Polydimethylsiloxane tissue-mimicking phantoms with tunable optical properties

SIGNIFICANCE

The polymer, polydimethylsiloxane (PDMS), has been increasingly used to make tissue simulating phantoms due to its excellent processability, durability, flexibility, and limited tunability of optical, mechanical, and thermal properties. We report on a robust technique to fabricate PDMS-based tissue-mimicking phantoms where the broad range of scattering and absorption properties are independently adjustable in the visible- to near-infrared wavelength range from 500 to 850 nm. We also report on an analysis method to concisely quantify the phantoms' broadband characteristics with four parameters.

AIM

We report on techniques to manufacture and characterize solid tissue-mimicking phantoms of PDMS polymers. Tunability of the absorption (μa  (  λ  )  ) and reduced scattering coefficient spectra (μs'(λ)) in the wavelength range of 500 to 850 nm is demonstrated by adjusting the concentrations of light absorbing carbon black powder (CBP) and light scattering titanium dioxide powder (TDP) added into the PDMS base material.

APPROACH

The μa  (  λ  )   and μs'(λ) of the phantoms were obtained through measurements with a broadband integrating sphere system and by applying an inverse adding doubling algorithm. Analyses of μa  (  λ  )   and μs'(λ) of the phantoms, by fitting them to linear and power law functions, respectively, demonstrate that independent control of μa  (  λ  )   and μs'(λ) is possible by systematically varying the concentrations of CBP and TDP.

RESULTS

Our technique quantifies the phantoms with four simple fitting parameters enabling a concise tabulation of their broadband optical properties as well as comparisons to the optical properties of biological tissues. We demonstrate that, to a limited extent, the scattering properties of our phantoms mimic those of human tissues of various types. A possible way to overcome this limitation is demonstrated with phantoms that incorporate polystyrene microbead scatterers.

CONCLUSIONS

Our manufacturing and analysis techniques may further promote the application of PDMS-based tissue-mimicking phantoms and may enable robust quality control and quality checks of the phantoms.

When rotational atherectomy is not enough

Extreme coronary calcification may require rotational atherectomy to create a navigable intravascular lumen followed by intravascular lithotripsy to fracture areas of deep calcification to allow for successful percutaneous coronary intervention.

Reducing Delay to Treatment of ST-Elevation Myocardial Infarction With Software Electrocardiographic Interpretation and Transmission (SCINET)

Background

Prehospital diagnosis of ST-elevation myocardial infarction (STEMI) has resulted in improved outcomes. However, many patients still walk in to the emergency department (ED) with STEMI, experiencing delays and worse outcomes. Software electrocardiogram (ECG) diagnosis of STEMI and electronic transmission to a cardiologist may result in improved door-to-device (D2D) times.

Methods

We retrospectively identified all patients presenting with STEMI from January 2015 to September 2016. Components of delay in D2D, ED variables, and the patients’ ECGs were extracted from our regional database. All ECGs performed for suspected myocardial infarction in the region were extracted over the study period. We assessed the accuracy of the software 12SL in diagnosing STEMI, ED contributors to delays in D2D, and the potential reduction in D2D if software diagnosis of STEMI resulted in activation of the cardiac catheterization laboratory.

Results

A total of 379 patients presented to an ED in our region and received primary percutaneous coronary intervention over the study period. In the 143,574 ECGs performed over the study period for suspected STEMI, the overall sensitivity and specificity of 12SL were 90.5% and 99.98%, respectively. We estimated a potential 17-minute reduction in D2D in the 90.5% of patients correctly identified as having STEMI, with a false activation rate of 4%. Female patients and older patients experienced an even larger potential benefit, with 24- and 25-minute reductions in D2D, respectively.

Conclusions

Patients who walk in to an ED with STEMI experience significant system-related delays in recognition and treatment. Automated software diagnosis of STEMI is accurate and could result in significant improvements in D2D times.

