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As of 2022, breast cancer continues to be the most diagnosed cancer worldwide. This problem persists within the United States as well, as the American Cancer Society has reported that ∼12.5% of women will be diagnosed with invasive breast cancer over the course of their lifetime. Therefore, a clinical need continues to exist to address this disease from a treatment and therapeutic perspective. Current treatments for breast cancer and cancers more broadly include surgery, radiation, and chemotherapy. Adjuncts to these methods have been developed to improve the clinical outcomes for patients. One such adjunctive treatment is mild hyperthermia therapy (MHTh), which has been shown to be successful in the treatment of cancers by increasing effectiveness and reduced dosage requirements for radiation and chemotherapies. MHTh-assisted treatments can be performed with invasive thermal devices, noninvasive microwave induction, heating and recirculation of extracted patient blood, or whole-body hyperthermia with hot blankets.One common method for inducing MHTh is by using microwave for heat induction and magnetic resonance imaging for temperature monitoring. However, this leads to a complex, expensive, and inaccessible therapy platform. Therefore, in this work we aim to show the feasibility of a novel all-acoustic MHTh system that uses focused ultrasound (US) to induce heating while also using US tomography (UST) to provide temperature estimates. Changes in sound speed (SS) have been shown to be strongly correlated with temperature changes and can therefore be used to indirectly monitor heating throughout the therapy. Additionally, these SS estimates allow for heterogeneous SS-corrected phase delays when heating complex and heterogeneous tissue structures.Feasibility to induce localized heat in tissue was investigated in silico with a simulated breast model, including an embedded tumor using continuous wave US. Here, both heterogenous acoustic and thermal properties were modeled in addition to blood perfusion. We further demonstrate, with ex vivo tissue phantoms, the feasibility of using ring-based UST to monitor temperature by tracking changes in SS. Two phantoms (lamb tissue and human abdominal fat) with latex tubes containing varied temperature flowing water were imaged. The measured SS of the water at each temperature were compared against values that are reported in literature.Results from ex vivo tissue studies indicate successful tracking of temperature under various phantom configurations and ranges of water temperature. The results of in silico studies show that the proposed system can heat an acoustically and thermally heterogenous breast model to the clinically relevant temperature of 42°C while accounting for a reasonable time needed to image the current cross section (200 ms). Further, we have performed an initial in silico study demonstrating the feasibility of adjusting the transmit waveform frequency to modify the effective heating height at the focused region. Lastly, we have shown in a simpler 2D breast model that MHTh level temperatures can be maintained by adjusting the transmit pressure intensity of the US ring.This work has demonstrated the feasibility of using a 256-element ring array transducer for temperature monitoring; however, future work will investigate minimizing the difference between measured SS and the values shown in literature. A hypothesis attributes this bias to potential volumetric average artifacts from the ray-based SS inversion algorithm that was used, and that moving to a waveform-based SS inversion algorithm will greatly improve the SS estimates. Additionally, we have shown that an all-acoustic MHTh system is feasible via in silico studies. These studies have indicated that the proposed system can heat a tumor within a heterogenous breast model to 42°C within a narrow time frame. This holds great promise for increasing the accessibility and reducing the complexity of a future all-acoustic MHTh system.

Objective To analyze the preferred tissue locations of common breast masses in relation to anatomic quadrants and the fat-glandular interface (FGI) using ultrasound tomography (UST). Methods Ultrasound tomography scanning was performed in 206 consecutive women with 298 mammographically and/or sonographically visible, benign and malignant breast masses following written informed consent to participate in an 8-site multicenter, Institutional Review Board-approved cohort study. Mass locations were categorized by their anatomic breast quadrant and the FGI, which was defined by UST as the high-contrast circumferential junction of fat and fibroglandular tissue on coronal sound speed imaging. Quantitative UST mass comparisons were done for each tumor and peritumoral region using mean sound speed and percentage of fibroglandular tissue. Chi-squared and analysis of variance tests were used to assess differences. Results Cancers were noted at the FGI in 95% (74/78) compared to 51% (98/194) of fibroadenomas and cysts combined (P Conclusion Breast cancers form adjacent to fat and UST localized the vast majority to the FGI, while cysts were most often completely surrounded by dense tissue. These observations were supported by quantitative peritumoral analyses of sound speed values for fat and fibroglandular tissue.

