Diffuse reflectance spectroscopy for determination of optical properties and chromophore concentrations of mice internal organs in the range of 350 nm to 1860 nm

The development of photomedical modalities for diagnostics and treatment has created a need for knowledge of the optical properties of the targeted biological tissues. These properties are essential to plan certain procedures, since they determine the light absorption, propagation and penetration in tissues. One way to measure these properties is based on diffuse reflectance spectroscopy (DRS). DRS can provide light absorption and scattering coefficients for each wavelength through a non-invasive, fast and in situ interrogation, and thereby tissue biochemical information. In this study, reflectance measurements of ex vivo mice organs were investigated in a wavelength range between 350 and 1860 nm. To the best of our knowledge, this range is broader than previous studies reported in the literature and is useful to study additional chromophores with absorption in the extended wavelength range. Also, it may provide a more accurate concentration of tissue chromophores when fitting the reflectance spectrum in this extended range. In order to extract these concentrations, optical properties were calculated in a wide spectral range through a fitting routine based on an inverse Monte-Carlo look-up table model. Measurements variability was assessed by calculating the Pearson correlation coefficients between each pair of measured spectra of the same type of organ

Real-time diagnosis of breast cancer during core needle biopsy

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Pages 1-36 (2nd group) has title: Raman clinical instrument manual, by Chae-Ryon Kong and Michael S. Feld; with contributions from Zoya Volynskaya and Luis Galindo. Cataloged from PDF version of thesis.Includes bibliographical references.Early detection of breast cancer is critical for improved survival. Currently, breast abnormalities are diagnosed based on a histopathological evaluation of tissue removed during core needle biopsy. Microcalcifications are used as targets to position biopsy devices, as they may indicate the presence of malignancy. Despite stereotactic guidance, needle biopsy fails to retrieve target microcalcifications in up to 15% of patients. Optical techniques may help clinicians accurately diagnose and treat patients by providing important diagnostic information in real time in a minimally invasive manner. This thesis describes the results of several studies we performed to evaluate the potential of Raman, reflectance, and intrinsic fluorescence spectroscopy to provide biochemical and morphological information for discriminating breast lesions. Each modality was evaluated individually, as well as in combination, using a technique known as multimodal spectroscopy (MMS). For the first part of this project we conducted a clinical study in which spectra were acquired from excised tissue in 99 patients and physically meaningful parameters were extracted by modeling the data. The goals of the study were as follows: 1) To prospectively validate previously developed diagnostic algorithms on the data from these patients; 2) To develop a new algorithm to evaluate additional histopathology diagnoses. Diffuse reflectance (DRS) spectra were modeled using diffusion theory and provided information about tissue absorbers and scatterers. Intrinsic fluorescence (IFS) spectra were extracted from the combined fluorescence and DRS spectra and analyzed using multivariate curve resolution. Raman spectroscopy data were fit using a linear combination of Raman active components (e.g. collagen, calcium, adipose) found in breast tissue. Prospective validation of Raman spectroscopy resulted in sensitivity and specificity and negative predictive value (NPV) of 78%, 98%, and 98%, respectively. An MMS system was developed to evaluate the benefit of combining information from all three spectroscopic modalities. We found that using new 3D Raman algorithm we could discriminate among 6 histopathology categories as compared to 4 categories previously diagnosed with Raman spectroscopy. For the second part of this project, we designed and developed a portable, miniature Raman clinical spectroscopy system to evaluate the potential of spectroscopy to guide the retrieval of microcalcifications during core needle biopsies. We focused specifically on the use of Raman spectroscopy for this application, as it is particularly sensitive to calcium-containing minerals. The system employs a side-viewing Raman probe that can be used in conjunction with commercial stereotactic needle biopsy devices. Prior to core needle excision, the Raman probe was inserted into the core needle biopsy device and spectra were acquired and analyzed in real time (<Is). The results from our work indicate that spectroscopy has the potential to accurately diagnose breast lesions and enable targeted biopsies of diseased tissue and retrieval of microcalcifications.by Zoya Volynskaya.Ph.D

Models and methods of quantitative single-fiber reflectance spectroscopy of tissue properties

