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Huda_questions > Huda MRI > Flashcards

Huda MRI Flashcards

1
Q 
1. Which would not be useful for medical MR
imaging?
(A) 1H
(B) 13C
(C) 16O
(D) 23Na
(E) 31P
A

C. 16-O
16O is an example of an even-even nucleus
(eight neutrons and eight protons), which has no
magnetic moment and thus cannot be used for
MR.

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2
Q 
2. The Larmor frequency is the frequency of:
(A) Pulse repetition
(B) Nuclear precession
(C) Phase encoding
(D) Spatial encoding
(E) Gradient switching
A

B. Magnetic nuclei precess at the Larmor frequency

when placed into a magnetic field.

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3
Q 
3. The resonance frequency for 'H in a 1.5 T
magnetic field is:
(A) 63 H3
(B) 63 kH3
(C) 63 MH3
(D) 63 GH3
(E) 63 TH3
A

C. 63 MHz.

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4
Q
  1. The maximum MR signal is obtained by using
    a:
    (A) 90 degree RF tip, short TE, and short TR
    (B) 45 degree RF tip, short TE, and short TR
    (C) 90 degree RF tip, short TE, and long TR
    (D) 90 degree RF tip, long TE, and short TR
    (E) 45 degree RF tip, long TE, and short TR
A

C. Maximum signal strength is obtained by using
a 90 degree pulse to maximize the magnetization
in the transverse plane, starting with the maximum
longitudinal magnetization (i.e., long TR)
and minimizing dephasing (i.e., short TE).

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5
Q
  1. For most tissues, which of the following is
    false?
    (A) T1 is of the order of a few seconds.
    (B) T2 is of the order of tens of milliseconds.
    (C) T2 is relatively independent of field strength.
    (D) T1 increases as field strength increases.
    (E) T1 and T2 often increase with malignancy
A

A. T1 is of the order of hundreds of milliseconds,

not a few seconds.

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6
Q 
6. The small amount of bound water produces no
detected MR signal because:
(A) T1 is too short
(B) T2 is too short
(C) T2* is very long
(D) T2 is longer than T1
(E) T2* is longer than T2
A

B. The T2 is too short (microseconds) to give
rise to a detected signal from all solids including
bone.

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7
Q 
7. For most biological tissues, T2 is:
(A) Less than T1
(B) More than T1
(C) Less than T2*
(D) More than 100 milliseconds
(E) Less than 5 milliseconds
A

A. T2 is generally of the order of tens of milliseconds,
whereas T1 is on the order of hundreds
of milliseconds.

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8
Q 
8. MR "shimming" is used to:
(A) Minimize noise in RF coils
(B) Correct for magnetic-field inhomogeneities
(C) Reduce the noise level in MR systems
(D) Minimize the possibility of quenches
(E) Increase signal phase
A

B. Shimming is used to reduce field inhomogeneities

to a few parts per million.

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9
Q
  1. The superconducting magnets used in MR
    normally have:
    (A) No magnetic-field inhomogeneities
    (B) Water cooling to dissipate heat production
    (C) Coils with alternating electric currents
    (D) Magnetic fields perpendicular to the bore axis
    (E) Liquid helium coolant
A

E. Superconductors normally require liquid helium

coolant.

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10
Q 
10. Gradient fields in MR are used most commonly
to:
(A) Increase T2
(B) Shorten T1 values
(C) Localize MR signal source
(D) Increase signal in large patients
(E) Reduce electronic noise
A

C. Gradients define the MR image plane and
are used for frequency and phase encoding to determine
the spatial origin of the detected signals.

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11
Q 
11. Which of the following is generally acceptable
for MR at 1.5 T?
(A) Cochlear implants
(B) Pacemakers
(C) Ferromagnetic aneurysm clips
(D) Claustrophobic patients
(E) Pregnant patients
A

E. Pregnant patients can undergo MR scans

no ionizing radiation

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12
Q 
12. Which line is an exclusion zone for persons
with pacemakers?
(A) 0.5 G
(B) 5 G
(C) 50 G
(D) 500G
(E) Over 500 G
A

B. Areas with magnetic fields greater than 5 G
(0.5 mT) should be restricted to individuals with
pacemaker implants.

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13
Q
  1. Safety concerns for 1.5 T MR include all of
    the following except:
    (A) Fringe magnetic fields
    (B) Electrical stimulation neurons
    (C) RF heating effects
    (D) Ferromagnetic surgical slips in patients
    (E) Flying metallic objects
A

B. For magnetic-field strengths below 2 T, the
effect of magnetic field-induced electrical potentials
in neurons has not been observed.

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14
Q
  1. The FDA limit on power deposition in patients
    undergoing MR does not include:
    (A) 3.2 W/kg averaged over the head
    (B) 8 W/kg peak value
    (C) 0.4 W/kg averaged over body
    (D) A less than 3 °C temperature rise in the heart
    (E) A less than 1 °C core body temperature rise
A

D. There are no specific temperature rise limits

set for the heart by the FDA in MR.

