Integration of single-fiber reflectance spectroscopy into ultrasound-guided endoscopic lung cancer staging of mediastinal lymph nodes

Tissue-probe contact assessment during robotic surgery using single-fiber reflectance spectroscopy

The introduction of robotic surgery has improved minimally invasive surgery, and now robotic surgery is used in several areas of surgical oncology. Several optical techniques can be used to discriminate cancer from healthy tissue based on their optical properties. These technologies can also be employed with a small fiber-optic probe during minimally invasive surgery; however, for acquiring reliable measurements, some optical techniques require the fiber-optic probe to be in direct contact with the tissue. The lack of tactile feedback in robotic surgery makes assessing tissue-probe contact suitable for optical contact measurements challenging for the surgeon. In this study, we investigated the use of single fiber reflectance (SFR) to determine tissue-probe contact adequately. A machine learning-based algorithm was developed to classify if direct tissue-probe contact was present during the measurement in an ex-vivo tissue setup. Using this classification algorithm, an average accuracy of 93.9% was achieved for assessing probe-tissue contact, suggesting that this technique can be utilized to assess tissue-probe contact in an in vivo clinical setting.

Optical Imaging in Human Lymph Node Specimens for Detecting Breast Cancer Metastases: A Review

Assessment of regional lymph node status in breast cancer is of important staging and prognostic value. Even though formal histological examination is the currently accepted standard of care, optical imaging techniques have shown promising results in disease diagnosis. In the present article, we review six spectroscopic techniques and focus on their use as alternative tools for breast cancer lymph node assessment. Elastic scattering spectroscopy (ESS) seems to offer a simple, cost-effective, and reproducible method for intraoperative diagnosis of breast cancer lymph node metastasis. Optical coherence tomography (OCT) provides high-resolution tissue scanning, along with a short data acquisition time. However, it is relatively costly and experimentally complex. Raman spectroscopy proves to be a highly accurate method for the identification of malignant axillary lymph nodes, and it has been further validated in the setting of head and neck cancers. Still, it remains time-consuming. Near-infrared fluorescence imaging (NIRF) and diffuse reflectance spectroscopy (DFS) are related to significant advantages, such as deep tissue penetration and efficiency. Fourier-transform infrared spectroscopy (FTIR) is a promising method but has significant drawbacks. Nonetheless, only anecdotal reports exist on their clinical use for cancerous lymph node detection. Our results indicate that optical imaging methods can create informative and rapid tools to effectively guide surgical decision-making.

Diffuse photon remission associated with the center-illuminated-area-detection geometry. II. Approach to the time-domain model

This part proposes a model of time-dependent diffuse photon remission for the center-illuminated-area-detection (CIAD) geometry, by virtue of area integration of the radially resolved time-dependent diffuse photon remission formulated with the master-slave dual-source scheme demonstrated in Part I for steady-state measurements. The time-domain model is assessed against Monte Carlo (MC) simulations limiting to only the Heyney-Greenstein scattering phase function for CIAD of physical scales and medium properties relevant to single-fiber reflectance (SfR) and over a 2 ns duration, in compliance with the timespan of the only experimental report of SfR demonstrated with a 50 µm gradient index fiber. The time-domain model-MC assessments are carried out for an absorption coefficient ranging three orders of magnitude over [0.001,0.01,0.1,1]m m -1 at a fixed scattering, and a reduced scattering coefficient ranging three orders of magnitude over [0.01,0.1,1,10]m m -1 at a fixed absorption, among others. Photons of shorter and longer propagation times, relative to the diameter of the area of collection, respond differently to the scattering and absorption changes. Limited comparisons of MC between CIAD and a top-hat geometry as the idealization of SfR reveal that the time-domain photon remissions of the two geometries differ appreciably in only the early arriving photons.

Pulsed Photothermal Radiometric Depth Profiling of Bruises by 532 nm and 1064 nm Lasers

Optical techniques are often inadequate in estimating bruise age since they are not sensitive to the depth of chromophores at the location of the bruise. To address this shortcoming, we used pulsed photothermal radiometry (PPTR) for depth profiling of bruises with two wavelengths, 532 nm (KTP laser) and 1064 nm (Nd:YAG laser). Six volunteers with eight bruises of exactly known and documented times of injury were enrolled in the study. A homogeneous part of the bruise was irradiated first with a 5 ms pulse at 532 nm and then with a 5 ms pulse at 1064 nm. The resulting transient surface temperature change was collected with a fast IR camera. The initial temperature-depth profiles were reconstructed by solving the ill-posed inverse problem using a custom reconstruction algorithm. The PPTR signals and reconstructed initial temperature profiles showed that the 532 nm wavelength probed the shallow skin layers revealing moderate changes during bruise development, while the 1064 nm wavelength provided additional information for severe bruises, in which swelling was present. Our two-wavelength approach has the potential for an improved estimation of the bruise age, especially if combined with modeling of bruise dynamics.

