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530: Data Acquisition > Chapter 8 > Flashcards

Chapter 8 Flashcards

1
Q

a series of vascular imaging techniques in MR are available to non-invasively evaluate both the __ (__) and the __ (__) of the vascular system. such techniques include __ (acquired with imaging options to enable vascular visualization) and __ (acquired to visualize __)

A

morphology (anatomy); hemodynamics (flow); convention MRI; MRA (magnetic resonance angiography); moving blood

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2
Q

most MRI and MRA techniques rely on the __ (rather than __) to demonstrate vasculature on MR images

A

motion of blood within the vessel; the anatomy of the vessel itself

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3
Q

__ (3) sequences (acquired with combinations of __ RF pulses) typically render images in which the signal from blood has been __, known as __

A

SE, FSE, and IR; 90 and 180 degree; largely eradicated; black blood imaging

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4
Q

__ sequences render blood __, in a technique known as __

A

GE; bright; bright blood imaging

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5
Q

GE sequences can be supplemented with options such as __ (__) to reduce __, and __ (__) to reduce __

A

gradient moment nulling (GMN); phase mis-mapping from high-signal inflowing blood; spatial pre-saturation (SAT); signal from inflowing blood

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6
Q

to detect signal on MR images acquired with SE, nuclei must receive a __. the most efficient combination includes a __ followed by a __

A

combination of (at least) 2 RF pulses; 90 degree excitation pulse; 180 degree refocusing pulse

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7
Q

in SE sequences, the 90 and 180 RF pulses are __ pulses, so that only the tissues within the __ receives and is affected by both pulses. __, however, may only receive one of these pulses but this depends on the __ (3)

A

slice selective; selected slice; flowing nuclei; slice thickness, velocity of flow, and TE

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8
Q

in fast IR, flowing blood can appear even __ by the application of __. a technique known as __ applies a __ pulse followed by a __ pulse that immediately restores __

A

darker; multiple inversion pulses; double IR prep; non-slice-selective 180; slice selective 180; longitudinal magnetization within the slice

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9
Q

in fast IR: a TI equal to the null point of __ enables saturation of this flow by the __

A

flowing spins in blood entering the slice; 90 excitation pulse

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10
Q

in fast IR: an additional, __ pulse may also be applied during the TI to null the signal specifically from __. this 3rd 180 pulse must be timed so that the __. in this way, both __ and __ are saturated. this is called __

A

slice-selective 180; fat within the slice; null points of fat and flowing spins coincide; blood; fat; triple IR prep

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11
Q

spatial pre-saturation (also known as __ or __ can be used to evaluate __ throughout the vascular system

A

SAT pulses; SAT bands; vascular patency

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12
Q

since SAT uses additional __, the __ is increased, and the __ may be reduced

A

RF pulses; SAR; number of slices (typically available for a given TR)

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13
Q

pre-saturation pulses applied __ flip the magnetization of the flowing spins __. flowing spins then flow into the slice and __. the magnetization of flowing spins is therefore __

A

outside the slice/FOV/imaging volume; 90 degrees into the transverse plane; receive an additional 90 RF pulse; flipped an additional 90 degrees

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14
Q

SAT: spins flowing into the slice/imaging volume are __ because they have received __

A

saturated; both the 90 degree saturation pulse and the 90 degree excitation pulse (total 180)

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15
Q

in GE sequences, flowing blood appears __, enabling visualization of __ relative to __. to detect signal acquired with GE acquisitions, nuclei must receive __ followed by __

A

bright; the vessel; surrounding tissues; at least 1 RF excitation pulse; gradient rephasing

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16
Q

GE/bright blood imaging: the excitation pulse can be a __ or a __ (depending on the desired __). the RF excitation pulse is __ but the rephasing gradient is __. thus, flowing spins are refocused irrespective of __ and __

A

90 RF pulse; different flip angle; image contrast; slice selective; applied to the entire imaging volume; their position within the imaging volume; return a high signal

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17
Q

imagine blood flowing with the carotid artery. if a __ slice is acquired, all spins within the slice receive the __. the spins with flowing blood in the artery are moving __ through the axial slice and will also receive __

A

axial brain; 90 excitation pulse; perpendicularly; this excitation pulse

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18
Q

bright blood/GE: a gradient rephasing pulse is applied to __, this will cause all the flowing spins to produce signal, provided they __

A

the entire imaging volume; have been excited at some point in time

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19
Q

bright blood/GE: example: a spin may have been located in slice 1 when the __ was applied, but will still emit signal if __ as it passes through slice 10. as a result, this technique is called __

A

excitation pulse; rephased by the gradient; bright blood imaging

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20
Q

gradient echo imaging can be further improved by the application of an imaging option known as __ or __, in which __ spins are rephased along with __ spins, reducing __

