Combining energy and Laplacian regularization to accurately retrieve the depth of brain activity of diffuse optical tomographic data

Antonio M. Chiarelli, Edward L. Maclin, Kathy A. Low, Kyle E. Mathewson, Monica Fabiani, Gabriele Gratton

Research output: Contribution to journalArticle

Abstract

Diffuse optical tomography (DOT) provides data about brain function using surface recordings. Despite recent advancements, an unbiased method for estimating the depth of absorption changes and for providing an accurate three-dimensional (3-D) reconstruction remains elusive. DOT involves solving an ill-posed inverse problem, requiring additional criteria for finding unique solutions. The most commonly used criterion is energy minimization (energy constraint). However, as measurements are taken from only one side of the medium (the scalp) and sensitivity is greater at shallow depths, the energy constraint leads to solutions that tend to be small and superficial. To correct for this bias, we combine the energy constraint with another criterion, minimization of spatial derivatives (Laplacian constraint, also used in low resolution electromagnetic tomography, LORETA). Used in isolation, the Laplacian constraint leads to solutions that tend to be large and deep. Using simulated, phantom, and actual brain activation data, we show that combining these two criteria results in accurate (error <2 mm) absorption depth estimates, while maintaining a two-point spatial resolution of <24 mm up to a depth of 30 mm. This indicates that accurate 3-D reconstruction of brain activity up to 30 mm from the scalp can be obtained with DOT.

Original languageEnglish (US)
Article number036008
JournalJournal of biomedical optics
Volume21
Issue number3
DOIs
StatePublished - Mar 1 2016

Keywords

  • 3-D reconstruction
  • Laplacian regularization, low resolution electromagnetic tomography
  • diffuse optical tomography
  • functional brain mapping
  • minimum-norm
  • near infrared spectroscopy

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • Atomic and Molecular Physics, and Optics
  • Biomedical Engineering

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