Time-domain optical mammography: initial clinical results on detection and characterization of breast tumors

Compact fiber-free parallel-plane multi-wavelength diffuse optical tomography system for breast imaging

To facilitate the clinical applicability of the diffuse optical inspection device, a compact multi-wavelength diffuse optical tomography system for breast imaging (compact-DOTB) with a fiber-free parallel-plane structure was designed and fabricated for acquiring three-dimensional optical properties of the breast in continuous-wave mode. The source array consists of 56 surface-mounted micro light-emitting diodes (LEDs), each integrating three wavelengths (660, 750, and 840 nm). The detector array is arranged with 56 miniaturized surface-mounted optical sensors, each encapsulating a high-sensitivity photodiode (PD) and a low-noise current amplifier with a gain of 24×. The system provides 3,136 pairs of source-detector measurements at each wavelength, and the fiber-free design largely ensures consistency between source/detection channels while effectively reducing the complexity of system operation and maintenance. We have evaluated the compact-DOTB system's characteristics and demonstrated its performance in terms of reconstruction positioning accuracy and recovery contrast with breast-sized phantom experiments. Furthermore, the breast cancer patient studies have been carried out, and the quantitative results indicate that the compact-DOTB system is able to observe the changes in the functional tissue components of the breast after receiving the neoadjuvant chemotherapy (NAC), demonstrating the great potential of the proposed compact system for clinical applications, while its cost and ease of operation are competitive with the existing breast-DOT devices.

Advanced Optical Imaging-Guided Nanotheranostics towards Personalized Cancer Drug Delivery

Nanomedicine involves the use of nanotechnology for clinical applications and holds promise to improve treatments. Recent developments offer new hope for cancer detection, prevention and treatment; however, being a heterogenous disorder, cancer calls for a more targeted treatment approach. Personalized Medicine (PM) aims to revolutionize cancer therapy by matching the most effective treatment to individual patients. Nanotheranostics comprise a combination of therapy and diagnostic imaging incorporated in a nanosystem and are developed to fulfill the promise of PM by helping in the selection of treatments, the objective monitoring of response and the planning of follow-up therapy. Although well-established imaging techniques, such as Magnetic Resonance Imaging (MRI), Computed Tomography (CT), Positron Emission Tomography (PET) and Single-Photon Emission Computed Tomography (SPECT), are primarily used in the development of theranostics, Optical Imaging (OI) offers some advantages, such as high sensitivity, spatial and temporal resolution and less invasiveness. Additionally, it allows for multiplexing, using multi-color imaging and DNA barcoding, which further aids in the development of personalized treatments. Recent advances have also given rise to techniques permitting better penetration, opening new doors for OI-guided nanotheranostics. In this review, we describe in detail these recent advances that may be used to design and develop efficient and specific nanotheranostics for personalized cancer drug delivery.

Wearable SiPM-Based NIRS Interface Integrated With Pulsed Laser Source

We present the design of a miniaturized probe integrating silicon photomultiplier and light-pulsing electronics in a single 2 × 2 mm² complementary metal-oxide-semiconductor (CMOS) chip which includes functional blocks such as a fast pulse-laser driver and synchronized single-photon detection circuit. The photon pulses can be either counted on-chip or processed by an external high-speed electronic module such as time-corelated single photon counting (TCSPC) unit. The integrated circuit was assembled on a printed circuit board (PCB) and also on a 2.5D silicon interposer platform of size 1 cm and interfaced with a silicon photomultiplier (SiPM), vertical cavity surface emitting laser (VCSEL) and other ancillary components such as capacitors and resistors. Our approach of integrating an optical interface to optimize light collection on the small active area and light emission from the vertical-cavity surface-emitting laser (VSCEL) will facilitate clinical adoption in many applications and change the landscape of Near Infrared Spectroscopy (NIRS) hardware commercially due to significant optode-size reduction and the elimination of optical fibers.

Diffuse near-infrared imaging of tissue with picosecond time resolution

Optical imaging of biological tissue in vivo at multiple wavelengths in the near-infrared (NIR) spectral range can be achieved with picosecond time resolution at high sensitivity by time-correlated single photon counting. Measuring and analyzing the distribution of times of flight of photons randomly propagated through the tissue has been applied for diffuse optical imaging and spectroscopy, e.g. of human breast tissue and of the brain. In this article, we review the main features and the potential of NIR multispectral imaging with picosecond time resolution and illustrate them by exemplar applications in these fields. In particular, we discuss the experimental methods developed at the Physikalisch-Technische Bundesanstalt (PTB) to record optical mammograms and to quantify the absorption and scattering properties from which hemoglobin concentration and oxygen saturation of healthy and diseased breast tissue have been derived by combining picosecond time-domain and spectral information. Furthermore, optical images of functional brain activation were obtained by a non-contact scanning device exploiting the null source-detector separation approach which takes advantage of the picosecond time resolution as well. The recorded time traces of changes in the oxy- and deoxyhemoglobin concentrations during a motor stimulation investigation show a localized response from the brain.

Stable tissue-simulating phantoms with various water and lipid contents for diffuse optical spectroscopy

We introduced a method for producing solid phantoms with various water-to-lipid ratios that can simulate the absorption, and to some extent the scattering characteristics of human breast tissue. We also achieved phantom stability for a minimum of one month by solidifying the emulsion phantoms. The characteristics of the phantoms were evaluated using the six-wavelength time-domain diffuse optical spectroscopy (TD-DOS) system we developed to measure water and lipid contents and hemoglobin concentration. The TD-DOS measurements were validated with a magnetic resonance imaging system.