A

gradient moment nulling (GMN) or gradient moment rephasing (GMR); moving; stationary; intra-voxel dephasing

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21
Q

magnetic resonance angiography (MRA) uses variations of __ acquisitions to yield high signal __. vascular contrast is maximized by enhancing the signal from __ and/or suppressing the signal from __

A

GE; within flowing vessels; moving spins in flowing blood; stationary spins residing in tissue

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22
Q

when stationary spins are suppressed, the appearance of __ is enhanced by the increased signal from __, which flow into the imaging volume and __

A

vasculature; unsaturated spins; receive RF excitation for the first time

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23
Q

2 approaches to suppress stationary spins:

A

digital subtraction MRA or DS-MRA; time-of-flight MRA or TOF-MRA

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24
Q

DS-MRA: two acquisitions are performed that treat __, but which differentiate __ and then subtract them

A

stationary spins identically; moving spins

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25
Q

TOF-MRA: if a __ that saturates spins within the imaging volume is used in combination with the __, a high degree of __ can be achieved

A

short TR; entry slice phenomenon; vascular contrast

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26
Q

in MRA it is not the __, but rather the __ that is visualized

A

vessel itself; flow within the vessel

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27
Q

DS-MRA, also known as __, allows visualization of the vasculature over a __ than can normally be achieved by other __ methods

A

fresh-blood imaging; wider FOV; flow-dependent

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28
Q

DS-MRA/fresh-blood imaging involves the acquisition of two __ data sets, one during __ flow, the other during __

A

T2-weighted; diastolic; systole

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29
Q

DS-MRA: the diastolic images display high signal from __, as the flow is __ at this point of the cardiac cycle

A

both arteries and veins; momentarily slow

30
Q

DS-MRA: the systolic images exhibit signal loss in __ due to __

A

the arteries; intra-luminal dephasing

31
Q

DS-MRA: by digitally subtracting the two data sets, it is therefore possible to __ the signal from either __ or __ whilst simultaneously subtracting out __

A

isolate; arteries; veins; any background signal

32
Q

DS-MRA offers some of the benefits associated with __, particularly the ability to achieve a __, but without the risks associated with __

A

contrast-enhanced MRA; large FOV; Gd-based contrast injection in those patients having a particular sensitivity to these agents

33
Q

the vascular signal produced in TOF-MRA relies on __ (__). this means that the vascular enhancement in TOF-MRA is related to __

A

flow-related enhancement (FRE); the flow of blood

34
Q

TOF-MRA provides information about blood flow that is __ and vascular contrast by manipulating the __

A

perpendicular to the slice plane; longitudinal magnetization of the stationary spins

35
Q

TOF-MRA: a __ pulse sequence is used in combination with __ to enhance __

A

incoherent GE; gradient moment rephasing; flow

36
Q

TOF-MRA: the __ and __ are selected so that stationary spins are __, while the __ effect from inflowing, __ spins produces __ vascular signal, such that flowing spins within __ appear bright

A

flip angle; TR; saturated; TOF; fully-magnetized fresh; high; patent vessels

37
Q

TOF-MRA: when __ and __ are selected to __ and when blood flows __, or within __ vessels, the nuclei stay within the volume long enough to become __ along with the __. the result of these phenomena is a reduction in __

A

TRs; flip angles; saturate stationary tissues; slowly; curved; suppressed; stationary tissues; vascular signal

38
Q

3D TOF-MRA acquisitions are optimal for high-__, high-__ scans for the evaluation of __ vessels with __ blood flow (e.g. __ vessels associated with the __)

A

resolution; SNR; smaller; high velocity; intracranial; Circle of Willis

39
Q

2D TOF-MRA acquisitions are capable of demonstrating __ flow and provide a __ area of coverage, which makes it best for imaging the __ (3)

A

slow; wider; carotid arteries; peripheral vascular and venous systems

40
Q

the manner in which the data from MRA images are __ plays a part in determining the way in which __ is perceived in the images

A

reformatted; vascular anatomy

41
Q

maximum intensity projection (MIP) is a technique for __ image formation where a reformatted image appears to be __

A

MRA; projected onto a 2D surface

42
Q

MIP: there is no __, and so the observer may find it difficult to appreciate __

A

depth cueing; which vessels are in the foreground and which vessels lie behind

43
Q

MRA: shaded surface display (SSD) improves __ perception of the data by creating __

A

3D; a boundary between high- and low-signal areas

44
Q

SSD: the boundary between high- and low-signal areas is treated as a __ which is presented to the observer as though __

A

surface; illuminated by a directional light source

45
Q

SSD: the benefit of the boundary is that structures appear to be __ and vessels closer to the observer’s point of view appear to __

