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I Jung Feng_Dissertation.pdf (2.51 MB)

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Dynamic Adjustment of Stimuli in Real-Time Functional Magnetic Resonance Imaging

FENG, I JUNG
http://rave.ohiolink.edu/etdc/view?acc_num=case1373025879

Abstract Details

, Doctor of Philosophy, Case Western Reserve University, Epidemiology and Biostatistics.
Conventional fMRI image analysis is performed by carrying out a massive number of parallel regression analyses. fMRI signal is known for its low signal-noise-ratio, and its complexity, such as reflected by spatial and temporal autocorrelation. In order to ensure accurate localization of brain activity, stimulus administration in an fMRI session is often lengthy and repetitive. In real time fMRI, signal processing is carried out while the signal is being observed. This method allows for the dynamic adjustment of stimuli through sequential experimental designs. We have developed a voxel-wise sequential probability ratio test (voxel-wise SPRT) approach for dynamically localizing activation associated with stimuli, as well as decision rules for the stopping of experimentation. Stopping is dynamically determined when sufficient statistical evidence is collected to assess the activation status of voxels across regions of interest. Simulation studies show that the number of scan units can be reduced substantially compared to standard fMRI experimental designs that are fixed and predetermined, while still achieving comparably high levels of classification accuracy. An analysis based on actual brain imaging confirms the promise of this approach. An interesting application of dynamic adjustment of fMRI stimuli is in the area of Alzheimer’s disease (AD). It is clear that there is a fair amount of heterogeneity in the cognitive course of the disease. This has led to the development of theories related to the notion of cognitive reserve, which posits that neural capacity, efficiency, and plasticity play a role in this heterogeneity. It has been further hypothesized that cognitive reserve levels at pre-symptomatic stage of AD will manifest specific neural activation patterns under carefully designed fMRI experimentation that systematically varies difficulty levels of a targeted task. A sequential testing approach is proposed for efficiently and accurately identifying and classifying such patterns. Methods for characterizing cognitive reserve that are studied here are comprised of two approaches. The first is sequential estimation through monitoring confidence interval lengths over a range of experimental conditions to assess efficiency and capacity. The other is sequential selection of difficulty levels, to detect neural compensation, which is a reflection of plasticity. Both approaches show high efficiencies and high detection accuracies in our fMRI simulation studies. These two approaches open up new possibilities for studying and characterizing cognitive reserve, which will in turn lead to a better understanding of processes in AD.
Curtis Tatsuoka (Advisor)
158 p.
Biostatistics

Recommended Citations

Citations

  • FENG, I. J. (2013). Dynamic Adjustment of Stimuli in Real-Time Functional Magnetic Resonance Imaging [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1373025879

    APA Style (7th edition)

  • FENG, I JUNG. Dynamic Adjustment of Stimuli in Real-Time Functional Magnetic Resonance Imaging. 2013. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1373025879.

    MLA Style (8th edition)

  • FENG, I JUNG. "Dynamic Adjustment of Stimuli in Real-Time Functional Magnetic Resonance Imaging." Doctoral dissertation, Case Western Reserve University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=case1373025879

    Chicago Manual of Style (17th edition)

case1373025879
516
© 2013, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.