Optical fiber probe spectroscopy for laparoscopic monitoring of tissue oxygenation during esophagectomies

Fiberoptic hemodynamic spectroscopy reveals abnormal cerebrovascular reactivity in a freely moving mouse model of Alzheimer's disease

Many Alzheimer's disease (AD) patients suffer from altered cerebral blood flow and damaged cerebral vasculature. Cerebrovascular dysfunction could play an important role in this disease. However, the mechanism underlying a vascular contribution in AD is still unclear. Cerebrovascular reactivity (CVR) is a critical mechanism that maintains cerebral blood flow and brain homeostasis. Most current methods to analyze CVR require anesthesia which is known to hamper the investigation of molecular mechanisms underlying CVR. We therefore combined spectroscopy, spectral analysis software, and an implantable device to measure cerebral blood volume fraction (CBVF) and oxygen saturation (SO2) in unanesthetized, freely-moving mice. Then, we analyzed basal CBVF and SO2, and CVR of 5-month-old C57BL/6 mice during hypercapnia as well as during basic behavior such as grooming, walking and running. Moreover, we analyzed the CVR of freely-moving AD mice and their wildtype (WT) littermates during hypercapnia and could find impaired CVR in AD mice compared to WT littermates. Our results suggest that this optomechanical approach to reproducibly getting light into the brain enabled us to successfully measure CVR in unanesthetized freely-moving mice and to find impaired CVR in a mouse model of AD.

Evaluation of visible diffuse reflectance spectroscopy in liver tissue: validation of tissue saturations using extracorporeal circulation

SIGNIFICANCE

Real-time information about oxygen delivery to the hepatic graft is important to direct care and diagnose vascular compromise in the immediate post-transplant period.

AIM

The current study was designed to determine the utility of visible diffuse reflectance spectroscopy (vis-DRS) for measuring liver tissue saturation in vivo.

APPROACH

A custom-built vis-DRS probe was calibrated using phantoms with hemoglobin (Hb) and polystyrene microspheres. Ex vivo (extracorporeal circulation) and in vivo protocols were used in a swine model (n  =  15) with validation via blood gas analysis.

RESULTS

In vivo absorption and scattering measured by vis-DRS with and without biliverdin correction correlated closely between analyses. Lin's concordance correlation coefficients are 0.991 for μa and 0.959 for μs  '  . Hb measured by blood test and vis-DRS with (R2  =  0.81) and without (R2  =  0.85) biliverdin correction were compared. Vis-DRS data obtained from the ex vivo protocol plotted against the PO2 derived from blood gas analysis showed a good fit for a Hill coefficient of 1.67 and P50  =  34  mmHg (R2  =  0.81). A conversion formula was developed to account for the systematic deviation, which resulted in a goodness-of-fit R2  =  0.76 with the expected oxygen dissociation curve.

CONCLUSIONS

We show that vis-DRS allows for real-time measurement of liver tissue saturation, an indicator for liver perfusion and oxygen delivery.

Risk Factors of Cervical Anastomotic Leakage after McKeown Minimally Invasive Esophagectomy: Focus on Preoperative and Intraoperative Lung Function

Background: Cervical anastomotic leakage (CAL) is one of the most common complications that occur minimally invasive esophagectomy (MIE). It is associated with high postoperative mortality. Some risk factors still remained controversial and so accurate prediction of risk groups for CAL remained very difficult. This study aimed to identify the risk factors of CAL after McKeown MIE to predict the accuracy of the technique as early as possible.

Material and Methods: A total of 129 patients with esophageal cancer who underwent McKeown MIE at the Department of Thoracic Surgery, the Fourth Hospital of Hebei Medical University, between January 2018 and June 2019 were retrospectively reviewed. Multivariate logistic regression analysis was used to identify the risk factors for CAL and receiver operating characteristic (ROC) curve analysis was used to predict the accuracy for each quantitative data variable and determine the cutoff value.

Results: There were statistically significant differences between Group CAL and Group NCAL in FEV₁ (p = 0.031), neoadjuvant chemotherapy (p = 0.001), intraoperative minimum PaCO₂ (p = 0.002), and hospital stays (p <0.001). In multivariate logistic regression, FEV₁ (OR = 0.440, p = 0.047), neoadjuvant chemotherapy (OR = 4.425, p = 0.003), and intraoperative minimum PaCO₂ (OR = 1.14, p <0.001) were identified to be three risk factors of CAL. The ROC curve analysis showed that FEV₁ <2.18L (p = 0.029) and intraoperative minimum PaCO₂ >45.5 mmHg (p = 0.002) demonstrated good accuracy.

Conclusion: FEV₁, neoadjuvant chemotherapy, and intraoperative minimum PaCO₂ in arterial blood gas (ABG) were considered as risk factors of CAL after McKeown MIE for esophageal cancer. Preoperative FEV₁ <2.18L and intraoperative minimum PaCO₂ >45.5 mmHg in ABG showed good accuracy in predicting risk factors for CAL.

