Measurements of wavelength dependent scattering and backscattering coefficients by low-coherence spectroscopy

Quantitative measurements of scattering properties are invaluable for optical techniques in medicine. However, noninvasive, quantitative measurements of scattering properties over a large wavelength range remain challenging. We introduce low-coherence spectroscopy as a noninvasive method to locally and simultaneously measure scattering μs and backscattering μb coefficients from 480 to 700 nm with 8 nm spectral resolution. The method is tested on media with varying scattering properties (μs = 1 to 34 mm−1 and μb = 2.10−6 to 2.10−3 mm−1), containing different sized polystyrene spheres. The results are in excellent agreement with Mie theor

Quantitative measurements of absorption spectra in scattering media by low-coherence spectroscopy

Low-coherence spectroscopy (LCS) is a spectroscopic method that allows for quantitative and localized assessment of absorption spectra by combining reflection spectroscopy with low-coherence interferometry. We describe absorption coefficient (µa) measurements by LCS in tissue simulating phantoms with varying scattering and absorbing properties. We used LCS in the 455–680 nm wavelength range with a spectral resolution of 8 nmto obtain µa spectra with ±0.5 mm−1 accuracy. We conclude that LCS is a promising technique for the in vivo determination of tissue chromophore concentrations

Association between anaesthesia-related factors and postoperative neurocognitive disorder:a post-hoc analysis

BACKGROUND: Postoperative neurocognitive disorder (pNCD) is common after surgery. Exposure to anaesthetic drugs has been implicated as a potential cause of pNCD. Although several studies have investigated risk factors for the development of cognitive impairment in the early postoperative phase, risk factors for pNCD at 3 months have been less well studied. The aim of this study was to identify potential anaesthesia-related risk factors for pNCD at 3 months after surgery.METHODS: We analysed data obtained for a prospective observational study in patients aged ≥ 65 years who underwent surgery for excision of a solid tumour. Cognitive function was assessed preoperatively and at 3 months postoperatively using 5 neuropsychological tests. Postoperative NCD was defined as a postoperative decline of ≥ 25% relative to baseline in ≥ 2 tests. The association between anaesthesia-related factors (type of anaesthesia, duration of anaesthesia, agents used for induction and maintenance of anaesthesia and analgesia, the use of additional vasoactive medication, depth of anaesthesia [bispectral index] and mean arterial pressure) and pNCD was analysed using logistic regression analyses. Furthermore, the relation between anaesthesia-related factors and change in cognitive test scores expressed as a continuous variable was analysed using a z-score.RESULTS: Of the 196 included patients, 23 (12%) fulfilled the criteria for pNCD at 3 months postoperatively. A low preoperative score on Mini-Mental State Examination (OR, 8.9 [95% CI, (2.8-27.9)], p &lt; 0.001) and a longer duration of anaesthesia (OR, 1.003 [95% CI, (1.001-1.005)], p = 0.013) were identified as risk factors for pNCD. On average, patients scored higher on postoperative tests (mean z-score 2.35[± 3.13]).CONCLUSION: In this cohort, duration of anaesthesia, which is probably an expression of the complexity of the surgery, was the only anaesthesia-related predictor of pNCD. On average, patients' scores on cognitive tests improved postoperatively.</p

Multidiameter single-fiber reflectance spectroscopy of heavily pigmented skin:modeling the inhomogeneous distribution of melanin

When analyzing multidiameter single-fiber reflectance (MDSFR) spectra, the inhomogeneous distribution of melanin pigments in skin tissue is usually not accounted for. Especially in heavily pigmented skins, this can result in bad fits and biased estimation of tissue optical properties. A model is introduced to account for the inhomogeneous distribution of melanin pigments in skin tissue. In vivo visible MDSFR measurements were performed on heavily pigmented skin of type IV to VI. Skin tissue optical properties and related physiological properties were extracted from the measured spectra using the introduced model. The absorption of melanin pigments described by the introduced model demonstrates a good correlation with the co-localized measurement of the well-known melanin index. (C) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License

Body mass index is associated with microvascular endothelial dysfunction in patients with treated metabolic risk factors and suspected coronary artery disease

Background--Obesity is key feature of the metabolic syndrome and is associated with high cardiovascular morbidity and mortality. Obesity is associated with macrovascular endothelial dysfunction, a determinant of outcome in patients with coronary artery disease. Here, we compared the influence of obesity on microvascular endothelial function to that of established cardiovascular risk factors such as diabetes mellitus, hypertension, hypercholesterolemia, and smoking in patients with suspected coronary artery disease. Methods and Results--Endothelial function was assessed during postocclusive reactive hyperemia of the brachial artery and downstream microvascular beds in 108 patients who were scheduled for coronary angiography. In all patients, microvascular vasodilation was assessed using peripheral arterial tonometry; laser Doppler flowmetry and digital thermal monitoring were performed. Body mass index was significantly associated with decreased endothelium-dependent vasodilatation measured with peripheral arterial tonometry (r=0.23, P=0.02), laser Doppler flowmetry (r=0.30, P < 0.01), and digital thermal monitoring (r=0.30, P < 0.01). In contrast, hypertension, hypercholesterolemia, and smoking had no influence on microvascular vasodilatation. Especially in diabetic patients, endothelial function was not significantly reduced (control versus diabetes mellitus, mean±SEM or median [interquartile range], peripheral arterial tonometry: 1.90±0.20 versus 1.67±0.20, P=0.19, laser Doppler flowmetry: 728% [interquartile range, 427-1110] v

Simple and robust calibration procedure for k-linearization and dispersion compensation in optical coherence tomography

In Fourier-domain optical coherence tomography (FD-OCT), proper signal sampling and dispersion compensation are essential steps to achieve optimal axial resolution. These calibration steps can be performed through numerical signal processing, but require calibration information about the system that may require lengthy and complex measurement protocols. We report a highly robust calibration procedure that can simultaneously determine correction vectors for nonlinear wavenumber sampling and dispersion compensation. The proposed method requires only two simple mirror measurements and no prior knowledge about the system's illumination source or detection scheme. This method applies to both spectral domain and swept-source OCT systems. Furthermore, it may be implemented as a low-cost fail-safe to validate the proper function of calibration hardware such as k-clocks. We demonstrate the method's simple implementation, effectiveness, and robustness on both types of OCT systems

The ACRA Anatomy Study (Assessment of Disability After Coronary Procedures Using Radial Access): A Comprehensive Anatomic and Functional Assessment of the Vasculature of the Hand and Relation to Outcome After Transradial Catheterization

BACKGROUND: The palmar arches serve as the most important conduits for digital blood supply, and incompleteness may lead to digital ischemia when the radial artery becomes obstructed after cardiac catheterization. The rate of palmar arch incompleteness and the clinical consequences after transradial access are currently unknown.METHODS AND RESULTS: The vascular anatomy of the hand was documented by angiography in 234 patients undergoing transradial cardiac catheterization. In all patients, a preprocedural modified Allen test and Barbeau test were performed. Upper-extremity function was assessed at baseline and 2-year follow-up by the QuickDASH. Incompleteness of the superficial palmar arch (SPA) was present in 46%, the deep palmar arch was complete in all patients. Modified Allen test and Barbeau test results were associated with incompleteness of the SPA (P=0.001 and P=0.001). The modified Allen test had a 33% sensitivity and 86% specificity for SPA incompleteness with a cutoff value of >10 seconds and a 59% sensitivity and 60% specificity with a cutoff value of >5 seconds. The Barbeau test had a 7% sensitivity and 98% specificity for type D and a 21% sensitivity and 93% specificity for types C and D combined. Upper-extremity dysfunction was not associated with SPA incompleteness (P=0.77).CONCLUSIONS: Although incompleteness of the SPA is common, digital blood supply is always preserved by a complete deep palmar arch. Preprocedural patency tests have thus no added benefit to prevent ischemic complications of the hand. Finally, incompleteness of the SPA is not associated with a loss of upper-extremity function after transradial catheterization