Monitoring stimulus-evoked hemodynamic response during deep brain stimulation with single fiber spectroscopy

Deep brain stimulation (DBS) is a revolutionary treatment for movement disorders. Measuring DBS-induced hemodynamic responses may be useful for surgical guidance of DBS electrode implantation as well as to study the mechanism and assess therapeutic effects of DBS. In this study, we evaluated the performance of a single fiber spectroscopic (SFS) system for measuring hemodynamic response in different cortical layers in a DBS animal model. We showed that SFS is capable of measuring minute relative changes in oxygen saturation and blood volume fraction in-vivo at a sampling rate of 22-33 Hz. During stimulation, blood volume fraction increased, while oxygen saturation showed both increases and decreases at different cortical depths across animals. In addition, we showed the potential of using SFS for measuring other physiological parameters, for example, heart rate, and respiratory rate.

Diffuse photon remission associated with the center-illuminated-area-detection geometry: Part I, an approach to the steady-state model

Diffuse photon remission associated with the center-illuminated-area-detection (CIAD) geometry has been useful for non-contact sensing and may inform single-fiber reflectance (SfR). This series of work advances model approaches that help enrich the understanding and applicability of the photon remission by CIAD. The general approach is to derive the diffuse photon remission by the area integration of the radially resolved diffuse reflectance while limiting the analysis to a medium exhibiting only the Heyney-Greenstein (HG) scattering phase function. Part I assesses the steady-state photon remission in CIAD over a reduced scattering scaled diameter of μ s ' d _{a r e a} ∈[0.5×10^-3,10³] that covers the range extensively modeled for SfR. The corresponding radially resolved diffuse reflectance is obtained by concatenating an empirical expression for the semi-ballistic region near the point-of-illumination and a formula utilizing a master-slave dual-source scheme over the semi-diffusive to a diffusive regime while being constrained by an extrapolated zero-boundary condition. The terminal algebraic photon remission is examined against Monte Carlo simulations for an absorption coefficient over [0.001,1]m m ^-1, a reduced scattering coefficient over [0.01,1000]m m ^-1, a HG scattering anisotropy factor within [0.5,0.95], and a diameter of the area of collection ranging [50,1000]µm. The algebraic model is also applied to phantom data acquired over a ∼2c m non-contact CIAD configuration and with a 200 µm SfR probe. The model approach will be extended in a subsequent work towards the time-of-flight characteristics of CIAD.

Detecting head and neck lymph node metastases with white light reflectance spectroscopy; a pilot study

INTRODUCTION

A challenge in the treatment of patients with head and neck cancer is the management of occult cervical lymph node (LN) metastases. Single-fiber reflectance (SFR) spectroscopy has the potential to detect physiological tissue changes that occur in a positive LN. This pilot study aimed to investigate whether SFR spectroscopy could serve as an alternative or additional technique to detect cervical lymph node metastases.

MATERIALS AND METHODS

We performed intraoperative SFR spectroscopy measurements of LNs with and without malignancies. We analyzed if physiological and scattering parameters were significantly altered in positive LNs.

RESULTS

Nine patients with a total of nineteen LNs were included. Three parameters, blood volume fraction (BVF), microvascular saturation (StO₂), and Rayleigh amplitude, were significantly lower in positive LNs. They were combined into one optical parameter 'delta', using discriminant analysis. Delta was significantly decreased in positive LNs, p = 0,0006. It had a high diagnostic accuracy where the sensitivity, specificity, PPV, and NPV were 90,0%, 88.9%, 90,0%, and 88.9%, respectively. The area under the ROC curve was 96.7% (95% confidence interval 89.7-100.0%).

CONCLUSION

This proof of principle study is a first step in the development of an SFR spectroscopy technique to detect LN metastases in real time. A next step towards this goal is replicating these results in LNs with smaller metastases and in a larger cohort of patients. This future study will combine SFR spectroscopy with fine-needle aspiration, using the same needle, to perform preoperative in vivo measurements.

Diffuse photon-remission associated with single-fiber geometry may be a simple scaling of that collected over the same area when under centered-illumination

Robust models for single-fiber reflectance (SFR) are relatively complex [Opt. Lett.45, 2078 (2020)OPLEDP0146-959210.1364/OL.385845] due to overlapping of the illumination and collection areas that entails probability weighting of the spatial integration of photon-remission. We demonstrate, via analytical means for limiting cases and Monte Carlo simulation of broader conditions, that diffuse photon-remission collected by single-fiber geometry may be scaled over the center-illuminated photon-remission. We specify for a medium revealing Henyey-Greenstein (HG) scattering anisotropy that the diffuse photon-remission from a sub-diffusive area of a top-hat illumination is ∼84.9% of that collected over the same area when under a centered-illumination. This ratio remains consistent over a reduced-scattering fiber-size product of μs'd_fib=[10^-5,10⁰], for absorption varying 3 orders of magnitude. When applied to hemoglobin oxygenation changes induced in an aqueous phantom using a 200 µm single-fiber probe, the center-illumination-scaled model of SFR produced fitting results agreeing with reference measurements.

