Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

RAD 512 > MR vascular imaging + contrast > Flashcards

MR vascular imaging + contrast Flashcards

1
Q

what contrast is mainly used in MRI and why

A

gadolinium

  • shortens t1 time of tissues (in this case blood)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what are 2 techniques used for contrast enhance MRA

A
  • single phase
  • time resolved (4D)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is single phase CE MRA

A
  • obtains image at single point in time POST CONTRAST
  • high SPATIAL resolution
  • need peak arrival time of contrast bolus to image at peak conc
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what is time resolve CE MRA

A
  • repeatedly imaging FOV as contrast passes thru vessels
  • high temporal resolution (fast imaging) (not high spatial resolution)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what type of sequence is used in time resolved CE MRA

A

t1 weighted gradient echo

(fast 2d less than 2sec/frame or fast 3D 5-7 sec within 1 breath hold)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

time resolved CE MRA is similar to x-ray digital subtraction angiography in the sense it uses a good mask subtraction and new k-space schemes

no need to estimate bolus arrival time

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what is the main adv of time resolved ce mra

A

high temporal (resolution with respects to time) and spatial (resolution with respects to distance) resolution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

ll the contrast-enhanced MRA techniques discussed up to now obtain images at a single point in time after injection. Time-resolved MRA sequences, known under acronyms such as TRICKS and TWIST, obtain a series of images displaying passage of the contrast bolus. A typical time-resolved MRA study might contain 20+ images obtained at rates as rapid as 1-2 frames per second.

An inherent trade-off exists between spatial and temporal resolution. The center of k-space contains information about basic image contrast, while edges and details are encoded in the k-space periphery. Increasing spatial resolution thus requires that more k-space points be sampled. However, sampling more points requires additional imaging time, adversely impacting temporal resolution.

Time-resolved MRA techniques balance these competing resolution requirements through a process known as view-sharing. Although the details of these methods vary, all begin by acquiring a non-contrast, full-resolution image of the area of interest. During passage of the contrast bolus, the center of k-space is sampled much more frequently than the periphery, which is updated only periodically. The data from the different partial k-space samplings are combined to create a series of time-resolved images with satisfactory spatial resolution. The original non-contrast image can be used as a mask for subtraction to improve vascular conspicuity.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

give pros and cons of CE MRA

A

PRO:
- high SNR
- high spatial resolution
- no flow artefacts

CONS:
- uses gadolinium
- bolus imaging (scan at time of peak bolus)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is NC MRA

A

non contrast magnetic resonance angiography

  • rely ONLY on effect of blood MOVING thru slice
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what are the 2 forms of NC MRA

A

time of flight
phase contrast

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what are some hardware improvements to consider to carry out NC MRA

A
  • higher MRI field (for higher SNR)
  • faster gradient ( decrease artefact)
  • multi receiver RF coils (higher SNR)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is TOF and how does the appearance of blood differ if the sequence used is SE/GRE

A

TOF= time taken for blood to flow thru a slice / effect when blood flows into or out of a slice b/w excitations

  • TOF blood is dark with SE and bright with GRE
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

explain why blood is dark or bright with SE/GRE

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what 3 things allow flow related enhancement to be increased

A
  1. flow velocity increase
  2. TR increase
  3. slice thickness decrease
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What orientation must slice selection be done in TOF

A

perpendicular to direction of flow

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

why is there a short TR/TE when using GRE sequence for TOF MRA

A
  • saturate static tissue
  • minimise phase -related signal loss
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

2D TOF SENSITIVE TO SLOW FLOW (VENOGRAPHY)(for veins)

3D TOF SENSITIVE TO FAST FLOW (ARTERIOGRAPHY)(for arteries)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

how would you plan a 2D TOF MRA e.g slices, orientation, TR/TE time

A
  • multiple thin, overlapping slices perpendicular to vessels
  • short TR (20-40ms)
  • VERY short TE (reduce flow effects due to dephasing)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

in 2D TOF MRA where would you position sat bands for arteriograms or venograms

A

presaturation volume goes above slices in arteriogram

presaturation volume goes below slices in venogram

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what does MIP stand for and how is this detected in 2D TOF MRA

A

maximum intensity projection

  • Detected using ray-tracing algorithm
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

how is the final image from 2D TOF MRA formed

A
  • single projected image from volume of data set formed based on MIP
  • can be done in any direction
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

how would you orientate the volume of a 3D TOF MRA, how does the thickness of the volume affect signal

A
  • VOLUME perpendicular to direction of flow
  • signal progressively saturates as blood moves thru volume (large 3D slabs increase saturation of spin so smaller slabs better)
  • limit thickness of volume to MAXIMISE inflow effect

(usually or fast flow)

