magnetic resonance angiography

MAGNETIC
RESONANCE
ANGIOGRAPHY
PRESENTED BY - DR. ABDUL QAVI

1.INTRODUCTION
2.INDICATIONS
3.TECHNIQUES & BASIC PRINCIPLES
4.NORMAL MRA AND ITS VARIANTS
5.CLINICAL APPLICATIONS
OUTLINE

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.
Introduction

MR ANGIOGRAPHY
NON INVASIVE
NO CONTRAST REQUIRED
NON IONISING
INVASIVE
NEPHROTOXIC CONTRAST
IONISING RADIATION
CONVENTIONAL ANGIO

Vascular structures of brain can be imaged by 4 means:
1. DSA: gold standard. Invasive and risk of nephrotoxic contrast,
ionising radiation
2. Vascular ultrasound: least invasive, can be done bedside, cost
effective. best choice for imaging vessels close to skin surface.
Drawback: limited anatomic coverage, deep vessels cant be imaged,
operator dependent, requires skill
3. CT angio: main drawbacks are contrast use and radiation exposure,
calcifications are overestimated. It is preferred for aorta and
coronaries
4. MRA : is non invasive, no radiation exposure. Preferred for carotids
and intracranial vessels as MRI brain can also be obtained and is
widely used in neurological disorders
DSA-USG-CTA-MRA

1. 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
who are candidates for carotid endarterectomy surgery
when a 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)
Indications of MRA

2. To rule out intracranial aneurysm (ICA), including aneurysms of the
Circle of Willis, in persons who are thought to be at higher risk (e.g.,
history of ICA in a first-degree relative or presence of polycystic
kidney disease);
3. As a follow-up study for a known arteriovenous malformation (AVM),
and for a known non-ruptured intracranial aneurysm that is greater
than 3 mm in size;
4. To evaluate patients with signs/symptoms highly suggestive of
leaking/ruptured aneurysm or AVM (i.e., sudden explosive headache,
stiff neck, blood in the cerebral spinal fluid);
5. To definitively establish presence of stenoses or other abnormalities
of the vertebrobasilar system in patients with symptoms highly
suggestive of vertebrobasilar syndrome (binocular vision loss,
positional vertigo, dysarthria, dysphagia, diplopia).
Indications of MRA contd..

1.TIME OF FLIGHT (TOF)
2.PHASE CONTRAST (PC)
3.CONTRAST ENHANCED MRA (CE MRA)
MRA TECHNIQUES

BASIC PRINCIPLES
PRINCIPLES Protons are excited using GRE pulse sequence
TOF MRA- “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

PC MRA- “manipulating phase of magnetization”
 directional flow encoding magnetic field gradient
causing difference in the phase/orientation
 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
 More time consuming

CE MRA -
 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
 It can be performed within seconds
 Nephrogenic systemic fibrosis is rare but serious
complication.

• In 2DFT technique, multiple thin sections of body are studied
individually and even slow flow is identified
• In 3DFT 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 minimised, and less likely to be
affected by loops and tortusity of vessels
• 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 tortusity, and have lesser chances of
overestimating carotid stenosis.
2D and 3D fourier transform

magnetic resonance angiography

Arteries of the brain (cranial view) - MRA
1. Anterior cerebral artery
2. Anterior communicating artery
3. Basilar artery
4. branches (in insula) of middle
cerebral artery
5. Cavernous portion of internal carotid
artery
6. Cervical portion of internal carotid
artery
7. Genu of middle cerebral artery
8. Intracranial (supraclinoid) internal
carotid artery
9. Middle cerebral artery
10. Ophthalmic artery
11. Petrous portion of internal carotid
artery
12. Posterior cerebral artery
13. Posterior cerebral artery in ambient
cistern
14. posterior cerebral artery in
interpeduncular cistern
15. Posterior communicating artery
16. Posterior inf cerebellar artery.
17. Quadrigeminal portion of posterior
cerebral artery
18. Superior cerebellar artery
19. Vertebral artery

Arteries of the brain (lateral view) - MRA
1. Anterior cerebral artery
2. Anterior communicating artery
3. Basilar artery
4. branches (in insula) of middle cerebral artery
5. Cavernous portion of internal carotid artery
6. Cervical portion of internal carotid artery
7. Genu of middle cerebral artery
8. Intracranial (supraclinoid) internal carotid artery
9. Middle cerebral artery
10. Ophthalmic artery
11. Petrous portion of internal carotid artery
12. Posterior cerebral artery
13. Posterior cerebral artery in ambient cistern
14. posterior cerebral artery in interpeduncular
cistern
15. Posterior communicating artery
16. Posterior inf cerebellar artery.
17. Quadrigeminal portion of posterior cerebral
artery
18. Superior cerebellar artery
19. Vertebral artery

VARIANTS OF CIRCLE OF WILLIS
Krabbe- Hartkamp et al 1998

Variants of circle of willis
Krabbe-Hartmann et al 1998

Anatomical variations in the anterior part of the circle of
Willis

Anatomical variations in the posterior part of the circle of Willis

TWO (OR MORE) ACOAS
Hypoplasia or absence of anterior
communication
Hypoplasia of the a1 segment of the right
ACA

Hypoplasia or absence of both PCoAs
HYPOPLASIA OF RIGHT PCA
B/L FTP
Hypoplastic or absent Rt PcoM