Fiber photometry for monitoring cerebral oxygen saturation in freely-moving rodents

Hemodynamic parameters, such as tissue oxygen saturation and blood volume fraction, are important markers of brain physiology. They are also widely used surrogate markers of electrophysiological activity. Here, we present a single fiber spectroscopic (SFS) system for monitoring cerebral oxygen saturation in localized, non-line-of-sight brain regions in freely-moving rodents. We adapted the implantation ferrule and patch cable design from commercialized optogenetics and fiber photometry systems, enabling stereotaxic fiber implantation, longitudinal tissue access and measurement from freely-moving animals. The optical system delivers and collects light from the brain through a 200 µm-core-diameter, 0.39NA multimode fiber. We robustly measured oxygen saturation from phantoms with different optical properties mimicking brain tissue. In mice, we demonstrated, for the first time, measurements of oxygen saturation from a highly-localized, targeted brain region over 31 days and continuous measurements from a freely-moving animal for over an hour. These results suggest that single fiber spectroscopy has enormous potential for functional brain monitoring and investigating neurovascular coupling in freely-moving animals. In addition, this technique can potentially be combined with fiber photometry systems to correct for hemodynamic artifacts in the fluorescence detection.

Simple analytical total diffuse reflectance over a reduced-scattering-pathlength scaled dimension of [10-5, 10-1] from a medium with HG scattering anisotropy

Model approximation is necessary for reflectance assessment of tissue at sub-diffusive to non-diffusive scale. For tissue probing over a sub-diffusive circular area centered on the point of incidence, we demonstrate simple analytical steady-state total diffuse reflectance from a semi-infinite medium with the Henyey-Greenstein (HG) scattering anisotropy (factor $g$g). Two physical constraints are abided to: (1) the total diffuse reflectance is the integration of the radial diffuse reflectance; (2) the radial and total diffuse reflectance at $g \gt {0}$g>0 analytically must resort to their respective forms corresponding to isotropic scattering as $g$g becomes zero. Steady-state radial diffuse reflectance near the point of incidence from a semi-infinite medium of $g \approx 0$g≈0 is developed based on the radiative transfer for isotropic scattering, then integrated to find the total diffuse reflectance for $g \approx 0$g≈0. The radial diffuse reflectance for $g \ge 0.5$g≥0.5 is semi-empirically formulated by comparing to Monte Carlo simulation results and abiding to the second constraint. Its integration leads to a total diffuse reflectance for $g \ge 0.5$g≥0.5 that is also bounded by the second constraint. Over a collection diameter of the reduced-scattering pathlength ($1/\mu _s^{ \prime}$1/μs') scaled size of [${{10}^{ - 5}}$10^-5, ${{10}^{ - 1}}$10^-1] for $g = [{0.5},{0.95}]$g=[0.5,0.95] and the absorption coefficient as strong as the reduced scattering coefficient, the simple analytical total diffuse reflectance is found to be accurate, with an average error of 16.1%.

Optical pre-screening for laryngeal cancer using reflectance spectroscopy of the buccal mucosa

A new approach in early cancer detection focuses on detecting field cancerization (FC) instead of the tumor itself. The aim of the current study is to investigate whether reflectance spectroscopy can detect FC in the buccal mucosa of patients with laryngeal cancer. The optical properties of the buccal mucosa of patients were measured with multidiameter single-fiber reflectance spectroscopy. The blood oxygen saturation and blood volume fraction were significantly lower in the buccal mucosa of laryngeal cancer patients than in non-oncologic controls. The data of these two parameters were combined to form a single 'biomarker α', which optimally discriminates these two groups. Alpha was lower in the laryngeal cancer group (0.28) than the control group (0.30, p = 0.007). Alpha could identify oncologic patients with a sensitivity of 78% and a specificity of 74%. These results might be the first step toward optical pre-screening for laryngeal cancer.

Toward optical guidance during endoscopic ultrasound-guided fine needle aspirations of pancreatic masses using single fiber reflectance spectroscopy: a feasibility study

Endoscopic ultrasound-guided fine needle aspirations (EUS-FNA) of pancreatic masses suffer from sample errors and low-negative predictive values. Fiber-optic spectroscopy in the visible to near-infrared wavelength spectrum can noninvasively extract physiological parameters from tissue and has the potential to guide the sampling process and reduce sample errors. We assessed the feasibility of single fiber (SF) reflectance spectroscopy measurements during EUS-FNA of pancreatic masses and its ability to distinguish benign from malignant pancreatic tissue. A single optical fiber was placed inside a 19-gauge biopsy needle during EUS-FNA and at least three reflectance measurements were taken prior to FNA. Spectroscopy measurements did not cause any related adverse events and prolonged procedure time with ? 5 ?? min . An accurate correlation between spectroscopy measurements and cytology could be made in nine patients (three benign and six malignant). The oxygen saturation and bilirubin concentration were significantly higher in benign tissue compared with malignant tissue (55% versus 21%, p = 0.038 ; 166 ?? ? mol / L versus 17 ?? ? mol / L , p = 0.039 , respectively). To conclude, incorporation of SF spectroscopy during EUS-FNA was feasible, safe, and relatively quick to perform. The optical properties of benign and malignant pancreatic tissue are different, implying that SF spectroscopy can potentially guide the FNA sampling.

