Article Database

Comparative Study of Texture Features in OCT Images at Different Scales for Human Breast Tissue Classification

Abstract:

Breast cancer is the second leading cause of death in women in the United States due to cancer. Early detection of breast cancerous regions will aid the diagnosis, staging, and treatment of breast cancer. Optical coherence tomography (OCT), a non-invasive imaging modality with high resolution, has been widely used to visualize various tissue types within the human breast and has demonstrated great potential for assessing tumor margins. Imaging large resected samples with a fast imaging speed can be accomplished by under-sampling in the spatial domain, resulting in a large image scale. However, it is unclear whether there is an impact on the ability to classify tissue types based on the selected imaging scale. Our objective is to evaluate how the scale at which the images are acquired impacts texture features and the accuracy of an automated classification algorithm. To this end, we present a comparative study of texture features in OCT images at two image scales for human breast tissue classification. Texture features and attenuation coefficients were inputs to a statistical classification model, relevance vector machine. The automated classification results from the two image scales were compared. We found that more informative tissue features are preserved in small image scale and accordingly, small image scale leads to more accurate tissue type classification.

Myocardial Imaging Using Ultrahigh-Resolution Spectral Domain Optical Coherence Tomography

Abstract:

We present an ultrahigh-resolution spectral domain optical coherence tomography (OCT) system in 800 nm with a low-noise supercontinuum source (SC) optimized for myocardial imaging. The system was demonstrated to have an axial resolution of 2.72μm with a large imaging depth of 1.78 mm and a 6-dB falloff range of 0.89 mm. The lateral resolution (5.52μm) was compromised to enhance the image penetration required for myocardial imaging. The noise of the SC source was analyzed extensively and an imaging protocol was proposed for SC-based OCT imaging with appreciable contrast. Three-dimensional datasets were acquired ex vivo on the endocardium side of tissue specimens from different chambers of fresh human and swine hearts. With the increased resolution and contrast, features such as elastic fibers, Purkinje fibers, and collagen fiber bundles were observed. The correlation between the structural information revealed in the OCT images and tissue pathology was discussed as well.

Near-infrared Spectroscopy Integrated Catheter for Characterization of Myocardial Tissues: Preliminary Demonstrations to Radiofrequency Ablation Therapy for Atrial Fibrillation

Abstract:

Effects of radiofrequency ablation (RFA) treatment of atrial fibrillation can be limited by the ability to characterize the tissue in contact. Parameters obtained by conventional catheters, such as impedance and temperature can be insufficient in providing physiological information pertaining to effective treatment. In this report, we present a near-infrared spectroscopy (NIRS)-integrated catheter capable of extracting tissue optical properties. Validation experiments were first performed in tissue phantoms with known optical properties. We then apply the technique for characterization of myocardial tissues in swine and human hearts, ex vivo. Additionally, we demonstrate the recovery of critical parameters relevant to RFA therapy including contact verification, and lesion transmurality. These findings support the application of NIRS for improved guidance in RFA therapeutic interventions.

A Continuous Fiber Distribution Material Model for Human Cervical Tissue

Abstract:

The uterine cervix during pregnancy is the vital mechanical barrier which resists compressive and tensile loads generated from a growing fetus. Premature cervical remodeling and softening is hypothesized to result in the shortening of the cervix, which is known to increase a woman’s risk of preterm birth. To understand the role of cervical material properties in preventing preterm birth, we derive a cervical material model based on previous mechanical, biochemical and histological experiments conducted on nonpregnant and pregnant human hysterectomy cervical tissue samples. In this study we present a three-dimensional fiber composite model that captures the equilibrium material behavior of the tissue in tension and compression. Cervical tissue is modeled as a fibrous composite material, where a single family of preferentially aligned and continuously distributed collagen fibers are embedded in a compressible neo-Hookean ground substance. The total stress in the collagen solid network is calculated by integrating the fiber stresses. The shape of the fiber distribution is described by an ellipsoid where semi-principal axis lengths are fit to optical coherence tomography measurements. The composite material model is fit to averaged mechanical testing data from uni-axial compression and tension experiments, and averaged material parameters are reported for nonpregnant and term pregnant human cervical tissue. The model is then evaluated by investigating the stress and strain state of a uniform thick-walled cylinder under a compressive stress with collagen fibers preferentially aligned in the circumferential direction. This material modeling framework for the equilibrium behavior of human cervical tissue serves as a basis to determine the role of preferentially-aligned cervical collagen fibers in preventing cervical deformation during pregnancy.

Analyzing three-dimensional ultrastructure of human cervical tissue using optical coherence tomography

Abstract:

During pregnancy, the uterine cervix is the mechanical barrier that prevents delivery of a fetus. The underlying cervical collagen ultrastructure, which influences the overall mechanical properties of the cervix, plays a role in maintaining a successful pregnancy until term. Yet, not much is known about this collagen ultrastructure in pregnant and nonpregnant human tissue. We used optical coherence tomography to investigate the directionality and dispersion of collagen fiber bundles in the human cervix. An image analysis tool has been developed, combining a stitching method with a fiber orientation measurement, to study axially sliced cervix samples. This tool was used to analyze the ultrastructure of ex-vivo pregnant and non-pregnant hysterectomy tissue samples taken at the internal os, which is the region of the cervix adjacent to the uterus. With this tool, directionality maps of collagen fiber bundles and dispersion of collagen fiber orientation were analyzed. It was found that that the overall preferred directionality of the collagen fibers for both the nonpregnant and pregnant samples were circling around the inner cervical canal. Pregnant samples showed greater dispersion than non-pregnant samples. Lastly, we observed regional differences in collagen fiber dispersion. Fibers closer to the inner canal showed more dispersion than the fibers on the radial edges.

