Kaisar Alam S.,Riverside Research |
Feleppa E.J.,Riverside Research |
Rondeau M.,Riverside Research |
Kalisz A.,Riverside Research |
Garra B.S.,U.S. Food and Drug Administration
Ultrasonic Imaging | Year: 2011
We have developed quantitative descriptors to provide an objective means of noninvasive identification of cancerous breast lesions. These descriptors include quantitative acoustic features assessed using spectrum analysis of ultrasonic radiofrequency (rf) echo signals and morphometric properties related to lesion shape. Acoustic features include measures of echogenicity, heterogeneity and shadowing, computed by generating spectral-parameter images of the lesion and surrounding tissue. Spectral-parameter values are derived from rf echo signals at each pixel using a sliding-window Fourier analysis. We derive quantitative acoustic features from spectral-parameter maps of the lesion and adjacent areas. We quantify morphometric features by geometric and fractal analysis of traced lesion boundaries. Initial results on biopsy-proven cases show that although a single parameter cannot reliably discriminate cancerous from noncancerous breast lesions, multi-feature analysis provides excellent discrimination for this data set. We have processed data for 130 biopsy-proven patients, acquired during routine ultrasonic examinations at three clinical sites and produced an area under the receiver-operating-characteristics (ROC) curve of 0.947±0.045. Among the quantitative descriptors, lesion-margin definition, spiculation and border irregularity are the most useful; some additional morphometric features (such as border irregularity) also are particularly effective in lesion classification. Our findings are consistent with many of the BI-RADS (Breast Imaging Reporting and Data System) breast-lesion-classification criteria in use today. Copyright 2011 by Dynamedia, Inc.
Fiorino S.T.,Air Force Institute of Technology |
Randall R.M.,Air Force Institute of Technology |
Via F.,Riverside Research |
Burley J.L.,U.S. Air force
Journal of Applied Meteorology and Climatology | Year: 2014
This paper demonstrates the capability of the Laser Environmental Effects Definition and Reference (LEEDR) model to accurately characterize the meteorological parameters and radiative transfer effects of the atmospheric boundary layer with surface observations or climatological values of temperature, pressure, and humidity ("climatology"). The LEEDR model is a fast-calculating, first-principles, worldwide surface-to- 100-km, ultraviolet-to-radio-frequency (UV to RF) wavelength, atmospheric characterization package. In general, LEEDR defines the well-mixed atmospheric boundary layer with a worldwide, probabilistic surface climatology that is based on season and time of day and, then, computes the radiative transfer and propagation effects from the vertical profile of meteorological variables. The LEEDR user can also directly input surface observations. This research compares the LEEDR vertical profiles created from input surface observations or numerical weather prediction (NWP) data with the LEEDR climatological profile for the same time of day and season. The different profiles are compared with truth radiosonde data, and the differences from truth are found to be smaller for profiles created from surface observations and NWP than for those made from climatological data for the same season and time. In addition, this research validates LEEDR's elevated aerosol extinction profile vertical structure against observed lidar measurements and details the advantages of using NWP data for atmospheric profile development. The impacts of these differences are demonstrated with a potential tactical high-energy-laser engagement simulation. © 2014 American Meteorological Society.
McKenna S.P.,Riverside Research |
Parkman K.B.,U.S. Army |
Perren L.J.,Bevilacqua Research Corporation |
McKenna J.R.,U.S. Army
IEEE Transactions on Geoscience and Remote Sensing | Year: 2011
The response of an electromagnetic gradiometer (EMG) system to a subsurface wire is analyzed in terms of experimental and analytical modeling results. Our objective is to explore characteristics of the response and assess the fidelity of our model. The EMG system consists of a static transmitter and a man-portable sensor, which uses a pair of receivers that yield a gradiometric measurement. Experimental results were collected over a range of wire depths from 3.4 to 8.5 m. A number of different transmitter positions were explored, and the tests studied were conducted at 200 kHz. Modeling results were consistent with the experimental results and supported a number of key findings. Results are presented showing that, in order to maximize the strength of the wire response, the transmitter should be positioned approximately 5 m off the wire axis. Furthermore, in order to avoid unwanted transmitter influence on the response, the EMG should be at least 30 m from the transmitter. Using the experimental and modeling results, we found a linear relationship between the width of the magnitude response peak and the wire depth. Based on our experimental results, the EMG is able to yield a discernible target response at a depth of at least 7 m. Lastly, an example of how the model can be used to optimize survey planning is presented. This paper illustrates how an EMG can be used to locate underground wires with applications ranging from underground utility mapping to the detection of shallow subsurface tunnels. © 2011 IEEE.