Single-fiber reflectance spectroscopy has unique clinical applications not amendable to other types of spectroscopy technologies when assessing a very small tissue domain. SfRS aims to quantify light propagation in the sub-diffusive regime by using a detection geometry that has the illumination and collection areas completely overlapped. This work presents models and methods of diffuse reflectance spectroscopy in a sub-diffusive domain that may be translated to single fiber reflectance spectroscopy (SfRS) measurements at steady-state and time-domain. By using Monte Carlo simulations and analytical approaches, this work specifically analyzes diffuse reflectance associated with a center-illuminated and area-collection round geometry (CIAC) that reveals patterns salient to SfRS, including the dependence on scattering anisotropy and scattering coefficient at low-scattering region, and independence on scattering over high-scattering region. Operating in this CIAC geometry with the tissue modeled as a semi-infinite homogeneous medium, this work demonstrates a few methods that are new to the modeling of diffuse reflectance at the scales relevant to SfRS: (1) two models of spatially-resolved diffuse reflectance applying to a scale as small as 10-5 of the reduced scattering pathlength that is two orders smaller than previously modeled are developed, (2) the total diffuse reflectance as the measurement is developed by taking the integration of the spatially resolved diffuse reflectance over the entire area of collection, (3) the analytical results reveal quantitatively the saturation level and the transition shoulder point that have been observed in steady-state SfRS measurements but without explanations. The analytical modeling approach demonstrated for steady-state measurements is also extended to time-revolved measurement for assessing the effect of absorption and scattering changes on the measurements. These models will be useful to rapid inversion for recovering tissue optical properties based on diffuse reflectance at a single-fiber scale

Fluorescence and Diffuse Reflectance Spectroscopy and Endoscopy for Tissue Analysis

Biophotonics techniques are showing great potential for practical tissue diagnosis, capable of localised optical spectroscopy as well as wide field imaging. Many of those are generally based on the same concept: the spectral information they enable to acquire encloses clues on the tissue biochemistry and biostructure and these clues carry diagnostic information. Biophotonics techniques present the added advantage to incorporate easily miniaturisable hardware allowing several modalities to be set up on the same systems and authorizing their use during minimally invasive surgery (MIS) procedures. The work presented in this thesis aims to build on these advantages to design biophotonics instruments for tissue diagnosis. Fluorescence and diffuse reflectance, the two modalities of interest in this work, were implemented in their single point spectroscopic and imaging declinations. Two “platforms”, a spectroscopic probe setup and an optical imaging laparoscope, were built; they included either one of the two aforementioned modalities or the two of them together. The spectroscopic probe system was assembled to detect lesions in the digestive tract. In its first version, the setup included a dual laser illumination system to carry out an ex vivo fluorescence study of non-alcoholic fatty liver diseases (NAFLD) in the mouse model. Outcomes of the study demonstrated that healthy livers could be distinguished from NAFLD livers with high classification accuracy. Then, the same fluorescence probe inserted in a force adaptive robotic endoscope was applied on a fluorescence phantom and a liver specimen to prove the feasibility of recording spectra at multiple points with controlled scanning pattern and probe/sample pressure (known to affect the spectra shape). This approach proposed therefore a convincing method to perform intraoperative fluorescence measurements. The fluorescence setup was subsequently modified into a combined fluorescence/diffuse reflectance spectroscopic probe and demonstrated as an efficient method to separate normal and diseased tissue samples from the human gastrointestinal tract. Following the single point spectroscopy work, imaging studies were conducted with a spectrally resolved laparoscope. The system, featuring a CCD/filter wheel unit clipped on a traditional laparoscope was validated on fluorescence phantoms and employed in two experiments. The first one, building on the spectroscopy study of the gastrointestinal tract, was originally aimed at locating tumour in the oesophagus but a lack of tissue availability prevented us from doing so. The system design and validation on fluorophores phantoms were nevertheless described. In the second one, the underarm of a pig was imaged after injection of a nerve contrast agent in order to test the feasibility of in vivo nerve delineation. Fluorescence was detected from the region of interest but no clear contrast between the nerve and the surrounding muscle tissue could be detected. Finally, the fluorescence imaging laparoscope was modified into a hyperspectral reflectance imaging laparoscope to perform tissue vasculature studies. It was first characterized and tested on haemoglobin phantoms with varying concentrations and oxygen saturations and then employed in vivo to follow the haemoglobin concentration and oxygen saturation temporal evolutions of a porcine intestine subsequently to the pig’s termination. A decrease in oxygen saturation was observed. The last experiment consisted in monitoring the tissue re-oxygenation of a rabbit uterus transplant on the recipient animal, a successful tissue re-perfusion after the graft was highlighted

