MRI
Phillip W Patton, Ph.D.
RAPHEX General
Question 2001
D43: In MRI, the RF frequency is dependent
on the:
A. Diameter of the body part being
imaged.
B. Magnetic field strength.
C. Pulse Sequence.
D. RF coil.
E. Relaxation time.
RAPHEX Answer to 2001
Question D43
B. The frequency used in MRI depends
on the product of the magnetic field
strength and the gyromagnetic ratio
of the element being imaged. Since
most MRI is of hydrogen atoms, the
frequency depends only on the
magnetic field strength.
RAPHEX General
Question 2001
D46: Gradient fields in MRI are
principally used to:
A. Maintain a uniform magnetic field in the field of
view.
B. Eliminate perturbations in the magnetic field due
to site location.
C. Shorten T1 to reduce scan time.
D. Provide spatial localization.
E. Measure the spin coupling.
RAPHEX Answer to 2001
Question D46
D. Gradient fields are used to modify
the magnetic field so that resonance
will be slightly different at different
points in the volume of interest. It is
then possible to localize these
points.
RAPHEX General
Question 2002
D51:A higher intensity MRI signal is
produced by:
A.
B.
C.
D.
Long T1, long T2.
Long T1, short T2.
Short T1, long T2.
Short T1, short T2.
RAPHEX Answer to 2002
Question D51
C. The MRI signal strength depends on the
value of the magnetization vector along the
constant field (z) axis, which is then tipped
into the x-y plane to produce the MRI signal. A
short T1 implies a rapid return of the
magnetization to the z axis following
excitation by the RF field. A long T2 implies a
long dephasing time for the individual nuclei
involved in producing the magnetization. Both
these effects will lead to a large value of
magnetization and a large MRI signal.
RAPHEX General
Question 2003
D53:For hydrogen imaging in a 1.0 T
MRI unit, the frequency of the RF
signal is about ________ .
A.
B.
C.
D.
E.
40 Hz
40 kHz
40 MHz
400 MHz
4 GHz
RAPHEX Answer to 2003
Question D53
C. The frequency for hydrogen is 42
MHz x magnetic field strength in
tesla.
Raphex 2001 Diagnostic
Questions
D43. In MRI, the RF frequency is dependent on
the:
A. Diameter of the body part being imaged
B. Magnetic field strength
C. Pulse sequence
D. Relaxation time
E. RF coil
RAPHEX Answer to 2001
Question D43
B. The frequency used in MRI depends on
the product of the magnetic field strength and
the gyromagnetic ratio of the element being
imaged. Since MRI is mainly of hydrogen
atoms, the frequency depends only on the
magnetic field strength.
Raphex 2001 Diagnostic
Questions
D46. Gradient fields in MRI are principally used
to:
A. Eliminate perturbations in the magnetic field
due to site location
B. Maintain a uniform magnetic field in the field
of view
C. Measure the spin coupling
D. Provide spatial localization
E. Shorten T1 to reduce scan time
RAPHEX Answer to 2001
Question D46
D. Gradient fields are used to modify the
magnetic field so that resonance will be
slightly different at different points in the
volume of interest.
Raphex 2000 Diagnostic
Questions
D48. In MRI images, motion during the scans
results in ghost images which appear in the
______ direction.
A. Amplitude
B. Frequency encoding
C. Phase encoding
D. Relaxation
E. Slice thickness
RAPHEX Answer to 2000
Question D48
B. Motion usually appears as a series of
ghost images of reduced intensity displaced
in phase encoded direction.
Raphex 2001 Diagnostic
Questions
D50. Which of the following does NOT generally
affect the total exam time of an MRI study?
A. # of acquisitions
B. # of frequency encoding steps
C. # of phase encoding steps
D. # of pulse sequences in the study
E. TR
RAPHEX Answer to 2001
Question D50
A. frequency encoding steps are determined
only by the resolution setting of the ADC.
Raphex 2003 Diagnostic
Questions
D54. In MRI the signal-to-noise ratio can be
increased by all of the following except:
A. Switching from a volume to a surface coil
B. Increasing the number of acquisitions
C. Increasing the static magnetic field strength
D. Decreasing the slice thickness
E. Increasing TR
RAPHEX Answer to 2003
Question D54
D.
Raphex 2001 Diagnostic
Questions
D45. Superconducting magnets, compared to
resistive magnets:
A. Are less expensive
B. Are more easily turned off
C. Do not require liquid helium
D. Have higher field strength
RAPHEX Answer to 2001
Question D45
D. Superconducting magnets have field
strengths of 0.3 – 10 T, while resistive
magnets have strengths below 0.2 T.
Raphex 2003 Diagnostic
Questions
D57-D59. Match the following MRI terms. (Answers may be used more than
once.)
A. Gradient fields
B. RF
C. Shim coils
D. T1
E. T2
D57. Used to adjust magnetic field uniformity
D58. Used to localize MR signal
D59. Used to tip the net magnetization of spins
Raphex 2003 Diagnostic
Answers
D57-D59. Match the following MRI terms. (Answers may be used more than
once.)
A. Gradient fields
B. RF
C. Shim coils
D. T1
E. T2
D57. Used to adjust magnetic field uniformity
D58. Used to localize MR signal
D59. Used to tip the net magnetization of spins
C
A
B
Raphex 2000 Diagnostic
Questions
D49. Patients who have MRI scans should be
screened to eliminate those who have:
A. Internal steel fragments
B. Metallic prostheses
C. Pacemakers
D. Surgical clips
E. All of the above
RAPHEX Answer to 2000
Question D49
E. Pacemakers can be affected an cause the
pulse rate to change dramatically. Some
surgical clips are magnetic and can move
causing bleeding. Metallic prostheses can
heat due to the RF pulses distorting the
images. Steel workers with small fragments
in their eyes have lost vision during an MRI
scan.
Raphex 2002 Diagnostic
Questions
D57. All of the following are MRI artifacts except:
A. Chemical shift
B. Ring
C. Susceptibility
D. Wrap-around
E. Zipper
RAPHEX Answer to 2002
Question D57
B. Bounce point artifact refers to a zero signal
that can occur with certain inversion recovery
pulse sequences. Chemical shift is a
displacement difference between lipids and
water. Zipper is a series of “dropouts” due to
RF problems. Wrap-around represents
aliasing due to the FOV being smaller than
the object size.