Real-time spectroscopic assessment of thermal damage: Implications for radiofrequency ablation

Radiofrequency ablation (RFA) is an evolving technology used to treat unresectable liver tumors. Currently, there is no accurate method to determine RFA margins in real-time during the procedure. We hypothesized that fiber-optic based spectroscopic monitoring system could detect thermal damage from RFA in real-time. Fluorescence (F) and diffuse reflectance (Rd) spectra were continuously acquired from within the expected ablation zone during canine hepatic RFA using a fiber-optic microinterrogation probe (MIP). The F and Rd spectral feedback were continuously monitored and ablations were stopped based on changes in spectra alone. After each ablation, the MIP tract was marked with India ink and the ablation zone was excised. The relationship of the MIP to the zone of ablation was examined grossly and microscopically. F and Rd spectral changes occurred in three characteristic phases as the ablation zone progresses past the MIP. Phase 1 indicates minimal deviation from normal lives. Phase 2 occurs as the MIP lies within the hemorrhagic zone of the ablated tissue. Phase 3 correlates with complete tissue coagulation. The absolute magnitude of spectral change correlates with the gross and histologic degree of thermal damage. Optical spectroscopy is a technology that allows real-time detection of thermal tissue damage. In this study, both F and Rd spectroscopy accurately defined the advancing hemorrhagic edge of the zone of ablation and the central coagulation zone. These results suggest that F and Rd spectroscopy can be used to create a real-time feedback system to accurately define RFA margins. Presented in part at the 2003 meeting of the American Hepato-Pancreato-Biliary Association, Miami Beach, Florida, February 27–March 2, 2003.     

Optical Analysis of the Cirrhotic Liver by Near-Infrared Time-Resolved Spectroscopy

Purpose. To assess the histological severity of liver cirrhosis in relation to the optical properties of liver tissue.Methods. Various grades of liver cirrhosis were induced in rats by giving intraperitoneal injections of thioacetamide (TAA) over periods ranging from 4 to 16 weeks. The optical properties of the liver, absorption coefficient (µ_a) and scattering coefficient (µ_s), were measured by near-infrared time-resolved spectroscopy.Results. Histological examination confirmed cirrhotic changes in the liver, which were more severe in the rats given TAA for longer periods. The µ_a increased in the 4- and 8-week rats, then decreased in the 12- and 16-week rats. The µ_a of the blood-free liver decreased as liver cirrhosis progressed. The hemoglobin concentration in the liver, calculated from the µ_a values, increased in the 4- and 8-week rats and decreased in the 12- and 16-week rats. The µ_s decreased in the cirrhotic liver, probably reflecting the loss of volume of hepatocytes. The product of µ_a and µ_s proved useful to evaluate the severity of cirrhosis.Conclusions. These results showed that the optical properties correlated well with the severity of liver cirrhosis, indicating that the clinical application of this method is encouraging.     

Spectroscopic and thermal analysis of a submandibular sialolith of Wharton’s duct resected using Nd:YAG laser

A sialolith observed in the Wharton’s duct of a male patient was resected using an Nd:YAG laser. This is the first report on the resection of sialolith using laser. The resected sample was analyzed for structural details using Fourier transform infrared (FTIR), FT-Raman, and fluorescence spectroscopic techniques. Other techniques like energy dispersive X-ray analysis, scanning electron microscopy, and thermal analysis were also used for the analysis of structural details. The major peaks of the vibrational spectra are observed to be due to the vibrations of the phosphate and hydroxyl groups of the inorganic part of the sample and the proteinaceous component of the organic part. The major elements in the sample are identified as calcium and phosphorous in the ratio 7:3. The fluorescence spectra recorded at excitation wavelengths 280, 325, and 410 nm showed emission maxima corresponding to the endogenous fluorescence of structural proteins and amino acids. The inorganic part of the sialolith remained stable even at temperatures up to 1,673 K. The spectroscopic studies indicated that the structure of the sialolith is similar to that of the dentine part of the human teeth. In situ disintegration of the sialolith involves very high temperature. High calcium and phosphorous content in the food may be attributed to one of the reasons for the formation of sialoliths.     