Comparative Performance of Prediction Models for Contrast-Associated Acute Kidney Injury After Percutaneous Coronary Intervention

BACKGROUND

Identifying patients at increased risk of contrast-associated acute kidney injury (CA-AKI) can help target risk mitigation strategies toward these individuals during percutaneous coronary intervention. Illuminating which risk models best stratify risk is an important foundation for such quality improvement efforts.

METHODS AND RESULTS

Seven previously published risk prediction models for CA-AKI and 3 models for kidney injury requiring dialysis were validated using 2 definitions for CA-AKI (the Kidney Disease: Improving Global Outcomes definition of ≥0.3 mg/dL within 48 hours or ≥50% increase in serum creatinine from baseline within 7 days and the historical definition of ≥0.5 mg/dL or ≥25% increase in serum creatinine from baseline within 48 hours), and AKI requiring dialysis within 30 days of percutaneous coronary intervention. Model performance was compared based on discrimination, calibration, and categorical net reclassification index before and after model recalibration. Among 7888 patients who underwent percutaneous coronary intervention in Alberta Canada, CA-AKI occurred in 330 patients (4.2%) when CA-AKI was defined using the Kidney Disease: Improving Global Outcomes definition and 571 (7.3%) when using the historical definition. CA-AKI requiring dialysis occurred in 42 (0.6%) patients. When validated using the Kidney Disease: Improving Global Outcomes definition for CA-AKI, the 2 most recently published models for CA-AKI showed better discrimination (C statistics, 0.75-0.76) than older models (C statistics, 0.61-0.68). C statistics of models for kidney injury requiring dialysis ranged from 0.70 to 0.86. The calibration of all models for CA-AKI deviated from ideal, and the proportion of patients classified into different risk categories for CA-AKI differed substantially for the 2 most recent models. Recalibration significantly improved risk stratification of patients into clinical risk categories for some models.

CONCLUSIONS

Recent prediction models for CA-AKI show better discrimination compared with older models; however, model recalibration should be examined in external cohorts to improve the accuracy of predictions, particularly if predicted risk strata are used to guide management approaches.

Atherectomy and Specialty Balloons in Percutaneous Coronary Intervention

PURPOSE OF REVIEW

Interventional cardiologists are increasingly being called upon to perform complex revascularization in patients who are deemed not to be candidates for surgical revascularization and, until recently, many of these patients would have only been offered medical management. Further, changing demographics have resulted in an increasingly elderly and frail population with diabetes and chronic kidney disease being referred for revascularization. Owing to the increasing prevalence of coronary artery calcification and the importance of achieving complete revascularization, advanced tools and techniques are required to safely revascularize this patient population.

RECENT FINDINGS

Coronary artery calcification is a marker for increased periprocedural complications and worse long-term outcomes in percutaneous intervention. Its presence may mandate advanced revascularization strategies to facilitate safe revascularization. Several studies have highlighted the importance of intracoronary imaging and there have been iterative changes and new devices that have been developed that can facilitate revascularization in the setting of significant coronary artery calcification. Successful coronary revascularization is increasingly dependent on the rational use of intraavascular imaging, specialized balloons and atherectomy to overcome complex coronary artery disease and calcification. A rational strategy for the safe use of advanced techniques and tools is presented here.

Synthesis of a solvatochromic triphenylphosphonium-p-toluenesulfonaminido betaine

The synthesis, crystal structure, and negative solvatochromism of the triphenylphosphonium- p-toluenesulfonaminido betaine (4) are described.

Hypervalent Intramolecular Coordination in Main Group Chemistry: A Template Synthesis and Crystal Structure of an Ortho-Oximinoarylphosphonium Salt

The nickel(II)-catalysed reaction of triphenylphosphine with the oxime of ortho-bromoacetophenone gives an ortho-oximinoarylphosphonium salt, which shows a hypervalent intramolecular coordinative interaction between the oximino-nitrogen and the phosphonium centre.

