Multi-channel medical device for time domain functional near infrared spectroscopy based on wavelength space multiplexing

Abstract

We have designed a compact dual wavelength (687 nm, 826 nm) multi-channel (16 sources, 8 detectors) medical device for muscle and brain imaging based on time domain functional near infrared spectroscopy. The system employs the wavelength space multiplexing approach to reduce wavelength cross-talk and increase signal-to-noise ratio. System performances have been tested on homogeneous and heterogeneous tissue phantoms following specifically designed protocols for photon migration instruments. Preliminary in vivo measurements have been performed to validate the instrument capability to monitor hemodynamic parameters changes in the arm muscle during arterial occlusion and in the adult head during a motor task experiment.

Keywords: (120.3890) Medical optics instrumentation; (170.1470) Blood or tissue constituent monitoring; (170.1610) Clinical applications; (170.2655) Functional monitoring and imaging; (170.3890) Medical optics instrumentation; (170.5280) Photon migration; (170.6920) Time-resolved imaging.

Fig. 1

(a) Complete scheme of the system. AE: Attenuation-Equalization stage; S: injection fiber; B: collection bundle; HPM: hybrid photomultiplier tube; A: amplifier; TCSPC: time correlated single photon counting board; μchip: microcontroller unit; Sync: synchronization signal. (b) Photo of the medical device with modules description.

Fig. 2

(a): an example of IRF. RED = 687nm, IR = 826nm. (b): stability test for the counts and the photon mean time-of-flight of the IRF at 687 nm for one detector.

Fig. 3

Linearity for the absorption (a) and reduced scattering (b) coefficients at 687 nm. Results are average values over detectors and repeated measurements. The lines represent the linear fit.

Fig. 4

Accuracy for the absorption (a) and reduced scattering (b) coefficients at 687 nm. Results are average values over detectors and repeated measurements. The lines link the conventional values.

Fig. 5

CV for the absorption and the reduced scattering coefficient at 687 nm. Lines: best fit with a power function. DET: Detector.

Fig. 6

(a) Contrast plotted against the inclusion depth at different time gates and in the CW case. (b) Contrast plotted against the photon time-of-flight for different inclusion depths.

Fig. 7

Contrast as a function of the absorption coefficient variations occurring in the only upper (a) or deeper (b) layer of a two-layered medium for different time gates (500, 2000, 4000ps and 4000ps obtained with the correction proposed by Contini et al. [7].

Fig. 8

Hemodynamic changes during an arterial cuff occlusion of the right arm. First column: right arm. Second column left arm. The bars represent the standard deviation over the four measurement points

Fig. 9

Optodes positions on the head: 5 injections (red circles) and 4 detections (green squares) optical fibers, around left and right motor cortex points (C3 and C4).

Fig. 10

Contrast for the intensity at 687 nm (red) and 826 nm (pink) integrated in different time-windows with fixed width (250 ps) and variable delay (panel 1 to 10: from 0 ps to 2250 ps) for a channel placed in the left hemisphere.

Fig. 11

Contrast for the intensity at 687 nm (red) and 826 nm (pink) integrated in different time-windows with fixed width (250 ps) and variable delay (panel 1 to 10: from 0 ps to 2250 ps) for a channel placed in the right hemisphere.

Fig. 12

Time courses (units: µs) of O₂Hb (red) and HHb (blue) concentration changes (units: µM) during the experiment for the right and left hemisphere.

Fig. 13

Time courses (units: µs) of O₂Hb (red) and HHb (blue) concentration changes (units: µM) during the experiment (folding average of the 6 blocks) for the right and left hemisphere.

Fig. 14

SPM maps of the cortical activations for O₂Hb (left) and HHb (right). p<0.001, uncorrected. The color bars represent the p-value.