The recent developments in light generation and detection techniques have opened new possibilities for optical medical imaging, tomography, and diagnosis at tissue penetration depths of ~10 cm. However, because light scattering and diffusion in biological tissue are rather strong, the reconstruction of object images from optical projections needs special attention. We describe a simple reconstruction method for diffuse optical imaging, based on a modified backprojection approach for medical tomography. Specifically, we have modified the standard backprojection method commonly used in x-ray tomographic imaging to include the effects of both the diffusion and the scattering of light and the associated nonlinearities in projection image formation. These modifications are based primarily on the deconvolution of the broadened image by a spatially variant point-spread function that is dependent on the scattering of light in tissue. The spatial dependence of the deconvolution and nonlinearity corrections for the curved propagating ray paths in heterogeneous tissue are handled semiempirically by coordinate transformations. We have applied this method to both theoretical and experimental projections taken by parallel- and fan-beam tomography geometries. The experimental objects were biomedical phantoms with multiple objects, including in vitro animal tissue. The overall results presented demonstrate that image-resolution improvements by nearly an order of magnitude can be obtained. We believe that the tomographic method presented here can provide a basis for rapid, real-time medical monitoring by the use of optical projections. It is expected that such optical tomography techniques can be combined with the optical tissue diagnosis methods based on spectroscopic molecular signatures to result in a versatile optical diagnosis and imaging technology.
Using a photon-counting setup and a streak-camera arrangement with time resolutions of 35 and 6 ps, respectively, we have investigated the spatial resolution of a time-gated transillumin tion technique applied to turbid media. In the case of large relative amounts of unscattered light, it is found that small detection angles improve the spatial resolution. For large concentrations of scatterers and large sample thicknesses, i.e., when the amount of unscattered light is negligible, the best time-gate position is found to be at times that are later than the minimum transit time. In this case (minimum transit time), temporal resolutions from small values up to approximately 50 ps yield almost the same image resolution. The only advantage of measuring systems with a higher than 50-ps temporal resolution is their ability to distinguish the diffused from the unscattered light, when a significant amount of the latter is present.
Using Photon-Density-Waves (PWD), (multiple) objects embedded in a highly scattering medium with optical properties similar to tissue are detected. The measurements were performed with near-infra-red laser light at 675 nm which was either kept continuous-wave (CW) or amplitude modulated (AM) at 219 MHz or 650MHz. We find that the spatial resolution of the projection image shows only slight improvements as the frequency is increased. This improvement comes at the expense of signal strength in the modulated part of the light. That is, the PWD shows a much stronger attenuation as compared to the CW light intensity. The implications of the lower signal-tonoise ratio at high modulation frequencies is that the modulated light projections are less suitable for further data processing. For a given data acquisition system, this fact cancels the advantages of the higher raw resolution of PWD as compared to CW light. Therefore, we find no clear advantage of PWD over CW light for obtaining sharper tomographic images of the diffuse media, regardless of the inverse scattering method used.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.