MR angiography is a type of MRI scan that uses magnetic fields and radio waves to provide pictures of blood vessels without using a catheter. It has advantages over conventional angiography in that it is less invasive, less expensive, and faster. Disadvantages include not depicting small vessels or slow blood flow as well. There are various techniques used in MR angiography including contrast enhanced MRA, which uses gadolinium contrast to visualize vascular structures, and non-contrast MRA such as time-of-flight angiography and phase contrast angiography. Artifacts that can occur include metal artifacts from implanted devices and blooming artifacts around paramagnetic substances.

1. MAGNETIC RESONANCE
ANGIOGRAPHY

2. MR angiography
• 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.
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 patient 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 damge
to an artery.
Disadvantages of MR angiography:
• It does not depict small vessels or extremely slow blood flow as well as
conventional angiography dose.

3. MR ANGIOGRAPHY IMAGES

4. CONTRAST ENHANCED MRANGIOGRAPHY
• It is a technique involving 3D spoiled gradient-echo(GE) sequences,
with administration of Gd-based contrast. It can be utilised to assess
vascular structures of almost any part of the body.
• It key features are as follows:
• T1- weighted spoiled gradient-echo(flip angle 25 degree- 50
degree allows T1- weighting)
• central k-space acquisition corresponding to arterial phase of the
study maximizes preferential visualization arteries
• use of Gd- based contrast to shorten T1-interval of the blood
which appears bright as a result

5. Black blood imaging
• 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.
Blood flow- black image
Slow flow and clot- bright image

6. BLACK BLOOD IMAGING

7. Bright blood imaging
• 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

8. BRIGHT BLOOD IMAGING

9. Non contrast enhanced MR angiography
• It is performed in several ways including:
1.Time of flight angiography(TOF- MRA)
2. Phase contrast angiography(PC- MRA)
• Generally, these techniques are time- consuming as compared with
contrast enhanced MR angiography.
Contrast image
Non- contrast
image

10. Time of flight angiography(TOF)
• It is an MRI technique to visualize flow within vessels, without the
need administer contrast.
• It is based on the phenomenon of flow- related enhancement of spins
entering into imaging slice.
• As a result of being unsaturated, these spins give more signal that
surrounding stationary spins.
• TOF can be of three types :
• 2D time of flight
• 3D time of flight
• MOTSA(Multiple overlapping thin slab (acquistion)

11. TIME OF FLIGHT IMAGES

12. 2D time of flight
• 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
• With 3-D TOF,a volume of images is obtained simultaneously
by phase- encoding in the slice-select direction.
• An angiographic appearance can be generated using MIP,as is
done with 2-D TOF.

13. 2D- TOF IMAGE 3D- TOF IMAGE

14. MOTSA(multiple overlapping thin slab acquisition)
• Combined advantages of 2D(large cover area) and (3D high resolution).
• Imaging volume is divided. these slabs are combined to single volume data.

15. MOTSA(MULTIPLE OVERLAPPING THIN SLAB ACQUISITION)
MRA IMAGE

16. Phase contrast imaging(PC-MRA)
• 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 expierence a different magnitude of the second gradient
compared to the first, because of its different spatial position.
• This result in net phase shift.

17. PHASED CONTRAST MRAIMAGES

18. ECG- Gated FSE MRA
• In the ECG gated fast spin echo techniques images of the
vessels are acquired during diastole and systole.
• On the diastole image both artery and vein are bright while on
the systole image the artery is dark due to slow flow .
• The systole images are subtracted from diastole images
giving the bright blood arteriography.
• The vein and background are subtracted.

19. Advantages of this technique involves:
• relatively short time
• sensitivity to slow flow
• ability to acquire in coronal plane parallel to the vessels. 4.It may not be
suitable for patients with arthythmia(asthamic patient)
• It is mainly used for peripheral arteries and aorta.
• Examples: FBI(fresh blood imaging, Toshiba) NATIVE
SPACE and NATIVE HASTE(SIEMENS)
• TRANCE(PHILIPS) and flow prep.

20. SSFP- Based MRA
• Balanced SSFP sequences are gradient echo steady state sequences with
very high SNR and motion insensitivity due to balanced gradients in all
three directions.
• These sequences are called True FISP(siemens),FIESTA(GE) and balanced
TFE(Philips).
• The contrast is determined by T2/T1 ration giving the blood very high signal
without dependence or inflow.
• Veins other fluid and fat are also bright on this sequences.
• Hence some form of subtraction is required arterial spin labelling(ASL) or
inversion recovery pulses are used for this purpose. Example: SLIP(Spatial
labelling inversion pulse, Toshiba)
• NATIVE True FISP(Siemens)
IFIR(Inflow inversion recovery, GE)

21. SSFP- BASED MRA IMAGES

22. ANGIOGRAPHYARTIFACTS
1. METALARIFACT
2. BLOOMINGARTIFACT
METALARTIFACT
It is intended to reduce the size and intensity of susceptibility artifacts
resulting from magnetic field distortion.
A variety of techniques are used foe reducing metal artifacts at MRI,
both for addressing artifacts due to the presence of metal in the image
plane(in- plane artifacts) and for artifacts due to metal in an adjacent
plane(through- plane artifacts).

23. METAL ARTIFACTS IMAGE

24. BLOOMING ARTIFACTS
• Blooming artifacts is a susceptibility artifact encountered on some MRI
sequences in the presence of paramagnetic substance that affect the
local magnetic milieux. Most affected sequences are T2*, and in many
instances they are designed to exploit this phenomenon to make certain
pathologies more conspicuous. As such although
• it is artifact, it is used deliberately to improve detection of certain
small lesion, much as the T1 shortening effect of low concentration
gadolinium are used to detect contrast enhancement.
• The term “blooming” refers to the fact that lesions appear larger than
they actually are.

25. BLOOMING ARTIFACT IMAGE

26. THANK YOU