In-vivo monitoring of tissue oxygen saturation in deep brain structures using a single fiber optical system

We propose a single fiber optical system for monitoring tissue oxygen saturation (sO₂) based on continuous-wave reflectance spectroscopy in the visible wavelengths. The system is designed for measurements in deep brain structures by stereotaxically implanting the 200 μm-core fiber probe into the tissue of interest. Monte Carlo (MC) simulations were used to estimate the measurement tissue volume between 0.02-0.03 mm³. Experiments in an optical phantom indicated the system had a root mean squared error (RMSE) of 4.21% compared with a commercial fluorescence-based tissue oxygen partial pressure measuring system. Finally, we used the system for continuously monitoring tissue sO₂ from a highly-localized volume in anesthetized mice.

In vivo assessment of diet-induced rat hepatic steatosis development by percutaneous single-fiber spectroscopy detects scattering spectral changes due to fatty infiltration

This study explores percutaneous single-fiber spectroscopy (SfS) of rat livers undergoing fatty infiltration. Eight test rats were fed a methionine-choline-deficient (MCD) diet, and four control rats were fed a normal diet. Two test rats and one control rat were euthanized on days 12, 28, 49, and 77 following initiation of the diet, after percutaneous SfS of the liver under transabdominal ultrasound guidance. Histology of each set of the two euthanized test rats showed mild and mild hepatic lipid accumulations on day 12, moderate and severe on day 28, severe and mild on day 49, and moderate and mild on day 77. Livers with moderate or higher lipid accumulation generally presented higher spectral reflectance intensity when compared to lean livers. Livers of the eight test rats on day 12, two of which had mild lipid accumulation, revealed an average scattering power of 0.37±0.14 in comparison to 0.07±0.14 for the four control rats (p<0.01 ). When livers of the test rats with various levels of fatty infiltration were combined, the average scattering power was 0.36±0.15 0.36±0.15 in comparison to 0.14±0.24 of the control rats (0.05<p<0.1). Increasing lipid accumulation in concentration and size seemed to cause an increase of the scattering power prior to increasing total spectral reflectance.

Design and validation of a fiber optic point probe instrument for therapy guidance and monitoring

Optical techniques for tissue diagnostics currently are experiencing tremendous growth in biomedical applications, mainly due to their noninvasive, inexpensive, and real-time functionality. Here, we demonstrate a hand-held fiber optic probe instrument based on fluorescence/reflectance spectroscopy for precise tumor delineation. It is mainly aimed for brain tumor resection guidance with clinical adaptation to minimize the disruption of the standard surgical workflow and is meant as a complement to the state-of-the-art fluorescence surgical microscopy technique. Multiple light sources with fast pulse modulation and detection enable precise quantification of protoporphyrin IX (PpIX), tissue optical properties, and ambient light suppression. Laboratory measurements show the system is insensitive to strong ambient light. Validation measurements of tissue phantoms using nonlinear least squares support vector machines (LS-SVM) regression analysis demonstrate an error of <5% for PpIX concentration ranging from 400 to 1000 nM, even in the presence of large variations in phantom optical properties. The mean error is 3% for reduced scattering coefficient and 5% for blood concentration. Diagnostic precision of 100% was obtained by LS-SVM classification for in vivo skin tumors with topically applied 5-aminolevulinic acid during photodynamic therapy. The probe could easily be generalized to other tissue types and fluorophores for therapy guidance and monitoring.

Percutaneous single-fiber reflectance spectroscopy of canine intervertebral disc: is there a potential for in situ probing of mineral degeneration?

BACKGROUND AND OBJECTIVES

Intervertebral disc herniation is a common disease in chondrodystrophic dogs, and a similar neurologic condition also occurs in humans. Percutaneous laser disc ablation (PLDA) is a minimally invasive procedure used increasingly for prevention of disc herniation. Currently, PLDA is performed on thoracolumbar discs with the same laser energy applied regardless of the differing extent of degeneration among mineralized discs. In a previous study performed on 15 normal and 6 degenerated intervertebral discs in chondrodystrophoid canine species, it was demonstrated that percutaneous single-fiber reflectance spectroscopy (SfRS) detected increased light scattering from mineralized intervertebral discs when comparing to normal discs. The objective of this study is to evaluate how SfRS evaluation of mineralized discs in situ fairs with X-ray radiography and computed tomography (CT) diagnoses and if SfRS sensing of the scattering changes correlates with the level of mineral degeneration in nucleus pulposus.