Laser Doppler Flowmetry and Visible Light Spectroscopy of the Gastric Tube During Minimally Invasive Esophagectomy

Introduction

Ischemia is considered as the main reason for thoracic gastroesophageal anastomotic leaks after esophagectomy. Microcirculatory monitoring with laser Doppler flowmetry and visible light spectroscopy may provide valuable intraoperative real-time information about the gastric tube’s tissue perfusion and circulation.

Patients and Methods

Ten patients with esophageal cancer operated with minimally invasive esophagectomy participated in this single-center, prospective, observational pilot study. A single probe with laser Doppler flowmetry and visible light spectroscopy was used to perform transserosal microcirculation assessment of the gastric tube at predefined anatomical sites during different operation phases. Group comparison and changes were evaluated using the paired sample t-test.

Results

A reduction in StO2 was found at all measuring sites after the gastric tube formation compared with the baseline measurements. The mean StO2 reduction from baseline to gastric tube formation and after anastomosis was 16% (range 4%–28%) and 42% (range, 35%–52%), respectively. A statistically significant increase in the rHb concentration, representing venous congestion, was detected at the most cranial part of the gastric tube (P = 0.04). Three patients developed anastomotic leaks.

Conclusion

Intraoperative real-time laser Doppler flowmetry and visible light spectroscopy are feasible and may provide insight to microcirculatory changes in the gastric tube and at the anastomotic site. Patients with anastomotic leaks seem to have critical local tissue StO2 reduction and venous congestion that should be further evaluated in studies with larger sample sizes.

A prospective trial of intraoperative tissue oxygenation measurement and its association with anastomotic leak rate after Ivor Lewis esophagectomy

Background

Anastomotic leak following Ivor Lewis esophagectomy is associated with increased morbidity/mortality and decreased survival. Tissue oxygenation at the anastomotic site may influence anastomotic leak. Methods for establishing tissue oxygenation at the anastomotic site are lacking.

Methods

Over a 2-year study period, 185 Ivor Lewis esophagectomies were performed. Study participants underwent measurement of gastric conduit tissue oxygenation at the planned anastomotic site using the wireless pulse oximetry device. Associations between anastomotic leaks or strictures and tissue oxygenation levels were analyzed using Wilcoxon rank sum test or Fisher’s exact test.

Results

Among study participants (n=114), median gastric conduit tissue oxygenation level was 92% (range, 62–100%). There were 8 (7.0%) anastomotic leaks and 3 (2.6%) strictures. Analysis of tissue oxygenation as a continuous variable showed no difference in median tissue oxygenation in patients with and without leaks (98% and 92%; P=0.2) and stricture formation (89% and 92%; P=0.6). Analysis of tissue oxygenation as a dichotomous variable found no difference in anastomotic leak rates [7.5% (n=93) in >80% vs. 0% (n=20) in ≤80%; P=0.3]. There were no significant differences in leak rates in concurrent study nonparticipants.

Conclusions

No significant association was observed between intraoperative tissue oxygenation at the anastomotic site and subsequent anastomotic leak or stricture formation among patients undergoing Ivor Lewis esophagectomy.

Laparoscopic diffuse reflectance spectroscopy of an underlying tubular inclusion: a phantom study

We demonstrate diffuse reflectance spectroscopy (DRS) of a subsurface tubular inclusion by using a fiber probe having a single source-detector pair attached to a laparoscopic bipolar device. A forward model was also developed for DRS sensing of an underlying long absorbing tubular inclusion set in parallel to the tissue surface, normal to the line of sight of the source-detector pair, and equidistant from the source and the detector. The model agreed with measurements performed at 500 nm and using a 10 mm source-detector separation (SDS) on an aqueous tissue phantom embedding a tubing of 2 or 4 mm inner diameter that contained 9.1% to 33.3% red dye at a depth of up to 11.5 mm. When tested on solid phantoms using the 10 mm SDS, a tubular inclusion of $ \ge 3\;{\rm mm}$≥3mm inner diameter containing 0.05% red dye at a background absorption coefficient of $ 0.021\;{\rm mm}^{-1} $0.021mm^-1 caused $ \ge 8\% $≥8% change of the signal at 500 nm versus the baseline when the inclusion was shallower than 5 mm. When assessed on avian muscle tissue having a 4 mm tubular inclusion embedded at an edge depth of 2 mm, DRS with the 10 mm SDS differentiated the following contents of the inclusion: 33.3% red dye (mimicking blood), 33.3% green dye, 33.3% yellow dye (mimicking bile), water (mimicking urine), and air.