Recent advances in optical diagnosis of oral cancers: Review and future perspectives

Optical diagnosis techniques offer several advantages over traditional approaches, including objectivity, speed, and cost, and these label‐free, noninvasive methods have the potential to change the future workflow of cancer management. The oral cavity is particularly accessible and, thus, such methods may serve as alternate/adjunct tools to traditional methods. Recently, in vivo human clinical studies have been initiated with a view to clinical translation of such technologies. A comprehensive review of optical methods in oral cancer diagnosis is presented. After an introduction to the epidemiology and etiological factors associated with oral cancers currently used, diagnostic methods and their limitations are presented. A thorough review of fluorescence, infrared absorption, and Raman spectroscopic methods in oral cancer diagnosis is presented. The applicability of minimally invasive methods based on serum/saliva is also discussed. The review concludes with a discussion on future demands and scope of developments from a clinical point of view. © 2015 Wiley Periodicals, Inc. Head Neck 38 : E2403–E2411, 2016     

Abnormal mitochondrial function and muscle wasting, but normal contractile efficiency, in haemodialysed patients studied non-invasively in vivo.

BACKGROUND: Muscle dysfunction, which contributes to morbidity in patients on haemodialysis, has several manifestations and a number of possible causes. We applied the non-invasive techniques of (31)P-magnetic resonance spectroscopy ((31)P-MRS), magnetic resonance imaging (MRI) and near-infrared spectroscopy (NIRS) to calf muscle of dialysed patients to define the abnormalities in muscle cross-sectional area (CSA), contractile efficiency, mitochondrial function and vascular O(2) supply. METHODS: We performed (31)P-MRS/NIRS/MRI studies on the lateral gastrocnemius during isometric plantarflexion and recovery in 23 male patients on haemodialysis (age 24-71 years; haemoglobin 9.9-14.2 g/dl; bicarbonate 17-30 mmol/l; urea reduction ratio 53-77%; parathyroid hormone 1-95 U/l) and 15 male controls (age 29-71 years). To understand the relationships between calf CSA and body mass we also performed MRI only in a further six male patients and 18 male controls. RESULTS: In patients, exercise duration was 30+/-11% lower than in controls. Muscle CSA was lower by 26+/-5%, but contractile efficiency (force/CSA/ATP turnover) was normal. Slowing of post-exercise phosphocreatine (PCr) recovery implied a 22+/-5% defect in effective 'mitochondrial capacity'. That PCr recovery was slow relative to NIRS recovery suggests that this is largely an intrinsic mitochondrial problem (not the result of impaired O(2) supply), one which, furthermore, correlated with CSA. Urea reduction ratio showed a negative correlation with body mass and CSA, but none with PCr rate constant. CONCLUSIONS: The relationships to urea reduction ratio reflect the effect of muscle mass on dialysis efficiency, rather than direct effects on muscle CSA or metabolism. The relationship between PCr recovery and calf CSA suggests a role for the mitochondrial defect, whatever its cause, in the development of muscle wasting, although a common cause (e.g. physical inactivity) for both abnormalities cannot be ruled out.     

Fourier transform infrared spectroscopy of the solution-mediated conversion of amorphous calcium phosphate to hydroxyapatite: New correlations between X-ray diffraction and infrared data

