Growth rate, impact of smoking and management of incidentally found paranasal sinus osteomas.

OBJECTIVE: To build upon existing literature regarding growth rate of asymptomatic, incidentally found paranasal sinus (PNS) osteomas, evaluate potential factors associated with growth rate and present an argument for how to follow up. METHODS: At our institution, EPIC SlicerDicer was used to screen imaging studies using keyword 'osteoma' and included patients with at least 2 imaging studies 6 months apart that both demonstrated a PNS osteoma(s). Imaging studies with the largest time interval were selected. Non-PNS osteomas were excluded. RESULTS: 47 patients that fit this criterion with a median duration of interval imaging of 35.9 months. Growth rate was measured to be 0.39 mm/year in the cephalocaudal direction and 0.45 mm/year in the mediolateral direction, together averaging 0.42 mm/year. Increases in growth rate additionally did not appear to impact the likelihood of developing conditions including nasal polyposis or chronic sinusitis and symptoms such as sinus pressure, headache, postnasal drip, or congestion. Those with interval scans >36 months were found to have a slower growth rate than those with closer interval scans. Furthermore, former smokers and current smokers had significantly greater growth rates than nonsmokers. CONCLUSION: Given their slow growth rate, we conclude that select lesions likely do not require follow-up. If there is concern that growth could cause an obstructive complication, such as blocking the frontal outflow tract, we argue a single scan at one year is appropriate. If there is additional growth on this scan, surveillance scans up to 3 years could be performed to assess stability. Lastly, while there was a significant growth rate for smokers compared to non-smokers, the slow growth rate is unlikely to influence management.

Noninvasive Temperature Measurements in Tissue-Simulating Phantoms Using a Solid-State Near-Infrared Sensor.

The monitoring of body temperature is a recent addition to the plethora of parameters provided by wellness and fitness wearable devices. Current wearable temperature measurements are made at the skin surface, a measurement that is impacted by the ambient environment of the individual. The use of near-infrared spectroscopy provides the potential for a measurement below the epidermal layer of skin, thereby having the potential advantage of being more reflective of physiological conditions. The feasibility of noninvasive temperature measurements is demonstrated by using an in vitro model designed to mimic the near-infrared spectra of skin. A miniaturizable solid-state laser-diode-based near-infrared spectrometer was used to collect diffuse reflectance spectra for a set of seven tissue phantoms composed of different amounts of water, gelatin, and Intralipid. Temperatures were varied between 20-24 °C while collecting these spectra. Two types of partial least squares (PLS) calibration models were developed to evaluate the analytical utility of this approach. In both cases, the collected spectra were used without pre-processing and the number of latent variables was the only optimized parameter. The first approach involved splitting the whole dataset into separate calibration and prediction subsets for which a single optimized PLS model was developed. For this first case, the coefficient of determination (R2) is 0.95 and the standard error of prediction (SEP) is 0.22 °C for temperature predictions. The second strategy used a leave-one-phantom-out methodology that resulted in seven PLS models, each predicting the temperatures for all spectra in the held-out phantom. For this set of phantom-specific predicted temperatures, R2 and SEP values range from 0.67-0.99 and 0.19-0.65 °C, respectively. The stability and reproducibility of the sample-to-spectrometer interface are identified as major sources of spectral variance within and between phantoms. Overall, results from this in vitro study justify the development of future in vivo measurement technologies for applications as wearables for continuous, real-time monitoring of body temperature for both healthy and ill individuals.

Selectivity and Sensitivity of Near-Infrared Spectroscopic Sensing of ß-Hydroxybutyrate, Glucose, and Urea in Ternary Aqueous Solutions.

