Quantitative oximetry of breast tumors: a near-infrared method that identifies two optimal wavelengths for each tumor

Insights into Biochemical Sources and Diffuse Reflectance Spectral Features for Colorectal Cancer Detection and Localization

Colorectal cancer (CRC) is the third most common and second most deadly type of cancer worldwide. Early detection not only reduces mortality but also improves patient prognosis by allowing the use of minimally invasive techniques to remove cancer while avoiding major surgery. Expanding the use of microsurgical techniques requires accurate diagnosis and delineation of the tumor margins in order to allow complete excision of cancer. We have used diffuse reflectance spectroscopy (DRS) to identify the main optical CRC biomarkers and to optimize parameters for the integration of such technologies into medical devices. A total number of 2889 diffuse reflectance spectra were collected in ex vivo specimens from 47 patients. Short source-detector distance (SDD) and long-SDD fiber-optic probes were employed to measure tissue layers from 0.5 to 1 mm and from 0.5 to 1.9 mm deep, respectively. The most important biomolecules contributing to differentiating DRS between tissue types were oxy- and deoxy-hemoglobin (Hb and HbO₂), followed by water and lipid. Accurate tissue classification and potential DRS device miniaturization using Hb, HbO₂, lipid and water data were achieved particularly well within the wavelength ranges 350-590 nm and 600-1230 nm for the short-SDD probe, and 380-400 nm, 420-610 nm, and 650-950 nm for the long-SDD probe.

Coregistration of Dynamic Contrast Enhanced MRI and Broadband Diffuse Optical Spectroscopy for Characterizing Breast Cancer

A handheld scanning probe based on broadband Diffuse Optical Spectroscopy (DOS) was used in combination with dynamic contrast enhanced MRI (DCE-MRI) to quantitatively characterize locally-advanced breast cancers in six patients. Measurements were performed sequentially using external fiducial markers for co-registration. Tumor patterns were categorized according to MRI morphological data, and 3D DCE-MRI slices were converted into a volumetric matrix with isotropic voxels to generate views that coincided with the DOS scanning plane. Tumor volume and depth at each DOS measurement site were determined, and a tissue optical index (TOI) that reflects both angiogenic and stromal characteristics was derived from broadband DOS data.

In all six cases, optical scans showed significant TOI contrast corresponding to MRI morphological information. Sharp TOI peaks were recovered for well-circumscribed masses. A reduction in TOI was found inside a tumor with a necrotic center. A broadened peak was observed for a diffuse tumor pattern, and an inflammatory septal case provided two TOI peaks that correlated qualitatively with MRI enhancement. These results provide qualitative confirmation of the common signal origin and complementary information content that can be achieved by combining optical and MR imaging for breast cancer detection and clinical management.

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.

GPC light shaping a supercontinuum source

Generalized Phase Contrast (GPC) is a versatile tool for efficiently rerouting and managing photon energy into speckle-free contiguous spatial light distributions. We have previously shown theoretically and numerically that a GPC Light Shaper shows robustness to shift in wavelength and can maintain both projection length scale and high efficiency over a range [0.75λ(0); 1.5λ(0)] with λ(0) as the characteristic design wavelength. With this performance across multiple wavelengths and the recent availability of tabletop supercontinuum lasers, GPC light shaping opens the possibility for creatively incorporating various multi-wavelength approaches into spatially shaped excitations that can enable new broadband light applications. We verify this new approach using a supercontinuum light source, interfaced with a compact GPC light shaper. Our experiments give ~70% efficiency, ~3x intensity gain, and ~85% energy savings, limited, however, by the illumination equipment, but still in very good agreement with theoretical and numerical predictions.

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.

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.

Paired-wavelength spectral approach to measuring the relative concentrations of two localized chromophores in turbid media: an experimental study

We present an experimental test of a new spectral approach that is aimed at quantifying the relative concentrations of two chromophores that are contained in a defect embedded in a turbid medium. The basic steps of our spectral approach are (a) perform a linear tandem scan of the source and detector across the defect; (b) measure the spectral dependence of the maximum change induced by the defect in the scanned intensity; (c) identify a set of appropriate pairs of wavelengths (lambda1, lambda2) at which such maximum intensity changes are the same; and (d) measure the reduced scattering coefficient spectrum of the background medium. For each wavelength pair (lambda1, lambda2), we obtain a measurement of the relative concentrations of the two chromophores, where the only required parameters are the extinction coefficients of the two chromophores and the ratio of the background scattering coefficients at lambda1 and lambda2. In a mixture of two test chromophores (blue food coloring dye and black India ink) contained in a 0.78-cm diameter cylinder, our spectral approach yielded relative concentrations values that were within 6% of their actual values. Although our paired-wavelength spectral approach is not generally applicable to any pair of chromophores, it is suitable for oxyhemoglobin and deoxyhemoglobin and is thus appropriate for oximetry of localized lesions in biological tissues.