Exposure study on UV-induced degradation of PTFE and ceramic optical diffusers

We report on a study of the ultraviolet (UV)-induced degradation on optical grade polytetrafluoroethylene (PTFE) and ceramic diffuser samples. Long-term UV exposure may significantly alter the reflectance and lead to an error in the calibration of optical instruments. A large integrating sphere was used to irradiate the samples for 334.7 days at an irradiance level of 194.9  W/m². Samples were qualified and measured for reflectance factor, bidirectional reflectance distribution function, and fluorescence, before and after the exposure, and at 12-week intervals during the exposure. This study revealed significant differences between the aging behavior of ceramic and PTFE samples.

Fabrication of a multilayer tissue-mimicking phantom with tunable optical properties to simulate vascular oxygenation and perfusion for optical imaging technology

Vast research has been carried out to fabricate tissue-mimicking phantoms, due to their convenient use and ease of storage, to assess and validate the performance of optical imaging devices. However, to the best of our knowledge, there has been little research on the use of multilayer tissue phantoms for optical imaging technology, although their structure is closer to that of real skin tissue. In this work, we design, fabricate, and characterize multilayer tissue-mimicking phantoms, with a morphological mouse ear blood vessel, that contain an epidermis, a dermis, and a hypodermis. Each tissue-mimicking phantom layer is characterized individually to match specific skin tissue layer characteristics. The thickness, optical properties (absorption coefficient and reduced scattering coefficient), oxygenation, and perfusion of skin are the most critical parameters for disease diagnosis and for some medical equipment. These phantoms can be used as calibration artifacts and help to evaluate optical imaging technologies.

Correction of an adding-doubling inversion algorithm for the measurement of the optical parameters of turbid media

We present broadband measurements of the optical properties of tissue-mimicking solid phantoms using a single integrating sphere to measure the hemispherical reflectance and transmittance under a direct illumination at the normal incident angle. These measurements are traceable to reflectance and transmittance scales. An inversion routine using the output of the adding-doubling algorithm restricted to the reflectance and transmittance under a direct illumination was developed to produce the optical parameters of the sample along with an uncertainty budget at each wavelength. The results for two types of phantoms are compared to measurements by time-resolved approaches. The results between our method and these independent measurements agree within the estimated measurement uncertainties.

Reference Data Set of Human Skin Reflectance

This data set contains 100 reference reflectance spectra of human skin, spanning the wavelength region from 250 nm to 2500 nm. The spectra were acquired with a commercial spectrophotometer and are directly traceable to the national scale for directional-hemispherical reflectance factor.

Risk Prediction Models for Contrast-Induced Acute Kidney Injury Accompanying Cardiac Catheterization: Systematic Review and Meta-analysis

BACKGROUND

Identification of patients at risk of contrast-induced acute kidney injury (CI-AKI) is valuable for targeted prevention strategies accompanying cardiac catheterization.

METHODS

We searched MedLine and EMBASE for articles that developed or validated a clinical prediction model for CI-AKI or dialysis after angiography or percutaneous coronary intervention. Random effects meta-analysis was used to pool c-statistics of models. Heterogeneity was explored using stratified analyses and meta-regression.

RESULTS

We identified 75 articles describing 74 models predicting CI-AKI, 10 predicting CI-AKI and dialysis, and 1 predicting dialysis. Sixty-three developed a new risk model whereas 20 articles reported external validation of previously developed models. Thirty models included sufficient information to obtain individual patient risk estimates; 9 using only preprocedure variables whereas 21 included preprocedural and postprocedure variables. There was heterogeneity in the discrimination of CI-AKI prediction models (median [total range] in c-statistic 0.78 [0.57-0.95]; I² = 95.8%, Cochran Q-statistic P < 0.001). However, there was no difference in the discrimination of models using only preprocedure variables compared with models that included postprocedural variables (P = 0.868). Models predicting dialysis had good discrimination without heterogeneity (median [total range] c-statistic: 0.88 [0.87-0.89]; I² = 0.0%, Cochran Q-statistic P = 0.981). Seven prediction models were externally validated; however, 2 of these models showed heterogeneous discriminative performance and 2 others lacked information on calibration in external cohorts.