An automated 3D registration method for optical coherence tomography volumes

Abstract:

Optical coherence tomography (OCT) is able to provide high resolution volumetric data for biological tissues. However, the field of view (FOV) of OCT is sometimes smaller than the field of interest, which limits the clinical application of OCT. One way to overcome the drawback is to stitch multiple 3D volumes. In this paper, we propose a novel method to register multiple overlapped volumetric OCT data into a single volume. The relative positions of overlapped volumes were estimated on en face plane and at depth. On en face plane, scale invariant feature transform (SIFT) was implemented to extract the keypoints in each volume. Based on the invariant features, volumes were paired through keypoint matching. Then, we formulated the relationship between paired offsets and absolute positions as a linear model and estimated the centroid of each volume using least square method. Moreover, we calibrated the depth displacement in each paired volume and aligned the z coordinates of volumes globally. The algorithm was validated through stitching multiple volumetric OCT datasets of human cervix tissue and of swine heart. The experimental results demonstrated that our method is capable of visualizing biological samples over a wider FOV, which enhances the investigation of tissue structure such as fiber orientation.

Atlanta’s urban heat island under extreme heat conditions and potential mitigation strategies

Abstract:

The urban heat island (UHI), together with summertime heat waves, foster’s
biophysical hazards such as heat stress, air pollution, and associated public health problems.
Mitigation strategies such as increased vegetative cover and higher albedo surface materials
have been proposed. Atlanta, Georgia, is often affected by extreme heat, and has recently
been investigated to better understand its heat island and related weather modifications. The
objectives of this research were to (1) characterize temporal variations in the magnitude of
UHI around Metro Atlanta area, (2) identify climatological attributes of the UHI under
extremely high temperature conditions during Atlanta’s summer (June, July, and August)
period, and (3) conduct theoretical numerical simulations to quantify the first-order effects
of proposed mitigation strategies. Over the period 1984–2007, the climatological mean UHI
magnitude for Atlanta-Athens and Athens-Monticello was 1.31 and 1.71C, respectively.
There were statistically significant minimum temperature trends of 0.70C per decade at
Athens and -1.79C per decade at Monticello while Atlanta’s minimum temperature
remained unchanged. The largest (smallest) UHI magnitudes were in spring (summer) and
may be coupled to cloud-radiative cycles. Heat waves in Atlanta occurred during 50% of the
years spanning 1984–2007 and were exclusively summertime phenomena. The mean
number of heat wave events in Atlanta during a given heat wave year was 1.83. On average,
Atlanta heat waves lasted 14.18 days, although there was quite a bit of variability (standard
deviation of 9.89). The mean maximum temperature during Atlanta’s heat waves was
35.85C. The Atlanta-Athens UHI was not statistically larger during a heat wave although
the Atlanta-Monticello UHI was. Model simulations captured daytime and nocturnal UHIs
under heat wave conditions. Sensitivity results suggested that a 100% increase in Atlanta’s
surface vegetation or a tripling of its albedo effectively reduced UHI surface temperature.
However, from a mitigation and technological standpoint, there is low feasibility of tripling albedo in the foreseeable future. Increased vegetation seems to be a more likely choice for
mitigating surface temperature.

Urban aerosols and their variations with clouds and rainfall: A case study for New York and Houston

Abstract:

[1] Diurnal, weekly, seasonal, and interannual variations of urban aerosols were analyzed with an emphasis on summer months using 4 years of the NASA Earth Observing System (EOS) Moderate Resolution Imaging Spectroradiometer (MODIS) observations, in situ Aerosol Robotic Network (AERONET) observations, and in situ U.S. Environmental Protection Agency (EPA) PM2.5 data for one midlatitude city (New York) and one subtropical city (Houston). Seasonality is evident in aerosol optical thickness measurements, with a minimum in January and a maximum in April to July. The diurnal variations of aerosols, however, are detectable but largely affected by local and regional weather conditions, such as surface and upper‐level winds. On calm clear days, aerosols peak during the two rush hours in the morning and evening. Furthermore, the anthropogenic‐induced weekly cycles of aerosols and clouds are analyzed, which by themselves are weak, as the anthropogenic signal is mixed with noise of natural weather variability. In addition, corresponding cloud properties observed from MODIS demonstrate an opposite phase to the seasonality of aerosols. Nevertheless, no clear relationship was observed between monthly mean aerosols and rainfall measurements from NASA’s Tropical Rainfall Measuring Mission (TRMM), implying that in the summer the aerosol impact may not be the primary reason for the change of urban rainfall amount.

Tropical cyclones in a year of rising global temperatures and a strengthening El Nino

Abstract:

The year 2015 is notable for the coincidence of several strong climate indicators that having bearing on the occurrence and intensity of tropical cyclones worldwide. This year, 2015, is clearly on track to become the warmest on record in terms of global temperatures. During the latter half of 2015, a very strong El Niño has formed and is predicted to build impressively, perhaps rivaling the memorable El Niño of 1997/1998. Warm Pacific Ocean temperatures, coupled with a strengthening El Niño, have supported the proliferation of Western North Pacific basin typhoons and Eastern/Central North Pacific Hurricanes. Most notable among these, Hurricane Patricia formed on October 20, 2015 and experienced extremely rapid intensification to become the strongest hurricane in the history of the Western Hemisphere and then weakened just as abruptly before dissipating on October 24, 2015. Rather than an aberration, these climate patterns of 2015 represent an ongoing trend with implications for the disaster health of coastal populations worldwide.

Mitigating tropical cyclone risks and health consequences: urgencies and innovations

Abstract: