Validating atlas-guided DOT: A comparison of diffuse optical tomography informed by atlas and subject-specific anatomies

Abstract

We describe the validation of an anatomical brain atlas approach to the analysis of diffuse optical tomography (DOT). Using MRI data from 32 subjects, we compare the diffuse optical images of simulated cortical activation reconstructed using a registered atlas with those obtained using a subject’s true anatomy. The error in localization of the simulated cortical activations when using a registered atlas is due to a combination of imperfect registration, anatomical differences between atlas and subject anatomies and the localization error associated with diffuse optical image reconstruction. When using a subject-specific MRI, any localization error is due to diffuse optical image reconstruction only. In this study we determine that using a registered anatomical brain atlas results in an average localization error of approximately 18 mm in Euclidean space. The corresponding error when the subject’s own MRI is employed is 9.1 mm. In general, the cost of using atlas-guided DOT in place of subject-specific MRI-guided DOT is a doubling of the localization error. Our results show that despite this increase in error, reasonable anatomical localization is achievable even in cases where the subject-specific anatomy is unavailable.

Comparison of a layered slab and an atlas head model for Monte Carlo fitting of time-domain near-infrared spectroscopy data of the adult head

“…The details of the MRI scan preprocessing steps and of the segmentation procedure have been previously described. 40 Contrary to a previous study where we reported the performance of the FDMD approach at one specific location on the head, 28 in the present work, we show a systematic characterization of the TD-NIRS fitting methods at various locations over the whole head. We defined three two-dimensional (2-D) arrays of optodes with 1 cm spacing, to be placed over the frontal (6 × 20 optodes), left parietotemporal (12 × 14), and occipital (8 × 20) regions.…”

“…Three subjects were selected from a library of 32 head volumes, previously used by Cooper et al to validate the use of atlas-based image reconstructions of functional data. 40 We chose three subjects which resulted in poor, average, and good performance in the functional NIRS study. The head volumes were segmented using FreeSurfer (http://surfer.nmr.mgh.harvard.edu) 41,42 into four tissue types: extracerebral tissue (skin and skull), cerebrospinal fluid (CSF), gray matter, and white matter.…”

“…For each array, four additional dummy optodes were defined to anchor the probe on a specific location on the surface of the head. The probe was then wrapped onto the scalp using an iterative, spring-relaxation algorithm that has been previously described by Cooper et al 40 The algorithm returns the three-dimensional (3-D) coordinates of all optodes on the surface of the head. The resulting probes wrapped on the head surface of subject 1 are displayed in Fig.…”

“…The use of a template atlas head in place of the true subject's anatomy has shown great promises for reconstructing functional NIRS activation data. 40,44,46 It allows the incorporation of a realistic brain structure without the need for costly individual MRI scans. If the optode locations have been registered with respect to specific superficial landmarks, such as the 10-20 reference points, the atlas head can be registered onto the subject's head using these superficial references, as was detailed in Singh et al 43 The optical reconstruction can then be performed on this registered atlas with a known internal structure.…”

Automated voxel classification used with atlas-guided diffuse optical tomography for assessment of functional brain networks in young and older adults

“…Custo et al 1 initially introduced the concept of atlas-DOT, after which it was further developed with high-density optodes and successfully validated using computational simulations and functional magnetic resonance imaging (fMRI) performed on human subjects. [2][3][4] Atlas-DOT utilized a finite element technique with either subject-specific models 3,4 or a standard magnetic resonance imaging (MRI) brain template (such as ICBM 256) in the forward calculation. 5,6 A significant improvement of accuracy in image reconstruction and source localization has been achieved with atlas-DOT.…”