CONCLUSIONS

Three published models were identified that produced generalizable risk estimates for predicting CI-AKI. Further research is needed to evaluate the effect of their implementation in clinical care.

Antigen retrieval prior to on-tissue digestion of formalin-fixed paraffin-embedded tumour tissue sections yields oxidation of proline residues

MALDI-mass spectrometry imaging (MALDI-MSI) has been shown to allow the study of protein distribution and identification directly within formalin-fixed paraffin-embedded (FFPE) tissue sections. However, direct protein identification from tissue sections remains challenging due to signal interferences and/or existing post-translational or other chemical modifications. The use of antigen retrieval (AR) has been demonstrated for unlocking proteins prior to in situ enzymatic digestion and MALDI-MSI analysis of FFPE tissue sections. In the work reported here, the identification of proline oxidation, which may occur when performing the AR protocol, is described. This facilitated and considerably increased the number of identified peptides when adding proline oxidation as a variable modification to the MASCOT search criteria. This article is part of a Special Issue entitled: MALDI Imaging, edited by Dr. Corinna Henkel and Prof. Peter Hoffmann.

National Institute of Standards and Technology measurement service of the optical properties of biomedical phantoms: Current status

The National Institute of Standards and Technology (NIST) has maintained scales for reflectance and transmittance over several decades. The scales are primarily intended for regular transmittance, mirrors, and solid surface scattering diffusers. The rapidly growing area of optical medical imaging needs a scale for volume scattering of diffuse materials that are used to mimic the optical properties of tissue. Such materials are used as phantoms to evaluate and validate instruments under development intended for clinical use. To address this need, a double-integrating sphere based instrument has been installed to measure the optical properties of tissue-mimicking phantoms. The basic system and methods have been described in previous papers. An important attribute in establishing a viable calibration service is the estimation of measurement uncertainties. The use of custom models and comparisons with other established scales enabled uncertainty measurements. Here, we describe the continuation of those efforts to advance the understanding of the uncertainties through two independent measurements: the bidirectional reflectance distribution function and the bidirectional transmittance distribution function of a commercially available solid biomedical phantom. A Monte Carlo-based model is used and the resulting optical properties are compared to the values provided by the phantom manufacturer.

Development of traceable measurement of the diffuse optical properties of solid reference standards for biomedical optics at National Institute of Standards and Technology

The development of a national reference instrument dedicated to the measurement of the scattering and absorption properties of solid tissue-mimicking phantoms used as reference standards is presented. The optical properties of the phantoms are measured with a double-integrating sphere setup in the steady-state domain, coupled with an inversion routine of the adding-doubling procedure that allows for the computation of the uncertainty budget for the measurements. The results are compared to the phantom manufacturer's values obtained by a time-resolved approach. The results suggest that the agreement between these two independent methods is within the estimated uncertainties. This new reference instrument will provide optical biomedical research laboratories with reference values for absolute diffuse optical properties of phantom materials.

Establishment and application of the 0/45 reflectance factor scale over the shortwave infrared

This paper describes the establishment and application of the 0/45 reflectance factor scale in the shortwave infrared (SWIR) from 1100 to 2500 nm. Design, characterization, and the demonstration of a four-stage, extended indium-gallium-arsenide radiometer to perform reflectance measurements in the SWIR have been previously discussed. Here, we focus on the incorporation of the radiometer into the national reference reflectometer, its validation through comparison measurements, and the uncertainty budget. Next, this capability is applied to the measurement of three different diffuser materials. The 0/45 spectral reflectance factors for these materials are reported and compared to their respective 6/di spectral reflectance factors.

Digital phantoms generated by spectral and spatial light modulators

A hyperspectral image projector (HIP) based on liquid crystal on silicon spatial light modulators is explained and demonstrated to generate data cubes. The HIP-constructed data cubes are three-dimensional images of the spatial distribution of spectrally resolved abundances of intracellular light-absorbing oxyhemoglobin molecules in single erythrocytes. Spectrally and spatially resolved image data indistinguishable from the real scene may be used as standard data cubes, so-called digital phantoms, to calibrate image sensors and validate image analysis algorithms for their measurement quality, performance consistency, and interlaboratory comparisons for quantitative biomedical imaging applications.

