ARRT PRINCIPLES OF MRI FINAL
EXAM REVIEW
3D gradient echo axial views can be used in cervical spine imaging to
provide - ANSWER- Thin, contiguous sections of the spine, the ability
to reformat into any other imaging plane, retrospectively, the ability to
get either T1, spin density or T2* information by changing parameters.
In complete spine imaging, to rule out metastatic lesions of the spinal
cord, contrast enhancement can be used with T1 weighted images
because - ANSWER- metastatic lesions enhance and normal cord does
not
Due to the differences in frequencies across the magnetic field we -
ANSWER- use gradients, use sat bands, . use different coils
,To avoid the "magic angle" (an artifactual brightness seen in the medial
segment of the posterior horn of the lateral meniscus when short TEs are
used) artifact when imaging the knee, - ANSWER- use a longer TE,
reposition the knee, orient the affected anatomy to another angle
To best visualize the anterior cruciate ligament on knee MR - ANSWER-
externally rotate the leg about 15
When using MRA to evaluate intracranial vascularity, flow within
smaller vessels can best be demonstrated by - ANSWER- 3D time of
flight MRA or 3D phase contrast MRA
To produce the echo, a gradient echo pulse sequence uses - ANSWER- a
gradient magnetic field only
The rate of dephasing due to inhomogeneities is called - ANSWER- T2
inhomogeneity
If the TR of a gradient echo pulse sequence is considerably less than the
T2 (and T2*), the condition that will exist is known as - ANSWER-
steady state
The gradient that is on during the production of the echo is the
__________ encoding gradient - ANSWER- frequency
, The gradient that is on longest is the __________ encoding gradient -
ANSWER- frequency
The four phases of a spin echo pulse sequence, in correct order, are -
ANSWER- Excitation, encoding, refocusing, readout.
Using an NSA of 3, if a phase resolution of 192 is desired, then the TR
must be repeated - ANSWER- 576 times
In a fast spin echo sequence, the effective TE is the echo that is
performed with the - ANSWER- Low amplitude phase encoding
gradient.
In a 2D multiecho pulse sequence, ETL = 8, scan time is given by the
equation TR x - ANSWER- Number of signals averaged x number of
phase encodings / the number of echoes.
When using MRA to evaluate extracranial vascular flow, such as that
within common carotid arteries, a recommended technique is -
ANSWER- 2D time of flight MRA
When using bright blood MRA to evaluate peripheral vascular flow,
such as that within the arteries of the legs, saturation pulses are -
ANSWER- placed inferior to the acquired slices
EXAM REVIEW
3D gradient echo axial views can be used in cervical spine imaging to
provide - ANSWER- Thin, contiguous sections of the spine, the ability
to reformat into any other imaging plane, retrospectively, the ability to
get either T1, spin density or T2* information by changing parameters.
In complete spine imaging, to rule out metastatic lesions of the spinal
cord, contrast enhancement can be used with T1 weighted images
because - ANSWER- metastatic lesions enhance and normal cord does
not
Due to the differences in frequencies across the magnetic field we -
ANSWER- use gradients, use sat bands, . use different coils
,To avoid the "magic angle" (an artifactual brightness seen in the medial
segment of the posterior horn of the lateral meniscus when short TEs are
used) artifact when imaging the knee, - ANSWER- use a longer TE,
reposition the knee, orient the affected anatomy to another angle
To best visualize the anterior cruciate ligament on knee MR - ANSWER-
externally rotate the leg about 15
When using MRA to evaluate intracranial vascularity, flow within
smaller vessels can best be demonstrated by - ANSWER- 3D time of
flight MRA or 3D phase contrast MRA
To produce the echo, a gradient echo pulse sequence uses - ANSWER- a
gradient magnetic field only
The rate of dephasing due to inhomogeneities is called - ANSWER- T2
inhomogeneity
If the TR of a gradient echo pulse sequence is considerably less than the
T2 (and T2*), the condition that will exist is known as - ANSWER-
steady state
The gradient that is on during the production of the echo is the
__________ encoding gradient - ANSWER- frequency
, The gradient that is on longest is the __________ encoding gradient -
ANSWER- frequency
The four phases of a spin echo pulse sequence, in correct order, are -
ANSWER- Excitation, encoding, refocusing, readout.
Using an NSA of 3, if a phase resolution of 192 is desired, then the TR
must be repeated - ANSWER- 576 times
In a fast spin echo sequence, the effective TE is the echo that is
performed with the - ANSWER- Low amplitude phase encoding
gradient.
In a 2D multiecho pulse sequence, ETL = 8, scan time is given by the
equation TR x - ANSWER- Number of signals averaged x number of
phase encodings / the number of echoes.
When using MRA to evaluate extracranial vascular flow, such as that
within common carotid arteries, a recommended technique is -
ANSWER- 2D time of flight MRA
When using bright blood MRA to evaluate peripheral vascular flow,
such as that within the arteries of the legs, saturation pulses are -
ANSWER- placed inferior to the acquired slices
