Refractive index of carcinogen-induced rat mammary tumours

Optical parameters of healthy and tumor breast tissues in mice

Knowledge of the optical parameters of tumors is important for choosing the correct laser treatment parameters. In this paper, optical properties and refraction indices of breast tissue in healthy mice and a 4T1 model mimicking human breast cancer have been measured. A significant decrease in both the scattering and refractive index of tumor tissue has been observed. The change in tissue morphology has induced the change in the slope of the scattering spectrum. Thus, the light penetration depth into tumor has increased by almost 1.5-2 times in the near infrared "optical windows." Raman spectra have shown lower lipid content and higher protein content in tumor. The difference in the optical parameters of the tissues under study makes it possible to reliably differentiate them. The results may be useful for modeling the distribution of laser radiation in healthy tissues and cancers for deriving optimal irradiation conditions in photodynamic therapy.

Immersion optical clearing of adipose tissue in rats: ex vivo and in vivo studies

Optical clearing (OC) of adipose tissue has not been studied enough, although it can be promising in medical applications, including surgery and cosmetology, for example, to visualize blood vessels or increase the permeability of tissues to laser beams. The main objective of this work is to develop technology for OC of abdominal adipose tissue in vivo using hyperosmotic optical clearing agents (OCAs). The maximum OC effect (77%) was observed for ex vivo rat adipose tissue samples exposed to OCA on fructose basis for 90 minutes. For in vivo studies, the maximum effect of OC (65%) was observed when using OCA based on diatrizoic acid and dimethylsulfoxide for 120 minutes. Histological analysis showed that in vivo application of OCAs may induce a limited local necrosis of fat cells. The efficiency of OC correlated with local tissue damage through cell necrosis due to accompanied cell lipolysis.

Cherenkov light emission in molecular radiation therapy of the thyroid and its application to dosimetry

Numerical experiments based on Monte Carlo simulations and clinical CT data are performed to investigate the spatial and spectral characteristics of Cherenkov light emission and the relationship between Cherenkov light intensity and deposited dose in molecular radiotherapy of hyperthyroidism and papillary thyroid carcinoma. It is found that Cherenkov light is emitted mostly in the treatment volume, the spatial distribution of Cherenkov light at the surface of the patient presents high-value regions at locations that depend on the symmetry and location of the treatment volume, and the surface light in the near-infrared spectral region originates from the treatment site. The effect of inter-patient variability in the tissue optical parameters and radioisotope uptake on the linear relationship between the dose absorbed by the treatment volume and Cherenkov light intensity at the surface of the patient is investigated, and measurements of surface light intensity for which this effect is minimal are identified. The use of Cherenkov light measurements at the patient surface for molecular radiation therapy dosimetry is also addressed.

Complex refractive index of freshly excised human breast tissue as a marker of disease

We report differences in the refractive index of healthy and tumorous freshly excised human breast tissue as determined from reflectance profile measurements at five wavelengths (432 nm, 532 nm, 633 nm, 964 nm, 1551 nm) in the visible and near-infrared using a standard prism-coupling refractometer. These refractive index differences, particularly in the near-infrared, can be used to distinguish fibroadenomas and cancerous growths not only from normal breast tissue but also from each other.

Refractive index of biological tissues: Review, measurement techniques, and applications

Refractive index (RI) is a characteristic optical variable that controls the propagation of light in the medium (e.g., biological tissues). Basic research with the aim to investigate the RI of biological tissues is of paramount importance for biomedical optics and associated applications. Herein, we reviewed and summarized the RI data of biological tissues and the associated insights. Different techniques for the measurement of RI of biological tissues are also discussed. Moreover, several examples of the RI applications from basic research, clinics and optics industry are outlined. This study may provide a comprehensive reference for RI data of biological tissues for the biomedical research and beyond.