MATERIALS AND METHODS

Percutaneous SfRS was performed on a total of 28 intervertebral discs of three dogs post-mortem, through a 20 gauge spinal needle standard to PLDA. The raw SfRS measurement was normalized to extract a dimension-less spectral intensity profile, from which the average over 600-900 nm was used as the SfRS intensity index to compare among the measured discs. The discs were imaged prior to percutaneous SfRS by radiography and CT, and harvested after percutaneous SfRS for histopathologic examinations.

RESULTS

Five among 10 discs of dog #1, six among 9 discs of dog #2, and nine out of 9 discs of dog #3 were determined by histopathology to have central focal or multi-focal areas of mineralization occupying 5-75% of the examined area of nucleus pulposus. The overall numbers of discs with detectable and undetectable central mineralization were 20 and 8, respectively. CT resulted in one false positive (FP) and four false negative (FN) diagnoses for dog #1, three FP and zero FN diagnoses for dog #2, and zero FP and one FN diagnosis for dog #3. Of the total 28 discs the CT had an overall positive predictive value (PPV) of 78.8% and an overall negative predictive value (NPV) of 44.4%. X-ray radiography gave five FN diagnoses for dog #1, two FN diagnoses for dog #2, and eight FN diagnoses for dog #3. Of the total 28 discs the radiography had an overall PPV of 100% and an overall NPV of 30.4%. The receiver-operating-characteristic analysis of the SfRS measurement was performed on 24 discs that had a central mineralization not greater than 50%. An area-under-curve of 0.6758 infers that the SfRS intensity weakly indicates the level of mineralization.

CONCLUSIONS

Percutaneous SfRS may be useful as an in situ sensing tool for assessing the level of mineral degeneration in intervertebral discs for the prospect of disc-specific dosage adjustment in PLDA.

In vivo optical spectroscopy for improved detection of pancreatic adenocarcinoma: a feasibility study

Pancreatic adenocarcinoma has a five-year survival rate of less than 6%. This low survival rate is attributed to the lack of accurate detection methods, which limits diagnosis to late-stage disease. Here, an in vivo pilot study assesses the feasibility of optical spectroscopy to improve clinical detection of pancreatic adenocarcinoma. During surgery on 6 patients, we collected spectrally-resolved reflectance and fluorescence in vivo. Site-matched in vivo and ex vivo data agreed qualitatively and quantitatively. Quantified differences between adenocarcinoma and normal tissues in vivo were consistent with previous results from a large ex vivo data set. Thus, optical spectroscopy is a promising method for the improved diagnosis of pancreatic cancer in vivo.

Optical techniques for the intraoperative assessment of nodal status

The lymphatic system is an important pathway in the metastatic spread of many malignancies and a key prognostic indicator. Nondestructive assessment of the nodal status during surgery could limit the amount of lymph nodes that need to be resected and allow for immediate regional lymphadenectomy during sentinel lymph node biopsy procedures. This review looks into the possibilities of conventional medical imaging methods that are capable of intraoperative nodal assessment and discusses multiple newly developed optical techniques. The physical background behind these techniques is reviewed and a concise overview of their main advantages and disadvantages is provided. These recent innovations show that while the application of optical modalities for intraoperative nodal staging is not yet applied routinely, there is reason enough to expect their introduction in the near future.

Characterizing human pancreatic cancer precursor using quantitative tissue optical spectroscopy

In a pilot study, multimodal optical spectroscopy coupled with quantitative tissue-optics models distinguished intraductal papillary mucinous neoplasm (IPMN), a common precursor to pancreatic cancer, from normal tissues in freshly excised human pancreas. A photon-tissue interaction (PTI) model extracted parameters associated with cellular nuclear size and refractive index (from reflectance spectra) and extracellular collagen content (from fluorescence spectra). The results suggest that tissue optical spectroscopy has the potential to characterize pre-cancerous neoplasms in human pancreatic tissues.

Use of a coherent fiber bundle for multi-diameter single fiber reflectance spectroscopy

Multi-diameter single fiber reflectance (MDSFR) spectroscopy enables quantitative measurement of tissue optical properties, including the reduced scattering coefficient and the phase function parameter γ. However, the accuracy and speed of the procedure are currently limited by the need for co-localized measurements using multiple fiber optic probes with different fiber diameters. This study demonstrates the use of a coherent fiber bundle acting as a single fiber with a variable diameter for the purposes of MDSFR spectroscopy. Using Intralipid optical phantoms with reduced scattering coefficients between 0.24 and 3 mm(-1), we find that the spectral reflectance and effective path lengths measured by the fiber bundle (NA = 0.40) are equivalent to those measured by single solid-core fibers (NA = 0.22) for fiber diameters between 0.4 and 1.0 mm (r ≥ 0.997). This one-to-one correlation may hold for a 0.2 mm fiber diameter as well (r = 0.816); however, the experimental system used in this study suffers from a low signal-to-noise for small dimensionless reduced scattering coefficients due to spurious back reflections within the experimental system. Based on these results, the coherent fiber bundle is suitable for use as a variable-diameter fiber in clinical MDSFR quantification of tissue optical properties.