Fourier Transform infrared spectroscopic analysis of maturing, poorly crystalline hydroxyapatite (HA) formed from the conversion of amorphous calcium phosphate (ACP) at constant pH or variable pH show only subtle changes in the ν₁, ν₃ phosphate absorption region (900 cm⁻¹−1200 cm⁻¹). This region is of interest because it can ve detected by analysis of mineralized tissue sections using FT-IR microscopy. To evaluate the subtle spectral changes occurring during the maturation, second derivatives of the spectra were calculated. HA formed at constant pH showed little or no variation in the second derivative peak positions with bands occurring at 960 cm⁻¹, 985 cm⁻¹, 1030 cm⁻¹, 1055 cm⁻¹, 1075 cm⁻¹, 1096 cm⁻¹, 1116 cm⁻¹, and 1145 cm⁻¹. These bands can be assigned to molecular vibrations of the phosphate (PO₄ ³⁻) moiety in an apatitic/stoichiometric environment of HA. In contrast, during the early stages of maturation of the HA formed at variable pH, second derivative peak positions occurring at 958 cm⁻¹, 985 cm⁻¹, 1020 cm⁻¹, 1038 cm⁻¹, 1112 cm⁻¹, and 1127 cm⁻¹ shifted in position with maturation, indicating, that the environment of the phosphate species is changing as the crystals mature. Peaks at 1020 cm⁻¹, 1038 cm⁻¹, 1112 cm⁻¹, and 1127 cm⁻¹ were attributable to nonstoichiometry and/or the presence of acid phosphate-containing species. This concept was supported by the lower Ca:P molar ratios measured by chemical analysis of the synthetic material made at variable pH. Using the second derivative peak positions as initial input parameters, the ν₁, ν₃ phosphate region of the synthetic HAs prepared at constant pH were curve fit. X-ray diffraction patterns of these same materials were also curve fit to calculate the changes in crystallinty (size/perfection) in the c-axis 002 reflection as well as the 102, 210, 211, 112, 300, 200, and 301 planes. Linear regression analysis showed that the changes in the percent area of the underlying bands at 982 cm⁻¹, 999 cm⁻¹, 1030 cm⁻¹, 1075 cm⁻¹, 1096 cm⁻¹, 1116 cm⁻¹, and 1145 cm⁻¹ were correlated with changes in crystallinity in one or more of the reflection planes. It is suggested that a combination of second-derivative and curve-fitting analysis of the ν₁, ν₃ phosphate contour allows the most reproducible evaluation of these spectra.     

Autofluorescence and diffuse reflectance spectroscopy for oral oncology

BACKGROUND AND OBJECTIVES: Autofluorescence and diffuse reflectance spectroscopy have been used separately and combined for tissue diagnostics. Previously, we assessed the value of autofluorescence spectroscopy for the classification of oral (pre-)malignancies. In the present study, we want to determine the contributions of diffuse reflectance and autofluorescence spectroscopy to diagnostic performance. STUDY DESIGN/MATERIALS AND METHODS: Autofluorescence and diffuse reflectance spectra were recorded from 172 oral lesions and 70 healthy volunteers. Autofluorescence spectra were corrected in first order for blood absorption effects using diffuse reflectance spectra. Principal Components Analysis (PCA) with various classifiers was applied to distinguish (1) cancer and (2) all lesions from healthy oral mucosa, and (3) dysplastic and malignant lesions from benign lesions. Autofluorescence and diffuse reflectance spectra were evaluated separately and combined. RESULTS: The classification of cancer versus healthy mucosa gave excellent results for diffuse reflectance as well as corrected autofluorescence (Receiver Operator Characteristic (ROC) areas up to 0.98). For both autofluorescence and diffuse reflectance spectra, the classification of lesions versus healthy mucosa was successful (ROC areas up to 0.90). However, the classification of benign and (pre-)malignant lesions was not successful for raw or corrected autofluorescence spectra (ROC areas <0.70). For diffuse reflectance spectra, the results were slightly better (ROC areas up to 0.77). CONCLUSIONS: The results for plain and corrected autofluorescence as well as diffuse reflectance spectra were similar. The relevant information for distinguishing lesions from healthy oral mucosa is probably sufficiently contained in blood absorption and scattering information, as well as in corrected autofluorescence. However, neither type of information is capable of distinguishing benign from dysplastic and malignant lesions. Combining autofluorescence and reflectance only slightly improved the results.     

