Multiple scattering model for the penetration depth of low-coherence enhanced backscattering

Controllable synthesis of rare earth (Gd3+,Tm3+) doped Prussian blue for multimode imaging guided synergistic treatment

Gd3+ and Tm3+ doped Prussian blue (Gd/Tm-PB) with high uniformity and dispersibility was synthesized by a facile solvothermal method. The conditions for the synthesis of Gd/Tm-PB were explored. Through the regulation of the ratio of Gd3+/Tm3+, the Gd/Tm-PB particles with the optimal size (about 150-200 nm) and the best fluorescence and photothermal effect were obtained. On the basis of the optimal Gd/Tm-PB, further coated by polydopamine (PDA) functionalized metal-organic frameworks (MOFs), a multifunctional platform Gd/Tm-PB@ZIF-8/PDA for cancer diagnosis and treatment was established. Doxorubicin (DOX) was selected as a drug model and the drug loading of Gd/Tm-PB@ZIF-8/PDA was found to be 81 mg g-1. Cytotoxicity analysis indicated that Gd/Tm-PB@ZIF-8/PDA was highly biocompatible. The DOX release at different pH values and GSH concentrations revealed an excellent pH/GSH-triggered drug release. Through the combination of the near infrared photothermal performance of Gd/Tm-PB, chemo-photothermal therapy can be achieved to further improve the anti-cancer efficiency. In addition, the Gd/Tm-PB@ZIF-8/PDA nanoparticles can be tracked by fluorescence imaging (FOI) and magnetic resonance imaging (MRI). Cell FOI and in vivo MRI experiments showed the potential application of Gd/Tm-PB@ZIF-8/PDA in dual mode imaging guided therapy. In vivo antitumor experiments demonstrated the higher anticancer efficacy of Gd/Tm-PB@ZIF-8/PDA with a combined effect of chemo-photothermal therapy. This work provides a new strategy for nano-drug carriers in the direction of integrated diagnosis and treatment.

Rectal Optical Markers for In Vivo Risk Stratification of Premalignant Colorectal Lesions

PURPOSE

Colorectal cancer remains the second leading cause of cancer deaths in the United States despite being eminently preventable by colonoscopy via removal of premalignant adenomas. In order to more effectively reduce colorectal cancer mortality, improved screening paradigms are needed. Our group pioneered the use of low-coherence enhanced backscattering (LEBS) spectroscopy to detect the presence of adenomas throughout the colon via optical interrogation of the rectal mucosa. In a previous ex vivo biopsy study of 219 patients, LEBS demonstrated excellent diagnostic potential with 89.5% accuracy for advanced adenomas. The objective of the current cross-sectional study is to assess the viability of rectal LEBS in vivo.

EXPERIMENTAL DESIGN

Measurements from 619 patients were taken using a minimally invasive 3.4-mm diameter LEBS probe introduced into the rectum via anoscope or direct insertion, requiring approximately 1 minute from probe insertion to withdrawal. The diagnostic LEBS marker was formed as a logistic regression of the optical reduced scattering coefficient [Formula: see text] and mass density distribution factor D.

RESULTS

The rectal LEBS marker was significantly altered in patients harboring advanced adenomas and multiple non-advanced adenomas throughout the colon. Blinded and cross-validated test performance characteristics showed 88% sensitivity to advanced adenomas, 71% sensitivity to multiple non-advanced adenomas, and 72% specificity in the validation set.

CONCLUSIONS

We demonstrate the viability of in vivo LEBS measurement of histologically normal rectal mucosa to predict the presence of clinically relevant adenomas throughout the colon. The current work represents the next step in the development of rectal LEBS as a tool for colorectal cancer risk stratification.

In vivo risk analysis of pancreatic cancer through optical characterization of duodenal mucosa

OBJECTIVES

To reduce pancreatic cancer mortality, a paradigm shift in cancer screening is needed. Our group pioneered the use of low-coherence enhanced backscattering (LEBS) spectroscopy to predict the presence of pancreatic cancer by interrogating the duodenal mucosa. A previous ex vivo study (n = 203) demonstrated excellent diagnostic potential: sensitivity, 95%; specificity, 71%; and accuracy, 85%. The objective of the current case-control study was to evaluate this approach in vivo.

METHODS

We developed a novel endoscope-compatible fiber-optic probe to measure LEBS in the periampullary duodenum of 41 patients undergoing upper endoscopy. This approach enables minimally invasive detection of the ultrastructural consequences of pancreatic field carcinogenesis.

RESULTS

The LEBS parameters and optical properties were significantly altered in patients harboring adenocarcinomas (including early-stage) throughout the pancreas relative to healthy controls. Test performance characteristics were excellent with sensitivity = 78%, specificity = 85%, and accuracy = 81%. Moreover, the LEBS prediction rule was not confounded by patients' demographics.

