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331 - imaging production > chap 2 > Flashcards

chap 2 Flashcards

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1
Q

low signal on ADC, high signal on extracellular space is small

A

restricted diffusion

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2
Q

high ADC, extracellular space is large

A

normal diffusion

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3
Q

T/F: the T1 relaxation times, although inherent to that tissue, are dependent on the field strength of the magnet

A

true

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4
Q

typical value for a T1 sequence

A

TR < 800

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5
Q

typical value for a T2 sequence

A

TR > 2000

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6
Q

how well it can be imaged or determined positive

A

sensitivity

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7
Q

how well it can distinguish those areas with disease from those without

A

specificity

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8
Q

effect of substances on relaxation rate

A

relaxivity

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9
Q

naturally toxic, chelated for excretion, has 7 unpaired electrons

A

gadolinium

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10
Q

the RF excitation is turned off, H return to the low-energy state. Magnetic moments dephase

A

relaxation

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11
Q

movement of molecules in extracellular space due to random thermal motion

A

diffusion

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12
Q

images where contrast is determined by the ADC

A

DWI

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13
Q

controls how much ADC influences contrast. Function of the amplitude, duration and interval of the gradients in ADC

A

b-value

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14
Q

uses the magnetic susceptibility b/t tissues to generate image contrast

A

susceptibility weighting (SWI)

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15
Q

net displacement of molecules diffusing across an area of tissue per second

A

apparent diffusion coefficient (ADC)

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16
Q

images function/physiology. Relies on BOLD to produce a signal in areas of the brain where there is increased activity

A

fMRI

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17
Q

effect of a substance on the relaxation rate

A

relaxivity

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18
Q

inherent to the body’s tissues. Cannot be changed. T1 recovery time, T2 decay time, PD, flow, ADC

A

intrinsic

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19
Q

Factors set by the technologist, can be changed (TR,TE, flip angle, TI, ETL, b-value)

A

extrinsic

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20
Q

how would a lesion look on a T1 after gadolinium injection

A

create bright lesions

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21
Q

how would a lesion look on a T2 after a gadolinium injection

A

create dark lesions

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22
Q

what series is usually performed after contrast injection

A

T1

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23
Q

lowering your flip angle also lowers your

A

SNR

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24
Q

short TR , short TE , large FA

A

T1

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25
long TR, long TE, small FA
T2
26
long TR, short TE, small FA
PD
27
relatively large flip angles (90+) produce
T1 contrast
28
relatively low flip angle values (45-90) produce
PD & T2 contrast
29
slow molecular tumbling rate. Closely packed molecules. Short T1 & short T2
fat
30
fast molecular tumbling rate. Molecules are spaced apart. Long T1 & T2
water
31
number of mobile hydrogen protons per unit volume of tissue determines contrast. Basic MRI contrast
proton density
32
controls the amount of T1 weighting
TR
33
controls the amount of T2 weighting
TE
34
for a T1 weighted image, the TR must be
short
35
for a T2 weighted image, the TE must be
long
36
caused by nuclei giving up energy to surrounding environment or lattice. Recovery of 63% longitudinal magnetization. Aka: spin lattice
T1 recovery
37
magnetic fields of neighboring nuclei interacting with each other. Results of 63% loss (37% remains) of transverse magnetization. Aka spin spin
T2 decay
38
the decay of the FID following the RF excitation pulse based on inhomogeneities
T2*
39
describe T1 recovery
- spin lattice relaxation - caused by the nuclei giving up their energy to the surrounding environment or lattice
40
what is the T2 relaxation time of tissue?
the time is takes 63% of the transverse magnetization to decay in the tissue
41
what factors do T1 & T2 relaxation depend on?
- inherent energy of the tissue - how closely packed the molecules are
42
a hyperintense area on your post contrast imaging, where your pre contrast image showed no enhancement, would most likely represent what
pathology
43
bright fat, dark water
T1
44
bright water, dark fat
T2
45
high proton density is bright, low proton density is dark. Basic MRI contrast
PD
46
gray on the image
intermediate signal
47
hypointense, black on the image. Small or no transverse component at TE
low signal
48
hyperintense, white on the image. Large transverse component of coherent magnetization at TE
high signal
49
images obtain contrast mainly through the mechanisms of
T1 recovery T2 decay Proton or spin density
50
T2 contrast depends predominantly on
T2 times between fat & water
51
why is T2 weighting long?
give fat and water time to decay
52
what would happen if the T2 weighting was too short?
no difference in the tissues demonstrated
53
used for anatomy and pathology post contrast
T1
54
used for pathology
T2
55
T/F: the TE would be shorter to take advantage of T2*
true
56
gadolinium raw element is
ferromagnetic
57
gadolinium chelate contrast media is
paramagnetic
58
T1 contrast depends predominantly on
the differences in the T1 times between fat & water
59
why is the T1 weighting short
neither fat nor water have sufficient time to return to B0
60
T2 graph
starts high ends low
61
T1 graph
starts low ends high
62
what are inhomogeneities
areas that do not match the external field strength

331 - imaging production (8 decks)

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