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The field of biomedical optics is experiencing tremendous growth. Biomedical technologies contribute in the creation of devices used in healthcare of various specialties (ophthalmology, cardiology, anesthesiology, and immunology, etc.). Recent research in biomedical optics is discussed. Overviews of meetings held at the 2002 Optical Society of America Biomedical Topical Meetings are presented. © 2003 Optical Society of America.

Optical tomography is being developed as a means of detecting and specifying disease in the adult female breast. We present a series of clinical three-dimensional optical images obtained with a 32-channel time-resolved system and a liquid-coupled interface. Patients place their breasts in a hemispherical cup to which sources and detectors are coupled, and the remaining space is filled with a highly scattering fluid. A cohort of 38 patients has been scanned, with a variety of benign and malignant lesions. Images show that hypervascularization associated with tumors provides very high contrast due to increased absorption by hemoglobin. Only half of the fibroadenomas scanned could be observed, but of those that could be detected, all but one revealed an apparent increase in blood volume and a decrease in scatter and oxygen saturation. OCIS codes: 110.6960, 170.3830.

Most research in optical imaging incorrectly assumes that light transport in nonscattering regions in the head may be modeled by use of the diffusion approximation. The effect of this assumption is examined in a series of experiments on tissue-equivalent phantoms. Images from cylindrical and head-shaped phantoms with and without clear regions [simulating the cerebrospinal fluid (CSF) filled ventricles] and a clear layer (simulating the CSF layer surrounding the brain) are reconstructed with linear and nonlinear reconstruction techniques. The results suggest that absorbing and scattering perturbations can be identified reliably with nonlinear reconstruction methods when the clear regions are also present in the reference data but that the quality of the image degrades considerably if the reference data does not contain these features. Linear reconstruction performs similarly to nonlinear reconstruction, provided the clear regions are present in the reference data, but otherwise linear reconstruction fails. This study supports the use of linear reconstruction for dynamic imaging but suggests that, in all cases, image quality is likely to improve if the clear regions are modeled correctly. OCIS codes: 170.3880, 170.6920.

Results are presented of a study to monitor the changes in the optical properties of breast tissue over a 12-month period after interstitial laser photocoagulation treatment of a fibroadenoma. The study involved generating cross-sectional images of the breast with a multichannel time-resolved imaging system and a nonlinear image reconstruction algorithm. Images of the internal absorbing and scattering properties revealed the expected initial inflammatory response, followed by the development of low-scattering cysts consistent with corresponding ultrasound examinations. Although results indicate that purely qualitative images can potentially provide clinically valuable data, means of enhancing diagnostic information by overcoming present limitations of the approach are discussed. America OCIS codes: 170.1610, 170.3830, 170.3880, 170.6920.

We have begun clinical trials of optical tomography of the neonatal brain. To validate this research, we have built and imaged an anatomically realistic, tissue-equivalent neonatal head phantom that is hollow, allowing contrasting objects to be placed inside it. Images were reconstructed by use of two finite-element meshes, one generated from a computed tomography image of the phantom and the other spherical. The phantom was filled with a liquid of the same optical properties as the outer region, and two perturbations were placed inside. These were successfully imaged with good separation between the absorption and scatter coefficients. The phantom was then refilled with a liquid of increased absorption compared with the background to simulate the brain, and the absolute properties of the two regions were found. These were used as a priori information for the complete reconstruction. Both perturbations were visible, superimposed on the increased absorption of the central region. The head-shaped mesh performed slightly better than the spherical mesh, particularly when the absorption of the central region of the phantom was increased. OCIS codes: 170.3880, 170.6920.

We have developed a methodology that can be used in reconstruction algorithms to quantify the optical coefficients and the geometrical cross section of a weakly abnormal optical target embedded in an otherwise homogeneous medium. This novel procedure uses different time-dependent point-spread functions to analyze the diffusive and absorptive contrasts obtained from time-of-flight measurements. Data obtained from time-resolved transillumination of a tissuelike phantom are used to test the accuracy of this new deconvolution methodology.

An investigation was performed of the effectiveness of a time-resolved method for imaging very-low-contrast features embedded in highly scattering media. Experiments employed slabs of breastlike material into which were inserted small cylindrical objects having either a scattering or an absorption coefficient of 4, 2, 1.5, and 1.1 times greater than the surrounding medium. An attempt was made to quantify the degree of contrast produced by each object. The results indicate that time-gating is far more effective at enhancing the contrast of the scattering inhomogeneities than of the absorbing inhomogeneities. This observation is shown to agree with a diffusion-based model, which also predicts that time-gating can decrease the contrast of absorbing inhomogeneities unless very short time-gates can be employed. Key words: Time-resolved imaging, time of flight, tissue optics.