Scott N.V.,Riverside Research |
Handler R.A.,Texas A&M University
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2016
A nonlinear cluster analysis algorithm is used to characterize the spatial structure of a wind-sheared turbulent flow obtained from the direct numerical simulation (DNS) of the three-dimensional temperature and momentum fields. The application of self-organizing mapping to DNS data for data reduction is utilized because of the dimensional similitude in structure between DNS data and remotely sensed hyperspectral and multispectral data where the technique has been used extensively. For the three Reynolds numbers of 150, 180, and 220 used in the DNS, self-organized mapping is successful in the extraction of boundary layer streaky structures from the turbulent temperature and momentum fields. In addition, it preserves the cross-wind scale structure of the streaks exhibited in both fields which loosely scale with the inverse of the Reynolds number. Self-organizing mapping of the along wind component of the helicity density shows a layer of the turbulence field which is spotty suggesting significant direct coupling between the large and small-scale turbulent structures. The spatial correlation of the temperature and momentum fields allows for the possibility of the remote extrapolation of the momentum structure from thermal structure. © SPIE.
Nix S.,Northcentral University |
Gossett K.,Northcentral University |
Shepherd A.D.,Riverside Research
Air Medical Journal | Year: 2013
Pilot error has caused the majority of helicopter emergency medical services (HEMS) accidents in the United States for almost 2 decades. Pilot fatigue may have contributed to some of these accidents. This nonexperimental quantitative study investigated the relationships between fatigue reported by on-duty HEMS pilots (the criterion variable) and consecutive HEMS pilot day shifts, consecutive HEMS pilot night shifts, age, and experience as an HEMS pilot (the predictor variables). Surveys completed by 395 on-duty HEMS pilots in the US were examined to quantify respondent fatigue with the Brief Fatigue Inventory (BFI). This study found some evidence of a statistically significant positive relationship between HEMS pilot night shift respondent BFI scores and experience as an HEMS pilot, while controlling for consecutive HEMS pilot night shifts and age. A 1-way analysis of variance suggested that the effect of experience as an HEMS pilot on HEMS pilot night shift respondent BFI scores was statistically significant. Multivariate regression analysis suggested that experience as an HEMS pilot predicted HEMS pilot night shift respondent BFI scores. Additional quantitative research is recommended to confirm the results of this study and to investigate relationships between fatigue experienced by HEMS pilots and other variables that were not considered in this investigation. Qualitative research to identify and document fatigue management strategies that are used by experience HEMS pilots is also recommended. © 2013 Air Medical Journal Associates.
