EXAM #13 — PHYSICS UNIT 06 Flashcards
spin echo pulse sequence.
a pulse sequence comprised of a 90° followed by a 180° RF pulse
gradient echo pulse sequence.
a pulse sequence comprised of an initial RF
pulse, often less than 90 followed by a gradient reversal
inversion recovery pulse sequence.
a pulse sequence comprised of a 180 ° RF pulse, followed by a 90°RF pulse, then another 180°RF pulse
repetition time (TR).
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)
echo time (TE).
the time between the initial excitation pulse (90° RF pulse in a spin echo) and the reception of the MR signal from the sample
inversion time (TI).
the time between the initial 180° RF pulse in an inversion recovery sequence and the 90° excitation RF pulse
Tl- weighted image.
an image in which the difference in the Tl relaxation times of tissues are accentuated to create tissue contrast
T2- weighted image.
an image in which the difference in the T2 relaxation times of tissues are accentuated to create tissue contrast
proton density- weighted image.
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
explain what TR values would be used to create a Tl- weighted spin echo image, and give approximate range of values.
short TR- less than 800 msec
explain what TE values would be used to create a Tl- weighted spin echo image, and give approximate range of values.
short TE- less than 25 msec
explain what TR values would be used to create a T2- weighted spin echo image, and give approximate range of values.
long TR- more than 2000 msec
explain what TE values would be used to create a T2- weighted spin echo image, and give approximate range of values.
long TE- more than 80 msec
explain what TR values would be used to create a proton density- weighted spin echo image, and give approximate range of values.
long TR- more than 2000 msec
explain what TE values would be used to create a proton density- weighted spin echo image, and give approximate range of values.
short TE- less than 35 msec
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.
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°
identify 1 advantage of gradient echo imaging over spin echo imaging.
scan time may be reduced
identify 2 advantages of spin echo imaging over gradient echo imaging.
180° RF pulse helps compensation for magnetic field inhomogeneity; more signal received from sample
discuss which type of pulse sequence creates a T2*- weighted image.
gradient echo
explain the timing relationship between a 180° refocusing pulse and a spin echo.
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
identify 1 use of inversion recovery imaging.
the ability suppress signal from specific tissues
discuss which type of pulse sequence uses variable (less than 90°) RF pulses.
gradient echo
discuss which type of pulse sequence uses the shortest TR and TE values.
gradient echo
explain how changes in flip angle affect image contrast in gradient echo imaging.
a lower flip angle creates a more T2* weighted image
explain the effect that Tl and T2 enhancement agents have on Tl and T2 relaxation times.
contrast agents shorten Tl and T2 relaxation times
identify the effect that Tl enhancement agents have on signal intensity.
increased signal intensity on Tl weighted images
identify the effect that T2 enhancement agents have on signal intensity.
decreased signal intensity on T2 weighted images
explain why Gadolinium contrast agents do not significantly affect T2 relaxation in the clinical setting.
Gadolinium is not in high enough concentration when given in clinical doses
explain how Gadolinium is made safe for injection into humans.
it is bound or chelated to an inert substance such as DTP