Initial screening test is noninvasive , either DS or MRA.
TOF MRA is less sensitive DS (75%Vs 87%) but more specific (88%Vs
46%).
Concordance in TOF and DS is more sensitive(96%) and specific
(85%) than either test alone.(Johnston, and Goldstein et al 2001)
2D TOF MRA over estimates the degree of stenosis.
3D TOF MRA is less likely to overestimate stenosis.
Combination of 2D and 3D TOF MRA results in greater specificity.
 ‘FLOW GAP’- segmental dropout , When the stenosis is more than
70%. ( Heiserman JE et al 1996)
3D CEMRA have greater anatomical coverage in terms of surface
morphology, carotid bifurcation, near occlusion
3D CE MRA is more sensitive(94.6% vs 91.2%) and specific ( 88.3%vs
91.9%) than TOF MRA for high grade ICA stenosis.
Carotid atherosclerotic narrowing

Carotid stenosis
2D TOF MRA 3D TOF MRA DSA

Carotid
stenosis
CE-MRA
3D TOF-
MRA

Basilar artery stenosis
3D TOF-MRA CTA DSA

 Catheter angiography has been traditionally used for diagnosis of
carotid dissection.
 MRI +fat saturation along with 3D TOF MRA characterise dissecting
hematoma, associated pseudo-aneurysm & length and caliber of
residual patent lumen.
 MRI with MRA is currently the investigation of choice for suspected
dissection.
 Not nearly as helpful in vertebral artery dissections
Carotid or Vertebral artery dissection

3D TOF is now accepted as a non-invasive screening tool for
familial aneurysmal disease.
Sensitivity is greater for detecting aneurysms > 3mm (94%) than
aneurysms < 3mm (38%). ( White et al 2000)
Overall inferior to DSA and misses aneurysm <3mm.(Adams et al
2000)
3D CE MRA is superior to TOF MRA .It is method of choice for
evaluation of giant cerebral aneurysms.
CE MRA shows promise in the follow-up of treated intracranial
aneurysms.
Aneurysms

Anterior communicating Artery aneurysm

Bilobed aneurysm at Rt MCA bifurcation

3D TOF MRA demonstrates a 6 mm aneurysm arising
from the basilar artery tip and projecting anteriorly

MCA aneurysm seen
In T2W MRI as flow void
MCA aneurysm seen
In CECT

 Secondary role to digital subtraction angiography.
 The typical AVM appears on spin-echo MRI as a cluster
of focal round lesions or serpentine areas of signal void
 3D CE MRA is superior to 3D TOF MRA and equivalent to
subtraction angiography in 70-90%of cases in depicting
AVM components.
A-V Malformations

Acute ischemic stroke
 A novel application of MRA is to guide acute stroke
intervention potentially.
 MRA can be a predictor of clinical outcome in acute
ischemic pt. undergoing thrombolysis with IV rtPA in
window period. ( Marks et al 2008).
 The Boston scale ( BASIS) is a classification tool to
help predict outcomes in acute stroke by using MRA
study. ( Torres-Mozqueda et al 2008)

1- No contrast material is required in
angiographic technique-
1. CE-MRA
2. CTA
3. DSA
4. TOF-MRA

2- Angiographic technique for estimation of
velocity and direction of flow-
1. CE-MRA
2. TOF-MRA
3. PC-MRA
4. CTA

3- Complication of gadolinium contrast is –
1- Nephrogenic diabetes insipidus
2- Pulmonary fibrosis
3- Fibrosing alveolitis
4- Neprogenic systemic fibrosis

4- Gold standard for diagnosis and evaluation of
aneurysm is-
1- CTA
2- MRA
3- DSA
4- USG

5- Yellow arrow demonstrate
stenosis of-
1- right ICA
2- right vertebral A.
3- right PCOM
4- Right MCA

6- MRA demonstrate
stenosis of -
1- vertebral artery
2- basilar artery
3- PICA
4- AICA

7- MRA demonstrate Right
MCA-
1- Aneurysm
2- AVM
3- Thrombus
4- Hypoplasia

8- Spetzler-Martin grading system is used for-
1- Aneurysm
2- AVM
3- Thrombosis
4- Arterial dissection

9- Light blue arrow
demonstrate-
1- Anterior choroidal artery
2- Posterior choroidal artery
3-PCOM
4- PCA

10- white arrow denotes-
1- Anterior choroidal artery
2- Posterior choroidal artery
3-PCOM
4- PCA

Summary
1. Two different approaches to MRA are
commonly used: Time-of-Flight (TOF-MRA) &
Phase Contrast (PC-MRA)
2. TOF-MRA is easy to implement and is robust but
has difficulty with slow flow
3. 3D TOF can be combined with fast imaging
methods and Gd contrast agents to obtain
improved depiction of vascular structures

Summary
4. PC-MRA requires more time to acquire
more images but can result in high
resolution, fewer flow related artifacts,
and quantitative measurement of flow
5. Phase-contrast MRI may provide the most
accurate, noninvasive method for
measuring blood flow in vivo

Multiple aneurysms in a 54-year-old woman.

Characteristics CT-angiography MR-angiography
Spatial resolution Good Fair
Size of vessel upto 0.6mm 1.0-1.5mm
Tortuous vessel better visualized -
Time seconds minutes
Risk of radiation exposure yes no
Use of contrast always +/-
Detection of calcification excellent -
CT-angiography vs MR-angiography:
ferromagnetic substance indicated not indicated

magnetic resonance angiography

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Editor's Notes