2026-09-18T19:10:23Zhttps://dspace.mit.edu/server/oai/requestoai:dspace.mit.edu:1721.1/385932026-06-11T15:03:41Zcom_1721.1_7582com_1721.1_7581col_1721.1_131022
Joseph B. Mandeville.
Leite, Francisca Maria Pais Horta
Harvard University--MIT Division of Health Sciences and Technology.
Harvard University--MIT Division of Health Sciences and Technology
2008-11-10T19:51:22Z
2008-11-10T19:51:22Z
2007
http://hdl.handle.net/1721.1/38593
156908733
Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, February 2007.
"September 2006."
Includes bibliographical references.
The main goal of this thesis was to systematically characterize the detection sensitivity, temporal response, and spatial resolution of IRON contrast for fMRI within the awake, behaving monkey. Understanding these issues provides insights into the physiology of the functional response to local changes in brain activity, enables researchers to optimize experimental designs, and delineates the advantages and limitations of neuroimaging within this important animal model. The injection of the iron oxide contrast agent (MION) provided a 9-fold increase in efficiency for block designs relatively to BOLD contrast. Because the hemodynamic response function acts as a low-pass filter on neural activation to attenuate the size of differential responses to alternate stimuli, this factor dropped to approximately 2 for rapidly presented stimuli. Detection efficiency for event-related stimulus designs for BOLD and IRON contrasts could be optimized using random or semi-random distributions for interstimulus intervals. Small increases in predictability could be traded for large gains in efficiency, particularly for the IRON method. A general linear model was successfully employed to describe IRON and BOLD impulse response functions. Both responses were accurately described by a bimodal exponential model with similar time constants, a fast (4.5 sec) and a slow (13.5 sec).
(cont.) The slow response comprised 80% of IRON signal, and was responsible for the BOLD post-stimulus undershoot. It likely encompasses changes in post-arteriole blood volume. Optimized IRON activation maps do not show activation in draining veins or draining tissue, in contrast with BOLD contrast. To examine what happens at the level of small vessels and capillaries, we used point-image stimuli to measure IRON and BOLD point spread functions (PSF) in V1. We estimated an IRON PSF no larger than approximately 0.4 mm, and a BOLD PSF with twice the size. Severe image distortions arising from monkey's body motion outside of the field of view currently limit the achievable spatial resolution. Preliminary data suggests multi-shot EPI with navigators may be useful in improving image stability at higher resolution for IRON fMRI, which can employ short echo times to minimize phase variations, while achieving maximum efficiency by increasing the MION dose.
by Francisca Maria Pais Horta Leite.
Ph.D.
131 p.
eng
Massachusetts Institute of Technology
M.I.T. theses are protected by
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http://dspace.mit.edu/handle/1721.1/7582
Harvard University--MIT Division of Health Sciences and Technology.
Detection power, temporal response, and spatial resolution of IRON fMRI in awake, behaving monkeys at 3 Tesla
Thesis
application/pdf
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Publication
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<Abstract>The main goal of this thesis was to systematically characterize the detection sensitivity, temporal response, and spatial resolution of IRON contrast for fMRI within the awake, behaving monkey. Understanding these issues provides insights into the physiology of the functional response to local changes in brain activity, enables researchers to optimize experimental designs, and delineates the advantages and limitations of neuroimaging within this important animal model. The injection of the iron oxide contrast agent (MION) provided a 9-fold increase in efficiency for block designs relatively to BOLD contrast. Because the hemodynamic response function acts as a low-pass filter on neural activation to attenuate the size of differential responses to alternate stimuli, this factor dropped to approximately 2 for rapidly presented stimuli. Detection efficiency for event-related stimulus designs for BOLD and IRON contrasts could be optimized using random or semi-random distributions for interstimulus intervals. Small increases in predictability could be traded for large gains in efficiency, particularly for the IRON method. A general linear model was successfully employed to describe IRON and BOLD impulse response functions. Both responses were accurately described by a bimodal exponential model with similar time constants, a fast (4.5 sec) and a slow (13.5 sec).</Abstract>
<Abstract>(cont.) The slow response comprised 80% of IRON signal, and was responsible for the BOLD post-stimulus undershoot. It likely encompasses changes in post-arteriole blood volume. Optimized IRON activation maps do not show activation in draining veins or draining tissue, in contrast with BOLD contrast. To examine what happens at the level of small vessels and capillaries, we used point-image stimuli to measure IRON and BOLD point spread functions (PSF) in V1. We estimated an IRON PSF no larger than approximately 0.4 mm, and a BOLD PSF with twice the size. Severe image distortions arising from monkey's body motion outside of the field of view currently limit the achievable spatial resolution. Preliminary data suggests multi-shot EPI with navigators may be useful in improving image stability at higher resolution for IRON fMRI, which can employ short echo times to minimize phase variations, while achieving maximum efficiency by increasing the MION dose.</Abstract>
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