Introduction to MR Angiography and Venography Procedure of Brain . Includes Indication, MRI protocol, planning and anatomy as well as brief intoduction to physics behind MRA and MRV principle.

1. MRA & MRV of Brain
Anjan Dangal
B.Sc.Medical Imaging Technology 3rd Year
National Academy of Medical Sciences
Kathmandu, Nepal

2. 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)

3. Indications for MRA Brain
1. For evaluation of known intracranial disease
 To evaluate known intracranial aneurysm or arteriovenous malformation (AVM).
 To evaluate known vertebrobasilar insufficiency (VBI).
 To re-evaluate vascular abnormality visualized on previous brain imaging.
 For evaluation of known vasculitis.

4. For evaluation of suspected intracranial vascular disease:
To screen for suspected intracranial aneurysm in patient whose parents has history
of intracranial aneurysm. .
Screening for aneurysm in polycystic kidney disease, Ehlers-Danlos syndrome,
fibromuscular dysplasia, neurofibromatosis, or known aortic coarctation.
To evaluate previously diagnosed subarachnoid hemorrhage (SAH).
To evaluate suspected vertebrobasilar insufficiency (VBI) in patients with symptoms
such as vision changes, vertigo, or abnormal speech.
To evaluate suspected arteriovenous malformation (AVM) in patient with previous or
indeterminate imaging study.
For evaluation of suspected venous thrombosis (dural sinus thrombosis).

5.  Distinguishing benign intracranial hypertension (pseudotumor cerebri) from
dural sinus thrombosis.
 For evaluation of pulsatile tinnitus for vascular etiology.
 For evaluation of suspected vasculitis with abnormal lab results suggesting
acute inflammation or autoimmune antibodies.
 For evaluation of stroke risk in sickle cell patients (2 - 16 years of age) with a
transcranial doppler velocity >200.
Pre-operative evaluation for brain/skull surgery.
Post-operative/procedural evaluation:
A follow-up study may be needed to help evaluate a patient’s progress after
treatment, procedure, intervention or surgery.

6. Intracranial aneurysm

7. Arteriovenous Malformation

8. Vertebro basilar Insufficiency

9. Vasculitis

10. Contraindications
• Any electrically , magnetically or mechanically activated implant e.g:
cardiac pacemaker, insulin pump biostimulator,neurostimulator,
cochlear imlant , and hearing aids.
• Intracranial aneurysm clips ( unless made of titanium )
• Pregnancy ( risk vs benifit ratio to be assessed )
• Feromagnetic surgical clips or staples
• Metallic foreign body in eye

11. Patient Preperation
• Satisfactory written consent
• Remove all metals and give hospital gown
• Bathroom going prior to examination
• Explain procedure and instruct properly
• Note the weight

12. Patient Position
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.

13. Pulse sequence for MRA in our department
SURVEY
FLAIR TRA
ANGIO SURVEY
COW
NECK
ARCH
T2W GRE TRA

14. SURVEY

15. 3D TOF Planning

18. Indication for MRV
To evaluate the patency of the venous sinuses.
The study can be performed with TOF, Phase contrast and IV contrast
enhanced techniques.

19. Pulse sequence for MRV in our department
SURVEY
VENOGRAM SAG

22. Vascular Anatomy of Brain

25. Arteries on the inferior surface of the brain (A)
. The internal carotid artery (1) divides into the middle (2)
and anterior (3) cerebral arteries after giving rise to the
posterior communicating (4) and anterior choroidal (5)
arteries. Collectively, these vessels supply anterior and
lateral parts of the cerebrum. The vertebral arteries (6) join
to form the basilar artery (9) after giving rise to the
posterior inferior cerebellar artery (7). The basilar artery in
turn gives rise to the anterior inferior (8) and superior (10)
cerebellar arteries before bifurcating into the posterior
cerebral arteries (11). Collectively, the vertebral-basilar
system supplies the brainstem, much of the diencephalon,
and inferior and posterior parts of the cerebral
hemispheres. The apparently very large left posterior
communicating artery in this specimen is actually a
relatively common variant in which the posterior cerebral
artery on one side originates from the internal carotid
artery instead of the basilar artery

26. Brain Vascular Anatomy: Arterial supply
The main arterial vessels of the head are associated with the circle of
Willis (COW). These vessels define the circulatory system for the brain.
The internal carotid arteries (right and left) enter the head bilaterally.
Each internal carotid artery curves at the level of the pituitary gland to
form a "saddle" shape known as the carotid siphon. Superior to that
structure,each internal carotid artery bifurcates into the anterior and
middle cerebral arteries (MCA). The anterior cerebral artery (ACA) feeds
the frontal lobes and the MCA feeds the parietal lobe.
A small vessel that communicates between the ACAs is known as the
anterior communicating artery. This artery forms the anterior portion of
the COW.