Improving breast cancer diagnosis by reducing chest wall effect in diffuse optical tomography

We have developed the ultrasound (US)-guided diffuse optical tomography technique to assist US diagnosis of breast cancer and to predict neoadjuvant chemotherapy response of patients with breast cancer. The technique was implemented using a hand-held hybrid probe consisting of a coregistered US transducer and optical source and detector fibers which couple the light illumination from laser diodes and photon detection to the photomultiplier tube detectors. With the US guidance, diffused light measurements were made at the breast lesion site and the normal contralateral reference site which was used to estimate the background tissue optical properties for imaging reconstruction. However, background optical properties were affected by the chest wall underneath the breast tissue. We have analyzed data from 297 female patients, and results have shown statistically significant correlation between the fitted optical properties ( ? a and ? s ? ) and the chest wall depth. After subtracting the background ? a at each wavelength, the difference of computed total hemoglobin (tHb) between malignant and benign lesion groups has improved. For early stage malignant lesions, the area-under-the-receiver operator characteristic curve (AUC) has improved from 88.5% to 91.5%. For all malignant lesions, the AUC has improved from 85.3% to 88.1%. Statistical test has revealed the significant difference of the AUC improvements after subtracting background tHb values.

Spatial and Spectral Information in Optical Mammography

This article reviews our research activities in the area of optical mammography and relates them to the historical developments and the current state and trends in the field. The guiding threads for this article are the roles played in optical mammography by spatial and spectral information. The first feature, spatial information, is limited by the diffusive nature of light propagation but can take advantage of the exceptionally high optical contrast featured by blood vessels and blood-rich areas in the breast. We describe a method to correct for edge effects, a spatial second-derivative algorithm, and a two-dimensional phased-array approach that enhance the image contrast, the spatial resolution, and the depth discrimination in optical mammograms. The second feature, spectral information, is the most powerful and unique capability of optical mammography, and allows for functional measurements associated with hemoglobin concentration and oxygenation, water concentration, lipids content, and the wavelength dependence of tissue scattering. We present oxygenation-index images obtained from multi-wavelength optical data that point to the diagnostic potential of oxygenation information in optical mammography. The optimization of the spatial and spectral information in optical mammography has the potential to create a role for this imaging modality in the detection and monitoring of breast cancer.

Time of flight dependent linearity in diffuse imaging: how effective is it to evaluate the spatial resolution by measuring the edge response function?

We describe the behavior of linearity in diffuse imaging by evaluating the differences between time-resolved images produced by photons arriving at the detector at different times. Two approaches are considered: Monte Carlo simulations and experimental results. The images of two complete opaque bars embedded in a transparent or in a turbid medium with a slab geometry are analyzed; the optical properties of the turbid medium sample are close to those of breast tissue. A simple linearity test was designed involving a direct comparison between the intensity profile produced by two bars scanned at the same time and the intensity profile obtained by adding two profiles of each bar scanned one at a time. It is shown that the linearity improves substantially when short time of flight photons are used in the imaging process, but even then the nonlinear behavior prevails. As the edge response function (ERF) has been used widely for testing the spatial resolution in imaging systems, the main implication of a time dependent linearity is the weakness of the linearity assumption when evaluating the spatial resolution through the ERF in diffuse imaging systems, and the need to evaluate the spatial resolution by other methods.

Broadband optical mammography instrument for depth-resolved imaging and local dynamic measurements

We present a continuous-wave instrument for non-invasive diffuse optical imaging of the breast in a parallel-plate transmission geometry. The instrument measures continuous spectra in the wavelength range 650-1000 nm, with an intensity noise level <1.5% and a spatial sampling rate of 5 points/cm in the x- and y-directions. We collect the optical transmission at four locations, one collinear and three offset with respect to the illumination optical fiber, to recover the depth of optical inhomogeneities in the tissue. We imaged a tissue-like, breast shaped, silicone phantom (6 cm thick) with two embedded absorbing structures: a black circle (1.7 cm in diameter) and a black stripe (3 mm wide), designed to mimic a tumor and a blood vessel, respectively. The use of a spatially multiplexed detection scheme allows for the generation of on-axis and off-axis projection images simultaneously, as opposed to requiring multiple scans, thus decreasing scan-time and motion artifacts. This technique localizes detected inhomogeneities in 3D and accurately assigns their depth to within 1 mm in the ideal conditions of otherwise homogeneous tissue-like phantoms. We also measured induced hemodynamic changes in the breast of a healthy human subject at a selected location (no scanning). We applied a cyclic, arterial blood pressure perturbation by alternating inflation (to a pressure of 200 mmHg) and deflation of a pneumatic cuff around the subject's thigh at a frequency of 0.05 Hz, and measured oscillations with amplitudes up to 1 μM and 0.2 μM in the tissue concentrations of oxyhemoglobin and deoxyhemoglobin, respectively. These hemodynamic oscillations provide information about the vascular structure and functional integrity in tissue, and may be used to assess healthy or abnormal perfusion in a clinical setting.

Effect of the chest wall on the measurement of hemoglobin concentrations by near-infrared time-resolved spectroscopy in normal breast and cancer

BACKGROUND

Optical imaging and spectroscopy using near-infrared light have great potential in the assessment of tumor vasculature. We previously measured hemoglobin concentrations in breast cancer using a near-infrared time-resolved spectroscopy system. The purpose of the present study was to evaluate the effect of the chest wall on the measurement of hemoglobin concentrations in normal breast tissue and cancer.

METHODS

We measured total hemoglobin (tHb) concentration in both cancer and contralateral normal breast using a near-infrared time-resolved spectroscopy system in 24 female patients with breast cancer. Patients were divided into two groups based on menopausal state. The skin-to-chest wall distance was determined using ultrasound images obtained with an ultrasound probe attached to the spectroscopy probe.

RESULTS

The apparent tHb concentration of normal breast increased when the skin-to-chest wall distance was less than 20 mm. The tHb concentration in pre-menopausal patients was higher than that in post-menopausal patients. Although the concentration of tHb in cancer tissue was statistically higher than that in normal breast, the contralateral normal breast showed higher tHb concentration than cancer in 9 of 46 datasets. When the curves of tHb concentrations as a function of the skin-to-chest wall distance in normal breast were applied for pre- and post-menopausal patients separately, all the cancer lesions plotted above the curves.