The next-generation artificial pancreas is under development with the goal to enhance tight glycemic control for people with type 1 diabetes. Such technology requires the integration of a chemical sensing unit combined with an insulin infusion device controlled by an algorithm capable of autonomous operation. The potential of near-infrared spectroscopic sensing to serve as the chemical sensing unit is explored by demonstrating the ability to quantify multiple metabolic biomarkers from a single near-infrared spectrum. Independent measurements of ß-hydroxy-butyrate, glucose, and urea are presented based on analysis of near-infrared spectra collected over the combination spectral range of 5000-4000 cm-1 for a set of 50 ternary aqueous standard solutions. Spectra are characterized by a 1 µAU root-mean-square (RMS) noise for 100% lines with a resolution of 4 cm-1 and an optical path length of 1 mm. Calibration models created by the net analyte signal (NAS) and the partial least squares (PLS) methods provide selective measurements for each analyte with standard errors of prediction in the upper micromolar concentration range. The NAS method is used to determine both the selectivity and sensitivity for each analyte and their values are consistent with these standard errors of prediction. The NAS method is also used to characterize the background spectral variance associated with instrumental and environmental variations associated with buffer spectra collected over a multiday period.

Nocturnal Hypoglycemic Alarm Based on Near-Infrared Spectroscopy: In Vivo Studies with a Rat Animal Model.

A noninvasive method for detecting episodes of nocturnal hypoglycemia is demonstrated with in vivo measurements made with a rat animal model. Employing spectra collected from the near-infrared combination region of 4000-5000 cm-1, piecewise linear discriminant analysis (PLDA) is used to classify spectra into alarm and nonalarm data classes on the basis of whether or not they correspond to glucose concentrations below a user-defined hypoglycemic threshold. A reference spectrum and corresponding glucose concentration are acquired at the start of the monitoring period, and spectra are then collected continuously and converted to absorbance units relative to the initial reference spectrum. The resulting differential spectra correspond to differential glucose concentrations that reflect the differences in concentration between each spectrum and the reference. Given an alarm threshold (e.g., 3.0 mM), a database of calibration differential spectra can be partitioned into two groups containing spectra above and below the threshold. A classification model is then computed with PLDA. The resulting model can be applied to the differential spectra collected during the monitoring period in order to identify spectra whose corresponding glucose concentrations lie in the hypoglycemic range. In this work, the alarm algorithm was tested in two single-day studies performed with anesthetized rats. Glucose concentrations spanned the range of 1.6 to 13.5 mM (29 to 244 mg/dL). For both rats, the alarm algorithm performed well. On average, 87.5% of alarm events were correctly detected, and the occurrence of false alarms was 7.2%. False alarms were restricted to times when the glucose concentrations were very close to the alarm threshold rather than at random times, thus demonstrating the potential of the approach for practical use.

DFT Computed Dielectric Response and THz Spectra of Organic Co-Crystals and Their Constituent Components.

Terahertz (THz) spectroscopy has been put forth as a non-contact, analytical probe to characterize the intermolecular interactions of biologically active molecules, specifically as a way to understand, better develop, and use active pharmaceutical ingredients. An obstacle towards fully utilizing this technique as a probe is the need to couple features in the THz regions to specific vibrational modes and interactions. One solution is to use density functional theory (DFT) methods to assign specific vibrational modes to signals in the THz region, coupling atomistic insights to spectral features. Here, we use open source planewave DFT packages that employ ultrasoft pseudopotentials to assess the infrared (IR) response of organic compounds and complex co-crystal formulations in the solid state, with and without dispersion corrections. We compare our DFT computed lattice parameters and vibrational modes to experiment and comment on how to improve the agreement between theory and modeling to allow for THz spectroscopy to be used as an analytical probe in complex biologically relevant systems.

Mechanical Properties of a Series of Macro- and Nanodimensional Organic Cocrystals Correlate with Atomic Polarizability.

A correlation between Young's modulus, as determined by using nanoindentation atomic force microscopy (AFM), and atomic polarizability is observed for members of a series of cocrystals based on systematic changes to one cocrystal component. Time domain spectroscopy over terahertz frequencies (THz-TDS) is used for the first time to directly measure the polarizability of macro- and nanosized organic solids. Cocrystals of both macro- and nanodimensions with highly polarizable atoms result in softer solids and correspondingly higher polarizabilities.

Selectivity of Terahertz Gas-Phase Spectroscopy.

Analytical potential of terahertz (THz) spectroscopy is assessed by comparing selectivity for a set of eight environmentally important gases over THz and infrared (IR) optical frequencies. Selectivity coefficients are determined over selected spectral regions for acetaldehyde, acetonitrile, ethanol, water, methanol, ammonia, propionaldehyde, and propionitrile. These selectivity coefficients quantify the magnitude of the net analyte signal for each test compound relative to the other seven. In addition to the THz spectral range (2-125 cm(-1)), selectivity coefficients are determined for the following IR regions 600-1300, 1300-2000, 2600-3100, 3100-4000, and 4000-6500 cm(-1). Highest selectivity is afforded over the THz frequencies for six of the eight test compounds and THz selectivity coefficients for the other two gases (water and acetonitrile) are acceptable for environmental measurements.

Is Preoperative Chemoprophylaxis Safe for Venous Thromboembolism Prevention in Patients With Head and Neck Cancer?

OBJECTIVE: To assess the safety of preoperative chemoprophylaxis (PEC) in head and neck cancer (HNC) patients undergoing oncologic procedures. STUDY DESIGN: Retrospective cohort study. SETTING: Tertiary academic center. METHODS: HNC patients with Caprini risk score (CRS) ≥5 who underwent inpatient surgery ≥3 hours between 2015 and 2020 were included. Patients were divided into 2 cohorts, PEC and control, based on whether or not they received a single dose of low molecular weight heparin or unfractionated heparin prior to surgery. The primary endpoint was the 30-day rate of major bleeding events. RESULTS: A total of 539 patients were included; 427 patients received PEC prior to surgery. The rate of major bleeding was 6.7%. The PEC cohort was more likely to have received concurrent aspirin or ketorolac (225 of 427 patients vs 36 of 112 patients; P = .0002), greater duration of chemoprophylaxis (7.8 vs 5.0 days; P < .0001), have higher CRS (7.2 vs 6.6; P < .0001), longer operative times (596 vs 512 minutes; P < .0001), higher blood loss (265 vs 214 ml; P = .02), and higher bleeding rates when compared to the control (34 of 427 patients; P = .03). On multivariate analysis, only PEC was associated with bleeding (odds ratio, 8.74; 95% confidence interval, 1.15-66.5). The rate of VTE was 1.3% and was not significantly different between cohorts. CONCLUSION: PEC was associated with an increase in bleeding and did not result in lower rates of VTE in patients with HNC. This study highlights the need to determine the optimal regimen of chemoprophylaxis in this patient cohort.

Impact of pellet thickness on quantitative terahertz spectroscopy of solid samples in a polyethylene matrix.

Pellets composed of different weight-percent (wt-%) of lactose within a polyethylene (PE) matrix are used to examine how the physical thickness of solid samples impact analytical measurements performed over terahertz (THz) frequencies when using time-domain THz spectroscopy. Results indicate that the thickness of each pellet depends on the mass and physical properties of the individual components that comprise the pellet. Thickness of mixture pellets depends on the porosity of the individual pellet components. Porosity measurements presented here for PE and lactose give values of 25.6 ± 0.3 and 14.5 ± 0.1, respectively, which indicate that more air is trapped within the compressed PE matrix compared to that for lactose. This difference in porosity creates different pellet thicknesses for pellets of the same nominal mass but with different relative amounts of PE and lactose. For this binary matrix, the thickness of each pellet is found to be a linear combination of the compressed densities of the individual components. Analysis of the time-domain THz spectra reveals that thinner samples are confounded by a fringe pattern observed in the frequency-domain spectra. This fringe pattern is created by an etalon corresponding to the air/pellet interfaces for the sample in the optical path. Spectra collected from thicker pellets are confounded by a sloping baseline caused by scattering effects within the pellet matrix. The quantitative impact of pellet thickness is determined by comparing the mean standard error of calibration (MSEC) and mean standard error of prediction (MSEP) for a set of leave-three-out cross validation multivariate calibration models based on the partial least-squares (PLS) algorithm. Results indicate that PLS models are capable of analytical measurements with MSEC and MSEP values between 0.04 and 0.20 wt-%. Analysis of spectral variance captured within the corresponding spectral loadings for each model indicates that spectral variance is lowest for the 300 mg samples where the impact of scattering is minimal under conditions when the sample etalon is nonexistent.

Facial Trauma During the COVID-19 Pandemic.

