Chromophore reconstruction at depth in bilayered media: a method for quantification.

We report a method for deriving the absolute value of absorption coefficients at depth in bilayered media. The method was simplified from that of time-resolved diffuse optical tomography (TR-DOT) into one dimension to validate and set up the main parameters with the help of simulations, and to test it in an easy preclinical model. The method was applied to buried flaps as used in reconstructive surgery, and absolute chromophore concentrations in the flap and in the upper (skin and fat) layer were derived. The encouraging results obtained lay a foundation for developing more complex multidimensional models.

Noninvasive Monitoring of Deep Tissue Oxygenation in Buried Flaps by Time-Resolved Near-Infrared Spectroscopy in Pigs.

BACKGROUND: Flap monitoring in reconstructive surgery is particularly important because flap failure is a dramatic event for the patient and for the medical team. Noninvasive deep tissue oxygenation monitoring is a challenge. The aim of this experimental study was to assess the performance of time-resolved near-infrared spectroscopy compared with continuous-wave near-infrared spectroscopy and with invasive oxygen partial pressure measurement in pigs. METHODS: Thirty fasciocutaneous flaps based on the superficial epigastric inferior pedicle were harvested and buried under the transcutaneous dorsal muscle (approximately 1 cm thick). An optical probe was placed on the skin above each buried flap. For each pig, two buried flaps were performed, one submitted to arterial occlusion and one to venous occlusion. Oxyhemoglobin and deoxyhemoglobin concentrations were observed for over 40 minutes before clamping, almost 20 minutes during clamping and during a period of release of approximately 20 minutes. Variations in time-resolved near-infrared spectroscopy were compared to the oxygen partial pressure and continuous-wave near-infrared spectroscopy variations. RESULTS: All vascular events were detected by the time-resolved near-infrared spectroscopy. During arterial clamping, oxyhemoglobin decreased rapidly, whereas deoxyhemoglobin increased moderately. The divergence of oxyhemoglobin and deoxyhemoglobin curves indicated arterial occlusion. During venous clamping, deoxyhemoglobin increased, whereas oxyhemoglobin increased briefly then remained stable or decreased moderately. The initial increases in the oxyhemoglobin and deoxyhemoglobin curves indicated venous occlusion. Oxygen partial pressure failed to detect vascular events in three cases. Continuous-wave near-infrared spectroscopy could not clearly identify vascular occlusions. CONCLUSIONS: Thus, the authors demonstrated the relevance of time-resolved near-infrared spectroscopy to buried flap monitoring. Time-resolved near-infrared spectroscopy could differentiate between arterial occlusion and venous occlusion.

Distinction between arterial and venous occlusion with tissue oxygen pressure in a porcine fascio-cutaneous flap model.

BACKGROUND: In recent years, many devices have been developed to monitor free flaps. The Licox probe, which measures tissue oxygen pressure (PtO2 ), is one of the available devices. Our aim was to demonstrate that PtO2 could distinguish arterial from venous occlusion in a porcine fascio-cutaneous flap model. MATERIALS AND METHODS: Twenty pigs (Sus scrofa domestica, Youna strain, males) were included in this study. The median weight was 87.6 kg (84.6-90.8). Bilateral fascio-cutaneous flaps based on the superficial inferior epigastric pedicle were harvested from each pig. Thirty-eight flaps were analyzed in this study and were monitored by a Licox system during vascular occlusion. The flaps were randomized into two groups according to the clamped vessel: the arterial group (n = 19) and the venous group (n = 19). After a stabilization period of almost 40 min, vascular clamping (arterial or venous) was performed using a microvascular clamp for almost 20 min. The curve profiles were compared between arterial and venous occlusion. RESULTS: The inflection point was reached significantly faster in the arterial group: 11 min (9-16) for arterial clamping and 17 min (13-23) for venous clamping (p = .001). A total of 18/19 (95%) pigs in the arterial group and 13/19 (68%) in the venous group (p = .09) reached a level lower than 10 mmHg. The median duration for pressure to drop below 10 mmHg was 9 min (6-12) for arterial clamping and 10 min (9-16) for venous clamping (p = .06). CONCLUSION: We showed that PtO2 decreased faster in cases of arterial occlusion than in cases of venous occlusion in a pig model. Based on this observation, it may be possible to distinguish arterial from venous occlusion.

