ESTIMATING DIELECTRIC PROPERTIES OF BIOLOGICAL TISSUE

INTRODUCTION Microwave imaging has been of interest in recent decades, offering the potential of an affordable and non-ionizing medical diagnostic modality. This technique is sensitive to changes in dielectric properties such as permittivity and conductivity. One approach is microwave radar imaging, which creates images by focusing signals caused by reflections at material interfaces. In order to improve the images from radar approaches, patient-specific dielectric property estimations have been used to determine the speed of wave travel within the tissue [1]. Estimating dielectric properties of biological tissue can also be useful in emerging quantitative applications including bone health assessment. Methods such as local rod probes and antenna measurements of planar samples have been developed to estimate dielectric properties, but are of limited use for in vivo measurements. We have previously developed methods of permittivity estimation with a custom antenna, however this approach requires two measurements at different separation distances and is unable to estimate conductivity. This study aims to improve on methods of estimating permittivity and to add an estimate of conductivity of in vivo biological tissue by incorporating an antenna calibration method. METHODS In order to remove the influence of the antennas on measurements, a previously developed calibration method [2] was adapted to be used with a custom ultra-wideband antenna system [3], allowing permittivity and conductivity to be estimated over a range of frequencies. The two antennas are characterized as 2x2 matrices at each frequency, determined from two calibration measurements: the first is performed with the antennas separated by an electrical conductor, and the second measurement is done with the antennas in direct contact with one another. Measurements were performed using a vector network analyzer (Agilent, PNA-L, N5230A), and take less than 15 seconds. Measurement samples were placed between the two antennas, with their surfaces in contact with the entire antenna aperture. Dielectric properties were then estimated using the magnitude and phase of the calibrated transmission data. To validate this method, dielectric properties of several liquids were estimated and compared to literature values. RESULTS A general agreement was seen between the estimated and literature dielectric properties of several liquids, particularly for high permittivity materials. The estimated and literature permittivity of distilled water is shown in Figure 1. Several biological tissues were then measured such as human calf and heel, and porcine bone excisions. Literature values for these properties are limited as they are often done using local probes which only measure the properties at the surface of a sample.DISCUSSION AND CONCLUSIONS A calibration method has been adapted to enable an ultra-wideband antenna system to assess dielectric properties of in vivo tissue at microwave frequencies. The estimated properties of the tested liquids align closely to literature, providing confidence in estimates of biological tissues which have limited literature values. This technique can be used towards microwave radar signal speed estimates, and for quantitative property measurements. Future improvements could include a skin subtraction method to isolate the properties of bone or other tissue under the skin, and development towards microwave bone health assessment

The microlensing signatures of starspots

Point lens microlensing events with impact parameter close to the source stellar radius allow the observer to study the surface brightness profile of the lensed source. We have examined the effect of photospheric star spots on multicolour microlensing lightcurves and investigated the detectability of such spots in different wavebands as a function of spot temperature, position, radius and lens trajectories. We include the effect of limb darkening and spot projection as a function of position on the stellar disc. In particular we apply the updated, state-of-the-art NEXTGEN stellar atmosphere models of Hauschildt et al which predict very strong limb darkening and which are likely to be applicable to the source stars considered here. Our results indicate that star spots generally give a clear signature for transit events. Moreover, this signature is strongly suppressed by limb darkening for spots close to the limb, although the spots may still be clearly detected for favourable lens trajectories. It is also clear that intensive temporal sampling throughout the duration of the transit is necessary in order for such events to be effective as a tool for imaging stellar photospheres. Nonetheless, with sufficiently well sampled light curves of good photometric precision, microlensing can indeed place useful constraints on the presence or otherwise of photospheric starspots.Comment: 12 pages, 10 figures, MNRAS 335, 539 (2002

