Chapter 13 Common MR Pulse Sequences

Question 1

A pulse sequence can be defined as:

Answer 1

a series of pulse with periods of time in between.

Question 2

There are 2 major types of pulse sequences:

Answer 2

Spin Echo and Gradient Echo

Question 3

the spin echo category includes:

Answer 3

conventional spin echo
fast spin echo and inversion recovery sequences - STIR & FLAIR

Question 4

An Inversion Recovery (IR) sequence is basically a:

Answer 4

spin echo sequence except it begins with a 180 degree inversion pulse

Question 5

What is Time of Inversion (TI)?
(in an IR sequence)

Answer 5

the time between the initializing 180 degree pulse and the 90 degree pulse

Question 6

the time of inversion significantly affects MR Image contrast

Answer 6

following a 180 degree inversion pulse, the net magnetization will recover along the longitudinal axis, if one selects an inversion time that is 69% of a tissue’s T1 relaxation time, then at the time of the 90degree pulse application, that tissue would be crossing over the 0 longitudinal point and will in effect be nulled (No signal)

Question 7

As one changes the TI, one changes the

Answer 7

tissue which is nulled

Question 8

there are 2 ways in which IR sequences are used clinically:

Answer 8

nulling fat or nulling fluid (CSF)

Question 9

If a short inversion time (TI) is selected, we can null the signal from:

Answer 9

FAT

Question 10

what is STIR?

Answer 10

Short Tau Inversion Recovery
nulling fat from signal

Question 11

the exact TI depends on the

Answer 11

field strength

Question 12

the appropriate TI to null fat will _____as field strength ______.

Answer 12

increases;increases
TI depends on field strength

Question 13

what is FLAIR?

Answer 13

Fluid Attenuated Inversion Recovery
nulling CSF from signal

Question 14

a FLAIR sequence which utilizes a long TR and long TE is referred to as a

Answer 14

T2 FLAIR
the pathologic fluid remains bright

Question 15

what sequence is MS well visualized on

Answer 15

T2 FLAIR

Question 16

If one selects a more moderate TR and a short TE (along with TI to null CSF), one can obtain:

Answer 16

T1 weighted images with excellent gray/white matter contrast

Question 17

important points to remember regarding IR sequences:

Answer 17

1. selecting a T1 that is 69% of a tissues T1 relaxation time will null the signal from that tissue.
2. the TI will vary not only with tissue but field strength.
3. if nulling fat, the sequence is referred to as STIR
4. if nulling CSF, the sequence is referred to as FLAIR

Question 18

the main types of gradient echo sequences are :

Answer 18

steady state
spoiled
balanced gradient echos
echo planar imaging EPI

Question 19

basic contrast properties unique to gradient echo sequences are:

Answer 19

following an RF pulse, transverse magnetization decays due to several factors:
++ T2 relaxation - this rate varies with tissue’s fat and/or water content
++ T2* - a more rapid decay due to the addition of off resonance effects (T2 prime) which are inhomogeneities in the field and chemical shift

Question 20

gradient echo sequences do not utilize a

Answer 20

180 degree refocusing pulse prior to the formation of the echo so the transverse magnetization decays at a rate based on T2*

Question 21

gradient spin echo sequences are _____to inhomogenetities

Question 22

gradient echo sequences are _____to spin echo sequences with regards to sensitivity to small areas of hemorrhage, particularly in the brain

Answer 22

SUPERIOR

Question 23

gradient spin echo sequences are _____to inhomogeneities

Question 24

in a gradient echo sequences there is no

Answer 24

180 degree refocusing pulse prior to the formation and sampling of the echo.
if a voxel contains both water and fat protons, depending on the time at which the signal is sampled, the water and fat protons may either be in phase or out of phase

Question 25

the ______ the flip angle, the ____the TR require for complete longitudinal recovery to occur.

Answer 25

higher;longer

Question 26

T or F the flip angle in addition to TR is a parameter used to control the amount of T1 weighting in a gradient echo sequence

Answer 26

true

Question 27

_______a flip angle has the same contrast effect on the image as raising the TR

Answer 27

reducing (or lowering) both would result in reduced saturation

Question 28

for any tissue, based on it's T1 relaxation time and the TR selected, there is a flip angle which result in maximum signal. that flip angle is known as the:

Answer 28

Ernst Angle

Question 29

when the TR is shorter than the T2 (& T2*) of most tissues, after several pulses, longitudinal and transverse magnetization _____. This condition is known as________.

Answer 29

coexist; steady state