CONCLUSION

We demonstrate the feasibility of in vivo measurement of histologically normal duodenal mucosa to predict the presence of adenocarcinoma throughout the pancreas. This represents the next step in establishing duodenal LEBS analysis as a prescreening technique that identifies clinically asymptomatic patients who are at elevated risk of PC.

Buccal spectral markers for lung cancer risk stratification

Lung cancer remains the leading cause of cancer deaths in the US with >150,000 deaths per year. In order to more effectively reduce lung cancer mortality, more sophisticated screening paradigms are needed. Previously, our group demonstrated the use of low-coherence enhanced backscattering (LEBS) spectroscopy to detect and quantify the micro/nano-architectural correlates of colorectal and pancreatic field carcinogenesis. In the lung, the buccal (cheek) mucosa has been suggested as an excellent surrogate site in the “field of injury”. We, therefore, wanted to assess whether LEBS could similarly sense the presence of lung. To this end, we applied a fiber-optic LEBS probe to a dataset of 27 smokers without diagnosed lung cancer (controls) and 46 with lung cancer (cases), which was divided into a training and a blinded validation set (32 and 41 subjects, respectively). LEBS readings of the buccal mucosa were taken from the oral cavity applying gentle contact. The diagnostic LEBS marker was notably altered in patients harboring lung cancer compared to smoking controls. The prediction rule developed on training set data provided excellent diagnostics with 94% sensitivity, 80% specificity, and 95% accuracy. Applying the same threshold to the blinded validation set yielded 79% sensitivity and 83% specificity. These results were not confounded by patient demographics or impacted by cancer type or location. Moreover, the prediction rule was robust across all stages of cancer including stage I. We envision the use of LEBS as the first part of a two-step paradigm shift in lung cancer screening in which patients with high LEBS risk markers are funnelled into more invasive screening for confirmation.

Quantitative monitoring of radiation induced skin toxicities in nude mice using optical biomarkers measured from diffuse optical reflectance spectroscopy

Monitoring the onset of erythema following external beam radiation therapy has the potential to offer a means of managing skin toxicities via biological targeted agents - prior to full progression. However, current skin toxicity scoring systems are subjective and provide at best a qualitative evaluation. Here, we investigate the potential of diffuse optical spectroscopy (DOS) to provide quantitative metrics for scoring skin toxicity. A DOS fiberoptic reflectance probe was used to collect white light spectra at two probing depths using two short fixed source-collector pairs with optical probing depths sensitive to the skin surface. The acquired spectra were fit to a diffusion theory model of light transport in tissue to extract optical biomarkers (hemoglobin concentration, oxygen saturation, scattering power and slope) from superficial skin layers of nude mice, which were subjected to erythema inducing doses of ionizing radiation. A statistically significant increase in oxygenated hemoglobin (p < 0.0016) was found in the skin post-irradiation - confirming previous reports. More interesting, we observed for the first time that the spectral scattering parameters, A (p = 0.026) and k (p = 0.011), were an indicator of erythema at day 6 and could potentially serve as an early detection optical biomarker of skin toxicity. Our data suggests that reflectance DOS may be employed to provide quantitative assessment of skin toxicities following curative doses of external beam radiation.

In vivo quantification of the scattering properties of tissue using multi-diameter single fiber reflectance spectroscopy

Multi diameter single fiber reflectance (MDSFR) spectroscopy is a non-invasive optical technique based on using multiple fibers of different diameters to determine both the reduced scattering coefficient (μs') and a parameter γ that is related to the angular distribution of scattering, where γ = (1-g2)/(1-g1) and g1 and g2 the first and second moment of the phase function, respectively. Here we present the first in vivo MDSFR measurements of μs'(λ) and γ(λ) and their wavelength dependence. MDSFR is performed on nineteen mice in four tissue types including skin, liver, normal tongue and in an orthotopic oral squamous cell carcinoma. The wavelength-dependent slope of μs'(λ) (scattering power) is significantly higher for tongue and skin than for oral cancer and liver. The reduced scattering coefficient at 800 nm of oral cancer is significantly higher than of normal tongue and liver. Gamma generally increases with increasing wavelength; for tumor it increases monotonically with wavelength, while for skin, liver and tongue γ(λ) reaches a plateau or even decreases for longer wavelengths. The mean γ(λ) in the wavelength range 400-850 nm is highest for liver (1.87 ± 0.07) and lowest for skin (1.37 ± 0.14). Gamma of tumor and normal tongue falls in between these values where tumor exhibits a higher average γ(λ) (1.72 ± 0.09) than normal tongue (1.58 ± 0.07). This study shows the potential of using light scattering spectroscopy to optically characterize tissue in vivo.