Double-integrating-sphere system at the National Institute of Standards and Technology in support of measurement standards for the determination of optical properties of tissue-mimicking phantoms

There is a need for a common reference point that will allow for the comparison of the optical properties of tissue-mimicking phantoms. After a brief review of the methods that have been used to measure the phantoms for a contextual backdrop to our approach, this paper reports on the establishment of a standardized double-integrating-sphere platform to measure absorption and reduced scattering coefficients of tissue-mimicking biomedical phantoms. The platform implements a user-friendly graphical user interface in which variations of experimental configurations and model-based analysis are implemented to compute the coefficients based on a modified inverse adding-doubling algorithm allowing a complete uncertainty evaluation. Repeatability and validation of the measurement results of solid phantoms are demonstrated for three samples of different thicknesses, d = 5.08 mm, 7.09 mm, and 9.92 mm, with an absolute error estimate of 4.0% to 5.0% for the absorption coefficient and 11% to 12% for the reduced scattering coefficient (k = 2). The results are in accordance with those provided by the manufacturer. Measurements with different polarization angles of the incident light are also presented, and the resulting optical properties were determined to be equivalent within the estimated uncertainties.

Triphenylarsonium-functionalised gold nanoparticles: potential nanocarriers for intracellular therapeutics

Gold nanoparticles functionalised with triphenylarsonium alkylthiolate ligands have been synthesised; both arsonium ligands show comparatively low cytotoxicity in cells.

X-ray Structural Study of 5-Phenyl-10,11-dihydrodibenzo[b,f]phosphepin-5-oxide

Crystals of the title compound are triclinic, a = 8.533(5), b = 11.106(6), c = 8.815(5) Å, a = 107.83(6), β = 104.99(6), γ = 81.30(5)°, Z = 2, space group P1̄. The structure was determined by multisolution direct methods and electron density methods. Refinement by least-squares techniques gave a final R = 0.081 for the 1753 independent reflections. The molecule adopts a butterfly-type conformation such that the fused phenyl rings are inclined to each other at an angle of 56.8°. The P-0 bond distance is 1.506(4) Å; the endocyclic angle at phosphorus is 107.2(3)° and the exocyclic angles vary from 106.5 to 111.9(3)°.

A Comparison of the Effects of Steric Crowding at Phosphorus on the Steric Course of Wittig Reactions of Stabilised and Semistabilised Ylides

The cis-trans ratio of the alkenes formed in Wittig reactions of semistabilised ylides (derived from benzyltriarylphosphonium salts in ethanolic sodium ethoxide) with benz-aldehyde, acetaldehyde or trimethylacetaldehyde increases as steric crowding at phos-phorus increases. In contrast, the cis-trans ratio of the unsaturated esters formed in the related reactions of the stabilised ethoxycarbonylmethylene ylides decreases as steric crowding at phosphorus increases. The relevance of these results to recent proposals for the mechanism of the Wittig reaction is considered.

The Chemistry of Heteroarylphosphorus Compounds, Part 14 [1] Effects of Heteroaryl Substituents at Phosphorus on the Steric Course of Wittig Reactions of Semistabilised and Stabilised Ylides

The cis-trans ratio of the stilbenes formed in Wittig reactions of semistabilised ylides (derived from benzyltri(hetero)arylphosphonium salts in ethanolic ethoxide) with benz-aldehyde decreases markedly in the series 2-furyl >2-thienyl >phenyl > 1-methylpyrrol-2-yl. The 2-furyl group favours a greater proportion of the cis-isomer than m-trifiuoro-methylphenyl, whereas the 1-methylpyrrol-2-yl group favours a greater proportion of the trans isomer than p-methoxyphenyl. Similarly, in Wittig reactions of carbonyl-stabilised ylides with benzaldehyde and acetaldehyde, the presence at phosphorus of 2-furyl groups results in a significant increase in the proportion of the cis-alkene compared to that formed from the related triphenylphosphonium ylide.

These results are discussed in terms of both betaine and cycloaddition mechanisms for the Wittig reaction. Also discussed is their relevance to recent proposals concerning the elimination of alkene from the intermediate oxaphosphetan.

Reactions of Ferrocenyldiphenylphosphine. Effects of the Ferrocenyl Group at Phosphorus on the Course of Decomposition of Phosphonium Betaines and Vinylphosphonium Salts

The reaction of ferrocenyldiphenylphosphine with styrene oxide in ethanol gives, as the major product, ferrocenyl(phenyl)(1,2-diphenylethyl)phosphine oxide (5, R = Ph), the result of a rearrangement involving phenyl migration from phosphorus to adjacent carbon in the decomposition of a vinylphosphonium ion arising from protonation and subsequent elimination of water from the initially-formed phosphonium betaine. A related phenyl migration occurs in the reaction of the phosphine with ethyl propiolate in wet THF. The presence of a ferrocenyl group at phosphorus in Wittig reactions of semistabilised ylides causes the expected decrease in the cis-trans ratio of the resulting alkenes, consistent with its behaviour as an electron-donating substituent.

The Chemistry of Heteroarylphosphorus Compounds, Part 16.+ An X-Ray Structural Study of (2-Thienyl)bis(2,2′-biphenylylene)phosphorane. A Comparison with Related Methyl and Aryl bis(2,2′-biphenylylene)- spirophosphoranes

Crystals of the title compound are monoclinic, a= 18.9 93 (11), b = 8.757(5), c= 13.267(8) Å, β = 106.60(5)°, Z = 4 in space group Cc (Cs 4 , No. 9). The structure was determined by Patterson and electron-density methods and refined by least squares techniques to R= 0.081, R′ = 0.085 for 1293 independent reflections classified as observed. The molecule is found to adopt an almost regular trigonal bipyramidal geometry in which the two biphenylylene units span apical-equatorial positions and the 2-thienyl group occupies the remaining equatorial site. The 2-thienyl group, which is disordered, does not lie in the equatorial plane, and there is no indication of C2pπ → P3dπ-t interactions between the heteroaryl group and phosphorus. The steric requirements of the 2-thienyl group appear to be comparable with those of methyl and phenyl groups in bis(2,2′-biphenylylene)spiro-phosphoranes.

Electronic Effects of Aryl and Heteroaryl Groups on the Rate of Nucleophilic Displacement of Chlorine from 5-Heteroaryl(or Aryl)-2-chloropyrimidines by Piperidine

The kinetics of nucleophilic displacement of chlorine from a series of 2-chloro-5-heteroaryl( or aryl)pyrimidines by piperidine have been studied in order to assess the electronic effects of the 5-substituent. The observed order of reactivity is 5-(1-methylpyrrol-2-yl) < 5-p-anisyl < 5-p-tolyl < 5-phenyl < 5-(2-thienyl) < 5-(2-furyl) < 5-(m-chlorophenyl). The reactions are enthalpy-controlled and the rate data can be explained as a consequence of the electron-withdrawing or electron-donating ability of the 5-substituent. Synthetic routes to the compounds studied are also described.

Electronic Effects of Aryl and Heteroaryl Groups on the Rate of Quaternization of 5-Aryl(or Heteroaryl)pyrimidines

The kinetics of quaternization of a series of 5-aryl- and 5-heteroarylpyrimidines with phenacyl bromide in acetonitrile have been studied in order to assess the electronic effects of the 5-substituent. The observed order of reactivity is 5-(1-methylpyrrol-2-yl) > 5-panisyl >5-(2-furyl) >5-p-tolyl > 5-(2-thienyl) >phenyl > 5-(m-chlorophenyl). The reactions are enthalpy controlled and the rate data can be accounted for in terms of the electronwithdrawing or donating ability of the 5-substituent. The substituent effects of the 2-fury 1- and 2-thienyl groups in the above reaction are significantly different from those observed in the piperidinolysis of 2-chloro-5(2-heteroaryl)pyrimidines.