Study Design: Retrospective cohort study. Objective: The purpose of this study is to evaluate the impact of the COVID-19 global pandemic on the regional trends in facial trauma at a tertiary care, level 1 trauma center in Central New York. Methods: The study sample was derived from the population of patients who presented with facial trauma to the emergency department at the Downtown and/or Community Campuses of SUNY Upstate University Hospital between March 1, 2020, and May 15, 2020, and compared to two historical controls in 2018 and 2019. Descriptive and bivariate statistics were calculated for study variables in each cohort. Poisson regression was used to compare incident rate ratios (IRR) with 95% confidence intervals with significance set at P < .05. Results: Sixty five patients presented during the COVID-19 pandemic, while 83 presented in 2019 and 95 in 2018. For the study period, the most common mechanism was assault in 47.7%. IRR was significantly lower than in 2018 (IRR = 1.46, P = .018), but not significantly different from 2019 (IRR = 1.28, P = .14). During lockdown, IRR was significantly decreased compared to 2019 (IRR = 1.84, P = .0029) and 2018 (IRR = 2.16, P < .001). Conclusions: The volume of facial trauma seen in Central New York appears undeterred in the absence of "shelter in place" orders. Analysis of pandemic and regional trauma variations can offer valuable insight for improved resource allocation to better prepare for potentially high-risk procedures.

Pituitary Gland Surgical Emergencies: The Role of Endoscopic Intervention.

True pituitary surgical emergencies are rare. These events can occur throughout the perioperative period and are broadly categorized by the timing of occurrence. Acute indications for emergent pituitary surgery include pituitary apoplexy, vision loss, and severe Cushing presentation. Emergencies may also occur intraoperatively, secondary to bleeding. Postoperative emergencies include epistaxis, pneumocephalus, and intracranial bleeding. Cerebrospinal fluid (CSF) leak occurs in about 37.4% of transsphenoidal sellar surgery, yet postoperative CSF leaks are less frequent at approximately 2.6%. As they occur often during pituitary surgery, CSF leaks alone are generally not considered a true surgical emergency unless associated with symptomatic tension pneumocephalus.

Products for Monitoring Glucose Levels in the Human Body With Noninvasive Optical, Noninvasive Fluid Sampling, or Minimally Invasive Technologies.

BACKGROUND: Conventional home blood glucose measurements require a sample of blood that is obtained by puncturing the skin at the fingertip. To avoid the pain associated with this procedure, there is high demand for medical products that allow glucose monitoring without blood sampling. In this review article, all such products are presented. METHODS: In order to identify such products, four different sources were used: (1) PubMed, (2) Google Patents, (3) Diabetes Technology Meeting Startup Showcase participants, and (4) experts in the field of glucose monitoring. The information obtained were filtered by using two inclusion criteria: (1) regulatory clearance, and/or (2) significant coverage in Google News starting in the year 2016, unless the article indicated that the product had been discontinued. The identified bloodless monitoring products were classified into three categories: (1) noninvasive optical, (2) noninvasive fluid sampling, and (3) minimally invasive devices. RESULTS: In total, 28 noninvasive optical, 6 noninvasive fluid sampling, and 31 minimally invasive glucose monitoring products were identified. Subsequently, these products were characterized according to their regulatory, technological, and consumer features. Products with regulatory clearance are described in greater detail according to their advantages and disadvantages, and with design images. CONCLUSIONS: Based on favorable technological features, consumer features, and other advantages, several bloodless products are commercially available and promise to enhance diabetes management. Paths for future products are discussed with an emphasis on understanding existing barriers related to both technical and non-technical issues.

Improved accuracy for Raman spectroscopic determination of polyethylene property by optimization of measurement temperature and elucidation of its origin by multiple perturbation two-dimensional correlation spectroscopy.

A novel strategy is demonstrated to improve the accuracy for determination of polyethylene (PE) density using Raman spectroscopy by optimizing the temperature of sample measurement. Spectral features associated with the conformation change of the polymer induced by temperature may provide valuable information to quantify important polymer properties such as density. To evaluate possible existence of an optimal temperature providing improved quantitative accuracy, Raman spectra of PE pellets with different densities were collected at eight different temperatures from 30 to 100 °C at 10 °C intervals. Using the spectral datasets collected at each temperature, partial least squares (PLS) models were developed using the reference PE density values determined by a standard density gradient method at 23 °C. Interestingly, the most accurate determination of density was realized at 70 °C. Multiple perturbation two-dimensional (MP2D) correlation analysis and differential scanning calorimetry (DSC) were used to examine the origin of improved accuracy at 70 °C. From these analyses, the pre-melt behavior of the PE samples was identified below their melting temperatures. Structural variations induced at the pre-melt stages enhance Raman spectral selectivity among the samples, thereby providing more accurate determination of PE density. The MP2D correlation analysis revealed the unforeseen thermal behavior of PE samples and successfully explained the improved accuracy at 70 °C.

Crystal Structure-Free Method for Dielectric and Polarizability Characterization of Crystalline Materials at Terahertz Frequencies.

Terahertz (THz) time-domain spectroscopy provides a direct and nondestructive method for measuring the dielectric properties of materials directly from the phase delay of coherent electromagnetic radiation propagating through the sample. In cases when crystals are embedded within an inert polymeric pellet, the Landau, Lifshitz, and Looyenga (LLL) effective medium model can be used to extract the intrinsic dielectric constant of the crystalline sample. Subsequently, polarizability can be obtained from the Clausius-Mossotti (CM) relationship. Knowledge of the crystal structure density is required for an analytical solution to the LLL and CM relationships. A novel crystal structure-free graphical method is presented as a way to estimate both dielectric constants and polarizability values for the situation when the crystal structure density is unknown, and the crystals are embedded within a pellet composed of a non-porous polymer. The utility of this crystal structure-free method is demonstrated by analyzing THz time-domain spectra collected for a set of amino acids (L-alanine, L-threonine, and L-glutamine) embedded within pellets composed of polytetrafluoroethylene. Crystal structures are known for each amino acid, thereby enabling a direct comparison of results using the analytical solution and the proposed crystal structure-free graphical method. For each amino acid, the intrinsic dielectric constant is extracted through the LLL effective medium model without using information of their crystal structure densities. THz polarizabilities are then calculated with the CM relationship by using the determined intrinsic dielectric constant for each amino acid coupled with its crystal density as determined graphically. Comparison between the analytical and graphical solutions reveal relative differences between dielectric constants of 3.7, 5.1, and 13.6% for threonine, alanine, and glutamine, respectively, and relative differences between polarizability of 0.6, 0.9, and 5.4%, respectively. These values were determined over the 10-20 cm-1 THz frequency range. The proposed method requires no prior knowledge of crystal structure information.

Association of Prolonged-Duration Chemoprophylaxis With Venous Thromboembolism in High-risk Patients With Head and Neck Cancer.

Importance: Venous thromboembolism (VTE) is associated with substantial morbidity and is the most common factor associated with preventable death among hospitalized patients. Data from otolaryngologic studies suggest that the risk of VTE may be underestimated among high-risk patients, particularly among those undergoing oncologic procedures. The incorporation of prolonged-duration chemoprophylaxis (PDC) into preventive therapy has been associated with substantial decreases in VTE incidence among patients undergoing oncologic surgery. However, bleeding remains a major concern among otolaryngologists, and substantial variation exists in the use of thromboprophylaxis. Objective: To assess the association between PDC and VTE in high-risk patients with head and neck cancer undergoing oncologic procedures. Design, Setting, and Participants: This retrospective cohort study identified 750 patients with biopsy-confirmed head and neck cancer and a Caprini risk score of 8 or higher who underwent inpatient oncologic surgery at a tertiary care referral center between January 1, 2014, and February 1, 2020. After exclusions, 247 patients were included in the study; patients were divided into 2 cohorts, traditional and PDC, based on the duration of prophylaxis. Univariate and multivariate analyses were performed to examine the development of VTE and bleeding-associated complications during the 30-day postoperative period. Data were analyzed from April 1 to April 30, 2020. Exposures: PDC, defined as 7 or more postoperative days of chemoprophylaxis. Main Outcomes and Measures: VTE and bleeding events during the 30-day postoperative period. Results: Among 247 patients (mean [SD] age, 63.1 [11.1] years; 180 men [72.9%]) included in the study, 106 patients (42.9%) received traditional prophylaxis, and 141 patients (57.1%) received PDC. The incidence of VTE was 5 of 106 patients (4.7%) in the traditional cohort and 1 of 141 patients (0.7%) in the PDC cohort (odds ratio [OR], 0.15; 95% CI, 0.003-1.33). In the multivariate logistic regression analysis, PDC was independently associated with reductions in the risk of VTE (OR, 0.04; 95% CI, 0.001-0.46). The incidence of bleeding events was 1 of 106 patients (0.9%) in the traditional cohort and 6 of 141 patients (4.3%) in the PDC cohort (OR, 4.64; 95% CI, 0.55-217.00). Conclusions and Relevance: The use of chemoprophylaxis for high-risk patients with head and neck cancer remains a high-priority topic. The results of this study suggest that PDC may be associated with reductions in VTE among this patient population. However, the associated increase in nonfatal bleeding events warrants careful consideration and further highlights the need to determine an optimal duration for chemoprophylaxis among this distinct cohort.

