Scan Principles - 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.
None of the above
Conventional spin echo sequences begin with a 90° RF excitation pulse
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?
All of the above
Each train of echoes in a fast spin echo sequence reduces scan time but also lowers SNR and increases SAR absorption in the patient.
Which RF pulse is always absent in a gradient echo sequence?
180° refocusing pulse
The gradient echo sequence lacks a 180° refocusing RF pulse, making it more susceptible to magnetic field inhomogeneities.
The fastest sequence commonly and currently available is:
Echo planar imaging
Echo-planar imaging is a very fast magnetic resonance (MR) imaging technique capable of acquiring an entire MR image in only a fraction of a second
When performing a gradient echo pulse sequence, what is used to refocus the protons and create the echo?
Gradient coils
In a gradient echo pulse sequence, the gradient coils are used to refocus the protons and create the echo.
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
The TI (inversion time) is the time interval between the 180° RF pulse and the 90° RF pulse.
A STIR sequence with a TI time of 160 ms will null signal from fat at what field strength?
1.5 Tesla
The T1 time of fat at 1.5 Tesla is approximately 240 with a null point of 160 ms.
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
The gradient that is on during the production of the echo is the frequency encoding (readout) gradient
In order to produce an echo in a gradient echo pulse sequence, a ___________ is used.
A & B only
In order to produce an echo in a gradient echo pulse sequence, a gradient field and an RF pulse are used.
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 sequence, the effective TE are the echoes that are encoded with a low amplitude phase encoding gradient. This would occur at the line that is closest to the center of k-space (k0)
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 (echo train length) is increased by a factor of 3, the scan time will be three times faster.
In a spin echo sequence, the time between the 90° RF pulse and the 180° RF pulse is known as the:
1/2 TE
In a spin echo sequence, the time between the 90° RF pulse and the 180° RF pulse is known as the 1/2 TE time
The timing of RF pulses in an MRI pulse sequence controls:
Image contrast
The timing of RF pulses in an MRI pulse sequence controls the image contrast.
Which RF pulse refocuses a decaying spin echo?
180°
The 180° RF pulse refocuses a decaying spin echo.
As the TE is increased,
I. The available number of slices is increased
II. The available number of slices is decreased
III. SNR increases
IV. T1 contrast is maximized
II only
As the TE is increased, the available number of slices are decreased (longer TE means fewer slices can fit into the TR period)
As the TR is increased,
I. SNR is increased
II. Available number of slices is increased
III. T2 information is maximized
I and II only
Which of the following sequences is the most insensitive to magnetic field inhomogeneity?
Spin echo
Spin echo sequences contain 180° RF refocusing pulse(s), which aid in correcting for local field inhomogeneities, therefore making them the most INSENSITIVE to inhomogeneity.
CSF suppression is performed with which type of technique?
FLAIR
The echo time is the
Time between the 90º RF pulse and the peak of the signal in the receiver coil
The echo time (TE) is the time between the 90º RF pulse and the peak of the signal in the receiver coil
The repetition time is the:
Time between two 90º RF pulses
The repetition time (TR) is the time between two 90º RF pulses
Which of the following combinations of flip angle (FA) and TR would produce a T2 weighted gradient echo?
450 TR; 30º flip angle
450 TR; 30º flip angle combination would yield a T2 weighted gradient echo.
In a spin echo pulse sequence, an echo is produced from:
A combination of two or more RF pulses
In a spin echo pulse sequence, an echo is produced from a combination of two or more RF pulses.
Fast spin echo sequences are fast because:
More than 1 line of k-space is acquired in each TR period
Conventional spin echo techniques acquire one line of k-space during each repetition (TR). Fast spin echo techniques acquire multiple (2 to 50+) lines of k-space during each repetition.
What specifically is a SPGR sequence spoiling?
Transverse magnetization
Spoiled Gradient Recalled echo – The RF excitation pulse is phase shifted each time the RF is applied which prevents accumulation of the residual transverse magnetization effects throughout the acquisition.
