04) MRI Pulse Sequences

This pulse sequence is used to produce which of the following three clinical images:

A) B)

B) EPI

Feedback: The pulse sequence diagram represents an echo planar image (EPI). EPI images tend to be noisy and to demonstrate significant magnetic susceptibility artifacts.

Which of the following scan parameters would result in a spin-echo image with significant T2-weighting?

A) TR=500 msec, TE=20 msec

B) TR=2000 msec, TE=20 msec

C) TR=500 msec, TE=80 msec

D) TR=2000 msec, TE=80 msec

Feedback: In spin-echo imaging, use of a long TR and long TE produces T2 weighting.

Which of the following scan parameters would result in a spin-echo image with significant proton density weighting?

A) TR=500 msec, TE=20 msec

B) TR=2000 msec, TE=20 msec

C) TR=500 msec, TE=80 msec

D) TR=2000 msec, TE=80 msec

B) TR=2000 msec, TE=20 msec

Feedback: In spin-echo imaging, use of a long TR and short TE produces PD weighting.

Which of the following scan parameters would result in a spin-echo image with significant T1-weighting?

A) TR=500 msec, TE=20 msec

B) TR=2000 msec, TE=20 msec

C) TR=500 msec, TE=80 msec

D) TR=2000 msec, TE=80 msec

A) TR=500 msec, TE=20 msec

Feedback: In spin-echo imaging, use of a short TR and short TE produces T1 weighting.

Which family of pulse sequences is least susceptible to magnetic field inhomogeneities and magnetic susceptibilities?

A) Spin-Echo

B) Gradient Echo

C) Echo Planar

D) Saturation Recovery

A) Spin-Echo

Feedback: In spin-echo imaging, the 180 degree RF pulse corrects for phase changes caused by magnetic field inhomogeneities and magnetic susceptibilities.

In spin-echo imaging, increasing TR will cause T1 weighting of image contrast to:

A) Increase

B) Decrease

C) Remain the same

B) Decrease

In spin-echo imaging, increasing TE will cause T2 weighting of image contrast to:

A) Increase

B) Decrease

C) Remain the same

A) Increase

Which family of pulse sequences uses a small (<90⁰) excitation pulse and gradient reversal to produce an echo:

A) Spin-echo

B) Gradient-echo

C) Inversion recovery

D) Saturation recovery

B) Gradient-echo

Feedback: In spin-echo imaging, increasing TR reduces the contrast between tissues having different T1 values (e.g. grey matter and white matter).

When using 3D acquisition techniques, the acquired images can be reformatted in any plane without loss of resolution, if voxels are:

A) T1 weighted

B) Isotropic

C) Coplanar

D) Submillimeter

B) Isotropic

Feedback: Isotropic voxels have approximately the same dimensions along all axes (e.g. 1mm x 1mm x 1mm). For example, a sagittal image can be reformatted into an axial or coronal image without a significant loss of resolution.

10.

Which of the following factors is most significant in determining the acquisition time for 2D MRI images:

A) TR

B) TE

C) FOV

D) Proton density

A) TR

Feedback: The acquisition time for 2D MRI images is proportional to TR x Np x NEX, where:• TR = Repetition time (msec)• Np = Number of phase encodes• NEX = Number of excitations or averages

11.

The RF pulse “flip angle” is an important parameter for control of image contrast for which pulse sequence:

A) Gradient-echo

B) Spin-echo

C) Echo-planar

D) Inversion recovery

A) Gradient-echo

Feedback: In gradient-echo imaging, a small excitation pulse (flip angle) is used and the echo is produced by a reversal of the frequency encoding gradient.

12.

Which pulse sequence acquires only one row of k-space data during each TR time period?

A) Fast spin-echo

B) Fast spoiled gradient-echo

C) Spin-echo

D) Echo-planar

C) Spin-echo

Feedback: A spin-echo pulse sequence acquires only one row of k-space data during each TR time period. An exception occurs if parallel imaging (e.g. SENSE, GRAPPA) is used to accelerate imaging, in which case a few rows of k-space may be filled during each TR.

13.

In inversion recovery pulse sequences, selected tissues are suppressed through use of a:

A) Free induction decay

B) Gradient spoiler

C) Phase rewinder

D) 180 degree RF pulse

Feedback: In gradient-echo pulse sequences, the flip angle and TR and TE can be adjusted to control image contrast (e.g. T2*, T1, T1/T2*, T2/T1).

Feedback: A 180 degree RF pulse can be used to suppress the MRI signal of fat (e.g. STIR) or CSF (e.g. FLAIR).

14.

After the 90 degree RF pulse in a spin-echo pulse sequence, the signal from the transverse magnetization dissipates according to:

A) TR

B) TE

C) TI

D) T2

E) T2*

Feedback: The exponential decline in transverse magnetization is described by the T2 relaxation rate constant.

15.

In spin-echo imaging, which image contrast dominates if TR is approximately equal to the tissue T1 values with TE=20 msec:

A) T1 weighting

B) T2 weighting

C) PD weighting

D) Mixed T1 and T2 contrast

A) T1 weighting

Feedback: The use of a short TE and a TR in the range of tissue T1 values will maximize T1 contrast.

16.

The STIR inversion recovery technique is used to suppress the signal from:

A) Blood

B) Fat

C) Fluid

D) Muscle

B) Fat

Feedback: STIR (short tau inversion recovery) imaging will suppress the MRI contributions of fat.

17.

The FLAIR inversion recovery technique is used to suppress the signal from:

A) Blood

B) Fat

C) Fluid

D) Muscle

C) Fluid

Feedback: FLAIR (fluid attenuated inversion recovery) imaging will suppress the MRI contributions of CSF.

18.

In gradient-echo imaging, inversion recovery can be used to:

A) Suppress fat signal

B) Suppress fluid signal

C) Control T1 weighting

D) Control T2 weighting

C) Control T1 weighting

Feedback: An inversion recovery pulse can be used to control T1 contrast in gradient-echo images.

19.

If the number of phase encoding steps used for an image acquisition is reduced from 256 to 128, acquisition time will change by:

A) X4

B) X2

C) X0.5

D) X0.25

C) X0.5

Feedback: If the number of phase encode steps used for an image acquisition is reduced by half, the image acquisition time will be reduced by half.

20.

If the parallel imaging acceleration factor is increased from 1 to 2, acquisition time will change by:

A) X4

B) X2

C) X0.5

D) X0.25

C) X0.5

Feedback: If the acceleration factor is set to 2 for parallel imaging (e.g. SENSE, GRAPPA), the image acquisition time will be reduced by half).