Scan Principles - Pulse Sequences

Question 1

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

Answer 1

I & II only

Question 2

A fast spin echo sequence is faster than a conventional spin echo pulse sequence because:

Answer 2

Several echoes for each slice are collected during each TR period

Question 3

Lengthening TR with a short TE in a spin echo sequence will:

Answer 3

Increase proton density weighting

Question 4

Conventional spin echo sequences begin with a __________ RF excitation pulse.

Answer 4

None of the above
Conventional spin echo sequences begin with a 90° RF excitation pulse

Question 5

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?

Answer 5

3 ETL

Question 6

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?

Answer 6

3 minutes 28 seconds

Scan time — TR x Phase matrix x NEX = Scan time in milliseconds, ÷ 1000 to calculate scan time in seconds.

Question 7

Which of the following echo train lengths generates images in the shortest amount of time?

Answer 7

16 ETL

Scan time formula — TR x Matrix x NEX ÷ ETL…. More ETL = faster scan time.

Question 8

For a given number of slices, which of the following pulse sequences uses the most 180° RF pulses during each TR period?

Answer 8

Dual contrast spin echo

Question 9

Each train of echoes has what effect on the pulse sequence in a fast spin echo?

Answer 9

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.

Question 10

Which RF pulse is always absent in a gradient echo sequence?

Answer 10

180° refocusing pulse

The gradient echo sequence lacks a 180° refocusing RF pulse, making it more susceptible to magnetic field inhomogeneities.

Question 11

The fastest sequence commonly and currently available is:

Answer 11

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

Question 12

When performing a gradient echo pulse sequence, what is used to refocus the protons and create the echo?

Answer 12

Gradient coils

In a gradient echo pulse sequence, the gradient coils are used to refocus the protons and create the echo.

Question 13

A pulse sequence that begins with a 180° RF pulse, followed by a 90° RF excitation pulse, would be a(n):

Answer 13

Inversion recovery

Question 14

All of the following are types of inversion recovery sequences EXCEPT:

Answer 14

DWI

Question 15

In an inversion recovery sequence, the time interval between the 180° RF pulse and the 90° RF pulse is the:

Answer 15

TI

The TI (inversion time) is the time interval between the 180° RF pulse and the 90° RF pulse.

Question 16

A STIR sequence with a TI time of 160 ms will null signal from fat at what field strength?

Answer 16

1.5 Tesla
The T1 time of fat at 1.5 Tesla is approximately 240 with a null point of 160 ms.

Question 17

In which of the following pulse sequences would you expect to find the shortest TR?

Answer 17

Gradient echo

Question 18

The gradient that is on during the production of the echo is the:

Answer 18

Frequency encoding gradient

The gradient that is on during the production of the echo is the frequency encoding (readout) gradient

Question 19

In order to produce an echo in a gradient echo pulse sequence, a ___________ is used.

Answer 19

A & B only
In order to produce an echo in a gradient echo pulse sequence, a gradient field and an RF pulse are used.

Question 20

In a Fast Spin Echo sequence, the effective TE are the echoes that are encoded:

Answer 20

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)

Question 21

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:

Answer 21

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.

Question 22

In a spin echo sequence, the time between the 90° RF pulse and the 180° RF pulse is known as the:

Answer 22

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

Question 23

The timing of RF pulses in an MRI pulse sequence controls:

Answer 23

Image contrast

The timing of RF pulses in an MRI pulse sequence controls the image contrast.

Question 24

Which RF pulse refocuses a decaying spin echo?

Answer 24

180°
The 180° RF pulse refocuses a decaying spin echo.

Question 25

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

Answer 25

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)

Question 26

As the TR is increased,
I. SNR is increased
II. Available number of slices is increased
III. T2 information is maximized

Answer 26

I and II only

Question 27

Which of the following sequences is the most insensitive to magnetic field inhomogeneity?

Answer 27

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.

Question 28

CSF suppression is performed with which type of technique?

Answer 28

FLAIR

Question 29

The echo time is the

Answer 29

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

Question 30

The repetition time is the:

Answer 30

Time between two 90º RF pulses

The repetition time (TR) is the time between two 90º RF pulses

Question 31

Which of the following combinations of flip angle (FA) and TR would produce a T2 weighted gradient echo?

Answer 31

450 TR; 30º flip angle

450 TR; 30º flip angle combination would yield a T2 weighted gradient echo.

Question 32

In a spin echo pulse sequence, an echo is produced from:

Answer 32

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.

Question 33

Fast spin echo sequences are fast because:

Answer 33

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.

Question 34

What specifically is a SPGR sequence spoiling?

Answer 34

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.