Michael Marxen

Dr. Michael Marxen

Research Focus

My area of research is medical imaging physics and its applications. During my Ph.D. at Sunnybrook Health Sciences Centre, I studied the fractal properties of vascular structures and models of organ blood flow using computed tomography. In that time, I became more and more interested in human cognition and the brain. Consequently, after completing my Ph.D. research, I joined the Rotman Research Institute as a postdoctoral fellow in December 2006 to work on the advancement of brain imaging techniques.

Two research projects are currently in progress:

1. Functional Magnetic Resonance Imaging (fMRI) and Magnetoencephalography (MEG) of Brain Activity

Both fMRI and MEG provide measures of brain activity. However, fMRI signals are related to changes in local blood flow while MEG records changes in the magnetic field around the head related to changes in neuronal currents in the brain. In addition, a feature of fMRI is high spatial resolution with poor time resolution while MEG, in comparison, has lower spatial resolution and higher temporal resolution. Combining these two techniques offers therefore a more complete picture of brain activity than either technique by itself.

In the current project, we are using both of these techniques to measure the response of the brain to vibrational stimuli on a finger. The stimuli cause a neuronal response in the brain, associated with changes in the MEG signal, which then causes an increase in blood flow and a subsequent change in the fMRI signal. Based on our knowledge of both fMRI and MEG signals we are trying to improve our current understanding of this chain of events. This will improve our ability to detect changes in normal brain function, for example due to stroke. In stroke patients, the sense of touch is often impaired. Such patients will therefore be part of this study to investigate how the response of the brain to a vibrational stimulus has changed. This, in turn, may provide clues for future therapies.

2. Evaluation of Parallel Magnetic Resonance (MR) Imaging based on Quantitative Brain Morphometry

In recent years, a new technique in MR imaging called Parallel Imaging has created the potential to acquire images much faster than previously possible. However, this is also associated with a loss of image quality. In this study, we are comparing different levels of acceleration based on commonly performed measures of brain morphology, for example measures of local brain volume. If the change in these measures is minor, then acceleration is recommended. However, major changes would discourage acceleration.

Acceleration is possible for a number of sequences that are commonly employed clinically. The reduction in scan time benefits the comfort of patients and reduces the cost for their examination.

Publications

Title Source (Journal/Book/Conference) Authors/Presenters Published On Type
Intersubject Variability in Transient and Sustained fMRI Signals from Somatosensory and Motor Cortex Marxen M, Cassidy R, Ross B, Graham S 1275796800 Presentation
Adding Transients to model BOLD fMRI Time Courses for Somatosensory-Motor Activation Marxen M, Cassidy R, Dawson T, Ross B, Graham S 1272686400 Presentation
Correcting magnetic resonance K-space eata for in-plane motion using an optical position tracking system Medical Physics Marxen M, Marmurek J, Baker N, Graham SJ 1259643600 Journal Article
Spatial Correlations of BOLD fMRI and MEG Signal Components from Somatosensory Cortex NEUROIMAGE Marxen M, Dawson TL, Bardouille T, Ross B, Tam F, Graham SJ 1245297600 Abstract
Spatial Correlations of BOLD fMRI and MEG Signal Components from Somatosensory Cortex Marxen M, Dawson TL, Bardouille T, Ross B, Tam F, Graham S 1245297600 Presentation
Combining fMRI and MEG to investigate neurovascular coupling in the somatosensory system Rotman Rounds Marxen M 1243224000 Presentation
Volume ordering for analysis and modeling of vascular systems Annals of Biomedical Engineering Marxen M, Sled JG, Henkelman RM 1233550800 Journal Article
Transient and Steady-State Components of fMRI BOLD and MEG Signals from Somatosensory Cortex NEUROIMAGE Marxen M, Dawson TL, Bardouille T, Ross B, Tam F, Graham SJ 1213761600 Abstract
Evaluating Faster Structural MRI Acquisitions based on Automated Measures of Classified Local Brain Volumes NEUROIMAGE Marxen M, Dawson TL, Hanratty MK, Smith GS, Graham SJ 1213502400 Abstract
Transient and Steady-State Components of the fMRI BOLD Signal in Somatosensory Cortex ISMRM Marxen M, Marmurek J, Baker SN, Graham SJ 1209787200 Abstract
Transient and Steady-State Components of the fMRI BOLD Signal in Somatosensory Cortex Proceedings of the International Society for Magnetic Resonance in Medicine Marxen M, Dawson TL, Tam F, Graham SJ 1209614400 Abstract
Comparing microsphere deposition and flow modeling in 3D vascular trees American Journal of Physiology: Heart and Circulatory Physiology Marxen M,Sled JG, Yu LX, Paget C, Henkelman RM 1167541200 Journal Article
Estimating perfusion using microCT to locate microspheres Physics in Medicine and Biology Marxen M, Paget C, Yu LX, Henkelman RM 1156737600 Journal Article
MicroCT scanner performance and considerations for vascular specimen imaging Medical Physics Marxen M, Thornton MM, Chiarot CB, Klement G, Koprivnikar J, Sled JG, Henkelman RM 1093665600 Journal Article
Analysis of microvasculature in whole kidney specimens using micro-CT Proceedings of SPIE Sled JG, Marxen M, Henkelman RM 1093665600 Journal Article
Branching tree model with fractal vascular resistance explains fractal perfusion heterogeneity American Journal of Physiology: Heart and Circulatory Physiology Marxen M, Henkelman RM 1062043200 Journal Article
Comparison of Gaussian particle center estimators and the achievable measurement density for particle tracking velocimetry Experiments in Fluids Marxen M, Sullivan PE, Loewen MR, Jähne B 965102400 Journal Article

