This document provides an overview of magnetic resonance angiography (MRA). It discusses the physics behind MRA, different techniques used including time-of-flight imaging and phase contrast imaging, as well as considerations for patient preparation and contraindications. Advantages of MRA include being non-invasive and avoiding risks associated with conventional angiography such as damage to arteries. Limitations include inability to depict small vessels or slow blood flow as well as conventional methods. Overall, the document provides a comprehensive introduction to MRA.

1. Prepared by
Smrite Ranabhat
M. Optom
TIO

2.  Introduction
 Physics of MRA
 Techniques
 Patient preparation
 Contraindications
 Indications
 Cases

3.  The American college of Radiology ( ACR ) describes MRA as technique
using “MR pulse sequences “ to determine blood flow and image blood
vessels.
 It relies on time of flight (TOF) for flow images and quantitative measurements
for flow velocity by phase-contrast (PC)
 It is a type of magnetic resonance imaging(MRI) scan that uses a magnetic
field and pulses of radio wave energy to provide pictures of blood vessels
inside the body.

4.  Advantages of MR angiography:
Compared with catheter angiography, MRA is less invasive, less expensive, and
faster to perform.
For conventional angiography, catheter is inserted though the patients groin and
threaded up into the artery in the brain
MRA does not require this catheter. As a result, it eliminates related
complications such as possible damage to an artery
 Disadvantages of MR angiography:
Does not depict small vessels or extremely slow blood flow as well as
conventional angiography dose.

5.  Until the early 1990s, the only method for diagnosing disease in the
intracranial arteries was the invasive angiography .
 Angiography has 4% risk of minor stroke,1% risk of major stroke and 0.1%
risk of death.
MRA Conventional
angiography
Non invasive Invasive
No contrast required Nephrotoxic contrast
Non ionizing Ionizing radiation

7. Signal from flowing blood depends on
 TE
 TR
 Thickness of slice
 Position of slice
Characterstics of flow is given by Reynolds number
(density*viscosity*diameter) which is dimensionless and has no units.
 <2100 laminar flow
 >2100 turbulent flow

8. Signal loss in MRI is due to
 Turbulence
 High velocity of blood flow
 Dephasing
HVSL (high velocity signal loss)
Absent with GRE pulse sequence
Spins in slice ( stationary spin) or if they have moved ( flowing spin) relax at same
rate with same amplitude.
It is function of velocity and TE.

9.  In MR angiography it is often essential to eliminate arterial or venous signal
 Use of presaturation pulse to eliminate artifacts
 Eliminates flow related enhancement and phase ghosting
Flow related enhancement (FRE)
Slowing flowing blood enters the first slice of multislice imaging volume,
partially saturated blood remaining from previous sequence is totally replaced by
unsaturated flowing blood which elicits strong signal known as FRE or entry
phenomenan.
Depends on
 Blood velocity
 TR
 Number of slices

10. Maximise
signal from
flow
Supress
signal from
background
Maximise
difference in
signal
between
MRA
INTENDS
Flow
TOF with
GRE
Decreasing
TE
Increasing
field strength
Background
Decreasing
TR
Saturation
pulses

11.  STEPS INVOLVED IN GENERATING IMAGE
90 deg .
Turn on RF
Slice select gradient
Phase encoding gradient
Frequency encoding gradient
Time
TE

12.  Free induction decay (FID) refers a short-lived
sinusoidal electromagnetic signal which appears
immediately following the 90° pulse.
 It does not contribute to form MR image
 Either of the signals generated by the RF-pulse train
("FIDs" or "Echoes") can be temporarily suppressed
and then made to reappear at a chosen time (TE) by
application of an external magnetic gradient field.
 The gradient is typically applied in two steps:
1) a dephase portion that forces spins out of phase, and
2) a rephase portion that brings them back into phase
as the GRE.

13. Pulse sequences enable us to control the way in which the system applies pulses
and gradients.
In this way, image weighting and quality is determined.
There are many different pulse sequences available, and each is designed for a
specific purpose.

14. SPIN ECHO SEQUENCE
 It consists of 90 and 180degree RF pulse
 Initially 90 degree pulse is given
 After 90 degree pulse TM vector starts
dephasing
 Next we are going to give 180 degree pulse
 After giving 180 degree pulse TM vector
direction is changed
 Now TM vector started rephasing
 Getting good signal to form the image

15.  There is no 180 degree pulse in gradient echo
sequence.
 Rephasing of TM in GRE is done by gradients;
particularly by reversal of the frequency
encoding gradient.
 Since rephasing by gradient gives good signal.
 Initially 90 degree pulse is given
 TM vector started dephasing due to
inhomogeneity
 Gradient polarity is reversed
 TM vector started rephasing
 Completely rephasing TM vectors and good
signal is obtained

17.  In this type of imaging blood appear bright most of this are gradient echo
sequences.
 In this GRE sequences excitation pulse is slice selected but the rephrasing
which is done by gradient rather than 180 degree pulse is not limited to the
slice of interest and is applied to whole imaging volume therefore a flowing
proton will receive an excitation pulse is rephrased regardless of its slice
position.
 Blood flow- bright image
 Slow flow and clot- black image

18.  In this techniques blood appears as black as this are spin-echo based sequences
techniques.
 However proton in the flowing blood usually do not receive either 90 degree
or 180 degree pulse.
 Hence signal is not produced and flowing blood appear as dark.
 Slow flow and clots can produced bright signal because they received both 90
degree or 180 degree pulse.
 Maximum intensity projection is replaced by Minimum intensity projection
 Blood flow- black image
 Slow flow and clot- bright image

19. 1.TIME OF FLIGHT (TOF)
2.PHASE CONTRAST (PC)
3.CONTRAST ENHANCED MRA (CE MRA)
Non contrast enhanced( TOF , PC) are time consuming compared to contrast
enhanced.
BASIC PRINCIPLES
Protons are excited using GRE pulse sequence

20. MANIPULATING MAGNITUDE OF MAGNETIZATION
-Vascular contrast in TOF MRA is due to difference in the magnitude of the
inflowing protons in the blood and the surrounding stationary protons.
- No contrast agent injected
-Motion artifact
-Difficulty with slow flow

21. TOF MRA is based on the differences in saturation between the extravascular
and intravascular (moving blood) constituents.
A gradient pulse is repeatedly applied to a slice/slab (two-dimensional
[2D]/three-dimensional [3D]) of tissue.
The signal intensity of static tissue (extravascular) is progressively suppressed
by repetitive radio frequency pulses, the signal from the stationary tissue
decreases and becomes more saturated with each pulse.
The moving blood brings unsaturated protons into the tissue slice, which
generates a high signal intensity. and the inflow enhancement in the investigated
vessel produces the angiographic effect.

22. 2D time of flight
Multiple thin section of body are studied individually so even slow blood flow is
identified. With 2-D TOF, multiple thin imaging slices are acquired with a flow
compensated gradient- echo sequences. These images can be combined by using a
technique of reconstruction such as maximum intensity projection(MIP), to obtain a 3-
D image of the vessels analogous to conventional angiography
3D time of flight
In 3D technique , a large volume of tissue is studied ,which can be subsequently
partitioned into individual slices, hence high resolution can be obtained and flow
artifacts are minimized, and less likely to be affected by loops and tortuosity of vessels
An angiographic appearance can be generated using MIP, as is done with 2-D TOF
MOTSA(multiple overlapping thin slab acquisition)
Prevents proton saturation across the slab. This technique have advantage of both 2D
and 3D studies. It is better than 3D TOF MRA in correctly identifying vascular loops
and tortuosity.

23. Saturation pulses involve the application of RF energy
to suppress the MR signal from moving tissues outside
the imaged volume to reduce or eliminate motion
artifacts.

24. Misregistration artifact due to swallowing

25. ARETERIAL AND VENOUS BOOD FLOW IN BRAIN

26.  Uses parameters typical of 3D TOF MRA but gadolinium contrast is also
given.
 Data are acquired after contrast bolus infusion ( Gad. 0.1-.2 mmol/kg).
 Unlike, time-of-flight (TOF) or phase contrast (PC) imaging, the signals of the
blood in CEMRA is based on the intrinsic T1 signal of blood and rather less on
flow effects; therefore, this technique is less flow sensitive and counteracts
saturation effect.
 It can be performed within seconds
 Nephrogenic systemic fibrosis is rare but serious complication.

27.  Is based on the T1 values of blood, the surrounding tissue, and paramagnetic
contrast agent.
 T1-shortening contrast agents reduces the T1 value of the blood
(approximately to 50 msec, shorter than that of the surrounding tissues) and
allow the visualization of blood vessels, as the images are no longer dependent
primarily on the inflow effect of the blood.
 Contrast enhanced MRA is performed with a short TR to have low signal (due
to the longer T1) from the stationary tissue.
 Short scan time to facilitate breath hold imaging.

29.  Venous thrombosis
 Intracranial hypertension
 Drowsiness accompanying headache

31. MANIPULATING PHASE OF MAGNETIZATION
It is an MRI technique that can be used to visualize moving fluid.
It is typically used for MR venography as a non IV-contrast requiring technique.
Spin that are moving in the same direction as a magnetic field gradient develop a phase
shift that is proportional to the velocity of the spins. This is the basis of phase-contrast
angiography.
In the simplest phase- contrast pulse sequences, bipolar gradients are used to encode the
velocity of the spins.
Stationary spins undergo no net change in phase after the two gradients applied.
Moving spins will experience a different magnitude of the second gradient compared to
the first, because of its different spatial position. This result in net phase shift.
Mostly used for CSF

32.  In PC MRA bipolar gradient is applied and if the proton is stationary there is
no phase shift. However if the protons are moving, a phase shift occurs.
 The faster the proton moves greater the phase shift.
 Phase is proportional to velocity
 Allows quantification of blood flow and velocity
 Phase sensitization can be acquired along only one axis at a time.
 PC technique tends to be 4 times slower than TOF techniques

33.  Initial symptoms of cavernous sinus thrombosis are progressively severe
headache or facial pain, usually unilateral and localized to retro-orbital and
frontal regions. High fever is common.
 Later, ophthalmoplegia (typically the 6th cranial nerve in the initial stage),
proptosis, and eyelid edema develop and often become bilateral. Facial
sensation may be diminished or absent.
 Decreased level of consciousness, confusion, seizures, and focal neurologic
deficits are signs of central nervous system (CNS) spread.
 Patients with cavernous sinus thrombosis may also have anisocoria or
mydriasis (3rd cranial nerve dysfunction), papilledema, and vision loss.

34. • Satisfactory written consent
• Remove all metals and give hospital gown
• Bathroom going prior to examination
• Explain procedure and instruct properly
• Note the weight
Patient positioning for MRA of the brain is generally similar to positioning for
brain MRI. Patients are positioned supine and in a transmit-receive head coil.

35.  Any electrically , magnetically or mechanically activated implant e.g.: cardiac
pacemaker, insulin pump biostimulator,neurostimulator, cochlear implant , and
hearing aids.( active implant)
 Passive implants
-aneurysm clips( unless made of titanium), stents, hip prostheses, catheter
 Pregnancy ( risk vs benefit ratio to be assessed )
 Ferromagnetic surgical clips or staples
 Metallic foreign body in eye

39. To evaluate conditions of the carotid arteries such as:
 Stenotic / occlusive disease in symptomatic patients
(e.g., TIA or CVA)
 Stenotic / occlusive disease in asymptomatic members
when Doppler scan is abnormal
 Aneurysms
 Cervicocranial arterial dissection in members with
suggestive signs or symptoms (e.g., unilateral headache ,
oculosympathetic palsy, amaurosis fugax, and symptoms
of focal brain ischemia)

40.  To rule out intracranial aneurysm including aneurysm of
circle of wills.
 Screening for intracranial aneurysm in neurofibromatosis,
Ehler Danlos syndrome
 Evaluation of tinnitus of vascular etiology
 Evaluation of known vasculitis
 Pre operative evaluation of brain surgery
 Post operative follow up

41.  As a follow op study of arteriovenous
malformation
An arteriovenous malformation (AVM) is an
abnormal tangle of blood vessels connecting arteries
and veins, which disrupts normal blood flow and
oxygen circulation
To evaluate patients with signs/symptoms highly
suggestive of leaking/ruptured aneurysm or AVM
(i.e., sudden explosive headache, blurred vision, stiff
neck, pulsatile proptosis ,blood in the cerebral spinal
fluid);

42. A 58-year-old woman with 1 and a half years of right eye redness, ocular hypertension and recurrent headache.
Angiography done ,after endovascular embolism RX redness and hypertension reversed back.
Conclusion
In clinical practice, when corkscrew hyperaemia
accompanied by neurological symptoms is found,
cerebral vascular diseases might be considered.
RX. Endovascular embolization – cutting of blood
supply to certain part
sterotactic radiotherapy

44. Intracranial vascular disease
 A CCF carotid cavernous fistula refers to an aberrant connection between the
internal carotid artery (ICA), the external carotid artery (ECA) or any of their
branches within the cavernous sinus .
 The symptoms and signs of a CCF always include eyelid swelling, proptosis,
chemosis, and corkscrew hyperemia.
 Cranial nerves III,IV, V and VI can be affected

45.  To definitively establish presence of stenosis or other abnormalities of the vertebrobasilar
system in patients with symptoms highly suggestive of vertebrobasilar syndrome (binocular
vision loss, positional vertigo, dysarthria, dysphagia, diplopia)
The vertebrobasilar (VB) system, comprised of the vertebral and basilar arteries, serves as a
critical arterial supply to the cervical spinal cord brainstem, cerebellum, thalamus, and occipital
lobes.
One of the direct neurologic presentations, locked-in syndrome, is resultant from thrombosis of
the proximal and middle portions of the BA
Clinical manifestations of the locked-in syndrome include nearly complete paralysis of all
voluntary muscles, with preserved consciousness and cognitive function.
Alternatively, distal BA embolism may present with the features which include oculomotor and
pupillary disturbances, visual hallucinations, and alterations in consciousness.

47.  48 year old woman – TED- 4 week history of pain, redness, and reduced visual acuity
RE
 B/L three wall orbital decompression 8 YRS before
 VA @ CF1m OD and 6/9 OS
 B/L lid retraction and mild generalised restriction of eye movements.
 B/L proptosis measuring 24 mm in the right eye and 23 mm in the left.
 RAPD+ OD
 IOP - 50 mm Hg OD , 20 mm Hg .
 There was right corneal oedema, rubeosis iridis , and moderate anterior chamber
activity. Gonioscopy showed an open, grade 2 angle (Shaffer’s classification) with
rubeotic vessels present in the angle. Fundal examination was limited by the corneal
oedema but no specific abnormality was identified. Examination of the left eye was
normal.

48.  anti glaucomamedications , orbital decompression

49.  Various abnormalities of the orbital circulation have been reported in thyroid
ophthalmopathy. Blood flow in the superior ophthalmic vein has been shown to
be reduced or even reversed in some patient.
 Ischemia of the optic nerve head has been postulated to have a role in the
development of optic neuropathy in some patients with thyroid
ophthalmopathy.
 Ocular ischemic syndrome as a result of ophthalmic artery obstruction in
thyroid eye disease. Furthermore, it demonstrates the usefulness of MR
imaging in evaluation of the ophthalmic artery.
MRA for rubeosis iridis , rubeotic glaucoma, iritis