We have constructed a near-real-time combined imager suitable for simultaneous ultrasound and near-infrared diffusive light imaging and coregistration. The imager consists of a combined hand-held probe and the associated electronics for data acquisition. A two-dimensional ultrasound array is deployed at the center of the combined probe, and 12 dual-wavelength laser source fibers (780 and 830 nm) and 8 optical detector fibers are deployed at the periphery. We have experimentally evaluated the effects of missing optical sources in the middle of the combined probe on the accuracy of the reconstructed optical absorption coefficient and assessed the improvements of a reconstructed absorption coefficient with the guidance of the coregistered ultrasound. The results have shown that, when the central ultrasound array area is in the neighborhood of 2 cm × 2 cm, which corresponds to the size of most commercial ultrasound transducers, the optical imaging is not affected. The results have also shown that the iterative inversion algorithm converges quickly with the guidance of a priori three-dimensional target distribution, and only one iteration is needed to reconstruct an accurate optical absorption coefficient.

Enamel and dentin are the primary components of human teeth. Both of them have a strong polarization effect. We designed a polarization-sensitive optical coherence tomography (PSOCT) system to study the spatially resolved scattering and polarization phenomena of teeth. The system is constructed in free space to avoid the complexity of polarization control in fiber-based PSOCT. The structural features of enamel were evaluated in five human teeth that had no visible evidence of caries. The teeth were subsequently sectioned in mesial distal orientation and coronal orientation. Then the structural aspects of dentin were evaluated. OCT images were made of the mantel dentin near the dentin–enamel junction. Five teeth with interproximal and occlusal caries were also studied. With two channel and phase-retardation images, PSOCT provided better functional contrast and more detailed structural information than conventional OCT. For a better description of the measured PSOCT data, we classify these features by two types, i.e., the local textural features and the global structural features. This study indicates that PSOCT has the potential to be a powerful tool for research of dental formation and caries diagnosis.

We present an empirical master–slave dual-source configuration within the diffusion approximation that enhances modeling of spatially resolved diffuse reflectance at short-path and with low scattering from a semi-infinite homogeneous medium when irradiated by a pencil beam. An isotropic virtual source positioned at a depth of 1/(reduced scattering coefficient) is used as the master source. A second isotropic virtual source whose depth and intensity depend upon those of the master source and tissue property according to a set of simple empirical formulas is added as the slave source. When tested for a semi-infinite homogeneous medium, this master–slave dual-source model consistently produces the aggressive peaking of the diffuse reflectance toward the point of entry, which is significantly underestimated by the model prediction that involves only the master source. Monte Carlo simulations have shown the effectiveness of this empirical model at a short source–detector separation of 1/100 of 1/(reduced scattering coefficient) and an absorption to reduced scattering ratio as strong as 1, with an error within 20% in the near field (1/10 of 1/(reduced scattering coefficient)).

Frequency-domain near-infrared optical tomography systems have been widely used to study optical properties of breast cancers in vivo.^{1 2 3} In the Optical and Ultrasound Imaging Laboratory at the University of Connecticut, we are developing a hybrid imager that combines optical tomography and conventional ultrasound for breast cancer detection.^{4 5} The ultimate goal of our studies is to establish a method that is more accurate and efficient than conventional x-ray mammography for breast cancer detection and diagnosis, for assessing cancer treatment, and for monitoring cancer recurrence. The combination of ultrasound with optical imaging provides complementary diagnostic information. The acoustic property of a simple cyst can be well distinguished from that of a tumor, while the local blood volume and blood oxygenation can be related to tumor malignance. In addition, using high-resolution ultrasound images to guide optical imaging reconstruction can partly solve the ill-posed problem and lead to more accurate reconstructed values.^{6 7} As a similar idea, combination of optical imaging with MRI for small animal imaging has been reported recently.^{8 9} Our clinical experiments at the University of Connecticut Health Center and Hartford Hospital have been successful, but we do feel the need to update the optical imager we built two years ago. First of all, it is heavy and bulky, which makes the transportation to multiple clinical locations difficult. Second, we used electronic switching for the light sources. Because the laser diodes need a certain time period to stabilize after switching, the data acquisition time was about 8 sec for one scan. In general, three scans at lesion locations and at reference locations are necessary for checking patient motion and for calculating averages. To reduce the size, weight, and data acquisition time, we designed and built a completely new optical imager.

We investigate the feasibility of trans-rectal optical tomography of the prostate using an endo-rectal near-infrared (NIR) applicator that is to be integrated with a trans-rectal ultrasound (TRUS) probe. Integration with TRUS ensures accurate endo-rectal positioning of the NIR applicator and the utility of using TRUS spatial prior information to guide NIR image reconstruction. The prostate NIR image reconstruction is challenging even with the use of spatial prior owing to the anatomic complexity of the imaging domain. A hierarchical reconstruction algorithm is developed that implements cascaded initial-guesses for nested domains. This hierarchical image reconstruction method is then applied to evaluating a number of NIR applicator designs for integration with a sagittal TRUS transducer. A NIR applicator configuration feasible for instrumentation development is proposed that contains one linear array of optodes on each lateral side of the sagittal TRUS transducer. The performance of this NIR applicator is characterized for the recovery of single tumor mimicking lesion as well as dual targets in the prostate. The results suggest a strong feasibility of transrectal prostate imaging by use of the endo-rectal NIR/US probe.

This is believed to be the first demonstration of near-infrared (NIR) optical tomography employed at the endoscope scale and at a rapid sampling speed that allows translation to in vivo use. A spread-spectral-encoding technique based on a broadband light source and linear-to-circular fiber bundling was used to provide endoscopic probing of many source–detector fibers for tomography as well as parallel sampling of all source–detector pairs for rapid imaging. Endoscopic NIR tomography at an $8\mathrm{Hz}$ frame rate was achieved in phantoms and tissue specimens with a $12\mathrm{mm}$ probe housing eight sources and eight detectors. This novel approach provides the key feasibility studies to allow this blood-based contrast imaging technology to be attempted in detection of cancer in internal organs via endoscopic interrogation.