Filoux E.,Riverside Research |
Mamou J.,Riverside Research |
Aristizabal O.,New York University |
Ketterling J.A.,Riverside Research
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control | Year: 2011
The spatial resolution of high-frequency ultrasound (HFU, >20 MHz) imaging systems is usually determined using wires perpendicular to the beam. Recently, two tissue-mimicking phantoms (TMPs) were developed to estimate three-dimensional (3-D) resolution. Each TMP consists of nine 1-cm-wide slabs of tissue-mimicking material containing randomly distributed anechoic spheres. All anechoic spheres in one slab have the same dimensions, and their diameter is increased from 0.1 mm in the first slab to 1.09 mm in the last. The scattering background for one set of slabs was fabricated using 3.5-m glass beads; the second set used 6.4-m glass beads. The ability of a HFU system to detect these spheres against a speckle background provides a realistic estimation of its 3-D spatial resolution. In the present study, these TMPs were used with HFU systems using single-element transducers, linear arrays, and annular arrays. The TMPs were immersed in water and each slab was scanned using two commercial imaging systems and a custom HFU system based on a 5-element annular array. The annular array had a nominal center frequency of 40 MHz, a focal length of 12 mm, and a total aperture of 6 mm. A synthetic-focusing algorithm was used to form images with an increased depth-of-field. The penetration depth was increased by using a linear-chirp signal spanning 15 to 65 MHz over 4 s. Results obtained with the custom system were compared with those of the commercial systems (40-MHz probes) in terms of sphere detection, i.e., 3-D spatial resolution, and contrast-to-noise ratio (CNR). Resulting Bmode images indicated that only the linear-array transducer failed to clearly resolve the 0.2-mm spheres, which showed that the 3-D spatial resolution of the single-element and annulararray transducers was superior to that of the linear array. The single-element transducer could only detect these spheres over a narrow 1.5 mm depth-of-field, whereas the annular array was able to detect them to depths of at least 7 mm. For any size of the anechoic spheres, the annular array excited by a chirp-coded signal provided images of the highest contrast, with a maximum CNR of 1.8 at the focus, compared with 1.3 when using impulse excitation and 1.6 with the single-element transducer and linear array. This imaging configuration also provided CNRs above 1.2 over a wide depth range of 8 mm, whereas CNRs would quickly drop below 1 outside the focal zone of the other configurations. © 2011 IEEE.
Reinstein D.Z.,The London Clinic |
Reinstein D.Z.,Columbia University |
Reinstein D.Z.,Center Hospitalier National phtalmologie |
Yap T.E.,The London Clinic |
And 4 more authors.
Journal of Refractive Surgery | Year: 2015
PURPOSE: To compare measurements of corneal epithelial thickness using optical coherence tomography (OCT) and very high-frequency digital ultrasound (VHFDU). METHODS: Retrospective analysis of 189 virgin corneas and 175 post-laser refractive surgery (LRS) corneas that had corneal epithelial thickness measurement with RTVue Fourier-domain OCT (Optovue, Inc., Fremont, CA) (tear film included) and Artemis VHFDU (ArcScan Inc., Morrison, CO) (tear film excluded). Averages were calculated for the central 2-mm diameter zone and for two further concentric annuli of 1.5- and 0.5-mm width, each divided into eight sectors. Agreement was analyzed by mean difference (OCT - VHFDU), 95% limits of agreement (LoA) (1.96 standard deviation of the difference), and Bland-Altman analysis. RESULTS: In virgin epithelium, mean central thickness was 53.4 ± 3.20 μm (range: 46 to 62 μm) with OCT and 54.1 ± 2.96 μm (range: 48 to 61 μm) with VHFDU; OCT measured thinnest in 70% with a mean difference of -0.71 μm (95% LoA of ±3.94 μm, P < .001). In post-LRS epithelium, mean central thickness was 57.9 ± 6.08 μm (range: 42 to 77 μm) with OCT and 60.5 ± 6.47 μm (range: 42 to 79 μm) with VHFDU; OCT measured thinnest in 88%, with a mean difference of -2.48 μm (95% LoA of ±5.33 μm, P < .001). A larger difference between methods was more common with thicker epithelium. CONCLUSIONS: Corneal epithelial thickness measurements using OCT were found to be slightly thinner than for VHFDU. In contrast to VHFDU, OCT measurement includes the tear film, so the true difference is probably approximately 4 μm more than reported. The difference was greatest inferiorly and higher for post-LRS eyes and in thicker epithelium. © SLACK Incorporated.
