Estimation of free water-corrected microscopic fractional anisotropy

Arezza, Nico Joseph John; Santini, Tales; Omer, Mohammad; Baron, Corey A.

doi:10.3389/fnins.2023.1074730

Cited by 3 publications

(2 citation statements)

References 66 publications

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“…To counter the increased scan time needed for higher resolution, the field-of-view and number of slices could be reduced to capture a smaller subvolume of the brain containing the hippocampus. Additionally, techniques to mitigate CSF partial-volume effects, such as a recently proposed free water elimination μFA protocol 50 , could be employed.…”

Section: Limitationsmentioning

confidence: 99%

Microscopic fractional anisotropy asymmetry in unilateral temporal lobe epilepsy

Arezza

Abbas

Chadwick

et al. 2023

Preprint

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Objectives: Surgical resection is the method of choice for treating medically refractory unilateral temporal lobe epilepsy (TLE), but postsurgical prognosis depends on magnetic resonance imaging (MRI) findings. Seizure freedom is more often achieved after resection in MRI-positive patients (those with MRI abnormalities such as mesial temporal sclerosis) than in MRI-negative patients. Diffusion MRI shows promise as a marker of neuronal abnormalities due to its sensitivity to cellular changes such as axon damage, indexed by fractional anisotropy. However, fractional anisotropy is not specific to axon integrity in grey matter where axon orientation is not uniform. In contrast, microscopic fractional anisotropy is a recently introduced dMRI technique that is sensitive to axon integrity regardless of axon orientation. This work investigated whether microscopic fractional anisotropy may be sensitive to hippocampal abnormalities in unilateral TLE. Methods: Diffusion MRI was performed on a 3T scanner in 9 patients (age = 33 +/- 12 years) with unilateral TLE and 9 healthy volunteers (age = 26 +/- 6). A deep learning method was employed to segment the hippocampus into smaller subfields corresponding to the subiculum, cornu ammonis (CA) 1, CA2/3, and CA4 plus dentate gyrus (DG). Mean ipsilateral and contralateral measurements of subregion volume, diffusivity, fractional anisotropy, and microscopic fractional anisotropy were compared to investigate asymmetry in each subfield. Results: Microscopic fractional anisotropy was reduced, and diffusivity was elevated in the ipsilateral CA4/DG region relative to the contralateral side in all 9 patients. Asymmetries in diffusion metrics between the left and right sides of the hippocampus subfields were not observed in the healthy volunteers. Significance: Diffusion MRI may complement standard imaging procedures by detecting abnormalities in MRI-negative patients. Due to its insensitivity to axon orientation, microscopic fractional anisotropy may yield a more robust measurement than fractional anisotropy and may improve epileptic focus localization in surgical candidates.

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Section: Limitationsmentioning

confidence: 99%

Microscopic fractional anisotropy asymmetry in unilateral temporal lobe epilepsy

Arezza

Abbas

Chadwick

et al. 2023

Preprint

Self Cite

View full text Add to dashboard Cite

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“…The obtained MRI signal originates from both the CSF and as well as from the white matter partial, leading to potential misinterpretations. 9 Diffusion metrics are typically biased by Cerebrospinal fluid (CSF) contamination. 8 Diffusion tractography can be strongly influenced by these free water partial volume effects.…”

