TOMOGRAPHIC IMAGE-RECONSTRUCTION FROM OPTICAL PROJECTIONS IN LIGHT-DIFFUSING MEDIA

The recent developments in light generation and detection techniques h ave opened new possibilities for optical medical imaging, tomography, and diagnosis at tissue penetration depths of similar to 10 cm. Howeve r, because light scattering and diffusion in biological tissue are rat her strong, the reconstruction of object images from optical projectio ns needs special attention. We describe a simple reconstruction method for diffuse optical imaging, based on a modified backprojection appro ach for medical tomography. Specifically, we have modified the standar d 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 broaden ed image by a spatially variant point-spread function that is dependen t 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 coord inate transformations. We have applied this method to both theoretical and experimental projections taken by parallel- and fan-beam tomograp hy geometries. The experimental objects were biomedical phantoms with multiple objects, including in vitro animal tissue. The overall result s presented demonstrate that image-resolution improvements by nearly a n 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 suc h optical tomography techniques can be combined with the optical tissu e diagnosis methods based on spectroscopic molecular signatures to res ult in a versatile optical diagnosis and imaging technology. (C) 1997 Optical Society of America