Validation of optical properties quantification with a dual-step technique for biological tissue analysis.

To approach wide-field optical properties quantification in real heterogeneous biological tissue, we developed a Dual-Step setup that couples a punctual diffuse reflectance spectroscopy (DRS) technique with multispectral imaging (MSI). The setup achieves wide-field optical properties assessment through an initial estimation of scattering with DRS, which is used to estimate absorption with MSI. The absolute quantification of optical properties is based on the ACA-Pro algorithm that has been adapted both for DRS and for MSI. This paper validates the Dual-Step system not only on homogeneous Intralipid phantoms but also on a heterogeneous gelatine phantom with different scattering and absorbing properties.

Management of non variceal upper gastrointestinal bleeding: position statement of the Catalan Society of Gastroenterology. / Manejo de la hemorragia digestiva alta no varicosa: documento de posicionamiento de la Societat Catalana de Digestologia.

In recent years there have been advances in the management of non-variceal upper gastrointestinal bleeding that have helped reduce rebleeding and mortality. This document positioning of the Catalan Society of Digestologia is an update of evidence-based recommendations on management of gastrointestinal bleeding peptic ulcer.

Rate of adverse events of gastroduodenal snare polypectomy for non-flat polyp is low: A prospective and multicenter study.

AIM: To evaluate the rate of adverse events (AEs) during consecutive gastric and duodenal polypectomies in several Spanish centers. METHODS: Polypectomies of protruded gastric or duodenal polyps ≥ 5 mm using hot snare were prospectively included. Prophylactic measures of hemorrhage were allowed in predefined cases. AEs were defined and graded according to the lexicon recommended by the American Society for Gastrointestinal Endoscopy. Patients were followed for 48 h, one week and 1 mo after the procedure. RESULTS: 308 patients were included and a single polypectomy was performed in 205. Only 36 (11.7%) were on prior anticoagulant therapy. Mean polyp size was 15 ± 8.9 mm (5-60) and in 294 cases (95.4%) were located in the stomach. Hemorrhage prophylaxis was performed in 219 (71.1%) patients. Nine patients presented AEs (2.9%), and 6 of them were bleeding (n = 6, 1.9%) (in 5 out of 6 AE, different types of endoscopic treatment were performed). Other 24 hemorrhagic episodes could be managed without any change in the outcome of the endoscopy and, consequently, were considered incidents. We did not find any independent risk factor of bleeding. CONCLUSION: Gastroduodenal polypectomy using prophylactic measures has a rate of AEs small enough to consider this procedure a safe and effective method for polyp resection independently of the polyp size and location.

ACA-Pro: calibration protocol for quantitative diffuse reflectance spectroscopy. Validation on contact and noncontact probe- and CCD-based systems.

We have developed an adaptive calibration algorithm and protocol (ACA-Pro) that corrects from the instrumental response of various spatially resolved diffuse reflectance spectroscopy (DRSsr) systems to enable the quantification of absorption and scattering properties based on a Monte Carlo-based look-up-table approach. The protocol involves the use of a calibration reference base built with measurements of a range of different diffusive intralipid phantoms. Moreover, an advanced strategy was established to take into account the experimental variations with an additional measurement of a common solid material, allowing the use of a single calibration reference base for all experiments. The ACA-Pro is validated in contact and noncontact probe-based DRSsr systems. Furthermore, the first results of a setup replacing the probe with a CCD detector are shown to confirm the robustness of the approach.

Toward noninvasive assessment of flap viability with time-resolved diffuse optical tomography: a preclinical test on rats.

The noninvasive assessment of flap viability in autologous reconstruction surgery is still an unmet clinical need. To cope with this problem, we developed a proof-of-principle fully automatized setup for fast time-gated diffuse optical tomography exploiting Mellin-Laplace transform to obtain three-dimensional tomographic reconstructions of oxy- and deoxy-hemoglobin concentrations. We applied this method to perform preclinical tests on rats inducing total venous occlusion in the cutaneous abdominal flaps. Notwithstanding the use of just four source-detector couples, we could detect a spatially localized increase of deoxyhemoglobin following the occlusion (up to 550 µM in 54 min). Such capability to image spatio-temporal evolution of blood perfusion is a key issue for the noninvasive monitoring of flap viability.

Improving Surgical Resection of Metastatic Liver Tumors With Near-Infrared Optical-Guided Fluorescence Imaging.

Objective The aim of this study was to investigate the feasibility and future clinical applications of near-infrared (NIR) fluorescence imaging to guide liver resection surgery for metastatic cancer to improve resection margins. Summary Background Data A subset of patients with metastatic hepatic tumors can be cured by surgery. The degree of long-term and disease-free survival is related to the quality of surgery, with the best resection defined as "R0" (complete removal of all tumor cells, as evidenced by microscopic examination of the margins). Although intraoperative ultrasonography can evaluate the surgical margins, surgeons need a new tool to perfect the surgical outcome. Methods A preliminary study was performed on 3 patients. We used NIR imaging postoperatively "ex vivo" on the resected liver tissue. The liver tumors were preoperatively labelled by intravenously injecting the patient with indocyanine green (ICG), a NIR fluorescent agent (24 hours before surgery, 0.25 mg/kg). Fluorescent images were obtained using a miniaturized fluorescence imaging system (FluoStic, Fluoptics, Grenoble, France). Results After liver resection, the surgical specimens from each patient were sliced into 10-mm sections in the operating room and analyzed with the FluoStic. All metastatic tumors presented rim-type fluorescence. Two specimens had incomplete rim fluorescence. The pathologist confirmed the presence of R1 margins (microscopic residual resection), even though the ultrasonographic analysis indicated that the result was R0. Conclusions Surgical liver resection guided by NIR fluorescence can help detect potentially uncertain anatomical areas that may be missed by preoperative imaging and by ultrasonography during surgery. These preliminary results will need to be confirmed in a larger prospective patient series.

Photobiomodulation inside the brain: a novel method of applying near-infrared light intracranially and its impact on dopaminergic cell survival in MPTP-treated mice.

OBJECT: Previous experimental studies have documented the neuroprotection of damaged or diseased cells after applying, from outside the brain, near-infrared light (NIr) to the brain by using external light-emitting diodes (LEDs) or laser devices. In the present study, the authors describe an effective and reliable surgical method of applying to the brain, from inside the brain, NIr to the brain. They developed a novel internal surgical device that delivers the NIr to brain regions very close to target damaged or diseased cells. They suggest that this device will be useful in applying NIr within the large human brain, particularly if the target cells have a very deep location. METHODS: An optical fiber linked to an LED or laser device was surgically implanted into the lateral ventricle of BALB/c mice or Sprague-Dawley rats. The authors explored the feasibility of the internal device, measured the NIr signal through living tissue, looked for evidence of toxicity at doses higher than those required for neuroprotection, and confirmed the neuroprotective effect of NIr on dopaminergic cells in the substantia nigra pars compacta (SNc) in an acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of Parkinson disease in mice. RESULTS: The device was stable in freely moving animals, and the NIr filled the cranial cavity. Measurements showed that the NIr intensity declined as distance from the source increased across the brain (65% per mm) but was detectable up to 10 mm away. At neuroprotective (0.16 mW) and much higher (67 mW) intensities, the NIr caused no observable behavioral deficits, nor was there evidence of tissue necrosis at the fiber tip, where radiation was most intense. Finally, the intracranially delivered NIr protected SNc cells against MPTP insult; there were consistently more dopaminergic cells in MPTP-treated mice irradiated with NIr than in those that were not irradiated. CONCLUSIONS: In summary, the authors showed that NIr can be applied intracranially, does not have toxic side effects, and is neuroprotective.

Depth probing of diffuse tissues controlled with elliptically polarized light.

Polarization gating is a popular technique in biomedical optics. It is widely used to inspect the surface of the tissues (under colinear or cocircular detection) or instead to probe the volume (cross-linear detection), without information on the probed depth. Elliptical polarization is introduced to explore the possibility of probing diffuse tissues at selective depths. A thorough Monte Carlo simulation study shows complete correlation between the probed depths and the ellipticity of the polarized light, for a medium with known optical properties. Within a wide range of optical parameters, a linear relation between the backscattered intensity and the depth extension of the probed volume was found whatever the polarization used, but with a controlled extension depending on the ellipticity.

FluoSTIC: miniaturized fluorescence image-guided surgery system.

Over the last few years, near-infrared (NIR) fluorescence imaging has witnessed rapid growth and is already used in clinical trials for various procedures. However, most clinically compatible imaging systems are optimized for large, open-surgery procedures. Such systems cannot be employed during head and neck oncologic surgeries because the system is not able to image inside deep cavities or allow the surgeon access to certain tumors due to the large footprint of the system. We describe a miniaturized, low-cost, NIR fluorescence system optimized for clinical use during oral oncologic surgeries. The system, termed FluoSTIC, employs a miniature, high-quality, consumer-grade lipstick camera for collecting fluorescence light and a novel custom circular optical fiber array for illumination that combines both white light and NIR excitation. FluoSTIC maintains fluorescence imaging quality similar to that of current large-size imaging systems and is 22 mm in diameter and 200 mm in height and weighs less than 200 g.

Cell tolerability and biodistribution in mice of indocyanine green-loaded lipid nanoparticles.

Considering toxicity requirements for clinical translation of fluorescence imaging applications, the use of biocompatible carriers for designing near infrared emitting contrast agents appears as an attractive alternative to semiconductor nanocrystals. Lipid nanoparticles (LNP) have been designed to serve as carriers for indocyanine green (ICG), the presently only human-use approved near infrared dye. The cytotoxicity and hemocompatibility of these nanoparticle-based probes are determined in vitro, respectively in mouse 3T3 fibroblasts and human blood samples. Comparative biodistribution of free ICG and ICG-LNP in mice is monitored, and an ex vivo fluorescence organ quantification is performed considering large animal cohorts. Good tolerability and very low hemolytic activity are demonstrated for naked and ICG-loaded LNP. Interestingly, ICG-LNP lead to long-term plasma fluorescence (> 24 hours) but also a partial intestinal reabsorption of ICG between 5 and 24 hours after injection. This novel ICG nanoformulation is foreseen to expand rapidly the field of clinical fluorescence imaging applications.

Lipid nanoparticle vectorization of indocyanine green improves fluorescence imaging for tumor diagnosis and lymph node resection.

Fluorescence imaging is opening a new era in image-guided surgery and other medical applications. The only FDA approved contrast agent in the near infrared is IndoCyanine Green (ICG), which despites its low toxicity, displays poor chemical and optical properties for long-term and sensitive imaging applications in human. Lipid nanoparticles are investigated for improving ICG optical properties and in vivo fluorescence imaging sensitivity. 30 nm diameter lipid nanoparticles (LNP) are loaded with ICG. Their characterization and use for tumor and lymph node imaging are described. Nano-formulation benefits dye optical properties (6 times improved brightness) and chemical stability (>6 months at 4 degrees C in aqueous buffer). More importantly, LNP vectorization allows never reported sensitive and prolonged (>1 day) labeling of tumors and lymph nodes. Composed of human-use approved ingredients, this novel ICG nanometric formulation is foreseen to expand rapidly the field of clinical fluorescence imaging applications.

Fluorescence diffuse optical tomography for free-space and multifluorophore studies.

We present two major advances in preclinical fluorescence-enhanced diffuse optical tomography (fDOT) system and assess its performance. It is now possible to perform experiments without adaptation liquid or a glass plate over the animal, and our system is equipped with a filter wheel in order to discriminate two injected fluorophores. Evaluation carried out on characterization phantoms and in vivo on mice demonstrates enriched use of the system for biological studies on small animals.

Estimation of optical properties of turbid media: experimental comparison of spatially and temporally resolved reflectance methods.

We compare two methods for the optical characterization of turbid media. The estimates of the absorption and reduced scattering coefficients (mu(a) and mu(')(s)) by a spatially resolved method and a time-resolved method are performed on tissue-like phantoms. Aqueous suspension of microspheres and Intralipid are used as scattering media with the addition of ink as an absorber. mu(')(s) is first measured on weakly absorbing media. The robustness of these measurements is then tested with respect to a variation of mu(a). The spatially resolved method gave more accurate estimates for mu(')(s) whereas the time-resolved method gave better results for mu(a) estimates.

In vivo mice lung tumor follow-up with fluorescence diffuse optical tomography.

We present in vivo experiments conducted with a new fluorescence diffuse optical tomographic (fDOT) system on cancerous mice bearing mammary murine tumors. We first briefly present this new system that has been developed and its associated reconstruction method. Its main specificity is its ability to reconstruct the fluorescence yield even in heterogeneous and highly attenuating body regions such as lungs and to enable mouse inspection without immersion in optical index matching liquid (Intralipid and ink). Some phantom experiments validate the performance of this new system for heterogeneous media inspection. Its use for a mice study is then related. It consists in the follow-up of the lungs at different stages of tumor development after injection of RAFT-(cRGD)4-Alexa700. As expected, the reconstructed fluorescence increases along with the tumor stage. These results validate the use of our system for biological studies of small animals.

Effects of the surface boundary on the determination of the optical properties of a turbid medium with time-resolved reflectance.

Solutions of the time-dependent diffusion equation were developed to take into account the depth of the source and the detector inside a semi-infinite medium. These solutions permitted an evaluation of optical properties at different depths below the surface by fitting time-resolved data. Measurements were performed on liquid optical phantoms with optical fibers for delivering and collecting light. A time-correlated single-photon-counting chain was used for electronic detection. The determination of optical properties underlines the continuity between the surface model and the infinite model and shows the depth at which the derived solutions can be applied.

Photochemical patterning of biological molecules inside a glass capillary.

A simple way for photochemical patterning of biological molecules onto the inner wall of fused-silica capillary is described. The method is based on a modification of the inner capillary surface with photoactive benzophenone (BP) derivative. The UV irradiation at 365 nm of the capillary filled with a sample solution results in cross-linking of the solutes to the BP moiety via a stable covalent bond. As a proof of concept, oligonucleotides and proteins were arrayed inside the capillary using an inverted microscope as an irradiation device. We demonstrated that the capillary arrays produced in this way are functional and could be used in different bioassays including DNA hybridization, protein interaction studies, and immunoassays. Having a sensitivity comparable to the fluorophore-based assays in a planar format, the capillary array possesses several advantages including submicroliter sample volume and a short assay time. The capillary format should therefore be considered as a possible alternative to a planar format in a number of low-density array applications such as mutation detection and diagnostic immunoassays.

Withholding or withdrawing dialysis in the elderly: the perspective of a western region of France.

BACKGROUND: In the US and Canada, dialysis discontinuation is one of the more frequent causes of death in elderly patients on haemodialysis, particularly after the age of 75. The aim of this study was to analyse the practices of some French nephrologists, 17 of whom (in six nephrology units) were interviewed for this study. METHODS: A questionnaire was formulated on the basis of a bibliographical search of the topic. A series of questions, initially open and then more targeted, regarding scientific and non-scientific factors influencing the decision to discontinue or refuse haemodialysis in elderly patients, were put to nephrologists. RESULTS: Psychological and physical deterioration emerged as the principal factors governing decisions to refuse or discontinue treatment. The interviewees felt that severe dementia (15 out of 17 nephrologists), irreversible neurological sequelae of a CVA (11 out of 17) and, paradoxically, patient refusal (10 out of 17) were factors to be taken into account in the decision to discontinue haemodialysis. Although the main reasons for refusing dialysis were cognitive disorders, severe dementia and irreversible neurological conditions, none of these factors where actually found to be in and of themselves decisive. CONCLUSIONS: This study has shown that refusing or discontinuing dialysis are practices accepted by the vast majority of nephrologists in one region of France. Patient refusal is not a basis for denial or discontinuation of dialysis in elderly patients. Our investigation has demonstrated a consensus regarding decisions to refuse or discontinue dialysis.