A PRINCIPLE INVESTIGATION INTO THE FEASIBILITY OF USING MICROWAVE IMAGING TO MONITOR BONE HEALTH

INTRODUCTION Assessing bone health is of particular interest in age-associated disease and traumas such as osteoporosis, and fractures from extreme sports. Having tools that can safely and accurately assess bone health allows for the screening, diagnosis, and monitoring of disease or injury. The current gold standard for assessing bone health is high-resolution peripheral quantitative computed tomography (HR-pQCT) allowing direct three-dimensional (3D) visualization of bone. Recent evidence suggests microwave imaging can be a complementary medical imaging tool to HR-pQCT for dynamic assessment of full bone health [1]. Specifically, it was shown that microwave properties of cancellous bone are sensitive to physical changes in bone. However, this study was purely exploratory and provided no direct evidence for changes in dielectric properties with varying bone health. In this study, we aim to understand the interaction of electromagnetic waves with bone as a composite material, specifically the material anisotropy. Such information would be crucial to understanding how microwave measurements relate to the physical characteristics of the bone. METHODS Image data for the right and left tibia and radius of one female and two male subjects was acquired from HR-pQCT (XtremeCTII, Scanco Medical). The 3D image data was smoothed with a Gaussian filter (σ = 1.6) and segmented using histogram based segmentation. Cubes of edge length 82 voxels (5.002 mm) were extracted from the segmented images based on the bone center of geometry. The extracted cubes were imported into electromagnetic simulation software (SEMCAD X, Schmid & Partner Engineering AG). A parallel plate waveguide filled with air was excited with a Gaussian pulse polarized in the z-axis (f0 = 6.5 GHz, BW = 11 GHz). The bone and marrow were assigned material properties from literature [2]. Resulting data was exported and processed using custom MATLAB scripts (R2013a, MathWorks). Three simulations were performed per image such that the electromagnetic wave was polarized in each of the three anatomical directions: anterior-posterior, medial-lateral, and proximal-distal. RESULTS The effective permittivity, ε’r, was calculated for each of the anatomical directions and plotted across the frequency range of the input signal. A representative plot for all images is shown in Figure 1. The effective permittivity for each orientation tend to vary around a common permittivity.DISCUSSION AND CONCLUSIONS The results presented here provide a rudimentary but novel insight into the anisotropic behaviour of bone at microwave frequencies. Furthermore, it presents a technique for 3D model acquisition and simulation of bone not yet present in literature. This technique will allow further exploration of the electromagnetic properties of bone such as a deeper insight into the anisotropic behaviour and development of a model for the effective medium of bone as a composite material. With such information, the microwave measurements of bone could be directly related to the bone’s physical properties. This would prove the potential of microwaves to assess bone health for disease or trauma and allow the development of in vivo imaging tools for assessing disease and trauma

Detailed Visual Cortical Responses Generated by Retinal Sheet Transplants in Rats with Severe Retinal Degeneration.

To combat retinal degeneration, healthy fetal retinal sheets have been successfully transplanted into both rodent models and humans, with synaptic connectivity between transplant and degenerated host retina having been confirmed. In rodent studies, transplants have been shown to restore responses to flashes of light in a region of the superior colliculus corresponding to the location of the transplant in the host retina. To determine the quality and detail of visual information provided by the transplant, visual responsivity was studied here at the level of visual cortex where higher visual perception is processed. For our model, we used the transgenic Rho-S334ter line-3 rat (both sexes), which loses photoreceptors at an early age and is effectively blind at postnatal day 30. These rats received fetal retinal sheet transplants in one eye between 24 and 40 d of age. Three to 10 months following surgery, visually responsive neurons were found in regions of primary visual cortex matching the transplanted region of the retina that were as highly selective as normal rat to stimulus orientation, size, contrast, and spatial and temporal frequencies. Conversely, we found that selective response properties were largely absent in nontransplanted line-3 rats. Our data show that fetal retinal sheet transplants can result in remarkably normal visual function in visual cortex of rats with a degenerated host retina and represents a critical step toward developing an effective remedy for the visually impaired human population.SIGNIFICANCE STATEMENT Age-related macular degeneration and retinitis pigmentosa lead to profound vision loss in millions of people worldwide. Many patients lose both retinal pigment epithelium and photoreceptors. Hence, there is a great demand for the development of efficient techniques that allow for long-term vision restoration. In this study, we transplanted dissected fetal retinal sheets, which can differentiate into photoreceptors and integrate with the host retina of rats with severe retinal degeneration. Remarkably, we show that transplants generated visual responses in cortex similar in quality to normal rats. Furthermore, transplants preserved connectivity within visual cortex and the retinal relay from the lateral geniculate nucleus to visual cortex, supporting their potential application in curing vision loss associated with retinal degeneration

Multiwavelength transit observations of the candidate disintegrating planetesimals orbiting WD 1145+017

We present multiwavelength, ground-based follow-up photometry of the white dwarf WD 1145+017, which has recently been suggested to be orbited by up to six or more short-period, low-mass, disintegrating planetesimals. We detect nine significant dips in flux of between 10% and 30% of the stellar flux in our ~32 hr of photometry, suggesting that WD 1145+017 is indeed being orbited by multiple, short-period objects. Through fits to the asymmetric transits that we observe, we confirm that the transit egress is usually longer than the ingress, and that the transit duration is longer than expected for a solid body at these short periods, all suggesting that these objects have cometary tails streaming behind them. The precise orbital periods of the planetesimals are unclear, but at least one object, and likely more, have orbital periods of ~4.5 hr. We are otherwise unable to confirm the specific periods that have been reported, bringing into question the long-term stability of these periods. Our high-precision photometry also displays low-amplitude variations, suggesting that dusty material is consistently passing in front of the white dwarf, either from discarded material from these disintegrating planetesimals or from the detected dusty debris disk. We compare the transit depths in the V- and R-bands of our multiwavelength photometry, and find no significant difference; therefore, for likely compositions, the radius of single-size particles in the cometary tails streaming behind the planetesimals must be ~0.15 μm or larger, or ~0.06 μm or smaller, with 2σ confidence

Multi-level personalization of neuromusculoskeletal models to estimate physiologically plausible knee joint contact forces in children

Neuromusculoskeletal models are a powerful tool to investigate the internal biomechanics of an individual. However, commonly used neuromusculoskeletal models are generated via linear scaling of generic templates derived from elderly adult anatomies and poorly represent a child, let alone children with a neuromuscular disorder whose musculoskeletal structures and muscle activation patterns are profoundly altered. Model personalization can capture abnormalities and appropriately describe the underlying (altered) biomechanics of an individual. In this work, we explored the effect of six different levels of neuromusculoskeletal model personalization on estimates of muscle forces and knee joint contact forces to tease out the importance of model personalization for normal and abnormal musculoskeletal structures and muscle activation patterns. For six children, with and without cerebral palsy, generic scaled models were developed and progressively personalized by (1) tuning and calibrating musculotendon units' parameters, (2) implementing an electromyogram-assisted approach to synthesize muscle activations, and (3) replacing generic anatomies with image-based bony geometries, and physiologically and physically plausible muscle kinematics. Biomechanical simulations of gait were performed in the OpenSim and CEINMS software on ten overground walking trials per participant. A mixed-ANOVA test, with Bonferroni corrections, was conducted to compare all models' estimates. The model with the highest level of personalization produced the most physiologically plausible estimates. Model personalization is crucial to produce physiologically plausible estimates of internal biomechanical quantities. In particular, personalization of musculoskeletal anatomy and muscle activation patterns had the largest effect overall. Increased research efforts are needed to ease the creation of personalized neuromusculoskeletal models

Multiwavelength Transit Observations of the Candidate Disintegrating Planetesimals Orbiting WD 1145+017

We present multiwavelength, multi-telescope, ground-based follow-up photometry of the white dwarf WD 1145+017, that has recently been suggested to be orbited by up to six or more, short-period, low-mass, disintegrating planetesimals. We detect 9 significant dips in flux of between 10% and 30% of the stellar flux from our ground-based photometry. We observe transits deeper than 10% on average every ~3.6 hr in our photometry. This suggests that WD 1145+017 is indeed being orbited by multiple, short-period objects. Through fits to the multiple asymmetric transits that we observe, we confirm that the transit egress timescale is usually longer than the ingress timescale, and that the transit duration is longer than expected for a solid body at these short periods, all suggesting that these objects have cometary tails streaming behind them. The precise orbital periods of the planetesimals in this system are unclear from the transit-times, but at least one object, and likely more, have orbital periods of ~4.5 hours. We are otherwise unable to confirm the specific periods that have been reported, bringing into question the long-term stability of these periods. Our high precision photometry also displays low amplitude variations suggesting that dusty material is consistently passing in front of the white dwarf, either from discarded material from these disintegrating planetesimals or from the detected dusty debris disk. For the significant transits we observe, we compare the transit depths in the V- and R-bands of our multiwavelength photometry, and find no significant difference; therefore, for likely compositions the radius of single-size particles in the cometary tails streaming behind the planetesimals in this system must be ~0.15 microns or larger, or ~0.06 microns or smaller, with 2-sigma confidence.Comment: 16 pages, 12 figures, submitted to ApJ on October 8th, 201