27. The vertebral arteries (right and left) enter the skull through the foramen
magnum. These two vertebral arteries join to form the basilar artery,
which runs along the anterior surface of the pons.
Superior to this structure, these arteries bifurcate to form the posterior
cerebral arteries (PCA). These PCAs supply blood to the posterior portion
of the brain.
Two small vessels "communicate" from the internal carotid arteries and
the PCA bilaterally. These are known as the posterior communicating
arteries (PCOM). The PCA (bilaterally) and the PCOM form the posterior
portion of the COW

30. Veins of Brain
Venous structures begin with the large drainage vein located along the
longitudinal axis of the patient. This vein runs under the skull but on top of the
brain, from the forehead to the middle of the back of the skull, known as the
superior sagittal sinus.
Below to the superior sagittal sinus and running along the top of the corpus
callosum is another drainage vein known as the inferior sagittal sinus.
The inferior sagittal sinus drains into the straight sinus that runs in the tentorium
to the confluence of sinuses.
The superior sagittal sinus drains into the confluence of sinuses and into the
transverse sinuses, and then runs from medial to lateral on both sides of the
posterior portion of the brain at the level of the cerebellum.
The transverse sinuses drain into the sigmoid sinus, which drains into the internal
jugular vein

34. MRA Brain Techniques
 Non Contrast Technique
Time of Flight ( TOF )
Phace Contrast ( PC )
 Contrast Technique
GD-enhanced 3D MRA

35. For the head, arterial blood flow velocity is high, vessel diameter is
small, and direction is multidirectional. Although there is
multidirectional flow, and becauseflow velocity is high and vessels are
small, 3-D TOF is the best choice for arterial brain imaging
Principal advantage of this technique are :
acquisition time is shorter than those of phase contrast,
a single slice thickness of 1 mm or less can be obtained ,
matrix of 512 x 512 can be acquired with reasonable time ,
finally arteries can be imaged selectively due to elevated saturation of
veins
For venous flow, however, PC MRA is best.

36. Major Limitation of 3D TOF
Saturation of Slow Spins in more distal arterial branches with
consequent reduction of diagnostic accuracy .

37. Solution
Increased magnetic field
use of contrast agent

38. WHY CE-MRA ?A pitfall of the TOF technique, particularly 3D TOF, is that in areas of
slowly flowing blood, turbulence or blood which flows in the imaging
plane there can be regions of absent or diminished signal. The signal
loss can be confused with vascular occlusion or thrombi. To avoid this
pitfall, MRA performed after the intravenous administration of
gadolinium based contrast agents is utilized at many facilities.

39. MRA Intracranial Venous System
Both 2D TOF and 2D-3D PC sequences are available to study the cerebral
venous circulation
PC MRA is based on the accumulated phase difference between mobile
spins and stationary spins. This characteristic renders PC acquisition
more sensitive to slow flow, such as occurs in veins.

40. Time oF Flight MR Angiography
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.

41. 2D / 3D TOF :
In 3D TOF, one single volume (slab) is excited
and segmented into small slices by a second-
phase encoding gradient,
while in 2D TOF, multiple single slices are
acquired sequentially.

42. 2D TOF
slice thickness usually varies between 2 and 3 mm, which makes this technique
more prone to dephasing effects as the number of different possible phases
within the voxel increase.
the 2D method shows an improved sensitivity for inflowing magnetization
based on minimized flow saturation effects: In sequential acquisitions, each
slice of the data set represents an “entry” slice with the strongest possible
intravascular signal.
This enables the use of a slightly higher flip angle and as a consequence an
overall improvement in signal-to-noise ratio (SNR). Therefore, this technique is
well suited for the detection of slow laminar flow conditions.
2D TOF MRA is used for the depiction of the slower flowing cerebral veins.

44. Method to reduce Inflow related echancement in MRA
Titled Optimized nonsaturating excitation ( TONE )
Multiple Overlapping thin slice Acquisition ( MOTSA )

45. TONE IN MRA
To reduce saturation effects in 3D TOF MRA, titled optimized nonsaturating
excitation (TONE) radio frequency pulses are frequently used. These pulses
provide flip angles that are variable along the slice selection direction.
Typically,low flip angles are applied at the entrance side of the arteries in the
volume of interest to delay saturation. The flip angle is then steadily
increased in cranial direction; the increasing flip angles offer maximal signal
recovery from that which remains in the flowing blood, deeper in the slab.
The gradient of the TONE pulse (or ramped flip angle) depends on the
velocity and the slab thickness (e.g., for imaging of the intracranial arteries
10 degrees at the entrance side and 30 degrees near the top of the volume).

46. Multiple Overlapping Thin slice Acquistion
(MOTSA )
Instead of one thick slab,
multiple, consecutively acquired
3D data sets are combined to
yield a single reconstruction of
the final volume.

47. Phase - contrast Magnetic Resonance Angiography
PC MRA is based
on the application
of a bipolar
gradient pulse
pair producing a
phase shift
depending on the
velocity
component along
the gradient

48. PC: Explained
In PC MRA, the applied gradient imparts a phase shift to the inflowing
protons proportional to their velocity. Two data sets are acquired with
opposite sensitization resulting in opposite phase for moving protons
and indentical phase for the stationary protons. On subtraction of the
data sets, signal from stationary protons is eliminated and just the
moving protons are seen. Information about the quantity and direction
of flow is obtained.

49. The technique is very flow sensitive and provides full background
suppression but requires a relatively long acquisition time if flow is
encoded in all three spatial directions (3D PC MRA).
A velocity-encoding gradient (VENC) of 15 to 20 cm per second for
imaging of the venous system and of 60 to 80 cm per second for display
of the arteries is usually recommended.
However, a variety of velocities can occur in cerebral arterial disease,
complicating the correct selection of the VENC. Thus, the method is not
as widely used for depiction of the cerebral arterial vessels as is the
TOF technique.

50. Projective 2D PC MRA images on the other hand can be acquired fast (
1 min) and easily.
This technique is often used to determine the topographic location of
the craniocervical arteries in coronal direction, enabling an adequate
volume to be investigated by contrast-enhanced MRA methods. It can
also provide a good depiction of flow in the major cerebral veins.

51. The unique capability for PC
MRA to measure the flow
velocity offers information
unobtainable by other MRA
strategies. In neurovascular
applications, MR flow
quantification techniques
have most often been
applied to evaluate the
carotid arteries, intracranial
arteries, and venous sinuses.

52. Contrast -enhanced MR Angiography
CE MRA does not rely on the natural flow effects, but on the
shortening of the T1 relaxation time of blood after intravenous
injection of a paramagnetic contrast agent bolus.
While for TOF techniques an acquisition perpendicular to the vessel is
recommended to reduce saturation effects, CE MRA can be
generated in any desired orientation, including acquisitions in the
plane of the vessels of interest. The considerably shorter
measurement times minimize the vulnerability to motion artifacts.

53. Two methods of CE MRA
1. During steady state after IV CM
2. During Initial transit of contrast bolus

54. CE MRA during the steady state is
technically less demanding, and a
high resolution can be obtained .
Helpful in differentiating true
stenosis of large arteries from
artifactual narrowing, to visualize
distal intracranial arteries, and to
image vascularpathologies that
can contain areas of slow flow
(e.g., largeaneurysms,
arteriovenous malformations)
A. 3D TOF MRA MIP B.After Iv 10ml Gadopentate
dimeglumine. small peripheral vessel are better visualized

55. Fluroscopic Triggering in CE MRA
The use of fluoroscopic triggering in CE MRA overcomes the need for the
separate test bolus.
The arrival ofthe contrast agent bolus is displayed on-line with the 2D
sequence. When the arteries in the monitoring image enhance, the
operator starts the angiographic 3D sequence without delay.
The contrast determining parts of k-space must be sampled early
because the bolus maximum has arrived at the time the 3D MRA
sequence begins.

59. THANKYOU

60. References:National Imaging Associates ,Inc: Clinical guideline MRA/MRV
Rad tech's guide to mri: MR Angiography
Applied Radiology: Comparison of magnetic resonance angiography and computed tomographic angiography
MR Angiography : Technique Indication and Practical Application, Springer, G . Scheneider