CONCLUSIONS

The skin-to-chest wall distance affected the measurement of tHb concentration of breast tissue by near-infrared time-resolved spectroscopy. The tHb concentration of breast cancer tissue was more precisely evaluated by considering the skin-to-chest wall distance.

Estimate of tissue composition in malignant and benign breast lesions by time-domain optical mammography

The optical characterization of malignant and benign breast lesions is presented. Time-resolved transmittance measurements were performed in the 630-1060 nm range by means of a 7-wavelength optical mammograph, providing both imaging and spectroscopy information. A total of 62 lesions were analyzed, including 33 malignant and 29 benign lesions. The characterization of breast lesions was performed applying a perturbation model based on the high-order calculation of the pathlength of photons inside the lesion, which led to the assessment of oxy- and deoxy-hemoglobin, lipids, water and collagen concentrations. Significant variations between tumor and healthy tissue were observed in terms of both absorption properties and constituents concentration. In particular, benign lesions and tumors show a statistically significant discrimination in terms of absorption at several wavelengths and also in terms of oxy-hemoglobin and collagen content.

3D Numerical modeling and its experimental verifications for an inhomogeneous head phantom using broadband fNIR system

Modeling behavior of broadband (30-1000 MHz) frequency modulated near infrared photons through a multilayer phantom is of interest to optical bio-imaging research. Photon dynamics in phantom are predicted using three-dimension (3D) finite element numerical simulation and are related to the measured insertion loss and phase for a given human head geometry in this paper based on three layers of phantom each with distinct optical parameter properties. Simulation and experimental results are achieved for single, two, and three layers solid phantoms using COMSOL (COMSOL AB, Tegnérgatan 23, SE-111 40, Stockholm, Sweden) (for FEM) simulation and custom-designed broadband free space optical transmitter (Tx) and receiver (Rx) modules that are developed for photon migration at wavelengths of 680, 795, and 850 nm. Standard error is used to compute error between two-dimension and 3D FE modeling along with experimental results by fitting experimental data to the functional form of afrequency+b. Error results are shown at narrowband and broadband frequency modulation. Confidence in numerical modeling of the photonic behavior using 3D FEM for human head has been established here by comparing the reflection mode's experimental results with the predictions made by COMSOL for known commercial solid brain phantoms.

Three-dimensional fluorescence tomography of human breast tissues in vivo using a hand-held optical imager

Diffuse optical imaging using non-ionizing radiation is a non-invasive method that shows promise towards breast cancer diagnosis. Hand-held optical imagers show potential for clinical translation of the technology, yet they have not been used towards 3D tomography. Herein, 3D tomography of human breast tissue in vivo is demonstrated for the first time using a hand-held optical imager with automated coregistration facilities. Simulation studies are performed on breast geometries to demonstrate the feasibility of 3D tomographic imaging using a hand-held imager under perfect (1:0) and imperfect (100:1, 50:1) fluorescence absorption contrast ratios. Experimental studies are performed in vivo using a 1 µM ICG filled phantom target placed non-invasively underneath the flap of the breast tissue. Results show the ability to perform automated tracking and coregistered imaging of human breast tissue (with tracking accuracy on the order of ∼1 cm). Three-dimensional tomography results demonstrated the ability to recover a single target placed at a depth of 2.5 cm, from both the simulated (at 1:0, 100:1 and 50:1 contrasts) and experimental cases on actual breast tissues. Ongoing efforts to improve target depth recovery are carried out via implementation of transmittance imaging in the hand-held imager.

US-guided optical tomography: correlation with clinicopathologic variables in breast cancer

We tested the relationships between total hemoglobin concentration (THC), as measured with ultrasound (US)-guided optical tomography, and clinicopathologic variables in invasive ductal cancers; and we evaluated the clinical significance of THC. Fifty-three patients with 65 invasive ductal carcinomas underwent US-guided biopsy and were scanned with a hand-held probe consisting of a co-registered US transducer and an NIR (near-infrared) imager. The lesion location provided by co-registered US was used to guide optical imaging. Light absorption was measured at two optical wavelengths. From this measurement, tumor angiogenesis was assessed on the basis of calculated THC. We investigated the relationships between maximum THC and clinicopathologic variables (tumor size [≤2 cm or >2 cm], metastasis to lymph node or distant organ, histologic grade, lymphovascular invasion, status of ER, PR, HER2 and Ki-67, and triple negativity). The mean maximum THC in the breast cancers was 223.3 ± 106.3 μmol/L. In univariate analysis, HER2 positivity, tumor size, and Ki-67 positivity showed significant correlations with maximum THC (p < 0.05). In multivariate analysis including tumor size, and ER, PR, HER2, and Ki-67 status, HER2 positivity correlated with maximum THC significantly (p = 0.007, parameter estimate 76.44). Maximum THC correlated with HER2, Ki-67 and tumor size in this group of ductal breast carcinomas. Thus, US-guided diffuse optical tomography (US-DOT) may potentially be used to predict tumor aggressiveness in patients with invasive breast cancers.

