In this report, we investigate the effects of array density and modulation frequency on spatial accuracy, resolution, and penetration of frequency domain high-density diffuse optical tomography (FD HD-DOT). The result shows that these metrics are improved by using higher array densities or an optimized modulation frequency, while array density is the stronger parameter. Additionally, the improvement of image quality shows diminishing effects with denser arrays.
We investigated the effects of modulation frequency on image quality with FD-HD-DOT through simulations with a realistic noise model of functional activations in human head models, arising from 11 source modulation frequencies between CW and 1,000 MHz. Functional reconstructions were simulated in five fMRI-based head models covered by 158 light sources and 166 detectors and a realistic noise model was considered. We quantitatively evaluated image quality by assessing the localization error (LE), success rate, full width at half maximum (FWHM), and full volume at half maximum (FVHM) of recoveries. The results show that the optimized frequencies are about 300~500 MHz for image quality and 300 MHz for reliable field of view when accounting for realistic noise.
High-frequency modulation has been shown to provide superior image quality over continuous wave high density diffuse optical tomography (HD-DOT). Herein, we evaluated a range of modulation frequencies on the image quality for frequency domain HD-DOT.
Significance: By incorporating multiple overlapping functional near-infrared spectroscopy (fNIRS) measurements, high-density diffuse optical tomography (HD-DOT) images human brain function with fidelity comparable to functional magnetic resonance imaging (fMRI). Previous work has shown that frequency domain high-density diffuse optical tomography (FD-HD-DOT) may further improve image quality over more traditional continuous wave (CW) HD-DOT.
Aim: The effects of modulation frequency on image quality as obtainable with FD-HD-DOT is investigated through simulations with a realistic noise model of functional activations in human head models, arising from 11 source modulation frequencies between CW and 1000 MHz.
Approach: Simulations were performed using five representative head models with an HD regular grid of 158 light sources and 166 detectors and an empirically derived noise model. Functional reconstructions were quantitatively assessed with multiple image quality metrics including the localization error (LE), success rate, full width at half maximum, and full volume at half maximum (FVHM). All metrics were evaluated against CW-based models.
Results: Compared to CW, localization accuracy is improved by >40% throughout brain depths of 13 to 25 mm below the surface with 300 to 500 MHz modulation frequencies. Additionally, the reliable field of view in brain tissue is enlarged by 35% to 48% within an optimal frequency of 300 MHz after considering realistic noise, depending on the dynamic range of the system.
Conclusions: These results point to the tremendous opportunities in further development of high bandwidth FD-HD-DOT system hardware for applications in human brain mapping.
We provide herein a simulation study of the effects of modulation frequency on the image quality obtainable with frequency domain high density diffuse optical tomography. Using an anatomical head model, we simulated point spread functions with modulation frequencies spanning 0-1,000 MHz throughout the optically accessible field of view. We assessed image quality using metrics of the full width at half maximum, the localization error, and the 50% success rate. Our results show higher modulation frequency improves image quality and provides access to deeper brain tissue.
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