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.
|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|