Endoscopic Optical Coherence Tomography imaging of the airway

A narrowing, either of the nasal airway or the large airways, causes impaired airflow and results in respiratory insufficiency. Imaging the airways is important for the diagnostic evaluation of airway disorders. Existing approaches, such as bronchoscopy/ endoscopy or Computed Tomography (CT), are either qualitative or are impractical to use for routine assessments. Endoscopic Optical coherence Tomography (OCT) can be used to obtain quantitative images of the dynamic airway in real-time and to reconstruct airway volumes.In order to image the large airways, an OCT system with a long imaging range and high sensitivity is necessary. The data acquisition scheme for an endoscopic OCT system with a wavelength swept laser source was developed and refined to enable imaging in the large airways. A pressure acquisition system was also integrated to allow synchronous, invasive, pressure measurements to be made in conjunction with OCT scans. Experiments were performed in mechanically ventilated pigs to demonstrate the airway imaging capabilities of the OCT system. The results obtained from OCT were validated against CT scans acquired during the same exam. The combined pressure and OCT-derived cross sectional area plots, measured in vivo over a respiratory cycle, exhibited hysteresis loops, indicating the viscoelastic nature of the airway deformation. Endoscopic OCT imaging was also performed in the nasal cavities of cadaver heads to assess the outcomes of functional rhinoplasty procedures. OCT-derived volumes of the nasal airway were compared against CT volumes and found to depict the nasal vault faithfully.A fiber-optic probe with a low numerical aperture lens at its tip is better suited for imaging large luminal organs, as the distance between the probe and the tissue surface is unknown and variable. A novel, multi-segment, all-fiber lens, that can produce nearly collimated beams with working distances larger than 14 mm, was designed, fabricated, and tested. Finally, the non-unform rotation distortion produced by a super-elastic Nitinol tube drive-shaft was compared against the performance of a torque coil drive-shaft. It is hoped that the results presented will help advance the adoption of endoscopic OCT in routine clinical practice for the assessment of airway disorders.Doctor of Philosoph

Paramagnetic magnetization signals and curious metastable behaviour in field-cooled magnetization of a single crystal of superconductor 2H-NbSe2

We present here some newer characteristics pertaining to paramagnetic Meissner effect like response in a single crystal of the low Tc superconducting compound 2H-NbSe2 via a detailed study of effects of perturbation on the field-cooled magnetization response. In the temperature range, where an anomalous paramagnetic magnetization occurs, the field-cooled magnetization response is found to be highly metastable: it displays a curious tendency to switch randomly from a given paramagnetic value to a diamagnetic or to a different paramagnetic value, when the system is perturbed by an impulse of an externally applied ac field. The new facets revealed in a single crystal of 2H-NbSe2 surprisingly bear a marked resemblance with the characteristics of magnetization behaviour anticipated for the giant vortex states with multiple flux quanta predicted to occur in mesoscopic-sized superconducting specimen and possible transitions amongst such states.Comment: 12 pages, 9 figures, submitted to Journal of Physics: Condensed Matte

Every Wheeze Does Not Merit a Puffer! Case of an Overnight Cure of Chronic Asthma

The peril of incorrect diagnostic labelling is highlighted by this case of acute respiratory distress caused by a retrosternal recurrent goitre. An initial clinical diagnosis which cannot be fully validated on investigation with unexpected or poor response to treatment should prompt consideration and investigation for an alternative explanation

Torque magnetometry study of the spin reorientation transition and temperature-dependent magnetocrystalline anisotropy in NdCo5

