Non-contact Diffuse Optical Tomography Research Articles

Extending dynamic range of detector in non-contact diffuse optical tomography system using deep learning

Extending dynamic range of detector in non-contact diffuse optical tomography system using deep learning

Multispectral, non-contact diffuse optical tomography of healthy human finger joints.

Rheumatoid arthritis (RA) is an inflammatory joint disease often affecting the hands, which if untreated causes disability. Diffuse optical tomography (DOT) provides information about the underlying functional properties of biological tissue. To detect pathophysiological changes in inflamed RA joints, a good understanding of the baseline values for healthy subjects is first required. Finger joints from healthy subjects were imaged using a non-contact, multispectral, continuous wave DOT system, recovering physiological parameters of oxygen saturation, total haemoglobin, water concentration and scatter amplitude. Reconstructed values across the cohort demonstrated good consistency between finger joints from the same participant, with greater variation seen between subjects.

Spatial-frequency-compression scheme for diffuse optical tomography with dense sampling dataset

Dense sampling of illumination and detection offers an effective way of improving the image-reconstruction performance of near-infrared diffuse optical tomography (DOT) at a cost of lengthy computation times. In this paper, we describe a fast DOT scheme for reconstructing the absorption coefficient image of a slab medium from dense sampling of both illumination and detection in the noncontact DOT. The proposed method is carried out with spatial-frequency encoding in both the source and detection spaces, and involves a spatial-frequency-compression (SFC) strategy for selecting the useful spatial frequency based on the tissue transfer function. The method is expected to considerably reduce the calculation time for reconstruction while improving the quality of the reconstructed images. Results from the simulated data show that the speed for absorption reconstruction with the proposed SFC method is more than 400 times faster than that with the conventional one. A noncontact DOT system for dense sampling of both illumination and detection is developed by using laser raster scanning and CCD-based data acquisition. Experimental measurements on several solid phantoms demonstrate that a high quantitativeness ratio can be obtained from the proposed method thanks to reduction of the ill-posedness of the inverse calculation. It takes less than 20 s for the proposed method to experimentally reconstruct one absorption image from a 256×256-sized dataset, which would take a few hours with the conventional method.

Three-dimensional surface reconstruction within noncontact diffuse optical tomography using structured light

A main field in biomedical optics research is diffuse optical tomography, where intensity variations of the transmitted light traversing through tissue are detected. Mathematical models and reconstruction algorithms based on finite element methods and Monte Carlo simulations describe the light transport inside the tissue and determine differences in absorption and scattering coefficients. Precise knowledge of the sample's surface shape and orientation is required to provide boundary conditions for these techniques. We propose an integrated method based on structured light three-dimensional (3-D) scanning that provides detailed surface information of the object, which is usable for volume mesh creation and allows the normalization of the intensity dispersion between surface and camera. The experimental setup is complemented by polarization difference imaging to avoid overlaying byproducts caused by inter-reflections and multiple scattering in semitransparent tissue.

A multi-view time-domain non-contact diffuse optical tomography scanner with dual wavelength detection for intrinsic and fluorescence small animal imaging

We present a non-contact diffuse optical tomography (DOT) scanner with multi-view detection (over 360°) for localizing fluorescent markers in scattering and absorbing media, in particular small animals. It relies on time-domain detection after short pulse laser excitation. Ultrafast time-correlated single photon counting and photomultiplier tubes are used for time-domain measurements. For light collection, seven free-space optics non-contact dual wavelength detection channels comprising 14 detectors overall are placed around the subject, allowing the measurement of time point-spread functions at both excitation and fluorescence wavelengths. The scanner is endowed with a stereo camera pair for measuring the outer shape of the subject in 3D. Surface and DOT measurements are acquired simultaneously with the same laser beam. The hardware and software architecture of the scanner are discussed. Phantoms are used to validate the instrument. Results on the localization of fluorescent point-like inclusions immersed in a scattering and absorbing object are presented. The localization algorithm relies on distance ranging based on the measurement of early photons arrival times at different positions around the subject. This requires exquisite timing accuracy from the scanner. Further exploiting this capability, we show results on the effect of a scattering hetereogenity on the arrival time of early photons. These results demonstrate that our scanner provides all that is necessary for reconstructing images of small animals using full tomographic reconstruction algorithms, which will be the next step. Through its free-space optics design and the short pulse laser used, our scanner shows unprecedented timing resolution compared to other multi-view time-domain scanners.