Single-fiber diffuse optical time-of-flight spectroscopy

We demonstrate interstitial diffuse optical time-of-fight spectroscopy based on a single fiber for both light delivery and detection. Detector saturation due to the massive short-time reflection is avoided by ultrafast gating of a single photon avalanche diode. We show that the effects of scattering and absorption are separable and that absorption can be assessed independently of scattering. Measurements on calibrated liquid phantoms and subsequent Monte Carlo-based evaluation illustrate that absorption coefficients can be accurately assessed over a wide range of medically relevant optical properties. Our findings pave the way to simplified and less invasive interstitial in vivo spectroscopy.

Limitations and opportunities of transcutaneous bilirubin measurements

OBJECTIVE

Although transcutaneous bilirubinometers have existed for over 30 years, the clinical utility of the technique is limited to a screening method for hyperbilirubinemia, rather than a replacement for invasive blood sampling. In this study, we investigate the reason for this limited clinical value and address possibilities for improvement.

METHODS

To obtain better insight into the physiology of bilirubin measurements, we evaluated a transcutaneous bilirubinometer that determines not only the cutaneous bilirubin concentration (TcB) but also the blood volume fraction (BVF) in the investigated skin volume. For 49 neonates (gestational age 30 ± 3.1 weeks, postnatal age 6 [4-10] days) at our NICU, we performed 124 TcB and 55 BVF measurements.

RESULTS

The TcB correlated well with the total serum bilirubin concentration (TSB) (r = 0.88) with an uncertainty of 55 µmol/L. The BVF in the measured skin volume ranged between 0.1% and 0.75%.

CONCLUSIONS

The performance of our bilirubinometer is comparable to existing transcutaneous devices. The limited clinical value of current bilirubinometers can be explained by the low BVF in the skin volume that is probed by these devices. Because the TcB depends for over 99% on the contribution of extravascular bilirubin, it is a physiologically different parameter from the TSB. Hence, the standard method of evaluation that compares the TcB to the TSB is insufficient to fully investigate the clinical value of transcutaneous bilirubinometers, ie, their predictive value for kernicterus. We suggest that the clinical value may be improved considerably by changing either the method of evaluation or the technological design of transcutaneous bilirubinometers.

Correlating light scattering with internal cellular structures

The origins of side scattering from a fibroblast and cervical cell line were determined by comparing side-scatter images with images stained for lysosomes, nuclei, and mitochondria on a cell by cell basis. Lysosomes or nuclei are the most efficient type of scatterer depending on the cell type and incident light polarization. The relative scattering efficiencies of lysosomes and mitochondria were the same for both cell lines, while the scattering efficiencies of the nuclei differed. The percent of 90° scattering from the nucleus, mitochondria, and lysosomes as well as the group of other internal cellular objects was estimated. The nucleus was the largest contributor to side scatter in the cervical carcinoma cells. The contributions of lysosomes, mitochondria, the nucleus, and particles unstained by either Hoechst, LysoSensor or MitoTracker ranges from ∼20% to ∼30% in fibroblast cells. The contribution of lysosomes to side scatter was much stronger when the incident light was polarized perpendicular to the scattering plane than when the polarization of the side scatter laser was parallel to the scattering plane. This dependence on side scatter polarization indicates that lysosomes contain scattering structures that are much smaller than the wavelength of light used in the measurements (785 nm). In conclusion, mitochondria were not found to be either the most efficient scatterer or to have the largest contribution to scattering in either cell line, in contrast to previous reports. Rather lysosomes, nuclei and unknown particles all have significant contributions to 90° scattering and the contributions of some of these particles can be modulated by changing the polarization of the incident light.

Development of a noncontact diffuse optical spectroscopy probe for measuring tissue optical properties

Optical reflectance probes are often used as tools to obtain optical spectra from superficial tissues and subsequently determine optical and physiological properties associated with early stage cancer. These probes, when placed directly on the tissue, are known to cause significant pressure-dependent changes in local optical properties. To address this, we fit the probe with an optical device that images the illumination and collection fibers onto the tissue surface, eliminating the influence of contact probe pressure on the sampling area. The noncontact probe addition addresses new optical conditions that may affect its performance such as tissue surface contour, and specular reflections by implementing an autofocusing mechanism and cross polarization. Extracted optical properties of tissue simulating phantoms yield errors of 3.46% in reduced scattering and 8.62% in absorbance. Autofocusing has extended the depth of field from 4 mm to throughout the 12 mm range of autofocus travel, while cross polarization has removed the incidence angle dependent specular reflection component from the collected signal.

