Alexandre Douplik

The refractive index of human hemoglobin in the visible range

Because the refractive index of hemoglobin in the visible range is sensitive to the hemoglobin concentration, optical investigations of hemoglobin are important for medical diagnostics and treatment. Direct measurements of the refractive index are, however, challenging; few such measurements have previously been reported, especially in a wide wavelength range. We directly measured the refractive index of human deoxygenated and oxygenated hemoglobin for nine wavelengths between 400 and 700 nm for the hemoglobin concentrations up to 140 g l(-1). This paper analyzes the results and suggests a set of model functions to calculate the refractive index depending on the concentration. At all wavelengths, the measured values of the refractive index depended on the concentration linearly. Analyzing the slope of the lines, we determined the specific refraction increments, derived a set of model functions for the refractive index depending on the concentration, and compared our results with those available in the literature. Based on the model functions, we further calculated the refractive index at the physiological concentration within the erythrocytes of 320 g l(-1). The results can be used to calculate the refractive index in the visible range for arbitrary concentrations provided that the refractive indices depend on the concentration linearly.

Refractive index of solutions of human hemoglobin from the near-infrared to the ultraviolet range: Kramers-Kronig analysis

Abstract. Because direct measurements of the refractive index of hemoglobin over a large wavelength range are challenging, indirect methods deserve particular attention. Among them, the Kramers-Kronig relations are a powerful tool often used to derive the real part of a refractive index from its imaginary part. However, previous attempts to apply the relations to solutions of human hemoglobin have been somewhat controversial, resulting in disagreement between several studies. We show that this controversy can be resolved when careful attention is paid not only to the absorption of hemoglobin but also to the dispersion of the refractive index of the nonabsorbing solvent. We present a Kramers-Kroning analysis taking both contributions into account and compare the results with the data from several studies. Good agreement with experiments is found across the visible and parts of near-infrared and ultraviolet regions. These results reinstate the use of the Kramers-Kronig relations for hemoglobin solutions and provide an additional source of information about their refractive index.

Optical nerve detection by diffuse reflectance spectroscopy for feedback controlled oral and maxillofacial laser surgery.

BackgroundLaser surgery lacks haptic feedback, which is accompanied by the risk of iatrogenic nerve damage. It was the aim of this study to investigate diffuse reflectance spectroscopy for tissue differentiation as the base of a feedback control system to enhance nerve preservation in oral and maxillofacial laser surgery.MethodsDiffuse reflectance spectra of nerve tissue, salivary gland and bone (8640 spectra) of the mid-facial region of ex vivo domestic pigs were acquired in the wavelength range of 350-650 nm. Tissue differentiation was performed using principal component (PC) analysis followed by linear discriminant analysis (LDA). Specificity and sensitivity were calculated using receiver operating characteristic (ROC) analysis and the area under curve (AUC).ResultsFive PCs were found to be adequate for tissue differentiation with diffuse reflectance spectra using LDA. Nerve tissue could be differed from bone as well as from salivary gland with AUC results of greater than 88%, sensitivity of greater than 83% and specificity in excess of 78%.ConclusionsDiffuse reflectance spectroscopy is an adequate technique for nerve identification in the vicinity of bone and salivary gland. The results set the basis for a feedback system to prevent iatrogenic nerve damage when performing oral and maxillofacial laser surgery.

Diffuse reflectance spectroscopy for optical soft tissue differentiation as remote feedback control for tissue-specific laser surgery.

Laser surgery does not provide haptic feedback for operating layer‐by‐layer and thereby preserving vulnerable anatomical structures like nerve tissue or blood vessels. Diffuse reflectance spectra can facilitate remote optical tissue differentiation. It is the aim of the study to use this technique on soft tissue samples, to set a technological basis for a remote optical feedback system for tissue‐specific laser surgery.

In vivo optical tissue differentiation by diffuse reflectance spectroscopy: preliminary results for tissue-specific laser surgery.

Objectives. Laser surgery requires feedback to avoid the accidental destruction of critically important tissues. It was the aim of the authors to identify different tissue types in vivo by diffuse reflectance spectroscopy to set the basis for tissue-specific control of laser surgery. Methods. Tissue differentiation was performed on in vivo tissue of rats (skin, fat, muscle, and nerve) by diffuse reflectance spectroscopy between 350 and 650 nm. Data analysis was done using principal components analysis, followed by linear discriminant analysis (LDA). The differentiation performance was evaluated by receiver operating characteristic (ROC) analysis. Results. ROC analysis showed a tissue differentiation of 100%, with a high sensitivity of more than 99%. Only the tissue pair skin/fat showed a reduced differentiation performance and specificity. Conclusion. The results show the general viability of in vivo optical tissue differentiation and create a basis for the further development of a control system for tissue-specific laser surgery.

