1. TIME OF FLIGHT
Nafeesa M A C
B Sc (AHS) INTERNEE
Department of Radiology and Imaging Sciences
Sri Ramachandra University, Porur, Chennai

2. INTRODUCTION
• Time of flight is one of the MR Angiography techniques
which produces images of the blood vessels with out
using any contrast agent

3. TIME OF FLIGHT MR
ANGIOGRAPHY
Entry slice phenomenon

5. TIME OF FLIGHT MR
ANGIOGRAPHY
• Time of flight produces vascular contrast by
manipulating the longitudinal magnetization of the
stationary spins
• The TR is kept well below T1 time of the stationary
tissues so that T1 recovery is prevented

6. TIME OF FLIGHT MR
ANGIOGRAPHY
• Time of flight MR angiography uses incoherent gradient echo
sequence in combination with gradient moment rephasing
• Gradient moment rephasing is used to enhance flow
• It uses additional gradients to correct the altered phases back to
their original values
• The flowing spins travelling along the gradients accumulate
zero phase change

7. TIME OF FLIGHT MR
ANGIOGRAPHY
Gradient moment nulling

8. TIME OF FLIGHT MR
ANGIOGRAPHY
For evaluation of Cerebral arteries

9. TIME OF FLIGHT MR
ANGIOGRAPHY
For evaluation of Cerebral veins

10. TIME OF FLIGHT MR
ANGIOGRAPHY
2D TOF
In 2D TOF the signals are received sequentially from
a series of image slices.
MR Cerebral Venogram

11. TIME OF FLIGHT MR
ANGIOGRAPHY
3D TOF
In 3D TOF the signals are received from the entire
volume of interest
MR Cerebral Angiogram

12. TIME OF FLIGHT MR
ANGIOGRAPHY
3D TOF
MR Neck Angiogram

13. TIME OF FLIGHT MR
ANGIOGRAPHY
2D TOF
Advantages Disadvantages
Large area of coverage Lower resolution
Sensitive to slow flow Venetian blind artifact
3D TOF
Advantages Disadvantages
High resolution for smaller Saturation of in-plane flow
vessels
Sensitive to T1 effects Small area of coverage

14. TIME OF FLIGHT MR
ANGIOGRAPHY
PARAMETERS 2D TOF 3D TOF
TR 40-50ms 40-50ms
TE Minimum permissible Minimum permissible
Flip angle Approximately 600 Approximately 600
Saturation slab Inferior Superior
slice thickness 1.5mm and above 1mm and above

15. TIME OF FLIGHT MR
ANGIOGRAPHY
Multiple overlapping thin 3D slab acquisition
MOTSA
In MOTSA overlapping thin slabs are used
Advantages:
• Reduce flow signal saturation
• High spatial resolution
• Good SNR

16. TIME OF FLIGHT MR
ANGIOGRAPHY (MTC)
Magnetization Transfer contrast
MTC is used to improve the image contrast so as to
enhance the conspicuity of blood vessels by effectively
suppressing the intervening background tissue signals
WITHOUT MTC WITH MTC

18. TIME OF FLIGHT MR
ANGIOGRAPHY
ANEURYSM

19. TIME OF FLIGHT MR
ANGIOGRAPHY

20. TIME OF FLIGHT MR
ANGIOGRAPHY

21. TIME OF FLIGHT MR
ANGIOGRAPHY

22. TIME OF FLIGHT MR
ANGIOGRAPHY
Conclusion

23. THANK
YOU

24. IMAGING MODE
TOF MRA can be either acquired in 2d or 3d mode
Applications:
2D:
• Optimal in areas of slower signal velocity flow
• Used where larger area of coverage is required.
3D:
• Used in high areas of velocity flow
• For high resolution to visualize small vessels

25. TIME OF FLIGHT MR
ANGIOGRAPHY
Gradient moment nulling

26. ADVANTAGES AND DISADVANTAGES
Advantages:
• Reasonable imaging time
• Sensitive to slow flow
• Reduced sensitivity to intra voxel dephasing
Disadvantages:
• Sensitive to T1 effects
• Saturation of in plane flow
• Enhancement is limited to either flow entering
the fov or very high velocity flow.

27. VENETIAN BLIND ARTIFACT
venetian blind artifact occurs due to the
respiration and the patient motion that moves
tissue in and out of the slice that is being
suppressed.

28. MOTSA(multiple overlapping thin slab
acquisition)
Multiple thin slab acquisition reduces the signal
saturation of slowly flowing blood compared to
one thick single-slab acquisition, and
overlapping slab acquisition eliminates the
signal void from each slab boundary region
often called the venetian blind artifact. The
slices located in the overlapped region can be
acquired twice with an entry slice from the first
slab and an exit slice from the next slab.

29. MOTSA(multiple overlapping thin slab
acquisition)
Increasing the amount of slab can reduce the
slab boundary artifact. Increasing the slab by
50% completely reduces the slab boundary
artifact.
The disadvantage is increasing the overlap
increases the scan time per unit coverage in the
slice direction

30. INTRODUCTION
Time-of-flight techniques derive contrast between
flowing blood and stationary tissues by
manipulating the magnitude of the
magnetization, such that the magnitude of the
magnetization from the moving spins is large and
the magnitude of the magnetization from the
stationary spins is small. this leads to a large signal
from moving blood spins
and a diminished signal from stationary tissue spins.

32. TIME OF FLIGHT MR
ANGIOGRAPHY
2D TOF
Advantages Disadvantages
Large area of coverage Lower resolution
Sensitive to slow flow Venetian blind artifact
3D TOF
Advantages Disadvantages
High resolution for smaller Saturation of in-plane flow
vessels
Sensitive to T1 effects Small area of coverage