Multispectral sensing of biological liquids with hollow-core microstructured optical fibres

The state of the art in optical biosensing is focused on reaching high sensitivity at a single wavelength by using any type of optical resonance. This common strategy, however, disregards the promising possibility of simultaneous measurements of a bioanalyte's refractive index over a broadband spectral domain. Here, we address this issue by introducing the approach of in-fibre multispectral optical sensing (IMOS). The operating principle relies on detecting changes in the transmission of a hollow-core microstructured optical fibre when a bioanalyte is streamed through it via liquid cells. IMOS offers a unique opportunity to measure the refractive index at 42 wavelengths, with a sensitivity up to ~3000 nm per refractive index unit (RIU) and a figure of merit reaching 99 RIU-1 in the visible and near-infra-red spectral ranges. We apply this technique to determine the concentration and refractive index dispersion for bovine serum albumin and show that the accuracy meets clinical needs.

Automated full-field polarization-sensitive optical coherence tomography diagnostic systems for breast cancer

Intraoperative delineation of breast cancer is a major challenge. An effective breast tissue screening technique may reduce the risk of re-excision during surgery by specifically identifying positive margins. In this study, a high-resolution automated full-field polarization-sensitive optical coherence tomography (FF-PS-OCT) system was developed to classify healthy and malignant human breast tissue from quantitative phase retardation information of the tissues in ex vivo. Twelve breast tissue samples [four healthy, eight malignant (cancerous)] were imaged with the FF-PS-OCT system and the different phase features were extracted from the acquired OCT images (106), based on the differences in the optical signatures of the healthy and malignant tissues. A linear support vector model classifier was trained using 75 images, with a sensitivity of 92.10% and specificity of 89.18% was achieved. Thirty-one images were used to test the model, with a sensitivity of 90.90% and specificity of 85.0% achieved.

Easy integrable refractometer for liquids on extended surfaces

Conventional Abbe refractometers are used to determine the refractive index (RI) of liquid samples placed on a prism surface by critical angle evaluation. However, the use of this method is limited to the investigation of fluids in a laboratory environment. With the purpose of monitoring fluids attaching to extended planar surfaces, a different method is required. We present a RI monitoring device for plates of any given geometry. The proposed method can easily be integrated into a variety of applications using the area of interest as a waveguide for optical radiation. The developed refractometer is tested with sucrose solutions of varying RIs ranging from 1.355 68 to 1.430 80 with an LED source at 589 nm. By implementing a calibration method using standardized solutions, the average uncertainty for the RI determination is 1.6 × 10^-3. Compared to the values measured by a state-of-the-art refractometer, the maximum deviation is 0.13%.

FullMonteCUDA: a fast, flexible, and accurate GPU-accelerated Monte Carlo simulator for light propagation in turbid media

Optimizing light delivery for photodynamic therapy, quantifying tissue optical properties or reconstructing 3D distributions of sources in bioluminescence imaging and absorbers in diffuse optical imaging all involve solving an inverse problem. This can require thousands of forward light propagation simulations to determine the parameters to optimize treatment, image tissue or quantify tissue optical properties, which is time-consuming and computationally expensive. Addressing this problem requires a light propagation simulator that produces results quickly given modelling parameters. In previous work, we developed FullMonteSW: currently the fastest, tetrahedral-mesh, Monte Carlo light propagation simulator written in software. Additional software optimizations showed diminishing performance improvements, so we investigated hardware acceleration methods. This work focuses on FullMonteCUDA: a GPU-accelerated version of FullMonteSW which targets NVIDIA GPUs. FullMonteCUDA has been validated across several benchmark models and, through various GPU-specific optimizations, achieves a 288-936x speedup over the single-threaded, non-vectorized version of FullMonteSW and a 4-13x speedup over the highly optimized, hand-vectorized and multi-threaded version. The increase in performance allows inverse problems to be solved more efficiently and effectively.

