SignificanceWe present a motion-resistant three-wavelength spatial frequency domain imaging (SFDI) system with ambient light suppression using an 8-tap complementary metal-oxide semiconductor (CMOS) image sensor (CIS) developed at Shizuoka University. The system addresses limitations in conventional SFDI systems, enabling reliable measurements in challenging imaging scenarios that are closer to real-world conditions.AimOur study demonstrates a three-wavelength SFDI system based on an 8-tap CIS. We demonstrate and evaluate the system’s capability of mitigating motion artifacts and ambient light bias through tissue phantom reflectance experiments and in vivo volar forearm experiments.ApproachWe incorporated the Hilbert transform to reduce the required number of projected patterns per wavelength from three to two per spatial frequency. The 8-tap image sensor has eight charge storage diodes per pixel; therefore, simultaneous image acquisition of eight images based on multi-exposure is possible. Taking advantage of this feature, the sensor simultaneously acquires images for planar illumination, sinusoidal pattern projection at three wavelengths, and ambient light. The ambient light bias is eliminated by subtracting the ambient light image from the others. Motion artifacts are suppressed by reducing the exposure and projection time for each pattern while maintaining sufficient signal levels by repeating the exposure. The system is compared to a conventional SFDI system in tissue phantom experiments and then in vivo measurements of human volar forearms.ResultsThe 8-tap image sensor-based SFDI system achieved an acquisition rate of 9.4 frame sets per second, with three repeated exposures during each accumulation period. The diffuse reflectance maps of three different tissue phantoms using the conventional SFDI system and the 8-tap image sensor-based SFDI system showed good agreement except for high scattering phantoms. For the in vivo volar forearm measurements, our system successfully measured total hemoglobin concentration, tissue oxygen saturation, and reduced scattering coefficient maps of the subject during motion (16.5 cm/s) and under ambient light (28.9 lx), exhibiting fewer motion artifacts compared with the conventional SFDI.ConclusionsWe demonstrated the potential for motion-resistant three-wavelength SFDI system with ambient light suppression using an 8-tap CIS.
We demonstrate a motion-resistant, three-wavelength, spatial frequency domain imaging (SFDI) system with ambient light suppression using a new 8-tap CMOS image sensor developed in our laboratory. Compared to the previous sensor (134×150), the new sensor’s readout maximum frame rate has improved to 33fps from 6.28fps, and the new 700×540- pixel sensor allows imaging at a higher spatial resolution over a larger field of view. Furthermore, the number of projected images needed per wavelength is reduced from three to two after applying the Hilbert transform. One image of planar illumination and one image for sinusoidal pattern projection at three wavelengths as well as one image of ambient light are captured by the 8-tap image sensor concurrently. The bias caused by ambient light is removed by subtracting the ambient light image from other images. Suppression of motion artifacts is achieved by reducing the exposure and projection time of each pattern. Sufficient signal level is maintained by repeating the exposure multiple times. In this study, LEDs with wavelengths of 554nm, 660nm, and 730nm were used to estimate oxy-/deoxyhemoglobin and melanin concentrations from in-vivo volar forearm skin.
We demonstrate simultaneous multi-band spatial frequency domain imaging (SFDI) and blood flow mapping by multi-exposure laser speckle contrast imaging (MELSCI) with a laboratory-designed 2x2-aperture 4-tap CMOS image sensor. The proposed imaging device is composed of an array of sub-image sensors. This multi-aperture configuration realizes multi-wavelength imaging to estimate chromophore concentrations and wavelength-division-multiplexed imaging for multi-band SFDI and MELSCI. For SFDI, 450, 550, 660nm LEDs were used as the light sources of a DMD. For MELSCI, a 785nm LD was used for flood illumination. Reflectance and K2 maps of a human arm before and after an exercise was measured.
We demonstrate three-wavelength spatial frequency domain imaging (SFDI) of a moving arm under a room light with suppressing motion artifact and biased reflectance based on an 8-tap CMOS image sensor developed in our research group. The images for two projected patters for three wavelengths and that for only ambient light are captured. Three LEDs with the wavelengths of 660nm, 780nm, and 850nm were utilized to decompose the oxy-/ deoxyhemoglobin and melanin concentrations. The exposure time for each frame was 70ms. The total hemoglobin, tissue oxygen saturation, and scattering coefficient maps were obtained without any significant motion artifact.
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