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  A general model for BOLD signal up to 16.4T for GRE and SE

Uludag, K., Müller-Bierl, B., & Ugurbil, K. (2008). A general model for BOLD signal up to 16.4T for GRE and SE. Magnetic Resonance Materials in Physics, Biology and Medicine, 21(Supplement 1): 48, 35-36.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0003-A151-B Version Permalink: http://hdl.handle.net/21.11116/0000-0003-A152-A
Genre: Meeting Abstract

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 Creators:
Uludag, K1, 2, Author              
Müller-Bierl, BM1, 2, Author              
Ugurbil, K, Author
Affiliations:
1Former Department MRZ, Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_2528700              
2Max Planck Institute for Biological Cybernetics, Max Planck Society, Spemannstrasse 38, 72076 Tübingen, DE, ou_1497794              

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 Abstract: Introduction: The blood oxygenation level-dependent (BOLD) signal using fMRI is currently the most popular imaging method to study brain function non-invasively. However, it is not fully understood quantitavely how the differ- ent water (proton) pools inside blood vessels and/or in tissue contribute to the total MRI signal both intrinsically and as a function of blood oxygenation and volume and how these effects change with magnetic field or spin preparation. In this study, through simulations, we quantitatively assess the various BOLD signal contributions by proposing a ge neral model for the BOLD signal for field strengths up to 16.4T for both gradient-echo (GRE) and spin-echo (SE). Methods: For each of the contributions, we provide analytical formulas for: a) intrinsic intra-vascular (IV) and extra-vascular (EV) relaxation rate (with no deoxygenated Hemoglobin (deoxy-Hb)) derived from published experimen- tal data; b) deoxy-Hb dependence, derived for EV BOLD signal from Monte- carlo Simulations and for IV BOLD signal, again from experimental values. This BOLD signal model was used to investigate the various contributions to the BOLD signal assuming oxygenation and blood volume values typical for micro- and macrovasculature. Results: The results indicate, most notably, that for SE: a) the IV BOLD sig- nal (Figure 1) does not disappear for high field strengths but rather shifts to blood vessels with high blood oxygenation; b) diffusion weighting at low field strengths increases micro-vasculature weighting; c) using a TE larger than the T2 of tissue also enhances micro-vasculat ure weighting, though compromising signal-to-noise ratio for sp atial specificity; d) surprisingly, the highest micro- vasculature weighting is achieved for field strength between 4 and 7T. For GRE, there is no field strength for which micro-vasculature BOLD signal is larger than macro-vasculature BOLD signal. Discussion: A general model of the BOLD signal up to 16.4T for GRE and SE was provided. For both IV and EV BOLD signal (Figure 1 and 2), analytical expressions for intrinsic relaxation rates and as a function blood oxygenation and volume were derived from experimental and computer simulation data. It was found that IV and EV signal contributions vary with field strength, echo time and MRI sequence used and these imaging parameters can be optimized to yield high micro-vasculature weighting. The results have consequences for assessing spatial specificity of fMRI and for the exact formulation of some standard fMRI techniques currently relying solely on theoretical estimates of EV BOLD signal, e.g. calibrated BOLD signal and vessel size imaging.

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 Dates: 2008-09
 Publication Status: Published in print
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 Rev. Type: -
 Identifiers: DOI: 10.1007/s10334-008-0123-5
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Title: ESMRMB 2008 Congress: 25th Annual Meeting
Place of Event: Valencia, Spain
Start-/End Date: 2008-10-02 - 2008-10-04

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Title: Magnetic Resonance Materials in Physics, Biology and Medicine
Source Genre: Journal
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Publ. Info: Amsterdam : No longer published by Elsevier
Pages: - Volume / Issue: 21 (Supplement 1) Sequence Number: 48 Start / End Page: 35 - 36 Identifier: ISSN: 0968-5243
CoNE: https://pure.mpg.de/cone/journals/resource/954926245532