CHAPTER 2 Flashcards
Recovery of longitudinal magnetization is called?
T1 Recovery
Decay of coherent transverse magnetization is called?
T2 Decay
Primary relaxation process?
T1 Recovery
Is T1 recovery slower or faster than T2 decay?
Slower
Spin-lattice recovery?
T1 Recovery
Time it takes for 63% of the longitudinal magnetization to recover in a tissue
T1 Recovery time
What kind of recovery happens during TR
T1 Recovery
Caused by the magnetic fields of the neighboring hydrogen nuclei interacting with each other
T2 Decay
Spin-spin relaxation process?
T2 Decay
Secondary relaxation process?
T2 Decay
Caused by inhomogeneties in B0
T2 Decay
Time it takes for 63% of the transverse magnetization to dephase
T2 Decay time
Type of relaxation that results in 37% of inphase left in a tissue
T2 Decay time
What determines how much decay happens?
TE
Made up of large molecules that are closely packed together and tumbling is slow
fat
Made of up molecules that are spaced apart and tumbling rate is fast
water
T1 Recovery in fat
short
T1 recovery in water
fast
T2 decay in fat
short
T2 decay in water
fast
T1 contrast is controlled by
TR
TR must be short or long in T1 contrast so vectors don’t fully recover
short
In T1 contrast, fat is… high/low signal & hyper/hypo intense on image?
High signal, hyperintense
In T1 contrast, water is… high/low signal & hyper/hypo intense on image?
low signal, hypointense
T1 contrast = short/long TR and short/long TE?
short TR, short TE
T1 contrast makes what kind of scans?
Anatomy scans & pathology with contrast
T2 contrast is controlled by what
TE
What must be long to allow protons to have time to dephase to create more differences in contrast
TE - T2 contrast
In T2 contrast, fat is… high/low signal & hyper/hypo intense on image?
low signal, hypointense
In T2 contrast, water is… high/low signal & hyper/hypo intense on image?
high signal, hyperintense
What controls amount of T2 contrast?
TE
T2 contrast = short/long TR, short/long TE
long TR, long TE
What kind of scans are T2 contrast scans?
Pathology
NMV pushed beyond 90deg is?
Partially saturated
NMV pushed to a fully 180deg is?
Fully saturated
What is differences in mobile hydrogen nuclei per unit volume of tissue?
Proton density
What component reflects the differences in proton density contrast?
Transverse
Tissues with high proton density have low/high signal and hypo/hyperintense?
High signal, hyperintense
What tissues have high proton density in PD scans?
CSF, infection, inflammation, fat
Tissues with low proton density have low/high signal and hypo/hyperintense?
Low signal, hypointense
What tissues have low proton density in PD scans?
Air, tendons, bone
What must be suppressed to see PD contrast?
T1 and T2 contrast
What type of scans does PD show?
Anatomy and Pathology
PD contrast = short/long TR, short/long TE
long TR, short TE
long TR allows vectors to fully recover minimizing T1 and short TE doesn’t give vectors enough time to dephase diminishing T2
What’s the movement of molecules in the extracellular space due to random thermal motion?
diffusion
The net displacement of molecules diffusing across an area of tissues per second
ADC - apparent diffusion coefficent
Areas of restricted diffusion because the extracellular space is small (ligaments & pathology) the ADC is low/high?
Low
Areas of free diffusion extracellular space is large (normal grey matter & normal liver tissue) the ADC is low/high?
High
Diffusion weighted images (DWI) are made using what?
Bipolar gradients (dephases and then rephases)
Normal tissues have a low/high ADC?
high
Low ADC = low/high signal
high signal = pathology
Controls how much a tissue’s intrinsic contrast parameter contributes towards image weighting
B value
Higher b values = less/more diffusion weighting
more
What type of sequence is used for DWI?
Spin-echo
ADC is intrinsic/extrinsic and b value is intrinsic/extrinsic?
intrinsic & extrinsic
Acquires images of brain during activity and at rest
function MRI, fMRI
fMRI contrast depends on what type of technique?
BOLD, Blood oxygenation level dependent
What exploits the differences of magnetic susceptibility of oxyhemoglobin and deoxyhemoglobin?
BOLD
In fMRI, rest images are subtracted from activity images (NO answer)
In fMRI, there is a long TR/TE while task is off and on?
TE
What uses the fast exchange of energy between bound and free nuclei?
MTC - Magnetization transfer contrast
In MTC, free nuclei are observable b/c they have longer what times?
T2 decay
In MTC, bound nuclei are restricted b/c they have a very short what time?
T2 decay
What uses the magnetic susceptibility differences between tissues to generate contrast?
Susceptibility weighting - SWI
What type of sequences are used to enhance the differences in magnetic susceptibility between tissues?
Gradient echo with a long TE
What is used to selectively change the relaxation times of certain tissues?
Contrast agents
Agents are not imaged themselves but are seen because they indirectly affect the relaxation times of what?
Water nuclei
T1 contrast agents = shorten/long T1 recovery times
shorten
T2 contrast agents = shorten/long T2 decay times
shorten
Degree of contrast shortening due to contrast agents depends on what of the agent?
concentration
What is a rare-earth metal and is toxic? Binding or chelation with other molecules such as DTPA makes it safe?
Gadolinium
Gadolinium is what and has a large magnetic moment?
Paramagnetic
T2 contrast agents are made up of what?
Superparamagnetic macromolecules of iron