Optimizing interstitial photodynamic therapy with custom cylindrical diffusers

Interstitial photodynamic therapy (iPDT) has shown promise recently as a minimally invasive cancer treatment, partially due to the development of non-toxic photosensitizers in the absence of activation light. However, a major challenge in iPDT is the pre-treatment planning process that specifies the number of diffusers needed, along with their positions and allocated powers, to confine the light distribution to the target volume as much as possible. In this work, a new power allocation algorithm for cylindrical light diffusers including those that can produce customized longitudinal (tailored) emission profiles is introduced. The proposed formulation is convex to guarantee the minimum over-dose possible on the surrounding organs-at-risk. The impact of varying the diffuser lengths and penetration angles on the quality of the plan is evaluated. The results of this study are demonstrated for different photosensitizers activated at different wavelengths and simulated on virtual tumors modeling virtual glioblastoma multiforme cases. Results show that manufacturable cylindrical diffusers with tailored emission profiles can significantly outperform those with conventional flat profiles with an average damage reduction on white matter of 15% to 55% and on gray matter of 23% to 58%.

Measurement of tissue optical properties in the context of tissue optical clearing

Nowadays, dynamically developing optical (photonic) technologies play an ever-increasing role in medicine. Their adequate and effective implementation in diagnostics, surgery, and therapy needs reliable data on optical properties of human tissues, including skin. This paper presents an overview of recent results on the measurements and control of tissue optical properties. The issues reported comprise a brief review of optical properties of biological tissues and efficacy of optical clearing (OC) method in application to monitoring of diabetic complications and visualization of blood vessels and microcirculation using a number of optical imaging technologies, including spectroscopic, optical coherence tomography, and polarization- and speckle-based ones. Molecular modeling of immersion OC of skin and specific technique of OC of adipose tissue by its heating and photodynamic treatment are also discussed.

Refractive index of adipose tissue and lipid droplet measured in wide spectral and temperature ranges

This study presents refractive index measurements of human and porcine adipose tissues and lipid droplet content in the visible and near-infrared. The coefficients of the Sellmeier formula were calculated for approximation of tissue dispersion. For the first time, to the best of our knowledge, the phase transition temperatures and temperature increments dn/dT of adipose tissue were quantified for a wide wavelength range from 480 to 1550 nm and from room temperature up to 50°C. For human abdominal adipose tissue, the refractive index increment averaged across all wavelengths is dn/dT=-(3.54±0.15)×10^-4°C^-1, for porcine tissue dn/dT=-7.92(0.74)×10^-4°C^-1, and for porcine lipid droplet dn/dT=-6.01(0.29)×10^-4°C^-1. Data available in literature for refractive indices of adipose tissues measured by different techniques are summarized and compared with the received data.

Automatic interstitial photodynamic therapy planning via convex optimization

Finding a high-quality treatment plan is an essential, yet difficult, stage of Photodynamic therapy (PDT) as it will determine the therapeutic efficacy in eradicating malignant tumors. A high-quality plan is patient-specific, and provides clinicians with the number of fiber-based spherical diffusers, their powers, and their interstitial locations to deliver the required light dose to destroy the tumor while minimizing the damage to surrounding healthy tissues. In this work, we propose a general convex light source power allocation algorithm that, given light source locations, guarantees optimality of the resulting solution in minimizing the over/under-dosage of volumes of interest. Furthermore, we provide an efficient framework for source selection with concomitant power reallocation to achieve treatment plans with a clinically feasible number of sources and comparable quality. We demonstrate our algorithms on virtual test cases that model glioblastoma multiforme tumors, and evaluate the performance of four different photosensitizers with different activation wavelengths and specific tissue uptake ratios. Results show an average reduction of the damage to organs-at-risk (OAR) by 29% to 31% with comparable runtime to existing power allocation techniques.