Hyperspectral imaging in automated digital dermoscopy screening for melanoma

Objectives

Early melanoma detection decreases morbidity and mortality. Early detection classically involves dermoscopy to identify suspicious lesions for which biopsy is indicated. Biopsy and histological examination then diagnose benign nevi, atypical nevi, or cancerous growths. With current methods, a considerable number of unnecessary biopsies are performed as only 11% of all biopsied, suspicious lesions are actually melanomas. Thus, there is a need for more advanced noninvasive diagnostics to guide the decision of whether or not to biopsy. Artificial intelligence can generate screening algorithms that transform a set of imaging biomarkers into a risk score that can be used to classify a lesion as a melanoma or a nevus by comparing the score to a classification threshold. Melanoma imaging biomarkers have been shown to be spectrally dependent in Red, Green, Blue (RGB) color channels, and hyperspectral imaging may further enhance diagnostic power. The purpose of this study was to use the same melanoma imaging biomarkers previously described, but over a wider range of wavelengths to determine if, in combination with machine learning algorithms, this could result in enhanced melanoma detection.

Methods

We used the melanoma advanced imaging dermatoscope (mAID) to image pigmented lesions assessed by dermatologists as requiring a biopsy. The mAID is a 21‐wavelength imaging device in the 350–950 nm range. We then generated imaging biomarkers from these hyperspectral dermoscopy images, and, with the help of artificial intelligence algorithms, generated a melanoma Q‐score for each lesion (0 = nevus, 1 = melanoma). The Q‐score was then compared to the histopathologic diagnosis.

Results

The overall sensitivity and specificity of hyperspectral dermoscopy in detecting melanoma when evaluated in a set of lesions selected by dermatologists as requiring biopsy was 100% and 36%, respectively.

Conclusion

With widespread application, and if validated in larger clinical trials, this non‐invasive methodology could decrease unnecessary biopsies and potentially increase life‐saving early detection events. Lasers Surg. Med. 51:214–222, 2019. © 2019 The Authors. Lasers in Surgery and Medicine Published by Wiley Periodicals, Inc.

Bayesian analyses demonstrate tissue blood volume is not decreased during acute sickle cell pain episodes: A preliminary study

BACKGROUND

Pain is the most common complication of Sickle Cell Disease (SCD). Tissue oximetry properties in SCD during steady state and acute pain are not well described.

METHODS

This was a cross sectional study of tissue oximetry properties in individuals with SCD during steady state, acute pain and healthy controls without SCD. A novel tissue oximetry device was used to better account for tissue pigmentation interference. We hypothesized that during acute SCD pain, blood volume to painful areas would be at least 10% less than steady state. Bayesian analyses of the data (with flat piors) were planned a priori because of the small projected sample size.

RESULTS

The sample included 14 individuals (4 during crisis, 5 steady state, and 5 controls). In individuals with SCD, blood volume to the lower back was higher during crisis (0.18% of tissue volume vs. 0.14% ). Bayesian analyses yielded a 3% probability that our hypothesis (that blood volume would decrease by 10% ) was correct.

CONCLUSIONS

During acute SCD pain, blood volume to painful areas is not decreased. Bayesian analyses were useful for interpretation of small sample data and may have utility in early phase trials for rare diseases.

Optical absorption and scattering properties of bulk porcine muscle phantoms from interstitial radiance measurements in 650-900 nm range

We demonstrated the application of relative radiance-based continuous wave (cw) measurements for recovering absorption and scattering properties (the effective attenuation coefficient, the diffusion coefficient, the absorption coefficient and the reduced scattering coefficient) of bulk porcine muscle phantoms in the 650-900 nm spectral range. Both the side-firing fiber (the detector) and the fiber with a spherical diffuser at the end (the source) were inserted interstitially at predetermined locations in the phantom. The porcine phantoms were prostate-shaped with ∼4 cm in diameter and ∼3 cm thickness and made from porcine loin or tenderloin muscles. The described method was previously validated using the diffusion approximation on simulated and experimental radiance data obtained for homogenous Intralipid-1% liquid phantom. The approach required performing measurements in two locations in the tissue with different distances to the source. Measurements were performed on 21 porcine phantoms. Spectral dependences of the effective attenuation and absorption coefficients for the loin phantom deviated from corresponding dependences for the tenderloin phantom for wavelengths <750 nm. The diffusion constant and the reduced scattering coefficient were very close for both phantom types. To quantify chromophore presence, the plot for the absorption coefficient was matched with a synthetic absorption spectrum constructed from deoxyhemoglobin, oxyhemoglobin and water. The closest match for the porcine loin spectrum was obtained with the following concentrations: 15.5 µM (±30% s.d.) Hb, 21 µM (±30% s.d.) HbO2 and 0.3 (±30% s.d.) fractional volume of water. The tenderloin absorption spectrum was best described by 30 µM Hb (±30% s.d), 19 µM (±30% s.d.) HbO2 and 0.3 (±30% s.d.) fractional volume of water. The higher concentration of Hb in tenderloin was consistent with a dark-red appearance of the tenderloin phantom. The method can be applied to a number of biological tissues and organs for interstitial optical interrogation.