EXAM #13 — PHYSICS UNIT 06

Question 1

spin echo pulse sequence.

Answer 1

a pulse sequence comprised of a 90° followed by a 180° RF pulse

Question 2

gradient echo pulse sequence.

Answer 2

a pulse sequence comprised of an initial RF

pulse, often less than 90 followed by a gradient reversal

Question 3

inversion recovery pulse sequence.

Answer 3

a pulse sequence comprised of a 180 ° RF pulse, followed by a 90°RF pulse, then another 180°RF pulse

Question 4

repetition time (TR).

Answer 4

the time between the first RF excitation pulse in a sequence and the next excitation pulse (from a 90° to the next 90° in a spin echo pulse sequence)

Question 5

echo time (TE).

Answer 5

the time between the initial excitation pulse (90° RF pulse in a spin echo) and the reception of the MR signal from the sample

Question 6

inversion time (TI).

Answer 6

the time between the initial 180° RF pulse in an inversion recovery sequence and the 90° excitation RF pulse

Question 7

Tl- weighted image.

Answer 7

an image in which the difference in the Tl relaxation times of tissues are accentuated to create tissue contrast

Question 8

T2- weighted image.

Answer 8

an image in which the difference in the T2 relaxation times of tissues are accentuated to create tissue contrast

Question 9

proton density- weighted image.

Answer 9

an image in which neither the difference in Tl or T2 relaxation times of the tissues are accentuated to create tissue contrast, and the primary contrast mechanism is relative proton density

Question 10

explain what TR values would be used to create a Tl- weighted spin echo image, and give approximate range of values.

Answer 10

short TR- less than 800 msec

Question 11

explain what TE values would be used to create a Tl- weighted spin echo image, and give approximate range of values.

Answer 11

short TE- less than 25 msec

Question 12

explain what TR values would be used to create a T2- weighted spin echo image, and give approximate range of values.

Answer 12

long TR- more than 2000 msec

Question 13

explain what TE values would be used to create a T2- weighted spin echo image, and give approximate range of values.

Answer 13

long TE- more than 80 msec

Question 14

explain what TR values would be used to create a proton density- weighted spin echo image, and give approximate range of values.

Answer 14

long TR- more than 2000 msec

Question 15

explain what TE values would be used to create a proton density- weighted spin echo image, and give approximate range of values.

Answer 15

short TE- less than 35 msec

Question 16

explain the RF pulse sequence for the following sequences:

a. single echo spin echo.
b. dual-echo or multi-echo spin echo.
c. gradient echo.
d. inversion recovery.

Answer 16

explain the RF pulse sequence for the following sequences:

a. single echo spin echo. 90° , 180°
b. dual-echo or multi-echo spin echo. 90° , 80° , 180° possibly more 180° pulses
c. gradient echo. usually less than 90 °, gradient refocusing pulse
d. inversion recovery. 180 90°, 180°

Question 17

identify 1 advantage of gradient echo imaging over spin echo imaging.

Answer 17

scan time may be reduced

Question 18

identify 2 advantages of spin echo imaging over gradient echo imaging.

Answer 18

180° RF pulse helps compensation for magnetic field inhomogeneity; more signal received from sample

Question 19

discuss which type of pulse sequence creates a T2*- weighted image.

Answer 19

gradient echo

Question 20

explain the timing relationship between a 180° refocusing pulse and a spin echo.

Answer 20

the 180° refocusing pulse occurs halfway between the initial excitation pulse (90° pulse in a spin echo) and the spin echo, or at ½ TE

Question 21

identify 1 use of inversion recovery imaging.

Answer 21

the ability suppress signal from specific tissues

Question 22

discuss which type of pulse sequence uses variable (less than 90°) RF pulses.

Answer 22

gradient echo

Question 23

discuss which type of pulse sequence uses the shortest TR and TE values.

Answer 23

gradient echo

Question 24

explain how changes in flip angle affect image contrast in gradient echo imaging.

Answer 24

a lower flip angle creates a more T2* weighted image

Question 25

explain the effect that Tl and T2 enhancement agents have on Tl and T2 relaxation times.

Answer 25

contrast agents shorten Tl and T2 relaxation times

Question 26

identify the effect that Tl enhancement agents have on signal intensity.

Answer 26

increased signal intensity on Tl weighted images

Question 27

identify the effect that T2 enhancement agents have on signal intensity.

Answer 27

decreased signal intensity on T2 weighted images

Question 28

explain why Gadolinium contrast agents do not significantly affect T2 relaxation in the clinical setting.

Answer 28

Gadolinium is not in high enough concentration when given in clinical doses

Question 29

explain how Gadolinium is made safe for injection into humans.

Answer 29

it is bound or chelated to an inert substance such as DTP