Monitoring of temperature-mediated phase transitions of adipose tissue by combined optical coherence tomography and Abbe refractometry

Observation of temperature-mediated phase transitions between lipid components of the adipose tissues has been performed by combined use of the Abbe refractometry and optical coherence tomography. The phase transitions of the lipid components were clearly observed in the range of temperatures from 24°C to 60°C, and assessed by quantitatively monitoring the changes of the refractive index of 1- to 2-mm-thick porcine fat tissue slices. The developed approach has a great potential as an alternative method for obtaining accurate information on the processes occurring during thermal lipolysis.

Diffractive refractometer for liquid characterization and transient processes monitoring

A simple refractometer using a reflective diffraction grating immersed in the test liquid is developed and its performance is studied. Due to the dependence of the light wavelength on the refractive index, determining the angle of the diffracted beam provides the refractive index of the liquid. The glass cell containing the test liquid is cylindrical, and the grating plane is parallel to the cylinder symmetry axis. The light beam normally impinges on the cell front wall and reaches the center of the grating so that the diffracted beam leaves the cell without being deviated by refraction. It is demonstrated that this characteristic of the optical setup minimizes important error sources due to undesired beam deviations and enables real-time refractive index measurement of liquids in transient processes. Moreover, the performances of the diffractive refractometer and of a commercial Abbe refractometer are compared in the measurement of the refractive indexes of aqueous NaCl solutions. A He-Ne laser at 632.8 nm is used as a light source, and the diffraction grating has 1200 lines/mm. Measurement precisions of the order of 8 × 10^-4 are achieved.

Complex refractive index of normal and malignant human colorectal tissue in the visible and near-infrared

A multi-wavelength prism coupling refractometer is utilized to measure the angular reflectance of freshly excised human intestinal tissue specimens. Based on reflectance data, the real and imaginary part of the refractive index is calculated via Fresnel analysis for three visible (blue, green, red) and two near-infrared (963 nm and 1551 nm) wavelengths. Averaged values of the complex refractive index and corresponding Cauchy dispersion fits are given for the mucosa, submucosa and serosa layers of the colorectal wall at the normal state. The refractive constants of tumorous and normal mucosa are then cross-compared for the indicative cases of one patient diagnosed with a benign polyp and three patients diagnosed with adenocarcinomas of different phenotype. Significant index contrast exists between the normal and diseased states, indicating the potential use of refractive index as a marker of colorectal dysplasia.

Immersed diffraction grating refractometers of liquids

In this work, we report the development, construction, and the performance of two liquid refractometers that use a reflective diffraction grating immersed in a test liquid. The liquid is contained in a transparent glass cell with a rectangular cross section. The grating is oriented in such a way that the propagation directions of the incident beam and the beam diffracted by the lower part of the grating immersed in the liquid are perpendicular. In this configuration, the refractive index is determined by measuring the angle of the zeroth-order diffraction beam coming from the upper part of the grating, which is in contact with air. The diffractive refractometers (DR-1 and DR-2) have different angle measurement procedures and different light detection systems, and their advantages and drawbacks are pointed out. In the experiments, precisions of the order of 10^-5 and 10^-4 for DR-1 and DR-2 are achieved, respectively. The performances of both systems are compared with the performance of a commercial Abbe refractometer in the measurement of sugar and NaCl aqueous solutions.

Visible to near-infrared refractive properties of freshly-excised human-liver tissues: marking hepatic malignancies

The refractive index is an optical constant that plays a significant role in the description of light-matter interactions. When it comes to biological media, refraction is understudied despite recent advances in the field of bio-optics. In the present article, we report on the measurement of the refractive properties of freshly excised healthy and cancerous human liver samples, by use of a prism-coupling technique covering the visible and near-infrared spectral range. Novel data on the wavelength-dependent complex refractive index of human liver tissues are presented. The magnitude of the real and imaginary part of the refractive index is correlated with hepatic pathology. Notably, the real index contrast is pointed out as a marker of discrimination between normal liver tissue and hepatic metastases. In view of the current progress in optical biosensor technologies, our findings may be exploited for the development of novel surgical and endoscopic tools.

Mammalian models of chemically induced primary malignancies exploitable for imaging-based preclinical theragnostic research

Compared with transplanted tumor models or genetically engineered cancer models, chemically induced primary malignancies in experimental animals can mimic the clinical cancer progress from the early stage on. Cancer caused by chemical carcinogens generally develops through three phases namely initiation, promotion and progression. Based on different mechanisms, chemical carcinogens can be divided into genotoxic and non-genotoxic ones, or complete and incomplete ones, usually with an organ-specific property. Chemical carcinogens can be classified upon their origins such as environmental pollutants, cooked meat derived carcinogens, N-nitroso compounds, food additives, antineoplastic agents, naturally occurring substances and synthetic carcinogens, etc. Carcinogen-induced models of primary cancers can be used to evaluate the diagnostic/therapeutic effects of candidate drugs, investigate the biological influential factors, explore preventive measures for carcinogenicity, and better understand molecular mechanisms involved in tumor initiation, promotion and progression. Among commonly adopted cancer models, chemically induced primary malignancies in mammals have several advantages including the easy procedures, fruitful tumor generation and high analogy to clinical human primary cancers. However, in addition to the time-consuming process, the major drawback of chemical carcinogenesis for translational research is the difficulty in noninvasive tumor burden assessment in small animals. Like human cancers, tumors occur unpredictably also among animals in terms of timing, location and the number of lesions. Thanks to the availability of magnetic resonance imaging (MRI) with various advantages such as ionizing-free scanning, superb soft tissue contrast, multi-parametric information, and utility of diverse contrast agents, now a workable solution to this bottleneck problem is to apply MRI for noninvasive detection, diagnosis and therapeutic monitoring on those otherwise uncontrollable animal models with primary cancers. Moreover, it is foreseeable that the combined use of chemically induced primary cancer models and molecular imaging techniques may help to develop new anticancer diagnostics and therapeutics.

Differentiation of ex vivo human breast tissue using polarization-sensitive optical coherence tomography

Successful treatment of breast cancer typically requires surgical removal of the tumor. Optical coherence tomography (OCT) has been previously developed for real-time imaging of the surgical margin. However, it can be difficult to distinguish between normal stromal tissue and cancer tissue based on scattering intensity and structure alone. Polarization-sensitive optical coherence tomography (PS-OCT) is sensitive to form birefringence of biological tissue. We report on the development of a high-speed PS-OCT system and imaging of ex vivo human breast tissue, showing enhanced contrast between healthy and cancerous tissues based upon collagen content confirmed with corresponding histology. These results demonstrate the feasibility of using PS-OCT to supplement structural OCT as a possible method for intraoperative tumor margin evaluation.

Three-Dimensional Holographic Refractive-Index Measurement of Continuously Flowing Cells in a Microfluidic Channel

Refractive index of biological specimens is a source of intrinsic contrast that can be explored without any concerns of photobleaching or harmful effects caused by extra contrast agents. In addition, RI contains rich information related to the metabolism of cells at the cellular and subcellular levels. Here, we report a no-moving parts approach that provides three-dimensional refractive index maps of biological samples continuously flowing in a microfluidic channel. Specifically, we use line illumination and off-axis digital holography to record the angular spectra of light scattered from flowing samples at high speed. Applying the scalar diffraction theory, we obtain accurate RI maps of the samples from the measured spectra. Using this method, we demonstrate label-free 3-D imaging of live RKO human colon cancer cells and RPMI8226 multiple myeloma cells, and obtain the volume, dry mass and density of these cells from the measured 3-D refractive index maps. Our results show that the reported method, alone or in combination with the existing flow cytometry techniques, promises as a quantitative tool for stain-free characterization of large number of cells.

A review of optical coherence tomography in breast cancer

Optical coherence tomography (OCT) is a medical imaging modality that opens up new opportunities for imaging in breast cancer. It provides two- and three-dimensional micro-scale images of tissue structure from bulk tissue,

Measurement of the complex refractive index of tissue-mimicking phantoms and biotissue by extended differential total reflection method

Refractive index of biotissue is a useful optical parameter in the biomedical field. An extended differential total reflection method is introduced to determine the complex refractive index. The real part is directly determined by differential of the reflectance curve, and the imaginary part is obtained from nonlinear fitting. The method is verified by a series of tissue-mimicking phantoms, porcine muscle and porcine adipose.

Design, construction, and performance of a real-time holographic refractometry prototype for liquid analysis

The development and the performance of a portable holographic refractometer prototype for liquid measurement employing multimode diode lasers with emission centered at 662 nm as light sources is reported. Due to the multiwavelength character of the holographic recording, a synthetic wavelength was generated, and the diffracted wave intensity was thus modulated as a function of the optical path difference between the reference and the object beams. The transparent test cell containing the liquid was placed at the reference-beam arm of the optical setup, while the contour interferogram generated on the holographic image of a flat object was used for fringe counting. A change ΔL on the liquid column length is proportional to the Δp running fringes on the object image, and from this relation the refractive index of the test liquid was obtained. The holograms were recorded on a photorefractive Bi(12)TiO(20) crystal whether using a single multimode diode laser or by combining two diode lasers. In the latter configuration the synthetic wavelength can be varied in order to enhance the measurement sensitivity and∕or to allow the analysis of turbid liquids. The size of the whole prototype is 54 × 22 × 14 cm(3). The refractive indexes of ethanol∕water mixtures with different concentrations were measured, as well as the NaCl concentrations in aqueous solutions were determined upon comparison with an empirical curve. In both cases the results were compared with the ones obtained through an Abbe refractometer.

Optical coherence tomography: the intraoperative assessment of lymph nodes in breast cancer

During breast-conserving surgeries, axillary lymph nodes draining from the primary tumor site are removed for disease staging. Although a high number of lymph nodes are often resected during sentinel and lymph-node dissections, only a relatively small percentage of nodes are found to be metastatic, a fact that must be weighed against potential complications such as lymphedema. Without a real-time in vivo or in situ intraoperative imaging tool to provide a microscopic assessment of the nodes, postoperative paraffin section histopathological analysis currently remains the gold standard in assessing the status of lymph nodes. This paper investigates the use of optical coherence tomography (OCT), a high-resolution real-time microscopic optical-imaging technique, for the intraoperative ex vivo imaging and assessment of axillary lymph nodes. Normal (13), reactive (1), and metastatic (3) lymph nodes from 17 human patients with breast cancer were imaged intraoperatively with OCT. These preliminary clinical studies have identified scattering changes in the cortex, relative to the capsule, which can be used to differentiate normal from reactive and metastatic nodes. These optical scattering changes are correlated with inflammatory and immunological changes observed in the follicles and germinal centers. These results suggest that intraoperative OCT has the potential to assess the real-time node status in situ, without having to physically resect and histologically process specimens to visualize microscopic features.

Intraoperative evaluation of breast tumor margins with optical coherence tomography

As breast cancer screening rates increase, smaller and more numerous lesions are being identified earlier, leading to more breast-conserving surgical procedures. Achieving a clean surgical margin represents a technical challenge with important clinical implications. Optical coherence tomography (OCT) is introduced as an intraoperative high-resolution imaging technique that assesses surgical breast tumor margins by providing real-time microscopic images up to 2 mm beneath the tissue surface. In a study of 37 patients split between training and study groups, OCT images covering 1 cm(2) regions were acquired from surgical margins of lumpectomy specimens, registered with ink, and correlated with corresponding histologic sections. A 17-patient training set used to establish standard imaging protocols and OCT evaluation criteria showed that areas of higher scattering tissue with a heterogeneous pattern were indicative of tumor cells and tumor tissue in contrast to lower scattering adipocytes found in normal breast tissue. The remaining 20 patients were enrolled into the feasibility study. Of these lumpectomy specimens, 11 were identified with a positive or close surgical margin and 9 were identified with a negative margin under OCT. Based on histologic findings, 9 true positives, 9 true negatives, 2 false positives, and 0 false negatives were found, yielding a sensitivity of 100% and specificity of 82%. These results show the potential of OCT as a real-time method for intraoperative margin assessment in breast-conserving surgeries.

