Chapter 2 - Image weighting and contrast Flashcards
Intrinsic contrast parameters are those that ____ be changed because they are inherent to the body tissue
can or cannot
cannot be changed.
Extrinsic contrast parameters are those that ____ be changed because they are under our control.
can or cannot
Can be changed.
Whats an example of intrinsic contrast parameters. Xray for example
a parameter that cant be changed is the tissue density of the structure that the xray beam passes thru. It’ll attenuate which is out of our control.
T1 recovery, T2 decay, PD, flow and ADC are all examples of ___ contrast parameters.
intrinsic
TR, TE, flip angle, and T1 , turbo, and B value are examples of ____ contrast parameters
extrinsic since we have control over those
During relaxation, hydrogen nuclei ___ absorbed RF energy.
give up or take?
give up
T2 decay occurs 5-10 faster than T1 recovery does.
True
What is T1 recovery caused by?
hydrogen nuclei giving up their energy to the surrounding environment.
T1 it is the primary relaxation process.
True
Longitudinal magnetization is related exponentially to recovery time.
True or False
true
What is the average t1 recovery time in water?
2500
What is the average t1 recovery time of fat?
200
What is the average t1 recovery time of CSF?
2000
What is the average t1 recovery time of white matter>
500
the term decay refers to the ____ of coherent transverse magnetization
loss or gain
loss
T2 decay is also called what?
spin-spin relaxation
transverse magnetization is related exponentially to decay time.
True
t2 decay time is the time it takes for 63% of the transverse magnetization to dephase
true
What is the average t2 decay time of water?
2500
What is the average t2 decay time of fat?
100
What is the average t2 decay time of CSF?
300
What is the average t2 decay time of white matter?
100
What is the difference in T2 and T2* ?
not sure
What is spin lattice energy transfer ?
a type of relaxation process where spins give up the energy absorbed thru RF exciation to the surrounding molecular lattice of the tissue.
Relaxation basicalled means the loss of energy,
True or False
true
What is the proton density of a tissue?
means the number of mobile hydrogen protons per unit volume of the tissue.
THe higher the PD of a tissue, the more signal available
True or false?
true
Once the b1 Field is removed, the hydrogen nuclei are then only under what influence?
the B0
When the RF exciation pulse is switched off the hydrogen nuclei return to their ___-energy state and their magnetic moments _____
High Low
Dephase/Inphase
they return to theier LOW energy state and their magnetic moments DEPHASE.
T2 Decay occurs 5-10 times faster than T1 recovery
True or False
true
What is spin-lattice energy transfer and does it occur more in t1 or t2/
energy released by spins to surrounding molecular lattice (structure), which then causes magnetic moments of hydrogen nuclei to recovery their longitudinal magnetization
How long is the “t1 recovery time?”
the time it takes for 63% of the longitudinal magnetization to recover in a tissue which depends on the tissue.
What is TR and how does it affect T1 Recovery?
TR is the time between one RF pulse to the next. It determines how much T1 occurs.
MzT and Mz is part of which recovery curve equation?
t1 or t2?
T1 Recovery
What is the spin-spin relaxation caused by?
Caused by one spin transfering energy into another spin rather than into the lattice like the “spin-lattice” in t1
How long is the T2 decay time?
the time it takes for 63% of the transverse magnetization to dephase
Mxyt and and Mxy are related to which equation ?
t1 or t2
t2 decay
The T2 decay time is the time between an RF excitation pulse and when the signal is collected in the receiver coil.
True or False
True
How is T2* different than T2 decay?
T2* is dephasing caused by inhomogenities in the B0 field. This produces its own decay curve.
This happens when the RF pulse switches off and the nuclei dephase very quick (10MS)
If something is HYPERintense, this will show up ___ on the image
Bright or Dark/Black
Bright
If something is HYPOintense, it will show up as ___ on image.
Bright or dark/black
Dark/black
Fat molecules ontain atoms of hydrogen arranged with ____- and Oxygen.
carbon and oxygen
Fat molecules have large molecules called lipids that are closely packed together.
True or False
true
Why does water have a faster tumbling rate than fat?
because fat has these lipids that are closely packed togehter and water’s molecules are spaced further apart.
T1 Recovery time in Fat is short.
True or False
True
T1 Recovery time in water is short.