A

solid; lie in front of the structures behind them

46
Q

in orthographic projections, the data used to reconstruct a 3D object are __. the resulting lack of __ tends to obscure any sense of __, but this can be partially offset by __

A

in parallel rows and columns; perspective; depth; reconstructing the data from different angles

47
Q

MIP simply assigns a numerical value to each pixel in terms of its __ and then projects the __ from each row/column within every slice onto a __

A

greyscale; maximum intensity; 2D plane

48
Q

MIP: allows data to be viewed as though __, and in the case of __ this tends to be a __ angles to the acquisition plane, because inflow studies require the slice to be __

A

from different angles; inflow angiography; right; perpendicular to the vessel

49
Q

MIP: __ affects the __ of the reformatted image, and this is the principal reason for the frequent use of __, rather than __ techniques

A

slice thickness; spatial resolution; 3D; 2D inflow

50
Q

MIP: by reformatting each image with __, the resulting images can be run as a __. this allows for a __ visualization of the data

A

an incremental change in angle; cine loop; pseudo-3D

51
Q

the vascular signal produced in phase contrast MRA (PC-MRA) relies on __. this means that the vascular enhancement seen in PC-MRA is related to __

A

velocity-induced phase shifts; the change in phase of flowing blood

52
Q

phase shift is related to __ (3). this means that PC-MRA (which relies on phase shifts) provides information about __ (4)

A

blood flow velocity, flow direction, and type of scan acquired; vascular anatomy, flow velocity, multi-directional blood flow, and flow direction

53
Q

PC-MRA uses a __ pulse sequence with __ flip angles and additional __ pulses to create changes in the __ within __

A

GE; small; gradient; phases of the nuclei; flowing blood

54
Q

the gradient pulses in PC-MRA are __ gradient pulses, which involve __

A

bipolar; two lobes that are equal in strength (one negative gradient pulse and one positive gradient pulse)

55
Q

PC-MRA: although bipolar gradient pulses are applied to __ tissues within the volume, application of these pulses allows for the distinction between __ within __

A

all of the; stationary tissues and spins; flowing blood

56
Q

PC-MRA: a gradient echo sequence is used, having a __ flip angle to prevent __, and an additional bipolar gradient known as a __

A

small; saturation; velocity-encoding gradient (VENC)

57
Q

PC-MRA: the strength and duration of the VENC is selected based on the __. VENC velocity settings should be selected to produce signal from __

A

blood flow velocity that is to be imaged; blood flowing at that velocity

58
Q

PC-MRA: VENC settings determine the __ and/or __ of the bipolar gradient pulses. when __ blood flow is to be imaged (flow has __ velocity) a __ VENC is required

A

amplitude; duration; arterial; high; high

59
Q

PC-MRA: if the VENC selected is __ than the velocity of blood flow within the vessel, __ can occur

A

lower; aliasing

60
Q

PC-MRA: lower-than-necessary VENC results in low signal intensity in the __, but better delineation of the __

A

center of the vessel; vessel wall itself

61
Q

PC-MRA: aliasing occurs because in __ flow, the __ of blood results in __, or __, against the __

A

laminar; viscosity; drag; friction; vessel wall

62
Q

PC-MRA: low VENC aliasing: the highest velocity of flow is found in the __, and the signal is aliased or __ out of the __.

A

center of the vessel; mis-mapped; vessel lumen

63
Q

PC-MRA: low VENC aliasing: even though there is signal void within the __, there is better delineation of the __

A

vessel lumen; vessel wall above background noise levels

64
Q

PC-MRA: with high VENC settings, __ signal is improved but __ is compromised

A

intraluminal; vessel wall delineation

65
Q

PC-MRA: __ is obtained along the direction of the applied bipolar gradient

A

sensitization to flow

66
Q

PC-MRA: if the bipolar gradient pulses are applied along the Z-axis, __ are induced in blood flowing from __ to __ or vice versa

A

phase shifts; superior to inferior/ head to foot

67
Q

PC-MRA: since flow can occur in other directions (known as __ flow), bipolar gradients are applied in __ and in doing so, flow is sensitized in all direction X, Y, and Z, known as __

A

multi-directional; all three dimensions; flow-encoding axes

68
Q

an advantage of PC-MRA is that it allows the creation of two types of images:

A

magnitude and phase images

69
Q

PC-MRA: magnitude images look much like other MRA images with __ signal vessels and a __ background, phase images on the other hand have a __ background but are able to show __

A

high; suppressed; somewhat pixelated, noisy-looking; direction of flow

70
Q

PC-MRA: flow that is in the same direction as the __ looks __ whereas flow in the opposite direction looks __

A

VENC; white; black

530: Data Acquisition (13 decks)

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