Dynamic phantom with two stage-driven absorbers for mimicking hemoglobin changes in superficial and deep tissues

Abstract

Abstract. In near-infrared spectroscopy (NIRS) for monitoring brain activity and cerebral functional connectivity, the effect of superficial tissue on NIRS signals needs to be considered. Although some methods for determining the effect of scalp and brain have been proposed, direct validation of the methods has been difficult because the actual absorption changes cannot be known. In response to this problem, we developed a dynamic phantom that mimics hemoglobin changes in superficial and deep tissues, thus allowing us to experimentally validate the methods. Two absorber layers are independently driven with two one-axis automatic stages. We can use the phantom to design any type of waveform (e.g., brain activity or systemic fluctuation) of absorption change, which can then be reproducibly measured. To determine the effectiveness of the phantom, we used it for a multiple source-detector distance measurement. We also investigated the performance of a subtraction method with a short-distance regressor. The most accurate lower-layer change was obtained when a shortest-distance channel was used. Furthermore, when an independent component analysis was applied to the same data, the extracted components were in good agreement with the actual signals. These results demonstrate that the proposed phantom can be used for evaluating methods of discriminating the effects of superficial tissue.

Mechanically switchable solid inhomogeneous phantom for performance tests in diffuse imaging and spectroscopy

“…A two-layered phantom with mechanical movement was employed to mimic hemoglobin changes in superficial and deep tissues. 34 Mechanical solid phantoms have a better control and reproducibility of the absorption changes compared to the other types of phantoms, while they offer lesser capabilities to reproduce dynamic changes. The switchable phantom here implemented can be classified as a mechanical solid phantom.…”

“…Different solutions for the construction of inhomogeneous phantoms were proposed, as shown in the review papers 25,26 and in a recent special issue of Biomedical Optics Express, 17 adopting liquid-liquid, 27 liquid-solid, [28][29][30] and solid-solid structures, [31][32][33][34] each of them with different advantages and criticalities. To comply with the requirements (1), (2), and (4) we opted for a solid-solid approach, obviously more practical than liquid-liquid or mixed approaches.…”

A New Approach to Separate Haemodynamic Signals for Brain-Computer Interface Using Independent Component Analysis and Least Squares

“…The concentration changes of oxyhaemoglobin, Δ[HbO 2 ], and deoxyhaemoglobin, Δ[HHb] were then derived with the MLBL. The concentration changes of oxyhaemoglobin, Δ[HbO 2 ], and the concentration changes of deoxyhaemoglobin, Δ[HHb], were separated using the ICA algorithm and the results are presented in Figures 2 and 3, respectively. ICA is a signal discrimination method that extracts independent components from multiple signals without knowledge of the obtained signal by utilizing the statistical independence of the source components [27].…”

Algorithm for removing scalp signals from functional near-infrared spectroscopy signals in real time using multidistance optodes

“…9 The dynamic phantom had two (upper and lower) scattering and absorbing layers, and the absorption changes in the two layers were independently created by their motions driven by two moving stages. We measured the absorbance changes by using the phantom irradiated by a diode-laser light with a wavelength of 695 nm at d ¼ 15 and 30 mm under three conditions: (1) only the absorption of the lower layer was changed with a specified activation pattern, (2) only the absorption of the upper layer was changed with another activation pattern, and (3) the absorptions of both the lower and upper layers were changed with the activation patterns used for the conditions 1 and 2, respectively.…”