Accurate optical parameter extraction procedure for broadband near-infrared spectroscopy of brain matter

Modeling behavior of broadband (30 to 1000 MHz) frequency modulated near-infrared (NIR) photons through a phantom is the basis for accurate extraction of optical absorption and scattering parameters of biological turbid media. Photon dynamics in a phantom are predicted using both analytical and numerical simulation and are related to the measured insertion loss (IL) and insertion phase (IP) for a given geometry based on phantom optical parameters. Accuracy of the extracted optical parameters using finite element method (FEM) simulation is compared to baseline analytical calculations from the diffusion equation (DE) for homogenous brain phantoms. NIR spectroscopy is performed using custom-designed, broadband, free-space optical transmitter (Tx) and receiver (Rx) modules that are developed for photon migration at wavelengths of 680, 780, and 820 nm. Differential detection between two optical Rx locations separated by 0.3 cm is employed to eliminate systemic artifacts associated with interfaces of the optical Tx and Rx with the phantoms. Optical parameter extraction is achieved for four solid phantom samples using the least-square-error method in MATLAB (for DE) and COMSOL (for FEM) simulation by fitting data to measured results over broadband and narrowband frequency modulation. Confidence in numerical modeling of the photonic behavior using FEM has been established here by comparing the transmission mode's experimental results with the predictions made by DE and FEM for known commercial solid brain phantoms.

The effect of temporal impulse response on experimental reduction of photon scatter in time-resolved diffuse optical tomography

New fast detector technology has driven significant renewed interest in time-resolved measurement of early photons in improving imaging resolution in diffuse optical tomography and fluorescence mediated tomography in recent years. In practice, selection of early photons results in significantly narrower instrument photon density sensitivity functions (PDSFs) than the continuous wave case, resulting in a better conditioned reconstruction problem. In this work, we studied the quantitative impact of the instrument temporal impulse response function (TIRF) on experimental PDSFs in tissue mimicking optical phantoms. We used a multimode fiber dispersion method to vary the system TIRF over a range of representative literature values. Substantial disagreement in PDSF width--by up to 40%--was observed between experimental measurements and Monte Carlo (MC) models of photon propagation over the range of TIRFs studied. On average, PDSFs were broadened by about 0.3 mm at the center plane of the 2 cm wide imaging chamber per 100 ps of the instrument TIRF at early times. Further, this broadening was comparable on both the source and detector sides. Results were confirmed by convolution of instrument TIRFs with MC simulations. These data also underscore the importance of correcting imaging PDSFs for the instrument TIRF when performing tomographic image reconstruction to ensure accurate data-model agreement.

Near-infrared imaging of breast cancer using optical contrast agents

Breast cancer is the most common malignancy in women worldwide and the second leading cause of cancer death. On the basis of three studies performed by our group, this article reviews the current status of optical breast imaging using extrinsic contrast agents. To date, only two contrast agents have been applied in human studies, indocyanine green (ICG) and omocianine. Both contrast media were used for absorption and fluorescence imaging. Generally speaking, malignant breast lesions exhibited higher absorption contrast as well as higher fluorescence contrast compared to benign lesions or non-diseased breast tissue. Some groups consider early enhancement characteristics helpful for differentiation between malignant and benign lesions. Late fluorescence ICG imaging - capitalizing on the extravasation of the dye through the wall of tumorous vessels - seems to be a promising technique to distinguish malignant from benign breast lesions.

Diffuser-aided diffuse optical imaging for breast tumor: a feasibility study based on time-resolved three-dimensional Monte Carlo modeling

This study proposed diffuser-aided diffuse optical imaging (DADOI) as a new approach to improve the performance of the conventional diffuse optical tomography (DOT) approach for breast imaging. The 3-D breast model for Monte Carlo simulation is remodeled from clinical MRI image. The modified Beer-Lambert's law is adopted with the DADOI approach to substitute the complex algorithms of inverse problem for mapping of spatial distribution, and the depth information is obtained based on the time-of-flight estimation. The simulation results demonstrate that the time-resolved Monte Carlo method can be capable of performing source-detector separations analysis. The dynamics of photon migration with various source-detector separations are analyzed for the characterization of breast tissue and estimation of optode arrangement. The source-detector separations should be less than 4 cm for breast imaging in DOT system. Meanwhile, the feasibility of DADOI was manifested in this study. In the results, DADOI approach can provide better imaging contrast and faster imaging than conventional DOT measurement. The DADOI approach possesses great potential to detect the breast tumor in early stage and chemotherapy monitoring that implies a good feasibility for clinical application.

Monitoring the response to primary medical therapy for breast cancer using three- dimensional time-resolved optical mammography

Primary medical therapy is used to reduce tumour size prior to surgery in women with locally advanced breast cancer. Optical tomography is a functional imaging technique using near- infrared light to produce three-dimensional breast images of tissue oxygen saturation and haemoglobin concentration. Its advantages include the ability to display quantitative physiological information, and to allow repeated scans without the hazards associated with exposure to ionising radiation. There is a need for a non-invasive functional imaging tool to evaluate response to treatment, so that non-responders can be given the opportunity to change their treatment regimen. Here, we evaluate the use of optical tomography for this purpose. Four women with newly diagnosed breast cancer who were about to undergo primary medical therapy gave informed and voluntary consent to take part in the study. Changes in physiological and optical properties within the tumour were evaluated during the course of neoadjuvant chemotherapy. Optical imaging was performed prior to treatment, after the first cycle of chemotherapy, halfway through, and on completion of chemotherapy. Images of light absorption and scatter at two wavelengths were produced, from which images of total haemoglobin concentration and oxygen saturation were derived. All patients that showed a good or complete response to treatment on MRI showed a corresponding recovery in the haemoglobin concentration images. Changes in mean tumour total haemoglobin concentration could be seen four weeks into treatment. The tumour oxygen saturation was low compared to background in three out of four patients, and also showed a return to baseline over treatment. Optical imaging of the breast is feasible during primary medical therapy and can be used to assess response to treatment over six months.