CH-overtone regions as diagnostic markers for near-infrared spectroscopic diagnosis of primary cancers in human pancreas and colorectal tissue

We have investigated the application of near-infrared spectroscopy for detection of human primary pancreatic and colorectal cancers. Spectra from cancerous and normal tissue were collected from a total of 37 surgically resected pancreatic and colorectal patient tissue specimens using a fibre-optic probe. Major spectral differences were observed in the CH-stretching first (6,000-5,400 cm(-1)) and second overtone (9,000-7,900 cm(-1)) regions. By use of artificial neural networks, linear discriminant analysis, and cluster analysis as pattern-recognition methods the spectra were classified into cancerous and normal tissue groups with accuracy up to 89%. We also explored differences between the spectra obtained from colorectal and pancreatic tissue. Spectral data from cancerous and normal tissue were classified organ-specifically into four groups with accuracy between 80 and 83%. Our results indicate that CH-overtone regions, besides serving as diagnostic markers for NIR spectroscopic diagnosis of primary human pancreas and colorectal cancers, are also useful for elucidating differences between the spectra obtained from colorectal and pancreatic cancerous tissue.

In vivo absorption, scattering, and physiologic properties of 58 malignant breast tumors determined by broadband diffuse optical spectroscopy

Diffuse optical imaging (DOI) may be a beneficial diagnostic method for women with mammographically dense breast tissue. In order to evaluate the utility of DOI, we are developing broadband diffuse optical spectroscopy (DOS) to characterize the functional origins of optical signals in breast cancer patients. Broadband DOS combines multifrequency intensity-modulated and continuous-wave near-infrared light to quantify tissue absorption and scattering spectra from 650 to 1000 nm. Values of intrinsic physiological properties (oxy- and deoxy-hemoglobin, water, lipid, and scatter power) derived from absorption and scattering spectra provide detailed information on breast physiology. We present the results of clinical studies of 58 stage II/III malignant breast tumors using a noninvasive, handheld, broadband DOS probe. On average, eight positions were scanned over tumor and contralateral normal breast for each subject. Intrinsic physiological properties were statistically significantly different for malignant vs. normal tissues for all subjects, without patient age or tumor size/type stratification. Breast tissues containing malignant tumors displayed reduced lipid content ( approximately 20%) and increased water, deoxy-, and oxy-hemoglobin (>50% each) compared to normal breast tissues. Functional perturbations by the tumor were significantly larger than functional variations in normal tissues. A tissue optical index (TOI) derived from intrinsic physiological properties yielded an average two-fold contrast difference between malignant tumors and intrinsic tissue properties. Our results demonstrate that intrinsic optical signals can be influenced by functional perturbations characteristic of malignant transformation; cellular metabolism, extracellular matrix composition, and angiogenesis. Our findings further underscore the importance of broadband measurements and patient age stratification in breast cancer DOI.

Monte Carlo simulations of increased/decreased scattering inclusions inside a turbid slab

We analyse the effect on scattered photons of anomalous optical inclusions in a turbid slab with otherwise uniform properties. Our motivation for doing so is that inclusions affect scattering contrast used to quantify optical properties found from transmitted light intensity measured in transillumination experiments. The analysis is based on a lattice random walk formalism which takes into account effects of both positive and negative deviations of the scattering coefficient from that of the bulk. Our simulations indicate the existence of a qualitative difference between the effects of these two types of perturbations. In the case of positive perturbations the time delay is found to be proportional to the square of the size of the inclusion while for negative perturbations the time delay is a linear function of its volume.