Intraoperative colon mucosal oxygen saturation during aortic surgery

BACKGROUND: Colonic ischemia after aortic reconstruction is a devastating complication with high mortality rates. This study evaluates whether Colon Mucosal Oxygen Saturation (CMOS) correlates with colon ischemia during aortic surgery. MATERIALS AND METHODS: Aortic reconstruction was performed in 25 patients, using a spectrophotometer probe that was inserted in each patient's rectum before the surgical procedure. Continuous CMOS, buccal mucosal oxygen saturation, systemic mean arterial pressure, heart rate, pulse oximetry, and pivotal intra-operative events were collected. RESULTS: Endovascular aneurysm repair (EVAR) was performed in 20 and open repair in 5 patients with a mean age of 75 +/- 10 (+/-SE) years. CMOS reliably decreased in EVAR from a baseline of 56% +/- 8% to 26 +/- 17% (P < 0.0001) during infrarenal aortic balloon occlusion and femoral arterial sheath placement. CMOS similarly decreased during open repair from 56% +/- 9% to 15 +/- 19% (P < 0.0001) when the infrarenal aorta and iliac arteries were clamped. When aortic circulation was restored in both EVAR and open surgery, CMOS returned to baseline values 56.5 +/- 10% (P = 0.81). Mean recovery time in CMOS after an aortic intervention was 6.4 +/- 3.3 min. Simultaneous buccal mucosal oxygen saturation was stable (82% +/- 6%) during aortic manipulation but would fall significantly during active bleeding. There were no device related CMOS measurement complications. CONCLUSIONS: Intra-operative CMOS is a sensitive measure of colon ischemia where intraoperative events correlated well with changes in mucosal oxygen saturation. Transient changes demonstrate no problem. However, persistently low CMOS suggests colon ischemia, thus providing an opportunity to revascularize the inferior mesenteric artery or hypogastric arteries to prevent colon infarction.     

Using the laser-induced fluorescence spectroscopy in the differentiation between normal and neoplastichuman breast tissue

This article reports results of the in vitro study for potential evaluation of the laser-induced fluorescence spectroscopy in the differentiation between normal and neoplastic human breast tissue. A coumarine dye laser pumped by nitrogen laser generated an excitation light centered at 458 nm. In order to collect the fluorescence signal was used an optical fiber catheter coupled to a spectrometer and CCD detector. Fluorescence spectra were recorded from normal and neoplastic (benign and malignant) human breast tissue, adding up 94 different areas. The discrimination between normal and neoplasm groups reach a sensitivity and specificity of 100%.     

Intraoperative measurement of the graft oxygenation state in living related liver transplantation by near infrared spectroscopy

Graft oxygenation plays an important role in successful liver transplantation. Intraoperative changes in the oxygenation state of the liver graft were measured by near infrared spectroscopy in 28 cases of living related liver transplantation. Oxygen saturation of hemoglobin in the liver (hepatic SO₂) changed from 81.2%±1.5% (mean±SEM) before donation (in the donor) to 49.7%±4.2% after portal reflow, to 58.4%±5.0% after arterial reflow, and then to 71.4%±3.9% before closure. Mean hepatic SO₂ was positively correlated with portal flow rate as measured by duplex Doppler sonography. Cases with low portal flow rate showed a high coefficient of variation (SD/mean) of hepatic SO₂, indicating heterogeneous tissue oxygenation. Though graft size was expected to affect the graft oxygenation state, hepatic SO₂ was fairly independent of the graft-to-recipient weight ratio. In two cases with markedly low hepatic SO₂, postoperative graft dysfunction occurred. This study suggest that the method of near infrared spectroscopy is reliable and useful for assessing the graft oxygenation state in liver transplantation.     