Endotracheal tube placement with fibre optic sensing

Unrecognised oesophageal intubation is often described as a ‘Never Event’; an entirely preventable and extremely serious incident. However, there is still prevalence, with severe consequences for the patient. The current gold standards of visually confirming passage through the vocal cords, observing chest movement, and end-tidal capnography all have limitations. There is an opportunity for an alternative method to determine the correct endotracheal tube placement in the trachea. One such solution is described here, through the development of a compact fibre optic sensor integrated into a standard endotracheal tube. The sensor contains no electrical components inside the invasive portion of the device, and it is magnetic resonance imaging safe. The spectral characteristics of the trachea and oesophagus are observed using a fibre optic probe, with the presence of oxyhaemoglobin being used to distinguish the tissues. A novel epoxy sensor is then designed using plastic optical fibres. A rounded top with a square base sensor shape had the least impact on the overall performance of the ETT. Furthermore, by forming the sensor with two illumination fibres, pulse oximetry can be performed. A fibre separation distance between 1.27 and 2.54 mm is optimal. However, a Monte Carlo simulation demonstrates a viable separation of 0.5 to 3 mm. ThereforeHowever, by reducing this to 0.88 mm, a more compact sensor can be produced whilst still retaining a classification rate (average correct identification of trachea and oesophagus) of >89.2% in ex-vivo models. Two methods for emitting light perpendicularly to the fibre axis are explored, demonstrating that bending the fibres caused an optical power loss of 29.0%, whereas cleaving the fibres at 45° produced an 81.9% loss. The position of the sensor on the endotracheal tube is investigated, finding that integration behind the cuff is preferable. However, placement outside the main lumen of the ETT is also a viable option. Computational methods to process spectral measurements are developed. Data for these methods was provided by two experiments on two different sensor types, providing a high tissue classification rate for both the trachea and oesophagus. The first experiment consisted of 9 ex-vivo porcine samples, producing a correct tissue identification of up to 100.0%. The second consisted of 10 sensors on 1 ex-vivo porcine sample, yielding a maximum correct tissue identification of 89.2% when a support vector machine classifier was used. Application of the sensor in an animal study, which consisted of 3 porcine subjects, generated a maximum correct tissue identification of 98.31.6% using principal component analysis and aa support vector machine. The data were recorded over a combined time of 348 minutes, obtained during varying cuff pressures, endotracheal tube orientations, and movement. Finally, suggested future developments to the sensor design and computational methods demonstrate a potential route to improving tissue identification rates. Changes to the experimental protocol are described to verify classification rates. Concepts for exchanging the spectrometer for photodiodes and optical filters to reduce the cost of the opto-electronic units display potential. The technology has applications in wider healthcare, with examples of integration within naso-/oro- gastric tubes and other invasive medical devices given

Endotracheal tube placement with fibre optic sensing

Unrecognised oesophageal intubation is often described as a ‘Never Event’; an entirely preventable and extremely serious incident. However, there is still prevalence, with severe consequences for the patient. The current gold standards of visually confirming passage through the vocal cords, observing chest movement, and end-tidal capnography all have limitations. There is an opportunity for an alternative method to determine the correct endotracheal tube placement in the trachea. One such solution is described here, through the development of a compact fibre optic sensor integrated into a standard endotracheal tube. The sensor contains no electrical components inside the invasive portion of the device, and it is magnetic resonance imaging safe. The spectral characteristics of the trachea and oesophagus are observed using a fibre optic probe, with the presence of oxyhaemoglobin being used to distinguish the tissues. A novel epoxy sensor is then designed using plastic optical fibres. A rounded top with a square base sensor shape had the least impact on the overall performance of the ETT. Furthermore, by forming the sensor with two illumination fibres, pulse oximetry can be performed. A fibre separation distance between 1.27 and 2.54 mm is optimal. However, a Monte Carlo simulation demonstrates a viable separation of 0.5 to 3 mm. ThereforeHowever, by reducing this to 0.88 mm, a more compact sensor can be produced whilst still retaining a classification rate (average correct identification of trachea and oesophagus) of >89.2% in ex-vivo models. Two methods for emitting light perpendicularly to the fibre axis are explored, demonstrating that bending the fibres caused an optical power loss of 29.0%, whereas cleaving the fibres at 45° produced an 81.9% loss. The position of the sensor on the endotracheal tube is investigated, finding that integration behind the cuff is preferable. However, placement outside the main lumen of the ETT is also a viable option. Computational methods to process spectral measurements are developed. Data for these methods was provided by two experiments on two different sensor types, providing a high tissue classification rate for both the trachea and oesophagus. The first experiment consisted of 9 ex-vivo porcine samples, producing a correct tissue identification of up to 100.0%. The second consisted of 10 sensors on 1 ex-vivo porcine sample, yielding a maximum correct tissue identification of 89.2% when a support vector machine classifier was used. Application of the sensor in an animal study, which consisted of 3 porcine subjects, generated a maximum correct tissue identification of 98.31.6% using principal component analysis and aa support vector machine. The data were recorded over a combined time of 348 minutes, obtained during varying cuff pressures, endotracheal tube orientations, and movement. Finally, suggested future developments to the sensor design and computational methods demonstrate a potential route to improving tissue identification rates. Changes to the experimental protocol are described to verify classification rates. Concepts for exchanging the spectrometer for photodiodes and optical filters to reduce the cost of the opto-electronic units display potential. The technology has applications in wider healthcare, with examples of integration within naso-/oro- gastric tubes and other invasive medical devices given