Multiresolution voxel decomposition of complex-valued BOLD signals reveals phasor turbulence

Zikuan Chen, Zeyuan Chen, Vince Daniel Calhoun

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

High spatial resolution functional MRI (fMRI) technology continues to enable smaller voxel sizes, providing details about neuronal activity in terms of spatial localization and specificity. The BOLD contrast mechanism can be examined by numerical simulation. By representing a complex timeseries with a dynamic phasor in a polar coordinate system, a complex-valued BOLD signal manifests as an inward spiral: the radial distance represents the signal amplitude and the polar angle the signal phase angle. For normal fMRI settings (millimeter resolution, 3T main field, and 30ms relaxation time), the BOLD phasors usually evolve in a form of inward spiraling. Under some extreme parameter settings (high resolution, high field, or long relaxation time), the phasors may become turbulent (i.e. exhibit disordered spiraling). In this paper, we will report on a BOLD phasor turbulence phenomenon resulting from coarse-to-fine multiresolution voxel decomposition. In our implementation, a vasculature-laden voxel (320×320×320 micron3) is decomposed into a sequence of subvoxels (160×160 ×160, 80×80×80, 40×40×40, 20×20×20 micron 3). Our simulations reveal the following phenomena: 1) Ultrahigh spatial resolution (several tens of microns, e.g. 20micron) BOLD fMRI may cause signal turbulence, primarily occurring at vessel boundaries; 2) The intravascular signal is prone to turbulence but its contribution to the voxel signal is greatly suppressed by the blood volume fraction; 3) There is no signal turbulence under small angle condition; 4) For millimeter-resolution fMRI with small relaxation time (<30ms), signal turbulence is unlikely to occur. We explain the high-resolution BOLD signal turbulence from the perspective of the emergence of BOLD field irregularity.

Original languageEnglish (US)
Title of host publicationProgress in Biomedical Optics and Imaging - Proceedings of SPIE
Volume7961
DOIs
StatePublished - 2011
Externally publishedYes
EventMedical Imaging 2011: Physics of Medical Imaging - Lake Buena Vista, FL, United States
Duration: Feb 13 2011Feb 17 2011

Other

OtherMedical Imaging 2011: Physics of Medical Imaging
CountryUnited States
CityLake Buena Vista, FL
Period2/13/112/17/11

Fingerprint

Turbulence
turbulence
Magnetic Resonance Imaging
Decomposition
decomposition
Relaxation time
Blood Volume
relaxation time
high resolution
spatial resolution
Technology
blood volume
Volume fraction
polar coordinates
Blood
irregularities
vessels
Computer simulation
phase shift
simulation

Keywords

  • BOLD simulation
  • Computational fMRI
  • field inhomogeneity
  • histogram
  • multiresolution BOLD signal
  • phasor turbulence
  • small angle approximation

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • Radiology Nuclear Medicine and imaging

Cite this

Chen, Z., Chen, Z., & Calhoun, V. D. (2011). Multiresolution voxel decomposition of complex-valued BOLD signals reveals phasor turbulence. In Progress in Biomedical Optics and Imaging - Proceedings of SPIE (Vol. 7961). [79613Y] https://doi.org/10.1117/12.877295

Multiresolution voxel decomposition of complex-valued BOLD signals reveals phasor turbulence. / Chen, Zikuan; Chen, Zeyuan; Calhoun, Vince Daniel.

Progress in Biomedical Optics and Imaging - Proceedings of SPIE. Vol. 7961 2011. 79613Y.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Chen, Z, Chen, Z & Calhoun, VD 2011, Multiresolution voxel decomposition of complex-valued BOLD signals reveals phasor turbulence. in Progress in Biomedical Optics and Imaging - Proceedings of SPIE. vol. 7961, 79613Y, Medical Imaging 2011: Physics of Medical Imaging, Lake Buena Vista, FL, United States, 2/13/11. https://doi.org/10.1117/12.877295
Chen Z, Chen Z, Calhoun VD. Multiresolution voxel decomposition of complex-valued BOLD signals reveals phasor turbulence. In Progress in Biomedical Optics and Imaging - Proceedings of SPIE. Vol. 7961. 2011. 79613Y https://doi.org/10.1117/12.877295
Chen, Zikuan ; Chen, Zeyuan ; Calhoun, Vince Daniel. / Multiresolution voxel decomposition of complex-valued BOLD signals reveals phasor turbulence. Progress in Biomedical Optics and Imaging - Proceedings of SPIE. Vol. 7961 2011.
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