Section: Introductionmentioning

confidence: 99%

Learning-based free-water correction using single-shell diffusion MRI

Yao,

Archer,

Kanakaraj

et al. 2024

Medical Imaging 2024: Image Processing

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Diffusion magnetic resonance imaging (dMRI) offers the ability to assess subvoxel brain microstructure through the extraction of biomarkers like fractional anisotropy, as well as to unveil brain connectivity by reconstructing white matter fiber trajectories. However, accurate analysis becomes challenging at the interface between cerebrospinal fluid and white matter, where the MRI signal originates from both the cerebrospinal fluid and the white matter partial volume. The presence of free water partial volume effects introduces a substantial bias in estimating diffusion properties, thereby limiting the clinical utility of DWI. Moreover, current mathematical models often lack applicability to single-shell acquisitions commonly encountered in clinical settings. Without appropriate regularization, direct model fitting becomes impractical. We propose a novel voxel-based deep learning method for mapping and correcting free-water partial volume contamination in DWI to address these limitations. This approach leverages data-driven techniques to reliably infer plausible free-water volumes across different diffusion MRI acquisition schemes, including single-shell acquisitions. Our evaluation demonstrates that the introduced methodology consistently produces more consistent and plausible results than previous approaches. By effectively mitigating the impact of free water partial volume effects, our approach enhances the accuracy and reliability of DWI analysis for single-shell dMRI, thereby expanding its applications in assessing brain microstructure and connectivity.

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Hippocampal microscopic fractional anisotropy is reduced in temporal lobe epilepsy

Arezza,

Abbas,

Chadwick

et al. 2024

Imaging Neuroscience

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Surgical resection is the method of choice for treating drug-resistant focal temporal lobe epilepsy (TLE). Postsurgical outcomes are better when magnetic resonance imaging (MRI) findings can localize the seizure focus for resection. However, many patients are MR-negative, meaning the focus cannot be differentiated from normal tissue in relaxation-weighted MRI. Diffusion MRI shows promise as a preoperative marker of neuronal abnormalities due to its sensitivity to cellular changes such as axon damage, indexed by fractional anisotropy. Microscopic fractional anisotropy is a recently introduced diffusion MRI metric that is sensitive to axon integrity regardless of axon orientation in both grey and white matter. In contrast, regular fractional anisotropy is only sensitive to axon integrity in coherently oriented bundles of fibers. This work investigated whether microscopic fractional anisotropy is sensitive to hippocampal abnormalities in drug-resistant TLE. Diffusion MRI was performed on a 3T scanner in 19 patients (age = 31±10 years) with drug-resistant TLE (of which 10 were MR-negative) and 18 healthy volunteers (age = 38±15). A deep-learning method was employed to segment the hippocampus into smaller subregions corresponding to the subiculum, cornu ammonis (CA) 1, CA2/3, and CA4 plus dentate gyrus (DG). Mean measurements of subregion volume, diffusivity, fractional anisotropy, and microscopic fractional anisotropy were compared between cohorts. In a subset of the TLE cohort suspected to have unilateral pathology (n=15, age = 32±10 years), the percentage differences between measurements ipsilateral and contralateral to the epileptogenic zone were evaluated to assess asymmetry. Microscopic fractional anisotropy was reduced in the hippocampus of drug-resistant TLE patients relative to healthy volunteers. In subregion-specific analysis, microscopic fractional anisotropy was significantly reduced in only the CA4/DG region in patients compared to healthy volunteers, after corrections for multiple comparisons. In the 15 patients with suspected unilateral pathology, microscopic fractional anisotropy was reliably and statistically lower in the ipsilateral CA4/DG region compared to the contralateral side. Significant differences were not observed between TLE patients and healthy volunteers, or between hemispheres for patients with suspected unilateral pathology, for the fractional anisotropy or volume metrics. Diffusion MRI may complement standard imaging procedures by detecting abnormalities in MRI-negative patients. Due to its ability to detect abnormality regardless of axon orientation, microscopic fractional anisotropy may improve seizure focus localization in surgical candidates.

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Estimation of free water-corrected microscopic fractional anisotropy

Cited by 3 publications

References 66 publications

Microscopic fractional anisotropy asymmetry in unilateral temporal lobe epilepsy

Microscopic fractional anisotropy asymmetry in unilateral temporal lobe epilepsy

Learning-based free-water correction using single-shell diffusion MRI

Hippocampal microscopic fractional anisotropy is reduced in temporal lobe epilepsy

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