The Twente Photoacoustic Mammoscope: system overview and performance

We present PAM, the Photoacoustic Mammoscope developed at the University of Twente, intended for initial retrospective clinical studies on subjects with breast tumours. A parallel plate geometry has been adopted and the breast will be gently compressed between a glass plate and a flat ultrasound detector matrix. Pulsed light (5 ns) from an Nd:YAG laser will impinge the breast through the glass plate in regions of interest; an appropriate number of the 590 elements of the detector matrix will be activated in succession to record photoacoustic signals. Three-dimensional image reconstruction employs a delay-and-sum beamforming algorithm. We discuss various instrumental aspects and the proposed imaging protocol. Performance studies of the ultrasound detector are presented in terms of sensitivity, frequency response and resolution. Details of the patient-instrument interface are provided. Finally some imaging results on well-characterized breast tissue phantoms with embedded tumour simulating inserts are shown.

Near-infrared imaging of the human breast: complementing hemoglobin concentration maps with oxygenation images

We have previously reported a comparison between edge-corrected near-infrared optical mammograms and those that have undergone a further image-processing step based on a spatial second derivative. In this work, we go a step further by combining the second-derivative images from four wavelengths (690, 750, 788, and 856 nm) to obtain oxygenation-index images. While the spatial second derivative improves contrast and allows for visibility of fine structures in the images, thereby improving the sensitivity to tumor detection, additional information is needed to avoid false-positive results. The oxygenation-index images are introduced to address this issue. Oxygenation information may help discriminate benign from malignant breast lesions, thereby effectively complementing single-wavelength optical mammograms that display optically dense regions within the breast with high sensitivity.

Breast cancer detection by mapping hemoglobin concentration and oxygen saturation

Near-infrared (NIR) spectroscopic imaging technology provides a new modality for measuring changes in total hemoglobin concentration (HbT) and blood oxygen saturation (SO2) in human tissue. The technology can be used to detect breast cancer because cancers may cause greater vascularization and greater oxygen consumption than in normal tissue. Based on the NIR technology, ViOptix, Inc., has developed an optical device that provides two-dimensional mapping of HbT and SO2 in human tissue. As an adjunctive tool to mammography, the device was preliminarily tested in a clinical trial with 50 mammogram-positive patients at the Massachusetts General Hospital. The results of the clinical trial demonstrate that the device can reach as much as 92% diagnostic sensitivity and 67% specificity in detecting ductal carcinoma. These results may indicate that the NIR technology can potentially be used as an adjunct to mammography for breast cancer detection to reduce the number of biopsies performed.

Detection of ultrawide-band ultrasound pulses in optoacoustic tomography

Laser optoacoustic imaging system (LOIS) uses time-resolved detection of laser-induced pressure profiles in tissue in order to reconstruct images of the tissue based on distribution of acoustic sources. Laser illumination with short pulses generates distribution of acoustic sources that accurately replicates the distribution of absorbed optical energy. The complex spatial profile of heterogeneous distribution of acoustic sources can be represented in the frequency domain by a wide spectrum of ultrasound ranging from tens of kilohertz to tens of megahertz. Therefore, LOIS requires a unique acoustic detector operating simultaneously within a wide range of ultrasonic frequencies. Physical principles of an array of ultrawide-band ultrasonic transducers used in LOIS designed for imaging tumors in the depth of tissue are described. The performance characteristics of the transducer array were modeled and compared with experiments performed in gel phantoms resembling optical and acoustic properties of human tissue with small tumors. The amplitude and the spectrum of laser-induced ultrasound pulses were measured in order to determine the transducer sensitivity and the level of thermal noises within the entire ultrasonic band of detection. Spatial resolution of optoacoustic images obtained with an array of piezoelectric transducers and its transient directivity pattern within the field of view are described. The detector design considerations essential for obtaining high-quality optoacoustic images are presented.

Spatial second-derivative image processing: an application to optical mammography to enhance the detection of breast tumors

We present an image-processing method that enhances the detection of regions of higher absorbance in optical mammograms. At the heart of this method lies a second-derivative operator that is commonly employed in edge-detection algorithms. The resulting images possess a high contrast, an automatic display scale, and a greater sensitivity to smaller departures from the local background absorbance. Moreover, the images are free of artifacts near the breast edge. This second-derivative method enhances the display of structural information in optical mammograms and may be used to robustly select areas of interest to be further analyzed spectrally to determine the oxygenation level of breast lesions.