In vivo validation of the bold mechanism: A review of signal changes in gradient echo functional MRI in the presence of flow

Haacke, E. Mark; Lai, Song; Yablonskiy, Dmitriy A.; Lin, Weili

doi:10.1002/ima.1850060204

Cited by 101 publications

(88 citation statements)

References 16 publications

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“…Yet, in voxels embedded in vascular compartments, and , where act indicates "on activation", rest indicates "on rest", is the susceptibility difference between fully oxygenated and deoxygenated blood and Hct is the fractional hematocrit in the vein. The latter relation was used for the estimation of functional oxygenation changes in large veins of the visual cortex and in pial veins of the motor cortex in humans (Haacke et al, 1997;Haacke et al, 1995;Hoogenraad et al, 1998). The 2013 study was performed at 2.5 mm isotropic resolution, and involved removal of non-local phase effects.…”

Section: Potentials and Pitfallsmentioning

confidence: 99%

Functional quantitative susceptibility mapping (fQSM)

et al. 2014

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Blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) is a powerful technique, typically based on the statistical analysis of the magnitude component of the complex time-series. Here, we additionally interrogated the phase data of the fMRI time-series and used quantitative susceptibility mapping (QSM) in order to investigate the potential of functional QSM (fQSM) relative to standard magnitude BOLD fMRI. High spatial resolution data (1 mm isotropic) were acquired every 3 seconds using zoomed multi-slice gradient-echo EPI collected at 7 T in single orientation (SO) and multiple orientation (MO) experiments, the latter involving 4 repetitions with the subject's head rotated relative to B0. Statistical parametric maps (SPM) were reconstructed for magnitude, phase and QSM time-series and each was subjected to detailed analysis. Several fQSM pipelines were evaluated and compared based on the relative number of voxels that were coincidentally found to be significant in QSM and magnitude SPMs (common voxels). We found that sensitivity and spatial reliability of fQSM relative to the magnitude data depended strongly on the arbitrary significance threshold defining "activated" voxels in SPMs, and on the efficiency of spatiotemporal filtering of the phase time-series. Sensitivity and spatial reliability depended slightly on whether MO or SO fQSM was performed and on the QSM calculation approach used for SO data. Our results present the potential of fQSM as a quantitative method of mapping BOLD changes. We also critically discuss the technical challenges and issues linked to this intriguing new technique. seconds using zoomed multi-slice gradient-echo EPI collected at 7 T in single orientation (SO) and multiple orientation (MO) experiments, the latter involving 4 repetitions with the subject's head rotated relative to B 0 . Statistical parametric maps (SPM) were reconstructed for magnitude, phase and QSM timeseries and each was subjected to detailed analysis. Several fQSM pipelines were evaluated and compared based on the relative number of voxels that were coincidentally found to be significant in QSM and magnitude SPMs (common voxels). We found that sensitivity and spatial reliability of fQSM relative to the magnitude data depended strongly on the arbitrary significance threshold defining "activated" voxels in SPMs, and on the efficiency of spatio-temporal filtering of the phase time-series. Sensitivity and spatial reliability depended slightly on whether MO or SO fQSM was performed and on the QSM calculation approach used for SO data.

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Section: Potentials and Pitfallsmentioning

confidence: 99%

Functional quantitative susceptibility mapping (fQSM)

et al. 2014

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“…First, the phase itself can be a superb source of image contrast. This has already been demonstrated for GM/WM contrast (10), small veins in the brain (11), and more recently in venous blood vessels in the peripheral vasculature (8). Second, the phase can be used as a mask to create magnitude images with suppressed/enhanced spectral components or modified contrast.…”

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confidence: 92%

Susceptibility weighted imaging (SWI)

Haacke¹,

Xu²,

Cheng³

et al. 2004

Magnetic Resonance in Med

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1,444

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Susceptibility differences between tissues can be utilized as a new type of contrast in MRI that is different from spin density, T 1 -, or T 2 -weighted imaging. Signals from substances with different magnetic susceptibilities compared to their neighboring tissue will become out of phase with these tissues at sufficiently long echo times (TEs). Thus, phase imaging offers a means of enhancing contrast in MRI. Specifically, the phase images themselves can provide excellent contrast between gray matter (GM) and white matter (WM), iron-laden tissues, venous blood vessels, and other tissues with susceptibilities that are different from the background tissue. Also, for the first time, projection phase images are shown to demonstrate tissue (vessel) continuity. In this work, the best approach for combining magnitude and phase images is discussed. The phase images are high-pass-filtered and then transformed to a special phase mask that varies in amplitude between zero and unity. This mask is multiplied a few times into the original magnitude image to create enhanced contrast between tissues with different susceptibilities.

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“…Also theory predicts the dependence of the signal phase on the orientation of WM fibers, holding promise as additional information for fiber tracking applications. cellular architecture ͉ contrast mechanisms ͉ grey matter ͉ white matter C onventional gradient-recalled echo (GRE) MRI phase images have been used to generate contrast in MRI of the human brain [see for example (1)(2)(3)]. This MRI contrast is profoundly enhanced at high magnetic fields (7 T and above) (4)(5)(6), allowing to visualize biological structures within gray matter (GM) and white matter (WM) that are not usually resolved with conventional MRI.…”

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confidence: 99%

Biophysical mechanisms of phase contrast in gradient echo MRI

He¹,

Yablonskiy

2009

Proc. Natl. Acad. Sci. U.S.A.

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264

430

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Recently reported contrast in phase images of human and animal brains obtained with gradient-recalled echo MRI holds great promise for the in vivo study of biological tissue structure with substantially improved resolution. Herein we investigate the origins of this contrast and demonstrate that it depends on the tissue ''magnetic architecture'' at the subcellular and cellular levels. This architecture is mostly determined by the structural arrangements of proteins, lipids, non-heme tissue iron, deoxyhemoglobin, and their magnetic susceptibilities. Such magnetic environment affects/shifts magnetic resonance (MR) frequencies of the water molecules moving/diffusing in the tissue. A theoretical framework allowing quantitative evaluation of the corresponding frequency shifts is developed based on the introduced concept of a generalized Lorentzian approximation. It takes into account both tissue architecture and its orientation with respect to the external magnetic field. Theoretical results quantitatively explain frequency contrast between GM, WM, and CSF previously reported in motor cortex area, including the absence of the contrast between WM and CSF. Comparison of theory and experiment also suggests that in a normal human brain, proteins, lipids, and non-heme iron provide comparable contributions to tissue phase contrast; however, the sign of iron and lipid contributions is opposite to the sign of contribution from proteins. These effects of cellular composition and architecture are important for quantification of tissue microstructure based on MRI phase measurements. Also theory predicts the dependence of the signal phase on the orientation of WM fibers, holding promise as additional information for fiber tracking applications. cellular architecture ͉ contrast mechanisms ͉ grey matter ͉ white matter

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In vivo validation of the bold mechanism: A review of signal changes in gradient echo functional MRI in the presence of flow

Cited by 101 publications

References 16 publications

Functional quantitative susceptibility mapping (fQSM)

Functional quantitative susceptibility mapping (fQSM)

Susceptibility weighted imaging (SWI)

Biophysical mechanisms of phase contrast in gradient echo MRI

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