Scientific evidence and principles for the use of endobronchial ultrasound and transbronchial needle aspiration

Endobronchial ultrasound (EBUS), using the radial EBUS probe and convex-probe EBUS-guided transbronchial needle aspiration, are increasingly advocated for a wide array of minimally invasive thoracic procedures. The effectiveness of EBUS-guided procedures has been demonstrated to a degree that, in many institutions, EBUS is becoming standard of practice for the diagnosis, staging and restaging of mediastinal lymphadenopathy in lung cancer, the diagnosis of sarcoidosis, and for bronchoscopic biopsy of peripheral lung lesions. Its role in other bronchoscopic procedures requires further study despite an already strong body of literature: diagnosis of lymphoma and benign infectious disease, diagnosis of early lung cancer and airway wall disorders, imaging of thoracic vascular disease such as pulmonary embolism, and therapeutic procedures such as placement of fiducial markers. In this article, we illustrate some of the principles of EBUS, describe major technical aspects pertaining to the procedure itself and provide a narrative review of original research addressing proposed roles of EBUS in a variety of indications. In closing, we describe future perspectives including new educational processes and philosophies that could favorably impact the rapid and safe dissemination of this evolving technology into clinical practice.

Recent advances in optical coherence tomography for the diagnoses of lung disorders

There have been many advances in the field of diagnostic and therapeutic pulmonary medicine in the past several years, with major progress in the field of imaging. Optical coherence tomography (OCT) is a high-resolution (micron level) imaging modality currently being advanced with the potential to image airway wall structures in real time and at higher resolution than previously possible. OCT has the potential to increase the sensitivity and specificity of biopsies, create 3D images of the airway to guide diagnostics, and may have a future role in diverse areas such as the evaluation and treatment of patients with obstructive sleep apnea, tracheal stenosis, airway remodeling and inhalation injury. OCT has recently been investigated to monitor airway compliance in chronic obstructive pulmonary disease and asthma patients as well as differentiate causes of pulmonary hypertension. In future clinical and research applications, OCT will likely be combined with other endoscopic based modalities such as ultrasound, spectroscopy, confocal, and/or photoacoustic tomography to determine functional and biomolecular properties. This article discusses the current uses of OCT, its potential applications, as it relates to specific pulmonary diseases, and the future directions for OCT.

Clinical feasibility of monitoring m-THPC mediated photodynamic therapy by means of fluorescence differential path-length spectroscopy

The objective quantitative monitoring of light, oxygen, and photosensitizer is challenging in clinical photodynamic therapy settings. We have previously developed fluorescence differential path-length spectroscopy (FDPS), a technique that utilizes reflectance spectroscopy to monitor microvascular oxygen saturation, blood volume fraction, and vessel diameter, and fluorescence spectroscopy to monitor photosensitizer concentration. In this paper the clinical feasibility of the technique is tested on eight healthy volunteers and on three patients undergoing PDT of oral cavity cancers. Model-based analysis of the measured spectra provide quantitative tissue parameters that are corrected for background tissue absorption, autofluorescence, and the transmission of the optical system; this method allows comparison of intra- and inter-subject parameters. The FDPS correctly estimated the absence of m-THPC in volunteers and detected photobleaching in the areas receiving treatment light in patients undergoing PDT treatment. This study demonstrates the feasibility of monitoring clinical photodynamic therapy treatments using optical spectroscopy.

Can color inhomogeneity of bruises be used to establish their age?

Bruises become spatially inhomogeneous during the healing process; a smaller red-blue core area, caused by hemoglobin, is surrounded by a larger yellow area, caused by bilirubin, which is enzymatically formed from hemoglobin. These two areas develop at different rates and hence carry information about the age of the bruise. We present a proof of principle demonstration that the age of bruises can be determined via an inverse procedure using a mathematical model and daily measurements of these two areas using a hyperspectral imaging system. The inaccuracy found is 2.3% for fresh bruises and 3 to 24% for bruises up to 3 days old. In conclusion, color inhomogeneity of bruises can be used to determine their age. We expect that future age determination of bruises by the inverse procedure described here, possibly also including the distribution of concentrations in the areas will open up a new phase in clinical bruise classification.

Method to quantitate absorption coefficients from single fiber reflectance spectra without knowledge of the scattering properties

This study presents a methodology to accurately extract the absorption coefficient from single fiber reflectance spectra measured in turbid media without a priori knowledge of either the reduced scattering coefficient or the phase function. This novel approach accounts for the interrelated effects these properties have on the photon path length, yielding estimates of an absorption coefficient on average within <7.5% of true values over a wide range of biologically relevant optical properties.

