pulse sequences Flashcards
In a dual contrast spin echo sequence with echo times of 25ms and 90ms, the second echo image has __________ than the first echo image
I. more T2 contrast
II. lower signal-to-noise ratio
III. more T1 contrast
I & II only
A fast spin echo sequence is faster than a conventional spin echo pulse sequence because:
Several echoes for each slice are collected during each TR period
Lengthening TR with a short TE in a spin echo sequence will
Increase proton density weighting
Conventional spin echo sequences begin with a __________ RF excitation pulse.
A. 25°
B. 45°
C. 180°
D. None of the above
None of the above
Which of the following echo train lengths generate a set of images with the greatest signal-to-noise, assuming all other parameters are the same?
3 ETL
What is the correct scan time for a spin echo sequence with the following parameters: TR 500 ms, TE 30 ms, matrix 208 x 208, 2 NEX, FOV 200mm?
3 minutes 28 seconds
Scan time — TR x Phase matrix x NEX = Scan time in milliseconds, ÷ 1000 to calculate scan time in seconds.
Which of the following echo train lengths generates images in the shortest amount of time?
16 ETL
Scan time formula — TR x Matrix x NEX ÷ ETL…. More ETL = faster scan time
For a given number of slices, which of the following pulse sequences uses the most 180° RF pulses during each TR period?
Dual contrast spin echo
Each train of echoes has what effect on the pulse sequence in a fast spin echo?
A. Increases SAR absorption
B. Reduces scan time
C. Lowers SNR
D. All of the above
All of the above
Which RF pulse is always absent in a gradient echo sequence
180° refocusing pulse
The fastest sequence commonly and currently available is
Echo planar imaging
When performing a gradient echo pulse sequence, what is used to refocus the protons and create the echo
Gradient coils
A pulse sequence that begins with a 180° RF pulse, followed by a 90° RF excitation pulse, would be a(n
Inversion recovery
All of the following are types of inversion recovery sequences EXCEPT:
DWI
In an inversion recovery sequence, the time interval between the 180° RF pulse and the 90° RF pulse is the:
TI
A STIR sequence with a TI time of 160 ms will null signal from fat at what field strength?
1.5 Tesla
In which of the following pulse sequences would you expect to find the shortest TR?
Gradient echo
The gradient that is on during the production of the echo is the:
Frequency encoding gradient
In order to produce an echo in a gradient echo pulse sequence, a ___________ is used
A. RF pulse
B. Gradient field
C. Combination of two RF pulses
D. 180° pulse, then 90° pulse
E. All of the above
F. A & B only
A & B only
: In a Fast Spin Echo sequence, the effective TE are the echoes that are encoded:
With a low amplitude phase encoding gradient
: In a fast spin echo pulse sequence, if the TSE factor (echo train length) is increased by a factor of 3, the scan time will be:
Three times faster
In a fast spin echo pulse sequence, if the TSE factor
In a spin echo sequence, the time between the 90° RF pulse and the 180° RF pulse is known as the:
1/2 TE
The timing of RF pulses in an MRI pulse sequence controls:
Image contrast
Which RF pulse refocuses a decaying spin echo?
180°