Search for Rayleigh scattering in the atmosphere of GJ1214b

We investigate the atmosphere of GJ1214b, a transiting super-Earth planet with a low mean density, by measuring its transit depth as a function of wavelength in the blue optical portion of the spectrum. It is thought that this planet is either a mini-Neptune, consisting of a rocky core with a thick, hydrogen-rich atmosphere, or a planet with a composition dominated by water. Most observations favor a water-dominated atmosphere with a small scale-height, however, some observations indicate that GJ1214b could have an extended atmosphere with a cloud layer muting the molecular features. In an atmosphere with a large scale-height, Rayleigh scattering at blue wavelengths is likely to cause a measurable increase in the apparent size of the planet towards the blue. We observed the transit of GJ1214b in the B-band with the FOcal Reducing Spectrograph (FORS) at the Very Large Telescope (VLT) and in the g-band with both ACAM on the William Hershel Telescope (WHT) and the Wide Field Camera (WFC) at the Isaac Newton Telescope (INT). We find a planet-to-star radius ratio in the B-band of 0.1162+/-0.0017, and in the g-band 0.1180+/-0.0009 and 0.1174+/-0.0017 for the WHT & INT observations respectively. These optical data do not show significant deviations from previous measurements at longer wavelengths. In fact, a flat transmission spectrum across all wavelengths best describes the combined observations. When atmospheric models are considered a small scale-height water-dominated model fits the data best.Comment: Accepted for publication in Ap

Psychometric Evaluation and Design of Patient-Centered Communication Measures for Cancer Care Settings

Objective To evaluate the psychometric properties of questions that assess patient perceptions of patient-provider communication and design measures of patient-centered communication (PCC). Methods Participants (adults with colon or rectal cancer living in North Carolina) completed a survey at 2 to 3 months post-diagnosis. The survey included 87 questions in six PCC Functions: Exchanging Information, Fostering Health Relationships, Making Decisions, Responding to Emotions, Enabling Patient Self-Management, and Managing Uncertainty. For each Function we conducted factor analyses, item response theory modeling, and tests for differential item functioning, and assessed reliability and construct validity. Results Participants included 501 respondents; 46% had a high school education or less. Reliability within each Function ranged from 0.90 to 0.96. The PCC-Ca-36 (36-question survey; reliability=0.94) and PCC-Ca-6 (6-question survey; reliability=0.92) measures differentiated between individuals with poor and good health (i.e., known-groups validity) and were highly correlated with the HINTS communication scale (i.e., convergent validity). Conclusion This study provides theory-grounded PCC measures found to be reliable and valid in colorectal cancer patients in North Carolina. Future work should evaluate measure validity over time and in other cancer populations. Practice implications The PCC-Ca-36 and PCC-Ca-6 measures may be used for surveillance, intervention research, and quality improvement initiatives

Multinuclear Solid-State Magnetic Resonance as a Sensitive Probe of Structural Changes upon the Occurrence of Halogen Bonding in Co-crystals

Although the understanding of intermolecular interactions, such as hydrogen bonding, is relatively well-developed, many additional weak interactions work both in tandem and competitively to stabilize a given crystal structure. Due to a wide array of potential applications, a substantial effort has been invested in understanding the halogen bond. Here, we explore the utility of multinuclear (13C, 14/15N, 19F, and 127I) solid-state magnetic resonance experiments in characterizing the electronic and structural changes which take place upon the formation of five halogen-bonded co-crystalline product materials. Single-crystal X-ray diffraction (XRD) structures of three novel co-crystals which exhibit a 1:1 stoichiometry between decamethonium diiodide (i.e., [(CH3)3N+(CH 2)10N+(CH3)3][2 I -]) and different para-dihalogen-substituted benzene moieties (i.e., p-C6X2Y4, X=Br, I; Y=H, F) are presented. 13C and 15N NMR experiments carried out on these and related systems validate sample purity, but also serve as indirect probes of the formation of a halogen bond in the co-crystal complexes in the solid state. Long-range changes in the electronic environment, which manifest through changes in the electric field gradient (EFG) tensor, are quantitatively measured using 14N NMR spectroscopy, with a systematic decrease in the 14N quadrupolar coupling constant (CQ) observed upon halogen bond formation. Attempts at 127I solid-state NMR spectroscopy experiments are presented and variable-temperature 19F NMR experiments are used to distinguish between dynamic and static disorder in selected product materials, which could not be conclusively established using solely XRD. Quantum chemical calculations using the gauge-including projector augmented-wave (GIPAW) or relativistic zeroth-order regular approximation (ZORA) density functional theory (DFT) approaches complement the experimental NMR measurements and provide theoretical corroboration for the changes in NMR parameters observed upon the formation of a halogen bond