Magnetomotive nanoparticle transducers for optical rheology of viscoelastic materials

The availability of a real-time non-destructive modality to interrogate the mechanical properties of viscoelastic materials would facilitate many new investigations. We introduce a new optical method for measuring elastic properties of samples which employs magnetite nanoparticles as perturbative agents. Magnetic nanoparticles distributed in silicone-based samples are displaced upon probing with a small external magnetic field gradient and depth-resolved optical coherence phase shifts allow for the tracking of scatterers in the sample with nanometer-scale sensitivity. The scatterers undergo underdamped oscillations when the magnetic field is applied step-wise, allowing for the measurement of the natural frequencies of oscillation of the samples. Validation of the measurements is accomplished using a commercial indentation apparatus to determine the elastic moduli of the samples. This real-time non-destructive technique constitutes a novel way of probing the natural frequencies of viscoelastic materials in which magnetic nanoparticles can be introduced.

Clinical feasibility of microscopically-guided breast needle biopsy using a fiber-optic probe with computer-aided detection

Needle biopsy of small or nonpalpable breast lesions has a high nondiagnostic sampling rate even when needle position is guided by stereotaxis or ultrasound. We assess the feasibility of using a near-infrared fiber optic probe and computer-aided detection for the microscopic guidance of needle breast biopsy procedures. Specimens from nine consented patients undergoing breast-conserving surgery were assessed intraoperatively using a needle device with an integrated fiber-optic probe capable of assessing two physical tissue properties highly correlated to pathology. Immediately following surgical resection, specimens were probed by inserting the optical biopsy needle device into the tissue, simulating the procedure used to position standard biopsy needles. Needle positions were marked and correlated with histology, which verified measurements obtained from 58 needle positions, including 40 in adipose and 18 in tumor tissue. This study yielded tissue classifications based on measurement of optical refractive index and scattering. Confidence-rating schemes yielded combined sensitivity of 89% (16/18) and specificity of 78% (31/40). Refractive index tests alone identified tumor tissue with a sensitivity of 83% (15/18) and specificity of 75% (30/40). Scattering profiles independently identified tumor tissue with a sensitivity of 61% (11/18) and specificity of 60% (24/40). These results show that a biopsy needle with an integrated fiber optic probe can be used to identify breast tumor tissue for sampling. Integration of this probe into current practices offers the potential to reduce nondiagnostic sampling rates by directly evaluating in situ microscopic tissue properties in real-time, before removal.

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.

In-fiber common-path optical coherence tomography using a conical-tip fiber

Common-path optical coherence tomography (CPOCT) is known to reduce group velocity dispersion and polarization mismatch between the reference and the sample arm as both arms share the same physical path. Existing implementations of CPOCT typically require one to incorporate an additional cover glass within the beam path of the sample arm to provide a reference signal. In this paper, we aim to further reduce this step by directly making use of the back-reflected signal, arising from a conical lens-tip fiber, as a reference signal. The conical lens, which is directly manufactured onto the optical fiber tip via a simple selective-chemical etching process, fulfils two functions acting as both the imaging lens and the self-aligning reference plane. We use a Fourier-domain OCT system to demonstrate the feasibility of this technique upon biological tissue. An in-fiber CPOCT technique may prove potentially useful in endoscopic OCT imaging.