Imaging tumor oxyhemoglobin and deoxyhemoglobin concentrations with ultrasound-guided diffuse optical tomography

We present an ultrasound (US)-guided diffuse optical tomography for mapping tumor deoxyhemoglobin (deoxyHb) and oxyhemoglobin (oxyHb) concentrations in blood phantoms and in in-vivo patients. Because oxyHb and deoxyHb respond differently at different wavelengths, four laser diodes of wavelengths 740 nm, 780 nm, 808 nm and 830 nm were used in the study. Tumor model experiments were performed using phantoms of different hemoglobin oxygen saturations (14%-89%) representing hemoglobin oxygenation in tissue. Targets of different sizes and located at different depths were used to validate the accuracy of oxygen saturation estimation. The absolute deviations between the estimated hemoglobin oxygen saturations obtained from reconstructed absorption maps and oxygen measurements obtained using a pO2 electrode were less than 8% over the measured range of oxygen saturation. An inhomogeneous concentric blood phantom of deoxygenated center core and oxygenated outer shell was imaged and deoxyHb and oxyHb maps revealed corresponding distributions which correlated well with inhomogeneous deoxy- and oxy- distributions frequently seen in breast cancers. Clinical examples are given to demonstrate the utility of US-guided optical tomography in mapping heterogeneous deoxyHb and oxyHb distributions in breast cancers.

Impact of contralateral and ipsilateral reference tissue selection on self-referencing differential spectroscopy for breast cancer detection

We previously developed a self-referencing differential spectroscopic (SRDS) method to detect lesions by identifying a spectroscopic biomarker of breast cancer, i.e., the specific tumor component (STC). The SRDS method is based on the assumption of the exclusive presence of this spectroscopic biomaker in malignant disease. Although clinical results using this method have already been published, the dependence of the STC spectra on the choice of reference tissue has not yet been addressed. In this study, we explore the impact of the selection of the reference region size and location on the STC spectrum in 10 subjects with malignant breast tumors. Referencing from both contralateral and ipsilateral sides was performed. Regardless of the referencing, we are able to obtain consistent high contrast images of malignant lesions using the STC with less than 13% deviation. These results suggest that the STC measurements are independent of any type, location, and amount of normal breast tissue used for referencing. This confirms the initial assumption of the SRDS analysis, that there are specific tumor components in cancer that do not exist in normal tissue. This also indicates that bilateral measurements are not required for lesion identification using the STC method.

Near-infrared optical mammography for breast cancer detection with intrinsic contrast

Optical methods to detect breast cancer on the basis of its increased opacity have been explored for some time. These methods have matured to a point in which they are capable of quantifying the optical properties of breast tissue and translating them into measures of concentrations of relevant tissue components. In particular, near-infrared spectroscopy has been employed to determine the concentrations of hemoglobin, water, and lipids, as well as oxygen saturation of hemoglobin and optical scattering properties in normal and cancerous breast tissue. Dynamic optical measurements can also identify abnormal hemodynamic patterns associated with breast cancer. We review, in this article, a number of results in the field, which show that cancerous tissue is associated with higher hemoglobin and water concentrations, and a lower lipid concentration with respect to normal breast tissue. Indications that breast cancers are characterized by lower hemoglobin saturation and stronger scattering decay as a function of wavelength are less robust, with variable results reported in the literature. Intrinsic sources of optical contrast associated with breast cancer can also be used to monitor individual response to neoadjuvant therapy.

Current and future clinical applications for optical imaging of cancer: from intraoperative surgical guidance to cancer screening

Optical imaging is an inexpensive, fast, and sensitive imaging approach for the noninvasive detection of human cancers in locations that are accessible by an optical imaging device. Light is used to probe cellular and molecular function in the context of cancer in the living body. Recent advances in the development of optical instrumentation make it possible to detect optical signals produced at a tissue depth of several centimeters. The optical signals can be endogenous contrasts that capture the heterogeneity and biological status of different tissues, including tumors, or extrinsic optical contrasts that selectively accumulate in tumors to be imaged after local or systemic delivery. The use of optical imaging is now being applied in the clinic and operating room for the localization and resection of malignant tumors in addition to screening for cancer.

Experimental measurement of time-dependent photon scatter for diffuse optical tomography

Time-resolved measurement of early arriving photons through diffusive media has been shown to effectively reduce the high degree of light scatter in biological tissue. However, the experimentally achievable reduction in photon scatter and the impact of time-gated detection on instrument noise performance is not well understood. We measure time-dependent photon density sensitivity functions (PDSFs) between a pulsed laser source and a photomultiplier tube operating in time-correlated single-photon-counting mode. Our data show that with our system, measurement of early arriving photons reduces the full width half maximum of PDSFs on average by about 40 to 60% versus quasicontinuous wave photons over a range of experimental conditions similar to those encountered in small animal tomography, corresponding to a 64 to 84% reduction in PDSF volume. Factoring in noise considerations, the optimal operating point of our instrument is determined to be about the 10% point on the rising edge of the transmitted intensity curve. Time-dependent Monte Carlo simulations and the time-resolved diffusion approximation are used to model photon propagation and are evaluated for agreement with experimental data.

Light-guided lumpectomy: device and case report

We describe the development, design, fabrication, and testing of an optical wire to assist in the surgical removal of small lesions during breast-conserving surgery. We modify a standard localization wire by adding a 200-μm optical fiber alongside it; the resulting optical wire fit through an 18 gauge needle for insertion in the breast. The optical wire is anchored in the lesion by a radiologist under ultrasonic and mammographic guidance. At surgery, the tip is illuminated with an eye-safe, red, HeNe laser, and the resulting glowball of light in the breast tissue surrounds the lesion. The surgeon readily visualizes the glowball in the operating room. This glowball provides sufficient feedback to the surgeon that it is used (1) to find the lesion and (2) as a guide during resection. Light-guided lumpectomy is a simple enhancement to traditional wire localization that could improve the current standard of care for surgical treatment of small, nonpalpable breast lesions.