Silverman R.H.,Columbia University |
Silverman R.H.,Riverside Research |
Urs R.,Columbia University |
Lloyd H.O.,Columbia University
Investigative Ophthalmology and Visual Science | Year: 2013
PURPOSE. While visualization of the retina and choroid has made great progress, functional imaging techniques have been lacking. Our aim was to utilize acoustic radiation force impulse (ARFI) response to probe functional properties of these tissues. METHODS. A single element 18-MHz ultrasound transducer was focused upon the retina of the rabbit eye. The procedure was performed with the eye proptosed and with the eye seated normally in the orbit. The transducer was excited to emit ARFI over a 10-ms period with a 25% duty cycle. Phase resolved pulse/echo data were acquired before, during, and following ARFI. RESULTS. In the proptosed eye, ARFI exposure produced tissue displacements ranging from 0 to 10 lm, and an immediate increase in choroidal echo amplitude to over 6 dB, decaying to baseline after about 1 second. In the normally seated eye, ultrasound phase shifts consistent with flow were observed in the choroid, but enhanced backscatter following ARFI rarely occurred. ARFI-induced displacements of about 10 lm were observed at the choroidal margins. Larger displacements occurred within the choroid and in orbital tissues. CONCLUSIONS. We hypothesize that elevated intraocular pressure occurring during proptosis induced choroidal ischemia and that acoustic radiation force produced a transient local decompression and reperfusion. With the eye normally seated, choroidal flow was observed and little alteration in backscatter resulted from exposure. Clinical application of this technique may provide new insights into diseases characterized by altered choroidal hemodynamics, including maculopathies, diabetic retinopathy, and glaucoma. © 2013 The Association for Research in Vision and Ophthalmology, Inc.
Hasan M.K.,Bangladesh University of Engineering and Technology |
Hasan M.K.,Kyung Hee University |
Anas E.M.A.,Bangladesh University of Engineering and Technology |
Alam S.K.,Riverside Research |
Lee S.Y.,Kyung Hee University
Ultrasound in Medicine and Biology | Year: 2012
Ultrasound elastography is emerging with enormous potential as a medical imaging modality for effective discrimination of pathological changes in soft tissue. It maps the tissue elasticity or strain due to a mechanical deformation applied to it. The strain image most often calculated from the derivative of the local displacement field is highly noisy because of the de-correlation effect mainly due to unstable free-hand scanning and/or irregular tissue motion; consequently, improving the SNR of the strain image is still a challenging problem in this area. In this paper, a novel approach using the nearest-neighbor weighted least-squares is presented for direct estimation of the 'mean' axial strain for high quality strain imaging. Like other time/frequency domain reported schemes, the proposed method exploits the fact that the post-compression rf echo signal is a time-scaled and shifted replica of the pre-compression rf echo signal. However, the elegance of our technique is that it directly computes the mean strain without explicitly using any post filter and/or previous local displacement/strain estimates as is usually done in the conventional approaches. It is implemented in the short-time Fourier transform domain through a nearest-neighbor weighted least-squares-based Fourier spectrum equalization technique. As the local tissue strain is expected to maintain continuity with its neighbors, we show here that the mean strain at the interrogative window can be directly computed from the common stretching factor that minimizes a cost function derived from the exponentially weighted windowed pre- and post-compression rf echo segments in both the lateral and axial directions. The performance of our algorithm is verified for up to 8% applied strain using simulation and experimental phantom data and the results reveal that the SNR of the strain image can be significantly improved compared to other reported algorithms in the literature. The efficacy of the algorithm is also tested with in vivo breast data known to have malignant or benign masses from histology. © 2012 World Federation for Ultrasound in Medicine & Biology.
Sampathkumar A.,Riverside Research
Proceedings of Meetings on Acoustics | Year: 2013
Conventional photoacoustic microscopy (PAM) employs light pulses to produce a photoacoustic (PA) effect and detects the resulting acoustic waves using an ultrasound transducer acoustically coupled to the target tissue. The resolution of conventional PAM is limited by the sensitivity and bandwidth of the ultrasound transducer. We have investigated an all-optical, pump-probe method employing interferometric detection of the acoustic signals that overcomes limitations of conventional PAM. This method does not require contact with the specimen and provides superior resolution. A 532-nm pump laser with a pulse duration of 5 ns excited the PA effect in tissue. Resulting acoustic waves produced surface displacements that were sensed interferometrically with a GHz bandwidth using a 532-nm continuous-wave (CW) probe laser and a Michelson interferometer. The pump and probe beams were coaxially focused using a 50X objective giving a diffraction-limited spot size of 0.5 μm. The phase-encoded probe beam was demodulated using a homodyne interferometer. The detected time-domain signal was time reversed using k-space wave-propagation methods to produce a spatial distribution of PA sources in the target tissue. Performance was assessed using 3D images of fixed, ex vivo, retina specimens. © 2013 Acoustical Society of America.