Chapter 8 Flashcards
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 __)
morphology (anatomy); hemodynamics (flow); convention MRI; MRA (magnetic resonance angiography); moving blood
most MRI and MRA techniques rely on the __ (rather than __) to demonstrate vasculature on MR images
motion of blood within the vessel; the anatomy of the vessel itself
__ (3) sequences (acquired with combinations of __ RF pulses) typically render images in which the signal from blood has been __, known as __
SE, FSE, and IR; 90 and 180 degree; largely eradicated; black blood imaging
__ sequences render blood __, in a technique known as __
GE; bright; bright blood imaging
GE sequences can be supplemented with options such as __ (__) to reduce __, and __ (__) to reduce __
gradient moment nulling (GMN); phase mis-mapping from high-signal inflowing blood; spatial pre-saturation (SAT); signal from inflowing blood
to detect signal on MR images acquired with SE, nuclei must receive a __. the most efficient combination includes a __ followed by a __
combination of (at least) 2 RF pulses; 90 degree excitation pulse; 180 degree refocusing pulse
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)
slice selective; selected slice; flowing nuclei; slice thickness, velocity of flow, and TE
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 __
darker; multiple inversion pulses; double IR prep; non-slice-selective 180; slice selective 180; longitudinal magnetization within the slice
in fast IR: a TI equal to the null point of __ enables saturation of this flow by the __
flowing spins in blood entering the slice; 90 excitation pulse
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 __
slice-selective 180; fat within the slice; null points of fat and flowing spins coincide; blood; fat; triple IR prep
spatial pre-saturation (also known as __ or __ can be used to evaluate __ throughout the vascular system
SAT pulses; SAT bands; vascular patency
since SAT uses additional __, the __ is increased, and the __ may be reduced
RF pulses; SAR; number of slices (typically available for a given TR)
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 __
outside the slice/FOV/imaging volume; 90 degrees into the transverse plane; receive an additional 90 RF pulse; flipped an additional 90 degrees
SAT: spins flowing into the slice/imaging volume are __ because they have received __
saturated; both the 90 degree saturation pulse and the 90 degree excitation pulse (total 180)
in GE sequences, flowing blood appears __, enabling visualization of __ relative to __. to detect signal acquired with GE acquisitions, nuclei must receive __ followed by __
bright; the vessel; surrounding tissues; at least 1 RF excitation pulse; gradient rephasing
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 __
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
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 __
axial brain; 90 excitation pulse; perpendicularly; this excitation pulse
bright blood/GE: a gradient rephasing pulse is applied to __, this will cause all the flowing spins to produce signal, provided they __
the entire imaging volume; have been excited at some point in time
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 __
excitation pulse; rephased by the gradient; bright blood imaging
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 __
gradient moment nulling (GMN) or gradient moment rephasing (GMR); moving; stationary; intra-voxel dephasing
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 __
GE; within flowing vessels; moving spins in flowing blood; stationary spins residing in tissue
when stationary spins are suppressed, the appearance of __ is enhanced by the increased signal from __, which flow into the imaging volume and __
vasculature; unsaturated spins; receive RF excitation for the first time
2 approaches to suppress stationary spins:
digital subtraction MRA or DS-MRA; time-of-flight MRA or TOF-MRA
DS-MRA: two acquisitions are performed that treat __, but which differentiate __ and then subtract them
stationary spins identically; moving spins
TOF-MRA: if a __ that saturates spins within the imaging volume is used in combination with the __, a high degree of __ can be achieved
short TR; entry slice phenomenon; vascular contrast
in MRA it is not the __, but rather the __ that is visualized
vessel itself; flow within the vessel
DS-MRA, also known as __, allows visualization of the vasculature over a __ than can normally be achieved by other __ methods
fresh-blood imaging; wider FOV; flow-dependent
DS-MRA/fresh-blood imaging involves the acquisition of two __ data sets, one during __ flow, the other during __
T2-weighted; diastolic; systole
DS-MRA: the diastolic images display high signal from __, as the flow is __ at this point of the cardiac cycle
both arteries and veins; momentarily slow
DS-MRA: the systolic images exhibit signal loss in __ due to __
the arteries; intra-luminal dephasing
DS-MRA: by digitally subtracting the two data sets, it is therefore possible to __ the signal from either __ or __ whilst simultaneously subtracting out __
isolate; arteries; veins; any background signal
DS-MRA offers some of the benefits associated with __, particularly the ability to achieve a __, but without the risks associated with __
contrast-enhanced MRA; large FOV; Gd-based contrast injection in those patients having a particular sensitivity to these agents
the vascular signal produced in TOF-MRA relies on __ (__). this means that the vascular enhancement in TOF-MRA is related to __
flow-related enhancement (FRE); the flow of blood
TOF-MRA provides information about blood flow that is __ and vascular contrast by manipulating the __
