1. Imaging of Small Vessels in the Brain using MRI
Susanne Schmid
Biomedical Engineering, University of Calgary
Seaman Family Centre, Foothills Medical Centre

2. Outline Small Vessel & Dementia – Clinical Aspects
MR Imaging Techniques
Angiography
Compressed Sensing
Research Activities
Simulation of Slow Blood Flow
Improved Phase Contrast
4. Future Activities

3. Outline Small Vessel & Dementia – Clinical Aspects
MR Imaging Techniques
Angiography
Compressed Sensing
Research Activities
Simulation of Slow Blood Flow
Improved Phase Contrast
4. Future Activities

4. Small Vessels

5. Imaging of the small vessels
Small Vessel Diseases
Imaging of the small vessels

6. Dementia 564,000 Canadians are currently living with dementia
(Global 47.5 Million)
5% - 6% of people over the age of 65 have some form of dementia
$33 billion combined cost to the health care system
50% over the age of 85 years suffer from dementia

7. Dementia
- “a chronic or persistent disorder of the mental processes caused by brain disease or injury and marked by memory disorders, personality changes, and impaired reasoning. “
Types of Dementia:
Alzheimer’s disease (50-70%)
Vascular Dementia (20%)
Lewy Body Dementia
Mixed Dementia
Frontotemporal Dementia ….
564,000 Canadians are currently living with dementia

8. Small Vessel Diseases - SVD
SVD Characteristics:
Lacunar infarcts
White matter hyperintensity
Lacune
Perivascular space
Cerebral microbleeds

9. Outline Small Vessel & Dementia – Clinical Aspects
MR Imaging Techniques
Angiography
Compressed Sensing
Research Activities
Simulation of Slow Blood Flow
Improved Phase Contrast
4. Future Activities

10. Challenges in Imaging Small vessel: diameter < 500 µm
blood velocities about ~ 8 cm/s
High resolution images
motion
low signal to noise ratio
Slow blood flow
signal loss due to saturation effects
(Kang 2009)
high resolution
more signal
Long acquisition time & slow blood flow
Motion
Slow blood flow (8 cm/s)
More saturation effects -> signal loss in the blood vessels

11. 7 Tesla Scanner Patient with Subcortical Vascular Dementia
Subject with Normal Cognition
(Kang 2012)

12. Non Contrast MR Angiography
Time of Flight (flow related enhancement)
Voxel Flow
Voxel Signal
No Flow
Flow = ½ voxel/ TR
Flow = 1 voxel/ TR
(Carr, 2012)

13. Non Contrast - MR Angiography
Time of Flight (flow related enhancement)
Phase Contrast
Signal intensity ∝ blood velocity
(Carr, 2012)

14. Non Contrast MR Angiography
Time of Flight (flow related enhancement)
Phase Contrast
Signal intensity ∝ blood velocity
Arterial Spin Labeling with Fast Spin Echo
(Carr, 2012)

15. Non Contrast MR Angiography
Tissue
T2/T1
Muscle
0.05
Liver
0.08
Brain
0.11
Arterial blood
0.21
Fat
0.30
CSF
0.70
Time of Flight (Flow related enhancement)
Phase Contrast
Signal intensity ∝ blood velocity
Arterial Spin Labeling with Fast Spin Echo
Balanced Steady-State Free Precession (bSSFP)
Signal intensity ∝ T2/T1
STARFIRE
(bSSFP sequence)
2D ToF
(Carr, 2012)

16. Compressed Sensing Retrospective compression Immediate compression
(Feng, 2016)

17. Outline Small Vessel & Dementia – Clinical Aspects
MR Imaging Techniques
Angiography
Compressed Sensing
Research Activities
Simulation of Slow Blood Flow
Improved Phase Contrast
4. Future Activities

18. Phase Contrast Simulation
Bloch equation simulation:
magnetization of tissue
moving blood
static magnetic field 3 T
spoiled Gradient Echo
phase contrast
TE = 11 ms , TR= 50 ms
flip angle: 14 degree

19. Phase Contrast Simulation
Bloch equation simulation:
magnetization of tissue
moving blood
static magnetic field 3 T
spoiled Gradient Echo
phase contrast
TE = 11 ms , TR= 50 ms
flip angle: 14 degree

20. Post Processing - Phase Contrast
Phase Difference
Magnitude
Complex Difference
Magnitude x
Phase Difference
Magnitude x (Phase Difference)2
Complex Difference X Phase Difference

21. Improved Phase Contrast

22. Future Research
Compressed Sensing may reduce effects of motion due to speed-up
bSSFP may increase signal to noise ratio, can also be used for static blood.
Combinations with e.g. arterial spin labeling, phase contrast possible?
Optimize pulse sequences & reconstruction for the visualization of the small vessels - How suitable are the different angiography techniques?
Non-cartesian acquisition pattern e.g. cylinder acquisition ?

23. Thank you! Acknowledgement Funding Sources: Dr. Richard Frayne
CREATE I3T
HBI Donald Burns and Louise Berlin Graduate Award
Dr. Richard Frayne
Dr. Louis Lauzon
Dr. Marc Lebel
Vascular Imaging Lab
Seaman Family MR Research Center
Thank you!