Optical tomography method that accounts for tilted chest wall in breast imaging

The chest wall underneath breast tissue distorts light reflection measurements, especially measurements obtained from distant source-detector pairs. For patients with a chest wall located at a shallower depth, the chest-wall effect needs to be considered in the image reconstruction procedure. Following our previous studies, this work systemically evaluates the performance of a two-layer model-based reconstruction using the finite element method, and compares it with the performance of the semi-infinite model. The results obtained from simulations and phantom experiments show that the two-layer model improves the light quantification of the targets. The improvements are attributed to improved background estimation and more accurate weight matrix calculation using a two-layer model compared to the semi-infinite model. Fitted two-layer background optical properties obtained from a group of ten patients with chest walls located less than 2 cm deep are more representative of breast tissue and chest-wall optical properties.

Combined domain-decomposition and matrix-decomposition scheme for large-scale diffuse optical tomography

Image reconstruction in diffuse optical tomography (DOT) is, in general, posed as a model-based, nonlinear optimization problem, which requires repeated use of the three-dimensional (3D) forward and inverse solvers. To cope with the computation and storage problem for some applications, such as breast tumor diagnosis, it is preferable to develop a subdomain-based parallel computation scheme. In this study, we propose a two-level image reconstruction scheme for 3D DOT, which combines the Schwarz-type domain-decomposition (DD)-based forward calculation and the matrix-decomposition (MD)-based inversion. In the forward calculation, the solution to the diffusion equation is initially obtained using a whole-domain finite difference method at a coarse grid, and then updated with a parallel DD scheme at a fine grid. The inversion procedure starts with the wavelet-decomposition-based reconstruction at a coarse grid, and then follows with a Levenberg-Marquardt least-squares solution at a fine grid, where an MD strategy is adopted for the relevant linear inversion. It is demonstrated that the combination of the DD-based forward solver and MD-based inversion allows for coarse-grain parallel implementation of both the forward and inverse issues and effectively reduces computation and storage loads for the large-scale problem. Also, both numerical simulations and phantom experiments show that MD-based linear inversion is superior to the row-fashioned algebraic reconstruction technique.

Light shadowing effect of large breast lesions imaged by optical tomography in reflection geometry

When a large, highly absorbing breast lesion is imaged by optical tomography in reflection geometry, most of the photons are absorbed by the top portion of the lesion. As a result, the lower portion of the lesion is not quantified correctly. This posterior light shadowing effect is similar to the sound shadowing effect frequently seen in pulse-echo ultrasound images. The presence of significant posterior shadowing of a lesion in ultrasound images suggests malignance. The light shadowing effect due to optical contrast is characterized using a simple measure and validated by the Monte Carlo photon-tracking method and phantom experiments. Clinical examples of large malignant and benign lesions are presented to demonstrate the shadowing effect and the utility of the measure. Understanding and quantifying the shadowing effect due to optical contrast is important for characterizing larger malignant cancers from benign lesions.

Quantitative characterization of optical and physiological parameters in normal breasts using time-resolved spectroscopy: in vivo results of 19 Singapore women

We report the quantitative measurements of optical and physiological parameters of normal breasts from 19 Singapore women by using time-resolved diffuse optical spectroscopy. Intrinsic absorption coefficient (mu(a)) and reduced scattering coefficients (mu(s) (')) of breasts were calculated from the time-resolved photon migration data. Physiology of breasts was characterized using the concentrations of oxyhemoglobin, deoxyhemoglobin, total hemoglobin (THC), and oxygenation saturation. On average, the experiment results showed that the mu(a) of young women (below 40 years old) was 36 to 38% greater than that of older women (above 40 years old) and that parameter THC was approximately 42% greater. Results also showed that the THC of premenopausal women was 24.3 microMol/L, which was approximately 69% larger than that of postmenopausal women at 14.1 microMol/L. Meanwhile, the mu(a) of premenopausal women was approximately 60% larger than that of postmenopausal women. Correlation analysis further showed that the optical and physiological parameters of breasts were strongly influenced by changes in the women's age, menopausal states, and body mass index. These in vivo experiment results will contribute to the breast tissue diagnosis between healthy and diseased breast tissues.

Seven-wavelength time-resolved optical mammography extending beyond 1000 nm for breast collagen quantification

Our multi-wavelength time-resolved optical mammograph was upgraded to improve its overall performances and extend its spectral coverage up to 1060 nm, with the aim of increasing the measurement sensitivity to the content of collagen in breast tissue. Late-gated intensity and reduced scattering images are routinely displayed for diagnostic purposes. Maps of tissue constituents (lipid, water and collagen) and blood parameters (total hemoglobin content and blood oxygenation) are built to highlight spatial changes due to physiological and pathological reasons. The upgraded instrument was tested on tissue phantoms. Then images were collected at 7 wavelengths (635-1060 nm) from 10 healthy volunteers. Average collagen content correlated with breast density whenever x-ray mammograms were available (6 subjects).

Phase-contrast diffuse optical tomography for in vivo breast imaging: a two-step method

We present a two-step reconstruction method that can qualitatively and quantitatively improve the reconstruction of tissue refractive index (RI) distribution by phase-contrast diffuse optical tomography (PCDOT). In this two-step method, we first recover the distribution of tissue absorption and scattering coefficients by conventional diffuse optical tomography to obtain the geometrical information of lesions, allowing the incorporation of geometrical information as a priori in the PCDOT reconstruction using a locally refined mesh. The method is validated by a series of phantom experiments and evaluated using in vivo data from 42 human subjects. The results demonstrate clear contrast of RI between the lesion and the surroundings, making the image interpretation straightforward. The sensitivity and specificity from these 42 cases are both 81% when RI is used as an imaging parameter for distinguishing between malignant and benign lesions.