perpendicular to the slice plane; longitudinal magnetization of the stationary spins
TOF-MRA: a __ pulse sequence is used in combination with __ to enhance __
incoherent GE; gradient moment rephasing; flow
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
flip angle; TR; saturated; TOF; fully-magnetized fresh; high; patent vessels
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 __
TRs; flip angles; saturate stationary tissues; slowly; curved; suppressed; stationary tissues; vascular signal
3D TOF-MRA acquisitions are optimal for high-__, high-__ scans for the evaluation of __ vessels with __ blood flow (e.g. __ vessels associated with the __)
resolution; SNR; smaller; high velocity; intracranial; Circle of Willis
2D TOF-MRA acquisitions are capable of demonstrating __ flow and provide a __ area of coverage, which makes it best for imaging the __ (3)
slow; wider; carotid arteries; peripheral vascular and venous systems
the manner in which the data from MRA images are __ plays a part in determining the way in which __ is perceived in the images
reformatted; vascular anatomy
maximum intensity projection (MIP) is a technique for __ image formation where a reformatted image appears to be __
MRA; projected onto a 2D surface
MIP: there is no __, and so the observer may find it difficult to appreciate __
depth cueing; which vessels are in the foreground and which vessels lie behind
MRA: shaded surface display (SSD) improves __ perception of the data by creating __
3D; a boundary between high- and low-signal areas
SSD: the boundary between high- and low-signal areas is treated as a __ which is presented to the observer as though __
surface; illuminated by a directional light source
SSD: the benefit of the boundary is that structures appear to be __ and vessels closer to the observer’s point of view appear to __
solid; lie in front of the structures behind them
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 __
in parallel rows and columns; perspective; depth; reconstructing the data from different angles
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 __
greyscale; maximum intensity; 2D plane
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 __
from different angles; inflow angiography; right; perpendicular to the vessel
MIP: __ affects the __ of the reformatted image, and this is the principal reason for the frequent use of __, rather than __ techniques
slice thickness; spatial resolution; 3D; 2D inflow
MIP: by reformatting each image with __, the resulting images can be run as a __. this allows for a __ visualization of the data
an incremental change in angle; cine loop; pseudo-3D
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 __
velocity-induced phase shifts; the change in phase of flowing blood
phase shift is related to __ (3). this means that PC-MRA (which relies on phase shifts) provides information about __ (4)
blood flow velocity, flow direction, and type of scan acquired; vascular anatomy, flow velocity, multi-directional blood flow, and flow direction
PC-MRA uses a __ pulse sequence with __ flip angles and additional __ pulses to create changes in the __ within __
GE; small; gradient; phases of the nuclei; flowing blood
the gradient pulses in PC-MRA are __ gradient pulses, which involve __
bipolar; two lobes that are equal in strength (one negative gradient pulse and one positive gradient pulse)
PC-MRA: although bipolar gradient pulses are applied to __ tissues within the volume, application of these pulses allows for the distinction between __ within __
all of the; stationary tissues and spins; flowing blood
PC-MRA: a gradient echo sequence is used, having a __ flip angle to prevent __, and an additional bipolar gradient known as a __
small; saturation; velocity-encoding gradient (VENC)
PC-MRA: the strength and duration of the VENC is selected based on the __. VENC velocity settings should be selected to produce signal from __
blood flow velocity that is to be imaged; blood flowing at that velocity
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
amplitude; duration; arterial; high; high
PC-MRA: if the VENC selected is __ than the velocity of blood flow within the vessel, __ can occur
lower; aliasing
PC-MRA: lower-than-necessary VENC results in low signal intensity in the __, but better delineation of the __
center of the vessel; vessel wall itself
PC-MRA: aliasing occurs because in __ flow, the __ of blood results in __, or __, against the __
laminar; viscosity; drag; friction; vessel wall
PC-MRA: low VENC aliasing: the highest velocity of flow is found in the __, and the signal is aliased or __ out of the __.
center of the vessel; mis-mapped; vessel lumen
PC-MRA: low VENC aliasing: even though there is signal void within the __, there is better delineation of the __
vessel lumen; vessel wall above background noise levels
PC-MRA: with high VENC settings, __ signal is improved but __ is compromised
intraluminal; vessel wall delineation
PC-MRA: __ is obtained along the direction of the applied bipolar gradient
sensitization to flow
PC-MRA: if the bipolar gradient pulses are applied along the Z-axis, __ are induced in blood flowing from __ to __ or vice versa
phase shifts; superior to inferior/ head to foot
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 __
multi-directional; all three dimensions; flow-encoding axes
an advantage of PC-MRA is that it allows the creation of two types of images:
magnitude and phase images
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 __
high; suppressed; somewhat pixelated, noisy-looking; direction of flow
PC-MRA: flow that is in the same direction as the __ looks __ whereas flow in the opposite direction looks __
VENC; white; black