True or false
FALSE
Recovery time in water in LONG.
T2 Decay in fat is short. Why is that?
Because T2 decay has todo with the interaction of hydrogen nuclei. Since fat molecules are packed closed together they are more likely to interact.
T2 Decay in Water is long. Why is that ?
because spin to spin interations are less likely to our due to the water molecules being spaced further apart than it is in fat.
T1 contrasts occurs when the vectors do not fully recover from their longitduinal magnetization between each RF excitation.
True or false
True .
If the TR is SHORT, then what happens to the T1 contrast?
the contrast increases since it has to do with the time in-between pulses.
When the net magnetization vector (NMV) is pushed beyond 90 degrees, its called _____ saturated.
partially
When the net magnetization vector (NMV) is pushed to a full 180 degrees, its called _____ saturated.
FULLY saturated.
What is proton density contrast?
differences in signal intensity between tissues depending on their relative number of mobile hydrogen protons per unit
A HIGH proton density tissue has a LARGE transverse component of magnetization therefore producing a ____ signal.
High or Low
high signal aka they are bright.
A low proton density tissue has a SMALL transverse component of magnetization therefore producing a ____ signal.
High or Low
Low/ Dark/Black signal.
We want the TR to be SHORT in T1-Weighted images. Why is that?
This is because we want the TR short enough so that neither the vector in fat nor the water has sufficient time to fully return to B0.
If its too long, both will recovery and therefore we couldn’t demostrate any contrast? Page 42
T1 Weighted images are best used to show anatomy.
True or false
True
For T1 Weighted images, the TR must be ____ and the TE must
be _____.
Short/Long
Short/Long
Short and short
Name a few types of tissues or pathology that have a high signal with T1?
(aka show up bright)
hemangioma fat Lipoma (fat tumor) Degeneration Fatty deposits Slow moving blood
Name a few types of tissues or pathology that have a low signal with T1?
(aka show up Dark)
BONE Avascular necrosis Tumors cysts calcifications infection or infarction.
For T2s we want the TE to be long. Why is that?
We need it long enough to give the vectors in both fat and water time to dephase.
If its too short, neither fat or water has time to dephase.
For T2 weighting, the TE must be ___ and the TR must be _____.
Long or short
long or short
long TE Long TR
Name a few things that would have a high signal in a T2 image.
Water Fluid Hemangioma infection or inflammation edema cysts
Name a few things that would have a low signal in a T2 image.
Bone
calcifications
a LONG TR combined with a LONG TE will
____ T1 contrast and ___ T2 contrast
Minimize/maximize.
LONG TE and TR will minimize T1 and maximize T2.
To achieve proton density (PD) weighting, we need to diminish the effects of T1 and T2, so that PD can dominate.
True oR false
True
Using a ____ TR and a ____ TE, we can make a PD image.
Using a LONG TR and a SHORT TE.
This therefore cancels out the T1 and T2- letting the PD be dominate.
Name a few things that would have a high signal in a PD image.
CSF Fluid Infection Edema Cysts and Fat
Name a few things that would have a low signal in a PD image
Air tendons bone scar tissue calcification
If you’re looking at an image and the water is bright, this is likely a ____ image.
t1 t2?
T2 using a long TE
If you’re looking at an image and the water is dark, this is likely a ____ Image?
T1 or T2
T1- using a short TR.
What is the difference in T1 CONTRAST and T1 Weighting??
T1 contrast is an image where fat is bright and water is dark because the TR is short enough not to have a full recovery
T1 Weighting is an image where the contrast is mostly because of the differenes in t1 Recovery times of the TISSUE.
What does diffusion mean?
the movement of molecules in the extracellular space due to random thermal motions
What does ADC stand for in regards to a DWI (diffusion) image?
It is called an apparent diffusion coefficient. page 54 come back to DWI
SWI uses the magnetic susceptibilty differences between tissues to generate contrast.
True or false?
True
SWI consists of a ____ TE and a gradient echo sequence
long or short
Long
Why is T2 images better at seeing pathology?
because most pathology has a high water nuclei content.
Gadolinium in its natural form is HIGHLY TOXIC. How is it made safe enough to put in bodies?
we make it sife by binding or (chelating) the gad to other molecules such as DTPA.
