Chapter 12 MR Image Contrast Weighting Flashcards
A MR images contrast weighting is determined by several factors:
intrinsic and extrinsic
what are intrinsic parameters that affect contrast weighting?
-T1 relaxation time
-T2 relaxation time
-Proton (Spin) Density
-Diffusion
-Perfusion & Flow
what are extrinsic parameters that affect contrast weighting?
-the particular pulse sequence
-contrast parameters such as TR, TE, TI and flip angle
water has ____ T1, T2, T2* relaxation times
LONG
fat has ____ T1, T2, T2* relaxation times
short
Most pathology will result in an increase in ______in the area of disease or injury
water
The TR (time of repetition) is the time
between the initial excitation pulses in sequence.
Based on the T1 relaxation time of a tissue the TR will
determine how much longitudinal magnetization recovers between repetitions of the sequence
TR controls the:
amount of T1 weighting in an image
the lower the TR, the _____T1 weighting
MORE
the higher the TR, the ____T1 weighting
LOWER
since fat has a short T1 relaxation time, tissues containing a significant amount of fat are _______on T1 weighted images
brighter
tissues containing a significant amount of fluid are _______on T1 weighted images
darker
CSF is pure water so it has the longest T1 relaxation time between it and white matter & gray matter
so it is dark on T1 images
white matter contains nerve fibers which are wrapped in myelin, a protective coating that is mostly fat.
it has the shortest T1 relaxation time because it contains the most fat and will be brighter
gray matter contains nerve cell bodies which are surrounded in extra cellular fluid so it
has a longer T1 relaxation time than white matter but still shorter than CSF
TE (Time to Echo)
the time period between excitation and the center of the echo
TE determines
how much transverse magnetization has decayed at the time of sampling based on the T2 relaxation time of the tissue
TE controls the amount of
T2 weighting in the image
the_____the TE, the _____the T2 weighting
shorter;less
For a gradient echo sequence, TE controls
the amount of T2* weighting in the image
If a T1 weighted image is desired, a ____ TR will be selected
Short. The TE will also be short. The short TE does not make it T1 weighted it makes it less T2 weighted.
If a T2 weighted image is desired, a ____ TR will be selected
LONG; the long TR does not make it T2 weighted, it makes it less T1 weighted.
For T2 weighting, a long TE will be selected
For a PD weighted image, a ___TR is selected to the contrast less T1 weighted and a ____TE is selected to make it less T2 weighted.
LONG TR;SHORT TE
For T1 weighting:
A short TR would likely be between ______.
a short TE would be short if it were ______.
400-700msec; 25 msec or less
For T2 weighting:
a long TR would likely be______
a long TE would be ________.
3000msec or higher
80-120msec
For Proton Density:
a long TR would likely be______
a short TE would be short if it were ______.
3000 msec or higher
25 msec or less
