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Bradley MacIntosh, PhD

Senior scientist

Canadian Partnership for Stroke Recovery
Sunnybrook Health Sciences Centre
2075 Bayview Ave., Room M6 180
Toronto, ON
M4N 3M5

Phone: 416-480-6100, ext. 7277
Fax: 416-480-4552


  • 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:

Research Foci:

  • Human brain mapping
  • Brain physiology
  • Arterial spin labeling
  • Stroke and stroke recovery
  • Vascular contributions to Alzheimer's disease

Research Summary:

As a neuroimaging scientist Dr. MacIntosh uses vascular imaging techniques to study brain function and physiology. The lab focuses on characterizing hemodynamic and cerebral blood flow in clinical populations, primarily using arterial spin labeling and blood oxygenation level-dependent functional magnetic resonance imaging. The lab develops analysis methods and image processing procedures aimed at new imaging metrics or improved image quality. In addition, the lab runs clinical trials on aerobic exercise in various groups: adults with chronic stroke or small vessel disease white matter hyperintensities. The lab also works closely with the Centre for Youth Bipolar Disorder at Sunnybrook.

The lab is currently conducting clinical trials on the effects of aerobic exercise on the brain. Dr. MacIntosh is interested in finding ways to improve recovery after stroke through imaging cerebrovascular disease to study small vessel disease such as Alzheimer’s disease and other dementias. He also maintains collaborative projects on hypertension, type 2 diabetes and youth bipolar disorder.

Arterial spin labeling

Perfusion is the process of delivering oxygen to tissue (units: mL blood /100g tissue /min). More than two decades ago, MRI scientists discovered that it was possible to measure perfusion by magnetically tagging water in arterial blood and measuring this effect in downstream tissue. This arterial spin labeling (ASL) technique has proved to be useful to non-invasive image perfusion, predominantly in the brain (i.e. cerebral blood flow). Arterial spin labeling can also be used to measure perfusion changes during a functional activation experiment while the participant is performing a task in the MRI scanner. Dr. MacIntosh has helped pioneer new methods for ASL by studing stroke and other vascular diseases of the brain, which includes measuring the time it takes for blood to move from the labeling region to tissue, known as arterial transit time. 

Effects of aerobic exercise on the brain

Despite all that is known about the beneficial effects of exercise, there are still many unanswered questions on how exercise affects the human brain. For instance, are the beneficial effects the same in young and old and among individuals that have cerebrovascular disease? What is the right aerobic exercise recipe that maximizes recovery after stroke? These are significant questions in this field of research that is growing quickly. The lab is currently conducting exercise trials to look at acute (short-term) and chronic (long-term) exercise effects on the brain. In particular, his group is investigating whether individuals with white matter hyperintensity, which are ischemic lesions caused by small vessel disease, can produce measurable changes in their cerebral blood flow and morphology after participating in an exercise program.

Functional magnetic resonance imaging

The blood oxygenation level dependent (BOLD) contrast technique was discovered in the early 1990s and is now used widely for functional MRI studies. Dr. MacIntosh has used fMRI to study how individuals generate movements, through coordinating muscles and generating electromyography signals; attention, arousal and the role of the autonomic nervous system; and acute and chronic changes in activation associated with aerobic exercise. In addition, analysis approaches for task and resting state fMRI is an active area of research in the lab.  

Selected Publications:

See current publications list at PubMed.

  1. 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.
  2. 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.
  3. 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.
  4. Makedonov I, Chen JJ, Masellis M, MacIntosh BJ. Physiological fluctuations in white matter are increased in Alzheimer's disease and correlate with neuroimaging and cognitive biomarkers. Neurobiol Aging. 2016 Jan;37:12–18.
  5. MacIntosh BJ, Swardfager W, Crane DE, Ranepura N, Saleem M, Oh PI, Stefanovic B, Herrmann N, Lanctôt KL. Cardiopulmonary fitness correlates with regional cerebral grey matter perfusion and density in men with coronary artery disease. PLoS One. 2014 Mar 12;9(3):e91251.

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