Comparing Kadish and Modified Dulguerov Staging Systems for Olfactory Neuroblastoma: An Individual Participant Data Meta-analysis.

OBJECTIVE: To compare the Kadish and the modified Dulguerov staging of individual participants to determine the impact of stage and other prognostic factors on disease-free (DFS) and overall survival (OS). DATA SOURCES: Systematic review of EMBASE, MEDLINE, Cochrane Library, and CINAHL databases. REVIEW METHODS: The Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) was followed for this study. Articles including patients with olfactory neuroblastoma (ONB) staged with both Kadish and Dulguerov staging systems were reviewed. The raw data from eligible studies were requested to perform an individual participant data (IPD) meta-analysis. RESULTS: Pooled data from 21 studies representing 399 patients with ONB undergoing treatment with curative intent showed that increasing age, treatment with chemotherapy, and positive or unreported margin status portended worse DFS (P < .05). Increasing stage for both Kadish and Dulguerov staging systems was prognostic for worse DFS and OS (P < .05), with Kadish C representing a heterogeneous group with regard to outcome and corresponding Dulguerov T stage. Using the Akaike information criterion, the Dulguerov staging system had superior performance to the Kadish system for DFS (1088.72 vs 1092.54) and OS (632.71 vs 644.23). CONCLUSION: This study represents the first IPD meta-analysis of ONB directly comparing the outcomes of Kadish and Dulguerov staging systems in patients treated with primary surgery. Both systems correlated with DFS and OS, with superior performance in the Dulguerov system. Furthermore, the Kadish C group represented a heterogeneous group with regard to outcomes after stratification by the Dulguerov system. Dulguerov T4 patients had the worst outcome, with most being approached with open resection.

Identifying cohort differences in children undergoing partial intracapsular tonsillectomy vs traditional tonsillectomy for sleep disordered breathing.

OBJECTIVE: Partial intracapsular tonsillectomy (PIT) is a well-established technique for reducing post-operative morbidity in pediatric patients with sleep disordered breathing (SDB). Although tonsillar re-growth rates are reported as low, risks of symptom recurrence or need for completion tonsillectomy are clear disadvantages when compared to traditional tonsillectomy (TT). We aim to identify cohort differences to better guide clinical decision making and identify patient-specific factors that may influence this decision. A secondary aim was to evaluate potential risk factors for tonsillar regrowth. METHODS: Retrospective chart review of pediatric patients who underwent TT or PIT for SDB between 2015 and 2019 at a tertiary care academic medical center. Records were reviewed for age, gender, race, body mass index, comorbidities, diagnosis, apnea-hypopnea index, pre-operative Brodsky tonsil size, length of stay, post-operative hemorrhage, tonsillar regrowth, symptom recurrence, and need for completion tonsillectomy. RESULTS: 315 patients were included: 174 underwent TT and 141 underwent PIT. Patients undergoing TT were more likely to have a sleep study showing OSA (OR 3.01, p < 0.0001), asthma (OR 4.28, p = 0.000124), and other comorbidities (OR 4.06, p = 0.0258). The overall complication rate was 4.44% (14/315). Tonsillar regrowth was exclusive to the PIT group, occurring in 7/141 patients (4.96%). Age ≤4 years was significantly associated with increased risk of tonsillar regrowth (≤4 years: 7.69%, >4 years: 0%; p = 0.049). Race and pre-operative tonsil size were not associated with regrowth. CONCLUSIONS: Our study supports the low incidence of tonsillar regrowth in PIT and suggests an association with younger age. Moreover, we found that patients undergoing TT are more likely to be older, have OSA, asthma, and other comorbidities.

