Chapter 2: Image Weighting and Contrast Flashcards
Intrinsic contrast parameters are those that CANNOT be changed. What are some examples of these?
T1 recovery time
T2 decay time
Proton density
Flow
ADC
Extrinsic contrast parameters are those than CAN be changed. What are some examples of these?
TR
TE
Flip angle
TI
Echo train length
b value
Which one happens more quickly, T1 recovery or T2 decay? How much is the difference between them?
T2 decay occurs 5-10 times faster than T1 recovery
What type of relaxation is called spin-lattice energy transfer?
T1 recovery
What is caused by hydrogen nuclei giving up their energy to the surrounding environment or molecular lattice?
T1 recovery
What is the time it takes for 63% of the longitudinal magnetization to recover in a tissue?
T1 recovery time
What determines how much T1 recovery occurs in a tissue?
TR
What is caused by the magnetic fields of neighboring hydrogen nuclei interacting with each other?
T2 decay
What type of relaxation is termed spin-spin relaxation?
T2 decay
What is caused by one spin transferring energy to another spin rather than into the lattice?
Spin-spin relaxation (T2 decay)
What determines how much T2 decay occurs in a tissue when signal is collected?
TE
What term do we use for dephasing caused by inhomogeneities in the Bo field, which produces its own decay curve?
T2*
What type of signal does tissue have when it has a large transverse component of coherent magnetization at time TE?
High signal
_______ of a tissue is the number of mobile hydrogen protons per unit volume of that tissue.
Proton density (PD)
The hydrogen in ______ recovers more rapidly along the longitudinal axis than ______ and loses transverse magnetization faster.
Fat
Water
The NMV of fat realigns with Bo, so the T1 recovery time of fat is ______.
Short
The NMV of water realigns with Bo, and so the T1 recovery time of water is ______.
Long
T2 decay occurs because the magnetic fields of hydrogen nuclei interact with each other. The T2 decay time of fat is ______.
Short
T2 decay time of water is ______.
Long
Whenever the NMV is pushed beyond 90 degrees, it is said to be what?
Partially saturated
When the NMV is pushed to a full 180 degrees, it is said to be what?
Fully saturated
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?
Steady-state
What refers to differences in signal intensity between tissues that are a consequence of their relative number of mobile hydrogen protons per unit volume?
Proton density contrast
Tissues with a _____ proton density have a ______ transverse component of magnetization.
High; Large
Tissues with a ______ proton density have a large transverse component of magnetization.
High
Tissues with a ______ proton density have a small transverse component of magnetization.
Low
The signal intensity of a tissue depends on it’s intrinsic contrast properties. Three of these are…..
Proton Density
T1 recovery time
T2 decay time
A short TR combined with a short TE maximizes ______ contrast and minimizes _______ contrast.
T1; T2
Why are T2-weighted images used to image pathology?
Because pathology has a high water content and is therefore relatively hyperintense on T2-weighed images.
A long TR combined with a long TE minimizes _______ contrast and maximizes _____ contrast.
T1; T2
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.
PD-weighted
So that PD can dominate image contrast, what is your TR and TE (long/short)?
Long TR and short TE.
______ is a term used to describe the movement of molecules in the extracellular space due to random thermal motion.
Diffusion
The net displacement of molecules diffusing across an area of tissue per second is called?
Apparent Diffusion Coefficient (ADC)
______ denotes those whose contrast is determined by the ADC. This is achieved by using gradients.
DWI
Signal change depends on the ADC of the tissue and the strength, duration and interval of the gradients. This is collectively known as what?
b factor/value
Gradient-echo sequences, in conjunction with a long TE, are commonly used for what type of images?
Susceptibility weighting (SWI)
_____ is a technique that sensitizes a spin-echo sequence to to diffusion motion by using strong gradients.
DWI
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.
fMRI
T or F: Contrast agents are not imaged themselves but are seen because they indirectly affect the relaxation times of water nuclei.
True
Most contrast agents used in MRI are what type?
T1 agents