Algorithm for automated selection of application-specific fiber-optic reflectance probes

Several optical techniques and fiber-optic probe systems have been designed to measure the optical properties of tissue. While a wide range of options is often beneficial, it poses a problem to investigators selecting which method to use for their biomedical application of interest. We present a methodology to optimally select a probe that matches the application requirements. Our method is based both on matching a probe's mean sampling depth with the optimal diagnostic depth of the clinical application and on choosing a probe whose interrogation depth and path length is the least sensitive to alterations in the target medium's optical properties. Satisfying these requirements ensures that the selected probe consistently assesses the relevant tissue volume with minimum variability. To aid in probe selection, we have developed a publicly available graphical user interface that takes the desired sampling depth and optical properties of the medium as its inputs and automatically ranks different techniques in their ability to robustly target the desired depth. Techniques investigated include single fiber spectroscopy, differential path length spectroscopy, polarization-gating, elastic light scattering spectroscopy, and diffuse reflectance. The software has been applied to biological case studies.

Numerical investigation of lens based setup for depth sensitive diffuse reflectance measurements in an epithelial cancer model

Lens based setups have been explored for non-contact diffuse reflectance measurements to reduce the uncertainty due to inconsistent probe-sample pressure in the past years. However, there have been no reports describing the details of Monte Carlo modeling of lens based non-contact setup for depth sensitive diffuse reflectance measurements to the best of our knowledge. In this study, we first presented a flexible Monte Carlo method to model non-contact diffuse reflectance measurements in a lens based setup. Then this method was used to simulate diffuse reflectance measurements from a squamous cell carcinoma (SCC) tissue model in the cone shell, cone and hybrid configurations, in which the cone shell configuration has not been previously proposed in optical spectroscopy. Depth sensitive measurements were achieved by adjusting the following two parameters: (1) the depth of focal point of the imaging lens in the SCC model; and (2) the cone radius in the cone configuration or the ring radius in the cone shell configuration. It was demonstrated that the cone shell and the hybrid configurations in general have better depth sensitivity to the tumor and the stroma than the more commonly used cone configuration for diffuse reflectance measurements in the SCC model.

Goniometric measurements of thick tissue using Monte Carlo simulations to obtain the single scattering anisotropy coefficient

The scattering anisotropy, g, of tissue can be a powerful metric of tissue structure, and is most directly measured via goniometry and fitting to the Henyey-Greenstein phase function. We present a method based on an independent attenuation measurement of the scattering coefficient along with Monte Carlo simulations to account for multiple scattering, allowing the accurate determination of measurement of g for tissues of thickness within the quasi-ballistic regime. Simulations incorporating the experimental geometry and bulk optical properties show that significant errors occur in extraction of g values, even for tissues of thickness less than one scattering length without modeling corrections. Experimental validation is provided by determination of g in mouse muscle tissues and it is shown that the obtained values are independent of thickness. In addition we present a simple deconvolution-based method and show that it provides excellent estimates for high anisotropy values (above 0.95) when coupled with an independent attenuation measurement.

Coherent backscattering cone shape depends on the beam size

Coherent backscattering (CBS) is a beautiful physical phenomenon that takes place in a highly scattering medium, which has potential application in noninvasive optical property measurement. The current model that explains the CBS cone shape, however, assumes the incoming beam diameter is infinitely large compared to the transport length. In this paper, we evaluate the effect of a finite scalar light illumination area on the CBS cone, both theoretically and experimentally. The quantitative relationship between laser beam size and the CBS cone shape is established by using two different finite beam models (uniform top hat and Gaussian distribution). A series of experimental data with varying beam diameters is obtained for comparison with the theory. Our study shows the CBS cone shape begins to show distortion when beam size becomes submillimeter, and this effect should not be ignored in general. In biological tissue where a normal large beam CBS cone is too narrow for detection, this small beam CBS may be more advantageous for more accurate and higher resolution tissue characterization.

A fiber optic probe design to measure depth-limited optical properties in-vivo with low-coherence enhanced backscattering (LEBS) spectroscopy

Low-coherence enhanced backscattering (LEBS) spectroscopy is an angular resolved backscattering technique that is sensitive to sub-diffusion light transport length scales in which information about scattering phase function is preserved. Our group has shown the ability to measure the spatial backscattering impulse response function along with depth-selective optical properties in tissue ex-vivo using LEBS. Here we report the design and implementation of a lens-free fiber optic LEBS probe capable of providing depth-limited measurements of the reduced scattering coefficient in-vivo. Experimental measurements combined with Monte Carlo simulation of scattering phantoms consisting of polystyrene microspheres in water are used to validate the performance of the probe. Additionally, depth-limited capabilities are demonstrated using Monte Carlo modeling and experimental measurements from a two-layered phantom.