Selectivity for glucose, glucose-6-phosphate, and pyruvate in ternary mixtures from the multivariate analysis of near-infrared spectra.

Near-infrared spectroscopy offers the potential for direct in situ analysis in complex biological systems. Chemical selectivity is a critical issue for such measurements given the extent of spectral overlap of overtone and combination spectra. In this work, the chemical basis of selectivity is investigated for a set of multivariate calibration models designed to quantify glucose, glucose-6-phosphate, and pyruvate independently in ternary mixtures. Near-infrared spectra are collected over the combination region (4,000-5,000 cm(-1)) for a set of 60 standard solutions maintained at 37 degrees C. These standard solutions are composed of randomized concentrations (0.5-30 mM) of glucose, glucose-6-phosphate, and pyruvate. Individual calibration models are constructed for each solute by using the partial least-squares (PLS) algorithm with optimized spectral range and number of latent variables. The resulting standard errors are 0.90, 0.72, and 0.32 mM for glucose, glucose-6-phosphate, and pyruvate, respectively. A pure component selectivity analysis (PCSA) demonstrates selectivity for each solute in these ternary samples. The concentration of each solute is also predicted for each sample by using a set of net analyte signal (NAS) calibration models. A comparison of the PLS and NAS calibration vectors demonstrates the chemical basis of selectivity for these multivariate methods. Selectivity of each PLS and NAS calibration model originates from the unique spectral features associated with the targeted analyte. Overall, selectivity is demonstrated for each solute with an order of sensitivity of pyruvate > glucose-6-phosphate > glucose.

Design considerations for near-infrared filter photometry: effects of noise sources and selectivity.

Optimal filter design of two-channel near-infrared filter photometers is investigated for simulated two-component systems consisting of an analyte and a spectrally overlapping interferent. The degree of overlap between the analyte and interferent bands is varied over three levels. The optimal design is obtained for three cases: a source or background flicker noise limited case, a shot noise limited case, and a detector noise limited case. Conventional photometers consist of narrow-band optical filters with their bands located at discrete wavelengths. However, the use of broadband optical filters with overlapping responses has been proposed to obtain as much signal as possible from a weak and broad analyte band typical of near-infrared absorptions. One question regarding the use of broadband optical filters with overlapping responses is the selectivity achieved by such filters. The selectivity of two-channel photometers is evaluated on the basis of the angle between the analyte and interferent vectors in the space spanned by the relative change recorded for each of the two detector channels. This study shows that for the shot noise limited or detector noise limited cases, the slight decrease in selectivity with the use of broadband optical filters can be compensated by the higher signal-to-noise ratio afforded by the use of such filters. For the source noise limited case, the best quantitative results are obtained with the use of narrow-band non-overlapping optical filters.

Polarizability of Aspirin at Terahertz Frequencies Using Terahertz Time Domain Spectroscopy (THz-TDS).

A novel application of terahertz time-domain spectroscopy (THz-TDS) is described for the determination of permittivity and polarizability of organic crystals, as exemplified by measurements with the polymorph I form of crystalline aspirin (acetylsalicylic acid). The coherent nature of the THz pulse experiment, coupled with gated-detection, permits direct measure of differences in the phase angle of the electric field vector after passing through a pellet composed of the aspirin crystals embedded within an inert polymer matrix. An effective media model is used to extract dielectric information for the crystals from the measured time-domain signal that is representative of the entire pellet composition. Polarizability is then obtained for these organic crystals by using the Clausius-Mossotti relationship. Dielectric spectra and polarizability spectra are presented over the 0.3-3 THz frequency range (10-100 cm-1). The average polarizability values measured over the low frequency range (10-20 cm-1) are 22.4 ± 0.3 and 22.4 ± 0.5 Å3 for aspirin crystals embedded within matrixes of polytetrafluoroethylene (PTFE) and polyethylene (PE), respectively.