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15
Q 
15. The most common reconstruction method for
MR units is:
(A) 2DFT
(B) 3DFT
(C) Algebraic reconstruction
(D) Back projection
(E) Filtered back projection
A

A. 2DFT is standard on virtually all commercial

MR units.

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16
Q 
16. Which does not generally affect the total patient
examination time in MR?
(A) Read encode matrix size
(B) Number of phase-encoding steps
(C) Number of pulse sequences used
(D) Acquisitions (Nex)
(E) TR
A

A. The number of pixels in the read-direction
is related only to the number of samples in FID
acquired and will not affect image acquisition
time.

17
Q 
17. In spin-echo imaging, the echo signal normally
is measured:
(A) Immediately (t = 0)
(B) After time TE
(C) After time 4 x T1
(D) After time T2
(E) After time TR
A

B. A phase-refocusing 180 degree pulse is applied
at time TE/2, which results in an echo at time
TE.

18
Q
  1. In IR sequences, the T1 value is the time:
    (A) Of the complete scan
    (B) To the interval echo
    (C) Between successive 90 degree pulses
    (D) Between successive 180 degree pulses
    (E) Between an initial 180 degree and subsequent
    90 degree pulse
A

E. An IR sequence starts with a 180 degree inversion
pulse followed by a 90 degree readout
pulse after time TI.

19
Q 
19. Increased signal intensity in MR cannot arise
as a result of:
(A) Short T1
(B) Long T2
(C) Flow effects
(D) Spin density
(E) Dephasing effects
A

E. Dephasing effects always reduce signal intensities
(they may increase contrast, but not signal
intensity per se).

20
Q 
20. MR SNR cannot be improved by increasing
the:
(A) Matrix size
(B) Number of acquisitions
(C) Static magnetic-field strength
(D) Section thickness
(E) RF coil sensitivity
A

A. Increasing the matrix size will not increase

SNR but will reduce the SNR per pixel.

21
Q
  1. Chemical shift artifacts are caused by:
    (A) Different resonant frequencies of 1H in water
    and fat
    (B) Foreign chemicals agents in the patient
    (C) Magnetic-field gradients
    (D) Contrast agents
    (E) Spin-lattice interactions
A

A. Chemical shift artifacts arise because of
the slightly differing resonance frequencies of proton
in different molecules.

22
Q 
22. In MR, motion results in ghost images that appear
in which direction?
(A) Read encode
(B) Phase encode
(C) Slice selection axis
(D) PA
(E) Lateral
A

B. Motion usually appears as a series of ghost

images of reduced intensity displaced in the phase encoding direction.

23
Q 
23. All of the following are MR artifacts except:
(A) Chemical shift
(B ) Bounce point
(C) Zipper
(D) Susceptibility
(E) Reverberation
A

E. Reverberation artifacts occur in ultrasound.

24
Q 
24. Superparamagnetic materials are not:
(A) Small particles (smaller than 350 A)
(B) Single domains
(C) Strongly magnetic
(D) Related to ferromagnetic materials
(E) Superconductors
A

E. Super paramagnetism has no relation to superconductivity.

25
Q 
25. Contrast in MR can be due to all the following
differences except:
(A) Presence of flow
(B) Proton density
(C) T1
(D) Atomic number
(E) T2
A

D. Atomic number (Z) does not give rise to
image contrast in MR but does give rise to image
contrast in x-ray imaging.

26
Q 
26. Proton relaxation by Gd-DTPA is owing
mainly to the effect of the:
(A) Gadolinium nucleus
(B) DTP A
(C) Unpaired gadolinium electrons
(D) Gadolinium K-edge energy
(E) K-shell electrons
A

C. The seven unpaired electrons in Gd result

in the relaxation of adjacent nuclei.

27
Q 
27. Common MR angiography techniques are
based on:
(A) Phase contrast
(B) Phase encoding
(C) T1 contrast
(D) Time to inversion
(E) FSE imaging
A

A. Phase-contrast and time-of-flight are the

two common methods used in MR angiography.

28
Q
  1. EPI generally requires all of the following except:
    (A) Gradient-recalled echoes
    (B) Gradients between 20 and 60 mT/m
    (C) Rapid gradient switching
    (D) High magnetic fields
    (E) Rapid repetition of 180 degree RF pulses
A

E. No MR sequences require a rapid set of RF

pulses.

29
Q 
29. MR spectroscopy is used to detect all the following
except:
(A) 31P
(B) 32P
(C) Inorganic phosphate
(D) Phosphocreatinine
(E) adenosine triphosphate
A

B. 32P is a radioactive beta emitter used as a
tracer in biomedical research, as is not used for
MR spectroscopy.

30
Q 
30. Functional imaging using magnetic resonance
does not show:
(A) Brain activation sites
(B) Increased venous oxygenation
(C) Increased spin density sites
(D) Superior temporal resolution to positron
emission tomography (PET)
(E) superior spatial resolution to PET
A

C. Functional MR has no direction relation to

spin density.

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