The use of skin surface electropotentials for breast cancer detection--preliminary clinical trial results obtained using the biofield diagnostic system

The purpose of this study is to evaluate the efficiency of the Biofield Diagnostic System (BDS) as an adjunct to established diagnostic techniques such as mammography and ultrasound in differentiating benign and malignant breast lesions. The clinical trial was conducted at the Tan Tock Seng hospital, Singapore. 103 women scheduled for mammography and/or ultrasound tests participated in the study. The BDS test recorded a sensitivity of 100%, specificity of 97.6%, and an accuracy of 98.1%. The area under the ROC curve was 0.988 which was slightly lower than that of ultrasound (0.994) and slightly higher than that of mammography (0.951). The BDS test has demonstrated high sensitivity and specificity values in the studied population. The accuracy is also comparable to that of diagnostic techniques like mammography and ultrasound. Thus, it is evident that BDS can be a fast and reliable adjunct tool for getting a secondary opinion on lesions with indeterminate mammographic and sonographic results.

CW transillumination imaging by extracting weakly scattered light from strongly diffused light

Transmitted light through a diffuse scattering medium includes strongly diffused light (SDL) and weakly scattered light (WSL). To realize clear transillumination imaging through thick body tissue, which is typically more than 10 mm, we developed a technique to extract the WSL component from diffused light. In experiments using a 15-mm-thick scattering medium (mu(s)' = 1.0/mm), the cross-section of the light propagation area at the center of the medium was confined to a 50% area. This method's usefulness was demonstrated by transillumination imaging through a 40-mm-thick piece of chicken meat. The possibility of depth evaluation was also verified.

Near-infrared spectral imaging of the female breast for quantitative oximetry in optical mammography

We present a hybrid continuous-wave, frequency-domain instrument for near-infrared spectral imaging of the female breast based on a tandem, planar scanning of one illumination optical fiber and one collection optical fiber configured in a transmission geometry. The spatial sampling rate of 25 points/cm(2) is increased to 400 points/cm(2) by postprocessing the data with a 2D cubic spline interpolation. We then apply a previously developed spatial second-derivative algorithm to an edge-corrected intensity image (N-image) to enhance the visibility and resolution of optical inhomogeneities in breast tissue such as blood vessels and tumors. The spectral data at each image pixel consist of 515-point spectra over the 650-900 nm wavelength range, thus featuring a spectral density of two data points per nanometer. We process the measured spectra with a paired-wavelength spectral analysis method to quantify the oxygen saturation of detected optical inhomogeneities, under the assumption that they feature a locally higher hemoglobin concentration. Our initial measurements on two healthy human subjects have generated high-resolution optical mammograms displaying a network of blood vessels with values of hemoglobin saturation typically falling within the 60%-95% range, which is physiologically reasonable. This approach to spectral imaging and oximetry of the breast has the potential to efficiently exploit the high intrinsic contrast provided by hemoglobin in breast tissue and to contribute a useful tool in the detection, diagnosis, and monitoring of breast pathologies.

Methodology development for three-dimensional MR-guided near infrared spectroscopy of breast tumors

Combined Magnetic Resonance (MR) and Near Infrared Spectroscopy (NIRS) has been proposed as a unique method to quantify hemodynamics, water content, and cellular size and packing density of breast tumors, as these tissue constituents can be quantified with increased resolution and overlaid on the structural features identified by the MR. However, the choices in how to reconstruct and visualize this information can have a dramatic impact on the feasibility of implementing this modality in the clinic. This is especially true in 3 dimensions, as there is often limited optical sampling of the breast tissue, and methods need to accurately reflect the tissue composition. In this paper, the implementation and display of fully 3D MR image-guided NIRS is outlined and demonstrated using in vivo data from three healthy women and a volunteer undergoing neoadjuvant chemotherapy. Additionally, a display feature presented here scales the transparency of the optical images to the sensitivity of the measurements, providing a logical way to incorporate partial volume sets of optical images onto the MR volume. These concepts are demonstrated with 3D data sets using Volview software online.

Optical imaging instrument for muscle oxygenation based on spatially resolved spectroscopy

An imaging instrument based on spatially resolved spectroscopy that enables temporal and spatial analyses of muscle oxygenation was designed. The instrument is portable and can be connected to 32 compact and separate-type optical probes. Its measurement accuracy of O(2) saturation and hemoglobin concentration was evaluated using a tissue-equivalent phantom. Imaging and multi-point measurements of tissue oxygen saturation (S(t)O(2)) in the quadriceps muscle were also performed, and dynamic changes in S(t)O(2) in response to increase in exercise intensity (within the rectus femoris region) and variation in exercise protocol (among the rectus femoris, vastus lateralis and vastus medialis) were clearly shown.

The Use of Tissue Electrical Characteristics for Breast Cancer Detection: A Perspective Review

Breast cancer is the most frequently occurring malignancy in women. It is characterized by a high mortality rate. For the purpose of detecting this life threatening disease, research efforts are being made worldwide to exploit new technologies, to improve the detection accuracy of current devices and to develop new detection devices, comprehensive diagnostic procedures, and protocols. One such technology that is gaining popular attention over the recent years is the usage of electrical characteristics of the breast tissue to differentiate normal and cancerous tissues. Most of the devices using this technology are currently being used as adjunct diagnostic tools to improve the detection accuracy of established techniques like mammography and ultrasound. Also, early detection of breast cancer can help save many thousands of lives every year and can also reduce unnecessary healthcare expenditure caused by advanced stage treatment options. Hence, more research is also being done to adapt these devices into screening tools for early detection of breast cancer.

The main objective of this review is to highlight the features of the currently available commercial devices that use this technology for breast cancer detection. The electrical behavior of normal and cancerous breast tissues is first presented. The various commercial devices that utilize electrical impedance or electropotentials for breast cancer detection are then described. Finally, conclusions and potential areas of research are highlighted.