Evaluation of a fluorescence feedback system for guidance of laser angioplasty

Background and Objective: Laser-induced fluorescence spectroscopy (LIFS) may be capable of guiding laser angioplasty by discriminating normal and atherosclerotic artery and by determining catheter-tissue environment. Previous optical multichannel analyzer based LIFS systems have been expensive and cumbersome. To simplify LIFS, a system based on photomultiplier tubes was developed and evaluated. Study Design/Materials and Methods: Tissue fluorescence was induced by a helium cadmium laser (wavelength = 325 nm, power = 0.2–0.5 mW), collected by clinical multifiber laser angioplasty catheters and directed through one of two filters (10 nm bandpass, 380 nm or 440 nm peak transmission) to a photomultiplier tube. An LIFS ratio was defined as the relative intensity at 380:440 nm after calibration with an elastin fluorescence spectrum; 157 coronary artery cadaveric specimens were evaluated spectroscopically and histologically. To evaluate the utility of LIFS to optimize catheter position by determining catheter–tissue contact, by determining saline dilution of blood, and by orienting eccentric multifiber catheters a new variable, the total fluorescence intensity (TFI) was defined as the sum of arterial fluorescence intensities at 380 nm and 440 nm. TFI was recorded in vitro through multifiber catheters from 20 arterial specimens in vitro in blood and evaluated as a function of the catheter-to-tissue distance (d) over a range from 0 to 400 μ. Results: Defining normal specimens as those with an intimal thickness ≤200 μ, and atherosclerotic as those with an intimal thickness <200 μ, 47/50 (94%) normal and 85/107 (79%) atherosclerotic specimens were correctly classified using a threshold LIFS ratio of 2.0. Mean (±SE) normal ratio was 1.76±0.02 and mean atherosclerotic ratio was 2.78±0.08 (P ≤ 0.01). The classification accuracy of atherosclerotic specimens increased with intimal thickness so that 95% of atherosclerotic specimens (69/73) with intimal thickness ≥400 μ were correctly classified. TFI was capable of determining catheter-tissue contact as maximal TFI was recorded with the catheter in contact with the tissue (d = 0 μ) and decreased markedly with distance (to 52 ± 6% at d = 100 μ, 19 ± 4% at d = 200 μ, and 3 ± 1% at d = 300 μ). TFI was recorded from ten arterial specimens in blood/saline mixtures ranging in hematocrit from 0% (saline) to 50% (whole blood). TFI was capable of detecting saline hemodilution of blood as TFI decreased markedly at higher hematocrits such that TFI could only by recorded at hematocrits <10 % for catheter-to-tissue distances ≥300 μ. TFI was recorded through eccentric multifiber catheters from 25 arterial specimens and evaluated as a function of the degree of catheter-tissue overlap. TFI was capable of detecting maximal catheter-tissue overlap as TFI correlated linearly with the area (A) of overlap (TFI = 1.12 A + .07, r = 0.92). Conclusions: By discriminating atherosclerotic from normal tissue and by confirming catheter-tissue contact and saline hemodilution, fluorescence feedback should minimize irradiation of normal tissue and/or blood and enhance the safety and efficacy of laser angioplasty. © 1995 Wiley-Liss, Inc.     

Optical spectroscopic determination of human meniscus composition

This study investigates the correlation between the composition of human meniscus and its absorption spectrum in the visible (VIS) and near infrared (NIR) spectral range. Meniscus samples (n = 24) were obtained from nonarthritic knees of human cadavers with no history of joint diseases. Specimens (n = 72) were obtained from three distinct sections of the meniscus, namely; anterior, center, posterior. Absorption spectra were acquired from each specimen in the VIS and NIR spectral range (400–1,100 nm). Following spectroscopic probing, the specimens were subjected to biochemical analyses to determine the matrix composition, that is water, hydroxyproline, and uronic acid contents. Multivariate analytical techniques, including principal component analysis (PCA) and partial least squares (PLS) regression, were then used to investigate the correlation between the matrix composition and it spectral response. Our results indicate that the optical absorption of meniscus matrix is related to its composition, and this relationship is optimal in the NIR spectral range (750–1,100 nm). High correlations (R²_uronic = 86.9%, R²_water = 83.8%, R²_{hydroxyproline} = 81.7%, p < 0.0001) were obtained between the spectral predicted and measured meniscus composition, thus suggesting that spectral data in the NIR range can be utilized for estimating the matrix composition of human meniscus. In conclusion, optical spectroscopy, particularly in the NIR spectral range, is a potential method for evaluating the composition of human meniscus. This presents a promising technique for rapid and nondestructive evaluation of meniscus integrity in real‐time during arthroscopic surgery. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:270–278, 2016.     

Catheters: instrumental advancements in biomedical applications of optical fibers

This review is focused on the advancements in biomedical engineering regarding the elaboration of new prototypes of optical fiber catheters to be applied in spectroscopic analysis, such as Raman and fluorescence spectroscopy. Our group has contributed to the development of new prototypes with interesting properties, such as side-viewing signal excitation and collection, distal tip with bending control, and Raman scattering minimization from the optical fiber. In addition, several groups have contributed to other new catheter-improving properties of this spectroscopic device. However, a relatively small number of studies has been published in the literature, due to industrial interest in this interdisciplinary and multidisciplinary area. To our knowledge, no review that has focused on the applications of catheters to several modes of spectroscopy has been published. In this work we revised this topic, analyzing the advancements and limitations of the recent biomedical catheters.     