Developing digital tissue phantoms for hyperspectral imaging of ischemic wounds

Hyperspectral imaging has the potential to achieve high spatial resolution and high functional sensitivity for non-invasive assessment of tissue oxygenation. However, clinical acceptance of hyperspectral imaging in ischemic wound assessment is hampered by its poor reproducibility, low accuracy, and misinterpreted biology. These limitations are partially caused by the lack of a traceable calibration standard. We proposed a digital tissue phantom (DTP) platform for quantitative calibration and performance evaluation of spectral wound imaging devices. The technical feasibility of such a DTP platform was demonstrated by both in vitro and in vivo experiments. The in vitro DTPs were developed based on a liquid blood phantom model. The in vivo DTPs were developed based on a porcine ischemic skin flap model. The DTPs were projected by a Hyperspectral Image Projector (HIP) with high fidelity. A wide-gap 2nd derivative oxygenation algorithm was developed to reconstruct tissue functional parameters from hyperspectral measurements. In this study, we have demonstrated not only the technical feasibility of using DTPs for quantitative calibration, evaluation, and optimization of spectral imaging devices but also its potential for ischemic wound assessment in clinical practice.

Algorithm validation using multicolor phantoms

We present a framework for hyperspectral image (HSI) analysis validation, specifically abundance fraction estimation based on HSI measurements of water soluble dye mixtures printed on microarray chips. In our work we focus on the performance of two algorithms, the Least Absolute Shrinkage and Selection Operator (LASSO) and the Spatial LASSO (SPLASSO). The LASSO is a well known statistical method for simultaneously performing model estimation and variable selection. In the context of estimating abundance fractions in a HSI scene, the "sparse" representations provided by the LASSO are appropriate as not every pixel will be expected to contain every endmember. The SPLASSO is a novel approach we introduce here for HSI analysis which takes the framework of the LASSO algorithm a step further and incorporates the rich spatial information which is available in HSI to further improve the estimates of abundance. In our work here we introduce the dye mixture platform as a new benchmark data set for hyperspectral biomedical image processing and show our algorithm's improvement over the standard LASSO.

Designing microarray phantoms for hyperspectral imaging validation

The design and fabrication of custom-tailored microarrays for use as phantoms in the characterization of hyperspectral imaging systems is described. Corresponding analysis methods for biologically relevant samples are also discussed. An image-based phantom design was used to program a microarrayer robot to print prescribed mixtures of dyes onto microscope slides. The resulting arrays were imaged by a hyperspectral imaging microscope. The shape of the spots results in significant scattering signals, which can be used to test image analysis algorithms. Separation of the scattering signals allowed elucidation of individual dye spectra. In addition, spectral fitting of the absorbance spectra of complex dye mixtures was performed in order to determine local dye concentrations. Such microarray phantoms provide a robust testing platform for comparisons of hyperspectral imaging acquisition and analysis methods.

2010 topical meeting on optical interference coatings: manufacturing problem

For the 2010 Manufacturing Problem, the participants were required to produce a filter that had normal incidence transmittances of 0.001, 0.01, 0.1, and 0.96, respectively, in four separate 60 nm wide bands in the 400 to 700 nm wavelength region. The problem is not unlike those that need to be routinely solved in the telecommunication industry. Nine groups submitted a total of 11 different filters for the contest. The number of layers in the filters received ranged from 28 to 678, and the total metric thicknesses varied between 4,038 and 22,513 nm. The transmittances of the filters were measured at two independent laboratories. Some of the performances were quite close to the specifications.

Light scattering of semitransparent sintered polytetrafluoroethylene films

Polytetrafluoroethylene (PTFE) is a strongly scattering material and has been regarded to have optical properties similar to biological tissues. In the present study, the bidirectional reflectance distribution function (BRDF) and the bidirectional transmittance distribution function (BTDF) of several PTFE films, with thicknesses from 0.11 to 10 mm, are measured using a laser scatterometer at the wavelength of 635 nm. The directional-hemispherical reflectance (R) and transmittance (T) were obtained by integrating BRDF and BTDF for normal incidence. Comparison of the ratio of the measured R and T with that calculated from the adding-doubling method allows the determination of the reduced scattering coefficient. Furthermore, the effect of surface scattering is investigated by measuring the polarization-dependent BRDF and BTDF at oblique incidence. By analyzing the measurement uncertainty of BTDF in the near-normal observation angles at normal incidence, the present authors found that the scattering coefficient of PTFE should exceed 1200 cm(-1), which is much greater than that of biological tissues. On the other hand, the absorption coefficient of PTFE must be less than 0.01 cm(-1), much smaller than that of biological tissues, a necessary condition to achieve R > or =0.98 with a 10-mm-thick slab.

Holmium Oxide Glass Wavelength Standards

Holmium oxide glass has been used as a wavelength standard for over four decades. These standards have shown insignificant spectral variation from batch to batch and from one manufacturer to another. The National Institute of Standards and Technology (NIST) has certified and recertified holmium oxide glass samples for over four decades. Over this period of time there has been no recorded instance of a spectral shift of the certified bands for any of the samples measured. Moreover, these samples are known to be robust and relatively insensitive to a normal range of temperature and humidity. Based on the extensive experience that NIST has with this material and its long-term stability, NIST will no longer recommend the recertification of these standards. Furthermore, traceability may be established either through the supplier or by the end user without the need for NIST involvement.

Thermodynamic-temperature determinations of the Ag and Au freezing temperatures using a detector-based radiation thermometer

The development of a radiation thermometer calibrated for spectral radiance responsivity using cryogenic, electrical-substitution radiometry to determine the thermodynamic temperatures of the Ag- and Au-freezing temperatures is described. The absolute spectral radiance responsivity of the radiation thermometer is measured in the NIST Spectral Irradiance and Radiance Responsivity Calibrations using Uniform Sources (SIRCUS) facility with a total uncertainty of 0.15% (k=2) and is traceable to the electrical watt, and thus the thermodynamic temperature of any blackbody can be determined by using Planck radiation law and the measured optical power. The thermodynamic temperatures of the Ag- and Au-freezing temperatures are determined to be 1234.956 K (+/-0.110 K) (k=2) and 1337.344 K(+/-0.129 K) (k=2) differing from the International Temperature Scale of 1990 (ITS-90) assignments by 26 mK and 14 mK, respectively, within the stated uncertainties. The temperatures were systematically corrected for the size- of-source effect, the nonlinearity of the preamplifier and the emissivity of the blackbody. The ultimate goal of these thermodynamic temperature measurements is to disseminate temperature scales with lower uncertainties than those of the ITS-90. These results indicate that direct disseminations of thermodynamic temperature scales are possible.

Phosphonioalkylthiosulfate zwitterions—new masked thiol ligands for the formation of cationic functionalised gold nanoparticles

We report the synthesis and structural characterisation of a new family of stable phosphonioalkylthiosulfate zwitterions, R3P+ (CH2)nS2O3- (R = Ph or Bu, n = 3,4,6, 8 or 10) which behave as cationic masked thiolate ligands with applications in the functionalisation of gold nanoparticles, having potential as new diagnostic biorecognition systems. The ligands were prepared by treatment of omega-bromoalkylphosphonium salts with sodium thiosulfate. The crystal and molecular structures of the zwitterions (R = Ph, n = 3) and (R = Bu, n = 3) were determined. A series of phosphonioalkanethiolate-capped gold nanoparticles dispersed in water was prepared by borohydride reduction of potassium tetrachloroaurate in the presence of the zwitterions in a dichloromethane-water system. UV-visible spectroscopy and scanning transmission electron-microscopy indicated that capped nanoparticles of ca. 5 nm diameter were present.