Optimal probe design for breast imaging using near-infrared diffused light

Shallow lesions less than 1.5-cm deep are frequently seen in breast patients when they are scanned in reflection geometry. Two boundary conditions are compared for imaging shallow lesions, and a new probe design is introduced. A partial reflection boundary condition is suitable for imaging shallow lesions less than 1.0-cm deep; whereas an absorption boundary condition is desirable for imaging lesions more than 1.5-cm deep. Our new probe design incorporates either a partial reflection boundary or an absorption boundary based on a priori knowledge of lesion depth provided by coregistered real-time ultrasound images. An angled source is introduced to further improve the illumination of the region between 1.0- to 1.5-cm depths. Simulation, phantom, and freshly excised mouse tumor experiments demonstrate that targets located at different depths can be uniformly reconstructed. A clinical example is given to demonstrate the utility of this new approach for optimally probing lesions located at different depths.

Automated breast cancer classification using near-infrared optical tomographic images

An automated procedure for detecting breast cancer using near-infrared (NIR) tomographic images is presented. This classification procedure automatically extracts attributes from three imaging parameters obtained by an NIR imaging system. These parameters include tissue absorption and reduced scattering coefficients, as well as a tissue refractive index obtained by a phase-contrast-based reconstruction approach. A support vector machine (SVM) classifier is utilized to distinguish the malignant from the benign lesions using the automatically extracted attributes. The classification results of in vivo tomographic images from 35 breast masses using absorption, scattering, and refractive index attributes demonstrate high sensitivity, specificity, and overall accuracy of 81.8%, 91.7%, and 88.6% respectively, while the classification sensitivity, specificity, and overall accuracy are 63.6%, 83.3%, and 77.1%, respectively, when only the absorption and scattering attributes are used. Furthermore, the automated classification procedure provides significantly improved specificity and overall accuracy for breast cancer detection compared to those by an experienced technician through visual examination.

Pass-through photon-based biomedical transillumination

We present the mathematical foundation and the experimental validation of a technique that utilizes pass-through (ballistic) photons in a partial coherence interferometric transillumination setup for biomedical analyses. We demonstrate that the implementation depends closely on tissue under test, incident power, spatial and spectral characteristics of the radiation source, and detection electronics. With the aid of the complex material coherence function concept, we foresee tissue characterization and diagnostic imaging as potential applications for the technique. We propose a normalization procedure for in vitro and in vivo measurements, where nontissue-related quantities are canceled out. The validation of the proposal is achieved by obtaining the sample coherence function of a tissue phantom. The expected exponential attenuation is confirmed, and the corresponding scattering coefficients are determined. A good agreement between theory and experiment, for the initial set of samples, serves to establish that pass-through photon-based transillumination is feasible for selected biomedical applications.

Phase-contrast diffuse optical tomography pilot results in the breast

RATIONALE AND OBJECTIVES

We sought to investigate the utility of phase-contrast diffuse optical tomography (PCDOT) for differentiation of malignant and benign breast masses in humans and to compare PCDOT with conventional diffuse optical tomography (DOT) for analysis of breast masses in humans.

MATERIALS AND METHODS

Thirty-five breast masses were imaged in 33 patients (mean age, 51 years; range, 22-80) using PCDOT. Images characterizing the tissue refractive index, and absorption and scattering coefficients of breast masses were obtained with a finite element-based reconstruction algorithm. Theses images were then analyzed and compared with the biopsy/pathology results for all the cases examined.

RESULTS

Malignant lesions tended to have a decreased refractive index, allowing them to be discriminated from benign lesions in most cases, whereas absorption and scattering images were unable to accurately discriminate benign from malignant lesions. The sensitivity, specificity, false-positive value, and overall accuracy for refractive index imaging were 81.8%, 70.8%, 29.2%, and 74.3%, respectively. The accuracy of refractive index imaging increases with increasing patient age.

CONCLUSION

Refractive index is a new parameter for optical imaging that may be helpful in differentiating between malignant and benign masses in the breast.

Time-resolved optical spectroscopy of wood

We have proposed and experimentally demonstrated that picosecond time-resolved optical spectroscopy in the visible/near-infrared (NIR) region (700-1040 nm) is a useful technique for noninvasive characterization of wood. This technique has been demonstrated on both softwood and hardwood samples treated in different ways simulating the aging process suffered by waterlogged woods. In all the cases, alterations of absorption and scattering spectra were observed, revealing changes of chemical and structural composition.

Diagnosis of breast cancer using fluorescence and diffuse reflectance spectroscopy: a Monte-Carlo-model-based approach

We explore the use of Monte-Carlo-model-based approaches for the analysis of fluorescence and diffuse reflectance spectra measured ex vivo from breast tissues. These models are used to extract the absorption, scattering, and fluorescence properties of malignant and nonmalignant tissues and to diagnose breast cancer based on these intrinsic tissue properties. Absorption and scattering properties, including beta-carotene concentration, total hemoglobin concentration, hemoglobin saturation, and the mean reduced scattering coefficient are derived from diffuse reflectance spectra using a previously developed Monte Carlo model of diffuse reflectance. A Monte Carlo model of fluorescence described in an earlier manuscript was employed to retrieve the intrinsic fluorescence spectra. The intrinsic fluorescence spectra were decomposed into several contributing components, which we attribute to endogenous fluorophores that may present in breast tissues including collagen, NADH, and retinol/vitamin A. The model-based approaches removes any dependency on the instrument and probe geometry. The relative fluorescence contributions of individual fluorescing components, as well as beta-carotene concentration, hemoglobin saturation, and the mean reduced scattering coefficient display statistically significant differences between malignant and adipose breast tissues. The hemoglobin saturation and the reduced scattering coefficient display statistically significant differences between malignant and fibrous/benign breast tissues. A linear support vector machine classification using (1) fluorescence properties alone, (2) absorption and scattering properties alone, and (3) the combination of all tissue properties achieves comparable classification accuracies of 81 to 84% in sensitivity and 75 to 89% in specificity for discriminating malignant from nonmalignant breast tissues, suggesting each set of tissue properties are diagnostically useful for the discrimination of breast malignancy.