Education

  • 2004: PhD, Physics, University of Toronto, Department of Medical Biophysics Toronto, Ontario, Canada (Supervisor: R. M. Henkelman Thesis: “Fractal Characteristics of Vascular Structure & Modeling of Blood Flow in Three Dimensions” Thesis)
  • 1998: MSc, Faculty of Physics and Astronomy, Ruprecht-Karls-Universität, Heidelberg, Germany (Supervisor: B. Jähne Thesis: “Particle Image Velocimetry in fluid flows with strong velocity gradients”)
  • 1995: Exchange Student, McMaster University Hamilton, Ontario, Canada
  • 1997: Research Stay, University of Toronto, Department of Mechanical and Industrial Engineering Toronto, Canada
  • 1993: BSc, Vordiplom , Universität Osnabrück, Department of Physics Osnabrück ,Germany

Academic Appointments

  • 2006–Present: Postdoctoral Fellow, Rotman Research Institute, Baycrest Centre for Geriatric Care, Toronto, Ontario, Canada (Functional Magnetic Resonance Imaging and Magnetoencephalography of Somatosensory Cortex)
  • 2005–2006: Independent Studies of Asian philosophies and associated journalistic work
  • 2004–2005: Research Associate, Sunnybrook & Women’s College Health Sciences Centre, Toronto, Ontario, Canada (Development of a new technique to measure blood flow distribution using computed tomography (CT) to quantitate microspheres deposition and three-dimensional measurements of blood flow distribution and vascular structure in the same organ.)
  • 1998: Research Associate, Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario, Canada (Software development for Particle Image Velocimetry1)
  • 1994–1991: Student Intern, Siemens AG, Berlin, Germany (Drive Technology, Circuitry and Installation Technology)

Distinctions and Awards

  • 2007: Edward Christie Stevens Fellowship, University of Toronto
  • 2003: Ontario Graduate Scholarship (for Science & Technology), Government of Ontario
  • 2002: Scholarship, Heart and Stroke Foundation of Canada
  • 1994: Student Exchange Scholarship, Ontario-Baden-Württemberg

Curriculum Vitae

Contact

The Rotman Research Institute
Baycrest
3560 Bathurst Street, 1022
Toronto, Ontario
Canada M6A 2E1 Phone: 416-785-2500 x3060 Email: mmarxen@rotman-baycrest.on.ca