Applying quantitative micro-Raman spectroscopy to analyze stone compositions extracted from ureteroscopic lithotripsy urine

ObjectiveIn this study we applied quantitative micro-Raman spectroscopy (MRS) in binary stone compositions extracted from ureteroscopic lithotripsy (URSL) urine. Urolithiasis is a severe disease with a great impact. For ureteral stone patients, a basket retractor is used to catch the stone for analysis when patients undergo URSL. However, this can cause potential ureteral-related complications. The identification of the composition of a urinary stone is important for metabolic evaluation, decision making, and diet control. In this study, we applied a quantitative MRS method in a clinical setting to measure the composition of binary urinary stones in urine extracted via URSL.Materials and MethodsThis study was approved by the Institutional Review Board of Taipei City Hospital, Taipei, Taiwan from November 2008 to November 2009. Urine samples from fragmented stone sites in the patients' ureters were collected via the URSL procedure by drawing at least 10 mL of urine with a syringe. The urine samples from 30 patients were analyzed using an MRS-based analysis method, both qualitatively and quantitatively.ResultsThe post-URSL urine powder from the samples was successfully analyzed using a quantitative MRS-based method, which was based on a linear equation developed according to the ratios of the relative intensities of the Raman bands corresponding to binary mixtures of known composition. Fourteen urine samples from 30 patients disclosed binary composition, and the ratio percentages were obtained using the equation along with a quantitative MRS-based method.ConclusionWe successfully applied the quantitative MRS-based method clinically to analyze the stone compositions extracted from URSL urine. This method decreases the need to use a basket to catch macrostones for Fourier transform infrared spectroscopy analysis, while also still providing quantitative and quantitative stone analysis information by using the microstones in urine.     

FT-IR photoacoustic depth profiling spectroscopy of enamel

Photoacoustic Fourier transform infrared (PA-FT-IR) depth profiling spectra of the enamel of an intact human tooth are obtained in a completely nondestructive fashion. The compositional and structural changes in the tissue are probed from the enamel surface to a depth of about 200 m. These changes reflect the state of tissue development. The subsurface carbonate gradient in the enamel could be observed over the range of about 10–100 m. The carbonate-to-phosphate ratio increases in the depth profile. The depth profile also reveals changes in the substitutional distribution of carbonate ions. Type A carbonates (hydroxyl substituted) increase relative to type B carbonates (phosphate substituted) with increasing thermal diffusion length. In addition to the changes in the carbonate ion distribution and content, the PA-FT-IR depth profile clearly indicates a dramatic increase in the protein content relative to the phosphate content with increased depth. The changes in the carbonate content and distribution, along with the changes in the protein content, may be responsible for the changes observed in the apatitic structure in the depth profile of the enamel.     

Characterization of the site dependency of normal canine arterial fluorescence

The difference in fluorescence between normal and atherosclerotic artery has been proposed as a feedback mechanism to guide selective laser ablation of atherosclerotic plaque. This fluorescence difference is due to the relative difference in collagen:elastin content of normal artery and atherosclerotic plaque. However, normal arteries have site-dependent variation in collagen: elastin content which may affect their fluorescence spectra. To evaluate the site dependency of normal arterial fluorescence, helium-cadmium (325 nm) laser-induced fluorescence spectra were analyzed in vitro from the ascending aorta, abdominal aorta, and carotid, femoral, renal, and coronary arteries (N = 57) of 12 normal mongrel dogs. Elastin and collagen contents were determined for a subset of these arteries (N = 15). The spectral width of normal arterial Fluorescence varied by site and correlated with the measured collagen:elastin content at each site (r = -0.84, P less than 0.005). Fluorescence spectra were decomposed into collagen and elastin spectral components by using a linear model with a least-squared error criterion fit. The derived collagen and elastin spectral coefficients correlated with the measured collagen and elastin tissue content (r = 0.75 and 0.83 respectively, P less than 0.005). Thus, the fluorescence spectra of normal arteries is site dependent and correlates with the collagen:elastin content. Therefore, spectral feedback algorithms for laser angioplasty guidance must be site specific.