Module 3

Question 1

On a T1 weighted would water be bright or dark ?

Answer 1

water would be dark on a T1 weighted image because the energy is not easily transferred

Question 2

On a T1 weighted image would fat be bright or dark?

Answer 2

fat would be bright on a T1 weighted image because the energy is transferred easily to the lattice

Question 3

What is the difference between intrinsic and extrinsic contrast parameters?

Answer 3

Intrinsic parameters cannot be changed because they are the properties of the tissues however extrinsic parameters can be manipulated by the MRI scanner

Question 4

Name 3 types of intrinsic contrast parameters:

Answer 4

1. T1 recovery time
2. T2 decay time
3. Proton density
4. Flow
5. Apparent diffusion coefficient

Question 5

Name 3 types of extrinsic contrast parameters :

Answer 5

1. TR
2. TE
3. Flip Angle
4. Inversion time
5. B-value
6. Turbo factor

Question 6

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

Answer 6

3 is incorrect

Question 7

What are the 3 main contributors to image contrast ?

Answer 7

1. T1 decay
2. T2 recovery
3. Proton density

Question 8

True or false : proton density is the amount of protons in a volume. A higher proton density results in a lower signal.

Answer 8

False: a higher proton density results in a higher signal

Question 9

Is the T2 decay of fat short or long?

Answer 9

Fat molecules are packed close so the decay is short.

Question 10

Is the T2 decay of water short or long?

Answer 10

Water molecules are loosely packed so the T2 decay is long.

Question 11

Does the NMV realign faster with B0 in fat or water?

Answer 11

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

Question 12

Why does water appear bright on a T2 weighted image?

Answer 12

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.

Question 13

True or False : High proton density tissues = large transverse magnetization —-> High signal

Answer 13

True - proton dense tissues are bright on PD images

Question 14

Why should TR be short for T1 images?

Answer 14

This reduces longitudinal recovery which allows for good contrast differences

Question 15

Should TE be short or long for T2 weighted images?

Answer 15

TE must be long to allow tissues time to decay allow for optimal contrast

Question 16

How do we minimize the T1 and T2 contrast for proton density weighting?

Answer 16

Long TR and short TE minimize T1 and T2

Question 17

In a spin echo pulse why is a 180 degree pulse applied after the initial excitation pulse?

Answer 17

The 180 degree pulse is applied because it rephases the rapidly degrading signal.

Question 18

What is TAU?

Answer 18

TAU is the time between the excitation pulse and the rephasing pulse.

Question 19

A spin echo using one echo results in what type of contrast?

Answer 19

T1 - as long as there is a short TE and TR

Question 20

A spin echo using two echos results in what types of contrast?

Answer 20

T2 or Proton density contrast

Question 21

What controls the weighting in spin echo pulse sequences?

Answer 21

TR and TE

Question 22

What controls the weighting in gradient echo pulse sequences ?

Answer 22

TR, TE and flip angle

Question 23

What is the difference in the flip angle to obtain a T1 vs. a T2/ PD weighted images?

Answer 23

small flip angle for T2 and PD

large flip angle for T1