An independent assessment is described of a dual-wavelength imaging technique, known as the temporally extrapolated absorbance method (TEAM), proposed by Yamada et al. [Opt. Eng. 32, 634-641 (1993)]. The technique involves recording the temporal distribution of light transmitted across a scattering medium at two carefully chosen wavelengths at which the scattering properties of the medium are assumed to be identical. The objective is to image internal structure that absorbs more strongly at one wavelength than it does at the other. A simple theoretical treatment of TEAM is presented that employs a perturbation model of photon transport. This indicates that despite the lack of a secure theoretical basis, the technique may provide a potentially effective ad hoc method of generating images of highly scattering media. The method was also evaluated experimentally by using, for the first time to our knowledge, a single object and two wavelengths. A single-projection, two-dimensional image was obtained of a solid phantom with optical properties representative of breast tissue. The results exhibited good agreement with the theoretical model, and a small embedded feature that absorbs 3.5 times as strongly as the surrounding medium at one wavelength was revealed successfully. Key words: Time-resolved imaging, diffusion theory, time of flight.

A method of generating images through highly scattering media is presented that involves comparing measurements of the time-dependent intensity of transmitted light with an analytical model describing the sensitivity of that intensity on localized changes in optical properties. A least-squares fitting procedure is employed to derive the amplitudes of the measurement perturbations caused by embedded absorbers and scatterers located along a line of sight between the source and detector. Images are presented of a highly scattering, solid plastic phantom with optical properties closely matched to those of human breast tissue at near-infrared wavelengths. The phantom is a 54-mm-thick slab, containing four small cylinders of contrasting scatter and absorption. Results show that embedded absorbers can be distinguished from embedded scatterers, and that the diffusion perturbation amplitude provides inherently greater spatial resolution than the absorption perturbation amplitude. Key words: Time-resolved imaging, diffusion theory, time of flight.

A solid plastic phantom has been developed with optical properties that closely match those of human breast tissue at near-IR wavelengths. The phantom is a 54-mm-thick slab containing four small cylinders of contrasting scatter and absorption. A detailed description of the phantom is followed by an account of an attempt to image the phantom by a time-resolved imaging technique. Images generated with transmitted light with the shortest flight times revealed the embedded cylinders with greater visibility than images obtained with continuous light transillumination. However, images corresponding to flight times of less than [approximately] 700 ps were severely degraded from a lack of detected photons. An attempt was made to overcome this degradation by extrapolating the measured temporal distributions with an analytic model of photon transport. Results suggest that subcentimeter resolution imaging of low-contrast tumors in the breast is scientifically possible. Our phantom is available to any other research groups wishing to evaluate their systems. Key words: Time-resolved imaging, time of flight, tissue optics, biomedical optics.

We have obtained transaxial slice images of a cylindrical object containing a highly scattering, low-absorbing solution by using picosecond pulses of visible light. Embedded in the solution was an assortment of six glass tubes containing different concentrations of absorbing dye. We reconstructed images tomographically from projections generated by using light transmitted through the object with the shortest flight times.

The neonatal brain undergoes dramatic structural and functional changes over the last trimester of gestation. The accuracy of source localisation of brain activity recorded from the scalp therefore relies on accurate age‐specific head models. Although an age‐appropriate population‐level atlas could be used, detail is lost in the construction of such atlases, in particular with regard to the smoothing of the cortical surface, and so such a model is not representative of anatomy at an individual level. In this work, we describe the construction of a database of individual structural priors of the neonatal head using 215 individual‐level datasets at ages 29–44 weeks postmenstrual age from the Developing Human Connectome Project. We have validated a method to segment the extra‐cerebral tissue against manual segmentation. We have also conducted a leave‐one‐out analysis to quantify the expected spatial error incurred with regard to localising functional activation when using a best‐matching individual from the database in place of a subject‐specific model; the median error was calculated to be 8.3 mm (median absolute deviation 3.8 mm). The database can be applied for any functional neuroimaging modality which requires structural data whereby the physical parameters associated with that modality vary with tissue type and is freely available at www.ucl.ac.uk/dot-hub. [ABSTRACT FROM AUTHOR]

A 32-channel time-resolved imaging device for medical optical tomography has been employed to evaluate a scheme for imaging the human female breast. The fully automated instrument and the reconstruction procedure have been tested on a conical phantom with tissue-equivalent optical properties. The imaging protocol has been designed to obviate compression of the breast and the need for coupling fluids. Images are generated from experimental data with an iterative reconstruction algorithm that employs a three-dimensional (3D) finite-element diffusion-based forward model. Embedded regions with twice the background optical properties are revealed in separate 3D absorption and scattering images of the phantom. The implications for 3D time-resolved optical tomography of the breast are discussed. OCIS codes: 170.3010, 170.6920, 170.6960.

Following several years of development the construction of a multichannel time-resolved imaging device for medical optical tomography has been completed. Images are reconstructed from time-resolved measurements by use of a scheme that employs a finite-element diffusion-based forward model and an iterative reconstruction solver. Prior to testing on clinical subjects the fully automated instrument and the reconstruction software are evaluated with tissue-equivalent phantoms. We describe our first attempt to generate multiple-slice images of a phantom without uniform properties along the axial direction, while still using a computationally fast two-dimensional reconstruction algorithm. The image quality is improved by the employment of an approximate correction method that uses scaling factors derived from the ratios of finite-element forward simulations in two and three spatial dimensions. The 32-channel system was employed to generate maps of the internal scattering and the absorption properties at 14 different transverse planes across the phantom. The images clearly reveal the locations of small inhomogeneous regions embedded within the phantom. These results were obtained by use of purely temporal data and without resource to reference measurements. OCIS codes: 170.3010, 170.6920, 170.6960, 170.0110.