Needle stylet with integrated optical fibers for spectroscopic contrast during peripheral nerve blocks

The effectiveness of peripheral nerve blocks is highly dependent on the accuracy at which the needle tip is navigated to the target injection site. Even when electrical stimulation is utilized in combination with ultrasound guidance, determining the proximity of the needle tip to the target region close to the nerve can be challenging. Optical reflectance spectroscopy could provide additional information about tissues that is complementary to these navigation methods. We demonstrate a novel needle stylet for acquiring spectra from tissue at the tip of a commercial 20-gauge needle. The stylet has integrated optical fibers that deliver broadband light to tissue and receive scattered light. Two spectrometers resolve the light that is received from tissue across the wavelength range of 500-1600 nm. In our pilot study, measurements are acquired from a postmortem dissection of the brachial plexus of a swine. Clear differences are observed between spectra acquired from nerves and those acquired from adjacent tissue structures. We conclude that spectra acquired with the stylet have the potential to increase the accuracy with which peripheral nerve blocks are performed.

EUS for the staging of gastric cancer: a meta-analysis

BACKGROUND

The role of EUS in the locoregional staging of gastric carcinoma is undefined.

OBJECTIVE

We aimed to comprehensively review and quantitatively summarize the available evidence on the staging performance of EUS.

DESIGN

We systematically searched the MEDLINE, Cochrane, CANCERLIT, and EMBASE databases for relevant studies published until July 2010.

SETTING

Formal meta-analysis of diagnostic accuracy parameters was performed by using a bivariate random-effects model.

PATIENTS

Fifty-four studies enrolling 5601 patients with gastric cancer undergoing disease staging with EUS were eligible for the meta-analysis.

MAIN OUTCOME MEASUREMENTS

EUS staging accuracy across eligible studies was measured by computing overall sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), and diagnostic odds ratio (DOR).

RESULTS

EUS can differentiate T1-2 from T3-4 gastric cancer with high accuracy, with overall sensitivity, specificity, PLR, NLR, and DOR of 0.86 (95% CI, 0.81-0.90), 0.91 (95% CI, 0.89-0.93), 9.8 (95% CI, 7.5-12.8), 0.15 (95% CI, 0.11-0.21), and 65 (95% CI, 41-105), respectively. In contrast, the diagnostic performance of EUS for lymph node status is less reliable, with overall sensitivity, specificity, PLR, NLR, and DOR of 0.69 (95% CI, 0.63-0.74), 0.84 (95% CI, 0.81-0.88), 4.4 (95% CI, 3.6-5.4), 0.37 (95% CI, 0.32-0.44), and 12 (95% CI, 9-16), respectively. Results regarding single T categories (including T1 substages) and Bayesian nomograms to calculate posttest probabilities for any target condition prevalence are also provided.

LIMITATIONS

Statistical heterogeneity was generally high; unfortunately, subgroup analysis did not identify a consistent source of the heterogeneity.

CONCLUSIONS

Our results support the use of EUS for the locoregional staging of gastric cancer, which can affect the therapeutic management of these patients. However, clinicians must be aware of the performance limits of this staging tool.

Measurement of the reduced scattering coefficient of turbid media using single fiber reflectance spectroscopy: fiber diameter and phase function dependence

This paper presents a relationship between the intensity collected by a single fiber reflectance device (R(SF)) and the fiber diameter (d(fib)) and the reduced scattering coefficient ( μs') and phase function (p(θ)) of a turbid medium. Monte Carlo simulations are used to identify and model a relationship between R(SF) and dimensionless scattering ( μs'dfib). For μs'dfib > 10 we find that R(SF) is insensitive to p(θ). A solid optical phantom is constructed with μs' ≈ 220 mm-1 and is used to convert R(SF) of any turbid medium to an absolute scale. This calibrated technique provides accurate estimates of μs' over a wide range ([0.05 - 8] mm(-1)) for a range of d(fib) ([0.2 - 1] mm).

Effect of bile absorption coefficients on the estimation of liver tissue optical properties and related implications in discriminating healthy and tumorous samples

We investigated differences between healthy tissue and metastatic tumor from ex vivo human partial liver resections using diffuse optical spectroscopy with a fiber optic probe. We extracted various physiological and morphological parameters from the spectra. During evaluation of the residual between the measurements and a fit model based on diffusion theory, we found that bile is an additional chromophore absorbing in the visible wavelength range that was missing in our model. Consistency of the residual with the absorption spectrum of bile was noticed. An accurate measurement of the absorption coefficient of bile from various human bile samples was performed and implemented into the fit model. Having the absorption coefficient of bile as a priori knowledge in the model showed a clear improvement in terms of reducing the fitting discrepancies. The addition of this chromophore yields significantly different estimates of the amount of blood. Furthermore, the estimated bile volume fraction and reduced scattering amplitude turned out to be two main relevant discriminators between normal and metastatic liver tissues.