We present the results of torque magnetometry and magnetic susceptibility measurements to study in detail the spin reorientation transition (SRT) and magnetic anisotropy in the permanent magnet NdCo5. We further show simulations of the measurements using first-principles calculations based on density-functional theory and the disordered local moment picture of magnetism at finite temperatures. The good agreement between theory and experimental data leads to a detailed description of the physics underpinning the SRT. In particular we are able to resolve the magnetization of, and to reveal a canting between, the Nd and Co sublattices. The torque measurements carried out in the ac and ab planes near the easy direction allow us to estimate the anisotropy constants, K 1, K 2 and K 4 and their temperature dependences. Torque curves, τ(γ) recorded by varying the direction of a constant magnetic field in the crystallographic ac plane show a reversal in the polarity as the temperature is changed across the SRT (240 < T < 285 K). Within this domain, τ(γ) exhibits unusual features different to those observed above and below the transition. The single crystals of NdCo5 were grown using the optical floating zone technique

Tunability of the spin reorientation transitions with pressure in NdCo5

We present pressure-dependent magnetization measurements carried out in the domain of the spin reorientation transitions (SRTs) of a NdCo5 single crystal. The application of a hydrostatic pressure leads to a shift in the SRTs to higher temperatures. This shift is found to be very sensitive to pressure, with the SRT temperatures increasing at a rate of ≈17 K/GPa. To explain the experimental results, we have also performed first-principles calculations of the SRT temperatures for different applied strains, which corroborate the experimental findings. The calculations attribute the pressure dependence of the SRTs to a faster weakening of the Co contribution to the magnetocrystalline anisotropy with pressure compared to the Nd contribution

Airway compliance measured by anatomic optical coherence tomography

Quantification of airway compliance can aid in the diagnosis and treatment of obstructive airway disorders by detecting regions vulnerable to collapse. Here we evaluate the ability of a swept-source anatomic optical coherence tomography (SSaOCT) system to quantify airway cross-sectional compliance (CC) by measuring changes in the luminal cross-sectional area (CSA) under physiologically relevant pressures of 10–40 cmH2O. The accuracy and precision of CC measurements are determined using simulations of non-uniform rotation distortion (NURD) endemic to endoscopic scanning, and experiments performed in a simplified tube phantom and ex vivo porcine tracheas. NURD simulations show that CC measurements are typically more accurate than that of the CSAs from which they are derived. Phantom measurements of CSA versus pressure exhibit high linearity (R2>0.99), validating the dynamic range of the SSaOCT system. Tracheas also exhibited high linearity (R2 = 0.98) suggestive of linear elasticity, while CC measurements were obtained with typically ± 12% standard error

Incidence of invasive candidal infection in very low birth weight neonates over a period of 5-year: A single institutional study

Background: Fungal infection is one of the important causes of bloodstream infection in very low birth weight (VLBW) and extremely low birth weight (ELBW) infants. Objective: To find out the incidence, mortality rate, and clinical spectrum of infants with invasive candidal infection (ICI) among VLBW infants. Materials and Methods: A retrospective descriptive study was conducted over a period of 5-year at a tertiary care hospital. VLBW infants admitted within 24 h of birth were included. The clinical characteristics and the outcome of the infants who developed fungal infection were studied. The end point was either discharge from the unit or death of the infants who developed fungal sepsis. Results: During the study period, there were a total of 641 VLBW infants admitted and 18 neonates had invasive fungal infections (ICI), which accounted to an incidence of 2.8%. The mean birth weight was 1010±289 g, and the mean gestational age (GA) was 28.6±2.93 weeks. End organ involvement was found in 9 (50%) infants with the eye being the most commonly involved organ (39%) followed by renal involvement (22%). Stratified analysis revealed that lower GA and lower birth weight were associated with higher incidence of ICI (p&lt;0.01). Out of 18 isolates that were identified, Candida albicans was the most common organism isolated in 13 (72%) infants. More than ¼ of the cultures (28%) isolated were non-albicans Candida species. The mortality rate among infants with ICI was 11% (2/18). The two infants who died had septicemia caused by C. albicans and multiple (renal and eye) end organ involvement. All-cause mortality in the study group was also 11% (73/641). Conclusion: The incidence of ICI without systemic antifungal prophylaxis was 2.8% and 5.3% in VLBW and ELBW infants, respectively. C. albicans was more common, but the emergence of Candida non-albicans is seen as a growing threat with some of them displaying resistance to azole group of antifungals