in the time domain will be _____ in the frequency domain.
a. broad, narrow
b. narrow, broad
c. a and b
d. none of the above

c. a and b

18

cross talk or cross excitation is due to
a. static magnetic field inhomogeneities
b. non linear gradient magnetic field
c. imperfect RF waveform
d. none of the above

c. imperfect RF waveform.

19

Demodulation refers to
a. a gray scale of an MRI image
b. shifting central RF frequency to zero
c. adding a gradient magnetic field to the static field
d. spatially encoding the MRI signal

b. shifting central RF frequency to zero

20

permanent magnets display which property
a. diamagnetism
b. paramagnetism
c. ferromagnetism
d. none of the above

c. ferromagnetism

21

when the readout gradient is turned on, a direct relationship is established between spatial position and ____
a. larmor frequency
b. precession phase
c. a and b
d. none of the above.

a. larmor frequency

22

for a 2D CSE acquisition with 1 NEX the number of phase encode steps performed is ____ the phase encode matrix
a. less than
b. greater than
c. the same as
d. either a or b

c. the same as

23

for a 256 square matrix and a FOV of 12cm, the pixel length is closest to
a. .25mm
b. .50 mm
c. .25 mm^2
d. .50 mm^2

b. .50mm

24

increasing the receiver bandwidth ____ the minimum TE and ____ the SNR
a. increases, increases
b. increases,decreases
c. decreases,increases
d. decreases, decreases

d. decreases,decreases

25

suppose that TR = repetition time, TE = echo time, Ts = sample time, T0 = overhead, then the # slices achievable in a period is
a. TE/(TR + Ts/2 + T0)
b. (TR + Ts/2 + T0)/TE
c. TR/(TE + Ts/2 + T0)
d. (TE + Ts/2 + T0)/TR

c. TR/(TE + Ts/2 + T0)

26

motion artifacts in 2D MRI scans are most likely to show up in which direction
a. slice select
b. frequency encode
c. phase encode
d. all of the above

c. phase encode

27

a typical value for the receiver bandwidth for a 1.5T superconducting scanner is
a. 16 Hz
b. 16 kHz
c. 16 MHz
d. none of the above

b. 16 kHz

28

the recognized units for SAR are
a. J/lb
b. J/kg
c. W/lb
d. W/kg

d. W/kg

29

for a 2D acquistion, the weakest phase encoding gradient amplitude (Gy = 0) has the ___ MRI signal and is positioned so that it occupies the ___ part of K space
a. lowest, central
b. lowest, peripheral
c. highest, central
d. highest, peripheral

c. highest, central

30

valid units for the spatial frequency k include
I. Hz
II. 1/seconds
III. cm
IV. 1/meter

a. I only
b. I and II only
c. III only
d. IV only

d. IV only