24
Q

what are 2 methods to reduce saturation effect in 3D MRA

A
  1. TONE ( titled optimised non saturating excitation)
  2. MOTSA (multiple overlapping thin slice acquisition)
25
how does TONE and MOTSA work
TONE = RF with variable flip angle (low angle at entrance, high angle near end) MOTSA= multiple smaller overlapped instead on one big slap, this can cover a large area without losing signal
26
what is PC MRA/ how does it work
phase contrast MRA - uses change in phase of moving spins (phase effect) to form image - phase is proportional to velocity of moving spins - signal is based on phase shift/change of moving spins - visualise and quantify blood flow and velocity in xyzzy direction
27
is PC MRA good for slow or fast flow? give some examples
slow flow e.g MR venography, csf flow studies (used in 2D and 3D)
28
note: spin phase increases/slows with time when moving into higher or lower magnetic field gradient
29
PRO and con of TOF
PRO: excellent contrast CONS: long acquisition time, sensitive to tissue with short T1
30
PRO and con of PC
pro: good contrast and spatial resolution, blood flow direction cons: loss of signal in vessels with turbulent flow, susceptible to motion artefacts
31
know PC has higher SNR, better background suppression and venous detail than TOF
32
what modality is used for non mri vascular imaging and what are the pros of this
ultrasound -no radiation or injections - can demonstrate flow - good for superficial vessels - BUT ca be limited due to body habitus
33
why might vascular mri be better than non vascular
- multi planar imaging - no ionising radiation - can show functional and anatomical structures
34
for TOF angiography, what sequence is used, specifically what TR times and why (blood bright)
Gradient echo sequences with SHORT TR, to saturate signal from stationary tissue
35
explain how blood is bright in TOF with GRE sequence
short TR in GRE sequence means that stationary tissue is saturated over time (continual RF pulse applied without letting stationary tissue have full t1 recovery) fresh blood slowing into slice hasn't been saturated so it presents with larger signal than adjacent stationary tissue
36
TOF essentially exploits longitudinal magnetisation for image contrast can be combined with pre saturation bands to supress arterial or venous flow
37
what post processing mechanism is used on TOF and why
maximum intensity projection (MIP), enables isolation of vessels from surrounding tissue
38
during TOF, ensure you enable enough time for saturated blood to move out of slice for new blood to enter
39
explain how phase contrast works
A stationary spin subjected to such a gradient pair will experience no net phase shift, but a moving spin will have a net phase shift proportional to its velocity. Two spins flowing at the same speed but in opposite directions will have equal but opposite phase shifts. By measuring changes in phase, therefore, velocity can be computed. Usually bipolar gradients are applied along only one anatomic axis (x-, y-, or z-) at a time to provide flow sensitivity in that specific direction. However, flow-encoding gradients may be applied along two or more axes simultaneously to measure flow sensitivity along any arbitrary direction
40
remember breath holds should be done for abdominal vessels
41
what plane is CE MRA often done in and why
coronal, largest coverage
42
note whilst CE MRA can be used for aortic dissection, Balanced SSFP / TRUE FISP is better and more rapid (orientated perpendicular to aorta)
43
note: if you scan at certain times after contrast administration, you can visualise certain anatomy. e.g if u scan early on you can visualise contrast in arterial anatomy but if u wait longer, you can get venous anatomy contrasted etc
44
what is a timed-bolus CE MRA
- test injection to determine precise travel time for bolus contrast injection - mask scan no contrast done 1st - care bolus image (similar to t1 localiser scan) has contrast in blood vessels showing bright - travel time is then calculate - additional 3D sequence done after contrast injection - post contrast sequence and mask sequence subtracted to result in image of contrast filled target vessels
45
explain process of FLURO CE MRA
- mr fluro used to observe arrival of contrast bolus - (pre contrast scan and post contrast scan have same scan parameters) - once contrast seen nearing anatomy of interest on fluro scan, live 3d scan is triggered - both mask(pre contrast) and live(post contrast) are 3d sequences. - the fluro scan (done between mask and live) is 2d sequence
46
why is precise timing for injection of contrast bolus not necessary in time resolve CE MRA
continual images of FOV are taken as contrast flows thru
47
what is the main limitation of time resolved CE MRA
scan for brain takes mins but blood flow takes seconds thus image is low quality as theres low data/ k-space isnt complete - low spatial resolution
48
what MRA technique would you use for brain vessels, neck vessels or aorta/abdominal vessels
brain = TOF and phase contrast neck = TOF and phase contrast Aorta = CE MRA (too long of a vessel for TOF (which works rapidly)
49
what part of k-space provides contrast/detail, thus what area should be filled more during peak signal intensity (esp if there is short time)
centre = contrast periphery = detail thus if there is a very short scan time (or something similar), you should focus on filling the centre of k-space at peak signal intensity to enable maximum contrast retrieval
50
Contrast-enhanced MR angiography (CE-MRA) is typically performed in three-dimensional (3D) mode, generating a rectangular (Cartesian) array of data. There are a few ways of filling k-space, what are the 3 ways
- linear/sequential (filling k-space from top - bottom vice versa) - elliptic centric (filling it in oval manner from middle out (not circular)) - centric (filling it from middle out in linearly)
51
Elliptical-centric ordering is now the preferred k-space sampling method used for most CE-MRA examinations. Linear methods may still be used on older equipment and for MRA of the distal extremities where arrival of the contrast bolus may be prolonged or its exact timing difficult to predict.
52
what is the safe egfr value to be give contrast
greater than 30
53
MRA TOF BRAIN for ?aneurysm, stroke, stenosis etc MRV TOF BRAIN for venous sinus tumour, thrombosis etc
54
what is AVM
A brain arteriovenous malformation (AVM) is a tangle of blood vessels that creates irregular connections between arteries and veins in the brain.
55
before feasible use of CE MRA, normal aortic pulsations limited the efficacy of unenhanced MRA
56
what sequence is commonly used to identify atherosclerosis ? (build up of fat in vessels)
CE MRA - TIME RESOLVED
57

RAD 512 (23 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions