Chapter 2: Image Weighting and Contrast

Question 1

Intrinsic contrast parameters are those that CANNOT be changed. What are some examples of these?

Answer 1

T1 recovery time
T2 decay time
Proton density
Flow
ADC

Question 2

Extrinsic contrast parameters are those than CAN be changed. What are some examples of these?

Answer 2

TR
TE
Flip angle
TI
Echo train length
b value

Question 3

Which one happens more quickly, T1 recovery or T2 decay? How much is the difference between them?

Answer 3

T2 decay occurs 5-10 times faster than T1 recovery

Question 4

What type of relaxation is called spin-lattice energy transfer?

Answer 4

T1 recovery

Question 5

What is caused by hydrogen nuclei giving up their energy to the surrounding environment or molecular lattice?

Answer 5

T1 recovery

Question 6

What is the time it takes for 63% of the longitudinal magnetization to recover in a tissue?

Answer 6

T1 recovery time

Question 7

What determines how much T1 recovery occurs in a tissue?

Answer 7

TR

Question 8

What is caused by the magnetic fields of neighboring hydrogen nuclei interacting with each other?

Answer 8

T2 decay

Question 9

What type of relaxation is termed spin-spin relaxation?

Answer 9

T2 decay

Question 10

What is caused by one spin transferring energy to another spin rather than into the lattice?

Answer 10

Spin-spin relaxation (T2 decay)

Question 11

What determines how much T2 decay occurs in a tissue when signal is collected?

Answer 11

TE

Question 12

What term do we use for dephasing caused by inhomogeneities in the Bo field, which produces its own decay curve?

Answer 12

T2*

Question 13

What type of signal does tissue have when it has a large transverse component of coherent magnetization at time TE?

Answer 13

High signal

Question 14

_______ of a tissue is the number of mobile hydrogen protons per unit volume of that tissue.

Answer 14

Proton density (PD)

Question 15

The hydrogen in ______ recovers more rapidly along the longitudinal axis than ______ and loses transverse magnetization faster.

Answer 15

Fat
Water

Question 16

The NMV of fat realigns with Bo, so the T1 recovery time of fat is ______.

Answer 16

Short

Question 17

The NMV of water realigns with Bo, and so the T1 recovery time of water is ______.

Answer 17

Long

Question 18

T2 decay occurs because the magnetic fields of hydrogen nuclei interact with each other. The T2 decay time of fat is ______.

Answer 18

Short

Question 19

T2 decay time of water is ______.

Answer 19

Long

Question 20

Whenever the NMV is pushed beyond 90 degrees, it is said to be what?

Answer 20

Partially saturated

Question 21

When the NMV is pushed to a full 180 degrees, it is said to be what?

Answer 21

Fully saturated

Question 22

The first few RF pulses result in different amounts of transverse magnetization. This is because they have recovered different amounts of longitudinal magnetization before the next RF was applied. Once the vectors recover to the same point and achieve the same amount of longitudinal magnetization and flipped to the same point to create the same amount of transverse magnetization, this is called what?

Answer 22

Steady-state

Question 23

What refers to differences in signal intensity between tissues that are a consequence of their relative number of mobile hydrogen protons per unit volume?

Answer 23

Proton density contrast

Question 24

Tissues with a _____ proton density have a ______ transverse component of magnetization.

Answer 24

High; Large

Question 25

Tissues with a ______ proton density have a large transverse component of magnetization.

Answer 25

High

Question 26

Tissues with a ______ proton density have a small transverse component of magnetization.

Answer 26

Low

Question 27

The signal intensity of a tissue depends on it’s intrinsic contrast properties. Three of these are…..

Answer 27

Proton Density
T1 recovery time
T2 decay time

Question 28

A short TR combined with a short TE maximizes ______ contrast and minimizes _______ contrast.

Answer 28

T1; T2

Question 29

Why are T2-weighted images used to image pathology?

Answer 29

Because pathology has a high water content and is therefore relatively hyperintense on T2-weighed images.

Question 30

A long TR combined with a long TE minimizes _______ contrast and maximizes _____ contrast.

Answer 30

T1; T2

Question 31

A _______ image is one where differences in the number of mobile hydrogen nuclei per unit volume of tissue are the main determining factor in forming image contrast.

Answer 31

PD-weighted

Question 32

So that PD can dominate image contrast, what is your TR and TE (long/short)?

Answer 32

Long TR and short TE.

Question 33

______ is a term used to describe the movement of molecules in the extracellular space due to random thermal motion.

Answer 33

Diffusion

Question 34

The net displacement of molecules diffusing across an area of tissue per second is called?

Answer 34

Apparent Diffusion Coefficient (ADC)

Question 35

______ denotes those whose contrast is determined by the ADC. This is achieved by using gradients.

Answer 35

DWI

Question 36

Signal change depends on the ADC of the tissue and the strength, duration and interval of the gradients. This is collectively known as what?

Answer 36

b factor/value

Question 37

Gradient-echo sequences, in conjunction with a long TE, are commonly used for what type of images?

Answer 37

Susceptibility weighting (SWI)

Question 38

_____ is a technique that sensitizes a spin-echo sequence to to diffusion motion by using strong gradients.

Answer 38

DWI

Question 39

What type of imaging relies on a process called BOLD to produce a signal in areas of the brain where there is increased activity after performing a function.

Answer 39

fMRI

Question 40

T or F: Contrast agents are not imaged themselves but are seen because they indirectly affect the relaxation times of water nuclei.

Answer 40

True

Question 41

Most contrast agents used in MRI are what type?

Answer 41

T1 agents