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

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

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

Small Vessels https://www.nia.nih.gov/alzheimers/scientific-images

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

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

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 …. https://www.nia.nih.gov/alzheimers/scientific-images 564,000 Canadians are currently living with dementia

Small Vessel Diseases - SVD SVD Characteristics: Lacunar infarcts White matter hyperintensity Lacune Perivascular space Cerebral microbleeds http://www.curediseasecouncil.com/small-vessel-disease-brain-prognosis-vascular-dementia-signs-symptoms-diagnosis.html.

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

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

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

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)

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

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)

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)

Compressed Sensing Retrospective compression Immediate compression (Feng, 2016)

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

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

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

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

Improved Phase Contrast

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 ?

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!