Physical sciences

Education:

• B.Sc., 1999, theoretical physiology, University of Toronto, Canada
• M.Sc., 2001, medical biophysics, Western University, Canada
• PhD, 2006, medical biophysics, U of T

Appointments and Affiliations:

• Senior scientist, Physical Sciences, Hurvitz Brain Sciences Research Program, Sunnybrook Research Institute
• Neuroimaging scientist, Sunnybrook
• Associate professor, department of medical biophysics, U of T

Research Foci:

• Computational neuroradiology
• Brain physiology
• Arterial spin labeling
• Stroke and stroke recovery
• Vascular contributions to Alzheimer's disease

Research Summary:

The MacIntosh lab uses neuroimaging techniques to study brain function and physiology. We focus on cerebral blood flow and functional MRI techniques that are deployed in clinical populations. The pulse sequences are arterial spin labeling and blood oxygenation level-dependent functional magnetic resonance imaging. The lab contributes to neuroimaging protocols & methods, works towards imaging biomarkers, and machine learning methods. The lab supports multi-site imaging initiatives, such the Canadian Dementia Imaging Protocol (CDIP) and the NeuroCOVID-19 study. In addition, the lab helps to conduct human clinical trials where neuroimaging is included as an outcome measure. Clinical trials target discoveries in the fields of stroke, diabetes, and psychiatry.

Arterial spin labeling

Perfusion refers to the delivery of blood to tissue, which we can measure empirically with units of mL blood /100g tissue /min. For more than two decades, MRI scientists have relied on highly versatile pulse sequence designs to tag and visualize the movement of water molecules in blood. Arterial spin labeling (ASL) is an MRI cerebral blood flow imaging technique that has gained attention in clinical and research settings. ASL-based CBF imaging has been validated against gold-standard Positron Emission Tomography. Dr. MacIntosh and team have pioneered ASL image processing methods and applied this neuroimaging tool to study stroke, Alzheimer’s disease, diabetes and bipolar disorder. Recent efforts aim to streamline ASL image processing, including artificial intelligence deep learning, to facilitate clinical translation and wider adoption.

Functional magnetic resonance imaging

Blood oxygenation level dependent (BOLD) MRI contrast was discovered in the 1990s and is now used widely to study human brain function. Dr. MacIntosh has used fMRI to address a wider range of neuroscience questions (motor system, stroke impairments, autonomic nervous system, cognition). BOLD imaging can also be used to assess blood vessel function. Therefore the lab uses BOLD to measure cerebrovascular reactivity and cardiac-related brain pulsations.

Selected Publications:

See current publications list at PubMed.

1. MacIntosh BJ, Shirzadi Z, Atwi S, Detre JA, Dolui S, Bryan RN, Launer LJ, Swardfager W. Metabolic and vascular risk factors are associated with reduced cerebral blood flow and poorer midlife memory performance. Hum Brain Mapp. 2020 Mar;41(4):855-864. doi: 10.1002/hbm.24844. PMID: 3484552.
2. MacIntosh BJ, Ji X, Chen JJ, Gilboa A, Roudaia E, Sekuler AB, Gao F, Chad JA, Jegatheesan A, Masellis M, Goubran M, Rabin J, Lam B, Cheng I, Fowler R, Heyn C, Black SE, Graham SJ. Brain structure and function in people recovering from COVID-19 after hospital discharge or self-isolation: a longitudinal observational study protocol. CMAJ Open. 2021 Nov 30;9(4):E1114-E1119. doi: 10.9778/cmajo.20210023. PMID: 34848552.
3. Luciw NJ, Toma S, Goldstein BI, MacIntosh BJ. Correspondence between patterns of cerebral blood flow and structure in adolescents with and without bipolar disorder. J Cereb Blood Flow Metab. 2021 Aug;41(8):1988-1999. doi: 10.1177/0271678X21989246. Epub 2021 Jan 24. PMID: 33487070.
4. Shirzadi Z, Stefanovic B, Chappell MA, Ramirez J, Schwindt G, Masellis M, Black SE, MacIntosh BJ. Enhancement of automated blood flow estimates (ENABLE) from arterial spin-labeled MRI. J Magn Reson Imaging. 2018 Mar;47(3):647–655. DOI: 10.1002/jmri.25807. Epub 2017 Jul 6.
5. Mutsaerts HJ, Petr J, Václavů L, van Dalen JW, Robertson AD, Caan MW, Masellis M, Nederveen AJ, Richard E, MacIntosh BJ. The spatial coefficient of variation in arterial spin labeling cerebral blood flow images. J Cereb Blood Flow Metab. 2017 Sep;37(9):3184–3192. DOI: 10.1177/0271678X16683690. Epub 2017 Jan 6.
6. Tchistiakova E, MacIntosh BJ, for the Alzheimer’s Disease Neuroimaging Initiative. Summative effects of vascular risk factors on cortical thickness in mild cognitive impairment. Neurobiol Aging. 2016 Sep;45:98–106.

Related News and Stories:

• Does being on a path to diabetes affect your brain? Obesity and high blood sugar, among other traits, linked to changes in brain blood flow and poorer memory: study (Dec. 10, 2019)
• Scientists secure investment from federal research funding agency: Grants will advance new approaches to treating cancer, and diseases of the heart and brain (July 16, 2019)
• Ask a scientist: "What is the biggest misconception about being a scientist?" (SRI Magazine, 2017)
• Back to basics: Federal agency invests in SRI scientists (June 30, 2016)
• Aerobic exercise as a "biological probe" in bipolar disorder (SRI Magazine, 2016)
• Illuminating frontotemporal dementia: Landmark study identifies imaging biomarker that can detect earliest signs of brain decay in those at risk for this devastating disease (SRI Magazine, 2015)
• Infrastructure issues: Congestion and chaos on the brain's highways: This is neurodegeneration (SRI Magazine, 2013)
• Spotted: Imaging and the injured brain: Detecting the obvious and the insidious (SRI Magazine, 2013)
• Driving progress: National health research agency funds a dozen SRI scientists (April 25, 2014)
• Q&A: Dr. Bradley MacIntosh (SRI Magazine, 2011)
• CV: Dr. Bradley MacIntosh (Nexus, Spring 2010)

Related Links:

• Centre for Research in Image-Guided Therapeutics