Absorption spectroscopy as a tool to control blood oxygen saturation during photodynamic therapy

The photodynamic therapy (PDT) is an effective method to treat cancer and other nononcological lesions by means of light action on photosensitizer in tissue. It is considered that destroying effect is mainly due to the formation of singlet oxygen resulting from the interaction of light excited photosensitizer with molecular oxygen (triplet state in the ground state). So the destroying effect will be proportional to the rate of singlet oxygen formation which is in turn depends on light intensity, photosensitizer concentration and molecular oxygen concentration. The present work deals with the investigation of blood oxygen saturation in microcircular vessels (SO2) during light irradiation in the PDT process. It has been observed that SO2 behavior strongly correlates with the light power density applied for PDT. The high power density resulted in sharp SO2 decrease. The connection of SO2 decrease with enhanced oxygen consumption rate and vessel destruction due to PDT is discussed.

Diffuse reflectance spectroscopy in Barrett’s Esophagus: developing a large field-of-view screening method discriminating dysplasia from metaplasia

We evaluated diffuse reflectance spectroscopy implemented as a small field-of-view technique for discrimination of dysplasia from metaplasia in Barretts esophagus as an adjuvant to autofluorescence endoscopy. Using linear discriminant analysis on 2579 spectra measured in 54 patients identified an optimum a 4-wavelength classifier (at 485, 513, 598 and 629 nm). Sensitivity and specificity for a test data set were 0.67 and 0.85, respectively. Spectroscopic results show that this technique could be implemented in wide-field imaging mode to improve the accuracy of existing endoscopy techniques for finding early pre-malignant lesions in Barretts esophagus. Results show that the discrimination occurs likely due to redistribution of blood content in the tissue sensed by the optical probing with the wavelength-dependent sampling depth.

Optical Scattering Properties of Intralipid Phantom in Presence of Encapsulated Microbubbles

In imaging, contrast agents are utilized to enhance sensitivity and specificity of diagnostic modalities. In ultrasound imaging, microbubbles (MBs)—a gas-core shell-encapsulated agent—are used clinically as contrast agents. The working hypothesis of this study is that microbubbles can be employed as an intravascular contrast agent in optical imaging systems. In this work, the interaction of light and microbubbles in a turbid medium (intralipid) was investigated, particularly, the effect of MBs on the reduced scattering and absorption coefficients. Diffuse reflectance (DR) and total transmittance (TT) measurements of highly scattering intralipid suspension (0.5–5%) were measured using spectroscopic integrating sphere system in the absence and presence of Definity microbubbles. The optical properties were computed using the inverse adding doubling (IAD) software. The presence of microbubbles increased DR and decreased TT of intralipid phantoms. In the presence of MBs (0.5% volume concentration), the reflectance of the intralipid phantom increased from 35% to 100%. The reduced scattering coefficient increased significantly (30%) indicating potential use of MBs as optical contrast agents in light based modalities.

LIMITATIONS OF CANCER MARGIN DELINEATION BY MEANS OF AUTOFLUORESCENCE IMAGING UNDER CONDITIONS OF LASER SURGERY

Limitations of cancer margin delineation and surgical guidance by means of autofluorescence imaging under conditions of laser ablation were investigated and preliminary results are presented. PinPoint™ (Novadaq Technologies Inc., Canada) was used to capture digital images and Er:YAG laser (2.94 μm, Glissando, WaveLight™, Germany) was exploited to cause laser ablation on both normal and cancer sites of the specimen. It was shown that changes of the autofluorescence image after ablation extend beyond the actual sizes of the ablation loci. The tumor tissue after the laser ablation starts to emit fluorescent light within the green wavelength band (490–550 nm) similar to normal tissue stating that the current technology of in-process tissue classification fails. However, when the autofluorescence was collected in the red range (600–750 nm), then the abnormal/normal contrast was reduced, but still present even after the laser ablation. The present study highlights the importance of finding a proper technology for surgical navigation of cancer removal under conditions of high power effects in biological tissues.

In vivo real time monitoring of vasoconstriction and vasodilation by a combined diffuse reflectance spectroscopy and Doppler optical coherence tomography approach

A combined diffuse reflectance (DR) spectroscopy and doppler optical coherence tomography (DOCT) approach may offer a powerful means for assessment of tissue function, and potentially provide a way for earlier cancer detection through non‐invasive local blood supply measurements. The goal of the study was to compare a DR‐derived blood‐content‐related index to a measure of local blood supply flow as furnished by DOCT during manipulations with blood circulation (vasoconstriction and vasodilation), investigate similarities and differences, complementarity of techniques, and then applying these results to the underlying biology.