Plastinated tissue samples as three-dimensional models for optical instrument characterization

Histology of biological specimens is largely limited to investigating two-dimensional structure because of the sectioning required to produce optically thin samples for conventional microscopy. With the advent of three-dimensional optical imaging technologies such as optical coherence tomography (OCT), diffuse optical tomography (DOT), and multiphoton microscopy (MPM), methods of tissue preparation that minimally disrupt three-dimensional structure are needed. We propose plastination as a means of transforming tissues into three-dimensional models suitable for optical instrument characterization. Tissues are plastinated by infusing them with transparent polymers, after which they can be safely handled, unlike fresh or fixed tissues. Such models are useful for investigating three-dimensional structure, testing and comparing the performance of optical instruments, and potentially investigating tissue properties not normally observed after the three-dimensional scattering properties of a biological samples are lost. We detail our plastination procedures and show examples of imaging several plastinated tissues from a pre-clinical rat model using optical coherence tomography.

Phase-resolved magnetomotive OCT for imaging nanomolar concentrations of magnetic nanoparticles in tissues

Magnetic nanoparticles (MNPs) are increasingly important in magnetic resonance and biomedical optical imaging. We describe a method for imaging MNPs by detecting nanoscale displacements using a phase-resolved spectral-domain optical coherence tomography (OCT) system. Biological tissues and phantoms are exposed to approximately 800 G magnetic fields modulated at 56 and 100 Hz to mechanically actuate embedded iron oxide MNPs (approximately 20 nm diameter). Sensitivity to 27 microg/g (approximately 2 nM) MNPs within tissue phantoms is achieved by filtering paramagnetic from diamagnetic vibrations. We demonstrate biological feasibility by imaging topically applied MNPs during their diffusion into an excised rat tumor over a 2 hour time period.

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.

Group refractive index reconstruction with broadband interferometric confocal microscopy

We propose a novel method of measuring the group refractive index of biological tissues at the micrometer scale. The technique utilizes a broadband confocal microscope embedded into a Mach-Zehnder interferometer, with which spectral interferograms are measured as the sample is translated through the focus of the beam. The method does not require phase unwrapping and is insensitive to vibrations in the sample and reference arms. High measurement stability is achieved because a single spectral interferogram contains all the information necessary to compute the optical path delay of the beam transmitted through the sample. Included are a physical framework defining the forward problem, linear solutions to the inverse problem, and simulated images of biologically relevant phantoms.

Needle-based refractive index measurement using low-coherence interferometry

We present a novel needle-based device for the measurement of refractive index and scattering using low-coherence interferometry. Coupled to the sample arm of an optical coherence tomography system, the device detects the scattering response of, and optical path length through, a sample residing in a fixed-width channel. We report use of the device to make near-infrared measurements of tissues and materials with known optical properties. The device could be used to exploit the refractive index variations of tissue for medical and biological diagnostics accessible by needle insertion.

Simulated parametric studies in optical imaging of tumors through temporal log-slope difference mapping

Numerical studies are conducted to evaluate the noninvasive imaging method of temporal log-slope difference mapping (TLSDM). Emphasis is placed on the parametric examination of tumor's size, enhanced absorption contrast ratio, and embedment depth on the imaging quality and accuracy. It is found that the imaging quality and accuracy are predominantly determined by the tumor size and its embedment depth. The TLSDM method can detect a small tumor of 10mm in size when the tumor is embedded at a shallow depth down to 10mm. With decreasing tumor size and/or increasing embedment depth, both image quality and accuracy worsen. The imaging method requires the enhanced absorption contrast ratio be 20:1 or above.

Computational methods for analysis of human breast tumor tissue in optical coherence tomography images

Optical coherence tomography (OCT) has been demonstrated as a promising means of identifying the boundaries between normal and diseased breast tissue. This capability has yielded promise for the development of OCT techniques for biopsy guidance, surgical margin assessment, and minimally invasive evaluation of disease states. We present methods for the assessment of human breast tissue based on spatial and Fourier-domain analysis. Derived from preliminary OCT data, these methods are aimed at the development of automated diagnostic tools that will aid in the translation of this technology into the clinical environment.