Quantifying Free Water Fraction in Phantoms

Evaluation of the free water volume fraction inside the phantoms with microbeads was performed based on percentage of the contrast-filled volume, quantified in 8 bits gray scale axial images. First, the central portion of the phantom volume, reflecting that from DWI analysis, was manually separated in ImageJ (v. 1.53 j, NIH, USA). The free fluid volume regions (filled with Omnipaque 350 solution) were of clearly higher Hounsfield Units (HU) intensities compared to those from the microbeads. Thus, the voxels belonging to the free fluid were empirically verified occupying >75^th percentile of the cumulative HU distribution in all the separated volume images, from all phantoms. Therefore, the voxels belonging to the free fluid were counted three times, considering only voxels above 75^th, 80^th, and 85^th percentile of HU distribution. For each phantom, the free fluid volume fraction was estimated as a mean voxel count from all thresholds, divided by the voxels count in the separated volume image. As objective separation of the fluid space was impossible in the phantom with the fine microbeads and lower HU thresholds would consider voxels affected by partial volume from the microbeads, proposed free fluid volume fraction estimation was found sufficient to correct for the changes in shape of voxels HU distribution from different phantoms.

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Gomolka R.S., Hablitz L.M., Mestre H., Giannetto M., Du T., Hauglund N.L., Xie L., Peng W., Martinez P.M., Nedergaard M, & Mori Y. (2023). Loss of aquaporin-4 results in glymphatic system dysfunction via brain-wide interstitial fluid stagnation. eLife, 12, e82232.

Publication 2023

Microbeads Omnipaque

Corresponding Organization :

Other organizations : Center for Translational Molecular Medicine, University of Copenhagen, University of Rochester Medical Center, University of Pennsylvania, China Medical University

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Variable analysis

independent variables

Percentage of the contrast-filled volume inside the phantoms with microbeads, quantified in 8 bits gray scale axial images

dependent variables

Free fluid volume fraction estimated as a mean voxel count from all thresholds (75th, 80th, and 85th percentile of HU distribution), divided by the voxels count in the separated volume image

control variables

Central portion of the phantom volume, reflecting that from DWI analysis, manually separated in ImageJ (v. 1.53 j, NIH, USA)
Omnipaque 350 solution used to fill the free fluid volume regions

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