We review the current state-of-the-art of diffuse optical imaging, which is an emerging technique for functional imaging of biological tissue. It involves generating images using measurements of visible or near-infrared light scattered across large (greater than several centimetres) thicknesses of tissue. We discuss recent advances in experimental methods and instrumentation, and examine new theoretical techniques applied to modelling and image reconstruction. We review recent work on in vivo applications including imaging the breast and brain, and examine future challenges.

https://iopscience.iop.org/article/10.1088/0031-9155/50/4/R01/pdf

Recent advances in diffuse optical imaging.

This review describes the diffusion model for light transport in tissues and the medical applications of diffuse light. Diffuse optics is particularly useful for measurement of tissue hemodynamics, wherein quantitative assessment of oxy- and deoxy-hemoglobin concentrations and blood flow are desired. The theoretical basis for near-infrared or diffuse optical spectroscopy is developed, and the basic elements of diffuse optical tomography are outlined. We also discuss diffuse correlation spectroscopy, a technique whereby temporal correlation functions of diffusing light are transported through tissue and are used to measure blood flow. Essential instrumentation is described, and representative brain and breast functional imaging and monitoring results illustrate the workings of these new tissue diagnostics.

/pdf/diffuse-optics-for-tissue-monitoring-and-tomography-curjv2s4p6.pdf

Diffuse optics for tissue monitoring and tomography

There is a wealth of new fluorescent reporter technologies for tagging of many cellular and subcellular processes in vivo. This imposed contrast is now captured with an increasing number of available imaging methods that offer new ways to visualize and quantify fluorescent markers distributed in tissues. This is an evolving field of imaging sciences that has already achieved major advances but is also facing important challenges. It is nevertheless well poised to significantly impact the ways of biological research, drug discovery, and clinical practice in the years to come. Herein, the most pertinent technologies associated with in vivo noninvasive or minimally invasive fluorescence imaging of tissues are summarized. Focus is given to small-animal imaging. However, while a broad spectrum of fluorescence reporter technologies and imaging methods are outlined, as necessary for biomedical research, and clinical translation as well.

/pdf/fluorescence-molecular-imaging-4km00t0azo.pdf

Fluorescence molecular imaging.

https://www.nmr.mgh.harvard.edu/DOT/PDF/2004/Boas_NI_23_s275_2004.pdf

Diffuse optical imaging of brain activation: approaches to optimizing image sensitivity, resolution, and accuracy.

This is a review of recent mathematical and computational advances in optical tomography. We discuss the physical foundations of forward models for light propagation on microscopic, mesoscopic and macroscopic scales. We also consider direct and numerical approaches to the inverse problems that arise at each of these scales. Finally, we outline future directions and open problems in the field.

https://iopscience.iop.org/article/10.1088/0266-5611/25/12/123010/pdf

Optical tomography: forward and inverse problems

We introduce a modified Tikhonov regularization method to include three-dimensional x-ray mammography as a prior in the diffuse optical tomography reconstruction. With simulations we show that the optical image reconstruction resolution and contrast are improved by implementing this x-ray-guided spatial constraint. We suggest an approach to find the optimal regularization parameters. The presented preliminary clinical result indicates the utility of the method.

/pdf/tomographic-optical-breast-imaging-guided-by-three-2qpdlum3ly.pdf

Tomographic optical breast imaging guided by three-dimensional mammography

We describe what is, to the best of our knowledge, the first pilot study of coregistered tomographic x-ray and optical breast imaging The purpose of this pilot study is to develop both hardware and data processing algorithms for a multimodality imaging method that provides information that neither x-ray nor diffuse optical tomography (DOT) can provide alone We present in detail the instrumentation and algorithms developed for this multimodality imaging We also present results from our initial pilot clinical tests These results demonstrate that strictly coregistered x-ray and optical images enable a detailed comparison of the two images This comparison will ultimately lead to a better understanding of the relationship between the functional contrast afforded by optical imaging and the structural contrast provided by x-ray imaging

/pdf/coregistered-tomographic-x-ray-and-optical-breast-imaging-1wkwshjkty.pdf

Coregistered tomographic x-ray and optical breast imaging: initial results.

Spectroscopic diffuse optical tomography (DOT) can directly image the concentrations of physiologically significant chromophores in the body. This information may be of importance in characterizing breast tumours and distinguishing them from benign structures. This paper studies the accuracy with which lesions can be characterized given a physiologically realistic situation in which the background architecture of the breast is heterogeneous yet highly structured. Specifically, in simulation studies, we assume that the breast is segmented into distinct glandular and adipose regions. Imaging with a high-resolution imaging modality, such as magnetic resonance imaging, in conjunction with a segmentation by a clinical expert, allows the glandular/adipose boundary to be determined. We then apply a two-step approach in which the background chromophore concentrations of each region are estimated in a nonlinear fashion, and a more localized lesion is subsequently estimated using a linear perturbational approach. In addition, we examine the consequences which errors in the breast segmentation have on estimating both the background and inhomogeneity chromophore concentrations.

/pdf/quantitative-spectroscopic-diffuse-optical-tomography-of-the-3fualvq5py.pdf

Quantitative spectroscopic diffuse optical tomography of the breast guided by imperfect a priori structural information.

To estimate the average optical properties of a heterogeneous medium, simulations show that multi-distance methods assuming homogeneous structure suffer from systematic modeling errors while single source-detector pair methods provides a more meaningful estimate.

Tina Chaves

Papers

Tomographic optical breast imaging guided by three-dimensional mammography

Coregistered tomographic x-ray and optical breast imaging: initial results.

Quantitative spectroscopic diffuse optical tomography of the breast guided by imperfect a priori structural information.

Estimating the average breast optical properties from transmission measurements despite intrinsic tissue heterogeneity: a Monte Carlo Simulation Study