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Effect of surrounding vasculature on intravoxel BOLD signal
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Image of FIG. 1.
FIG. 1.

2D illustration of vessel networks surrounding a VOI (situated in the central panel). (a) Random network (Nran), (b) symmetric network (Nsym), (c) replica network (Nrep), and (d) collage network (Nclg).

Image of FIG. 2.
FIG. 2.

2D illustration of 3D masks. (a) Concentric shell and concentric cube, (b) a shell mask applied to calculation, (c) case of no surrounding (VOI in Nzp), and (d) case of half-maximum surrounding [Nran is masked by ] for the VOI.

Image of FIG. 3.
FIG. 3.

Flowchart of our simulation program (, the colon symbol “:” is a MATLAB notation for running index).

Image of FIG. 4.
FIG. 4.

Top row: Nran geometries (in size of array) for three capillary radiuses: (a) , (b) , and (c) . The central voxels are VOI (highlighted in boxes). Bottom row: bfrac values of 27 voxels (in size array) in the corresponding Nran above.

Image of FIG. 5.
FIG. 5.

Demonstration of the effect of the surrounding vasculature in the absence of vessel discontinuity with a birdnestlike Nran. (a) Nran geometry with a void VOI-circumscribed egg region (marked by a ball). (b) The magnetic field pattern (grayscale bar unit: ppmT) at a slice as marked in a vertical plane in (a), in which the central box corresponds to the VOI and the circle to the egg in (a). (c) The point contribution from different surrounding distances [calculated by Eq. (13)]. (d) The accumulative contribution with respect to expanding surroundings.

Image of FIG. 6.
FIG. 6.

BOLD field distribution over a cross section at of the VOI. The BOLD fields were calculated in the presence of five different surrounding vessel networks {Nran, Nsym, Nrep, Nclg, Nzp}. The unit of the grayscale bar is ppmT.

Image of FIG. 7.
FIG. 7.

BOLD field difference of . The unit of the grayscale bar is ppmT.

Image of FIG. 8.
FIG. 8.

Radial shell distribution of inhomogeneous BOLD field within VOI due to different surroundings. Cancellation of bipolar magnetic field disturbance explains the difference between and .

Image of FIG. 9.
FIG. 9.

Effect of the surrounding vasculature in terms of different surrounding scenarios [indicated by legend in (d)] and varying surrounding thickness (sheath) on the average BOLD field over the VOI. Graphs with the same line style indicate realizations with the same parameter setting (different in random vessel network geometry).

Image of FIG. 10.
FIG. 10.

Effect of the surrounding vasculature on BOLD signal decay (top row) and on BOLD signal contrast (bottom row). The results were calculated for four surrounding scenarios: and three capillaries: with the reference to Nzp (baseline). The legends for the plots are provided at the left-hand panels.

Image of FIG. 11.
FIG. 11.

Effect of the surrounding thickness on BOLD signal decay for three capillaries ( for no surrounding, for maximum surrounding).


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Parameters for the numerical simulation.

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Statistics of bfrac values of Nran for capillaries .

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Bounds for BOLD field variations at VOI due to different surroundings . , . The statistics was based on eight realizations for each parameter setting with . Data format: .

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BOLD signal change percentages due to different surroundings . The results were calculated by Eq. (12) at and .


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Effect of surrounding vasculature on intravoxel BOLD signal