Flashcards in Module 3 Deck (23)
On a T1 weighted would water be bright or dark ?
water would be dark on a T1 weighted image because the energy is not easily transferred
On a T1 weighted image would fat be bright or dark?
fat would be bright on a T1 weighted image because the energy is transferred easily to the lattice
What is the difference between intrinsic and extrinsic contrast parameters?
Intrinsic parameters cannot be changed because they are the properties of the tissues however extrinsic parameters can be manipulated by the MRI scanner
Name 3 types of intrinsic contrast parameters:
1. T1 recovery time
2. T2 decay time
3. Proton density
5. Apparent diffusion coefficient
Name 3 types of extrinsic contrast parameters :
3. Flip Angle
4. Inversion time
6. Turbo factor
Which of the following is false about the properties of T1 recovery in fat?
1. The structure of fat has low inherent energy so energy can be absorbed easily
2. Fat appears bright on a T1 weighted image
3. T1 time of fat in long
#3 is incorrect
What are the 3 main contributors to image contrast ?
1. T1 decay
True or false : proton density is the amount of protons in a volume. A higher proton density results in a lower signal.
False: a higher proton density results in a higher signal
Is the T2 decay of fat short or long?
Fat molecules are packed close so the decay is short.
Is the T2 decay of water short or long?
Water molecules are loosely packed so the T2 decay is long.
Does the NMV realign faster with B0 in fat or water?
The NMV realign faster with B0 in water which results in water having a shorter longitudinal component of magnetization and less signal on a T1 weighted image
Why does water appear bright on a T2 weighted image?
Water appears bright because it has a large magnitude of transverse magnetization because it decays slowly which results in a high signal on a T2 weighted image.
True or False : High proton density tissues = large transverse magnetization ----> High signal
True - proton dense tissues are bright on PD images
Why should TR be short for T1 images?
This reduces longitudinal recovery which allows for good contrast differences
Should TE be short or long for T2 weighted images?
TE must be long to allow tissues time to decay allow for optimal contrast
How do we minimize the T1 and T2 contrast for proton density weighting?
Long TR and short TE minimize T1 and T2
In a spin echo pulse why is a 180 degree pulse applied after the initial excitation pulse?
The 180 degree pulse is applied because it rephases the rapidly degrading signal.
What is TAU?
TAU is the time between the excitation pulse and the rephasing pulse.
A spin echo using one echo results in what type of contrast?
T1 - as long as there is a short TE and TR
A spin echo using two echos results in what types of contrast?
T2 or Proton density contrast
What controls the weighting in spin echo pulse sequences?
TR and TE
What controls the weighting in gradient echo pulse sequences ?
TR, TE and flip angle