Isolating the mainlobe and sidelobe contribution to the ultrasound image can improve imaging contrast by removing off-axis clutter. Previous work achieves this separation of mainlobe and sidelobe contributions based on the covariance of received signals. However, the formation of a covariance matrix at each imaging point can be computationally burdensome and memory intensive for real-time applications. Our work demonstrates that the mainlobe and sidelobe contributions to the ultrasound image can be isolated based on the receive aperture spectrum, greatly reducing computational and memory requirements.The separation of mainlobe and sidelobe contributions to the ultrasound image is shown in simulation,The aperture spectrum approach improves contrast by 1.9 to 6.4 dB beyond MIST and 8.9 to 13.5 dB beyond conventional DAS B-mode imaging. However, the aperture spectrum approach yields speckle texture similar to DAS. As a result, the aperture spectrum-based approach has less CNR than MIST but greater CNR than conventional DAS. The CPU implementation of the aperture spectrum-based approach is shown to reduce computation time by a factor of 9 and memory consumption by a factor of 128 for a 128-element transducer.The mainlobe contribution to the ultrasound image can be isolated based on the receive aperture spectrum, which greatly reduces the computational cost and memory requirement of this approach as compared with MIST.

Ultrasound computed tomography (USCT) is a promising imaging technique for breast cancer diagnosis. Full-waveform inversion (FWI)-based image reconstruction methods based on the acoustic wave equation can produce quantitatively accurate images of acoustic properties with higher spatial resolution compared to ray-based methods. One common USCT design employs a circular ring-array of elevation-focused ultrasonic transducers that can be translated orthogonally to the imaging plane to achieve volumetric scanning. Currently, slice-by-slice (SBS) reconstruction methods are often used in this setting. Such methods use a 2D wave physic model to reconstruct a cross-sectional image for each position of the ring-array and vertically stack them together to render the 3D volume. However, this approach neglects the 3D wave propagation physics and transducer’s focusing properties, leading to out-of-plane scattering artifacts and degraded spatial resolution. To address this, a 3D time-domain FWI method that utilizes measurement data acquired at multiple adjacent ring-array locations is proposed. The reconstruction method was investigated using virtual imaging studies of ring-array-based USCT that employed realistic 3D numerical breast phantoms. The results demonstrated improved spatial resolution (both in-plane and off-plane) and reduced image artifacts compared to the SBS approach. Additionally, the impact of the number of ring-array locations on image quality is assessed.

Purpose: Women whose mammographic breast density declines within 12–18 months of initiating tamoxifen for chemoprevention or adjuvant treatment show improved therapeutic responses compared with those whose density is unchanged. We tested whether measuring changes in sound speed (a surrogate of breast density) using ultrasound tomography (UST) could enable rapid identification of favorable responses to tamoxifen. Methods: We evaluated serial density measures at baseline and at 1 to 3, 4 to 6, and 12+ months among 74 women (aged 30–70 years) following initiation of tamoxifen for clinical indications, including an elevated risk of breast cancer (20%) and diagnoses of in situ (39%) or invasive (40%) breast carcinoma, enrolled at Karmanos Cancer Institute and Henry Ford Health System (Detroit, MI, USA). For comparison, we evaluated an untreated group with screen negative mammography and frequency-matched on age, race, and menopausal status (n = 150), at baseline and 12 months. Paired t-tests were used to assess differences in UST sound speed over time and between tamoxifen-treated and untreated patients. Results: Sound speed declined steadily over the 12 month period among patients receiving tamoxifen (mean (SD): −3.0 (8.2) m/s; p = 0.001), whereas density remained unchanged in the untreated group (mean (SD): 0.4 (7.1) m/s; p = 0.75 (relative change between groups: p = 0.0009)). In the tamoxifen group, we observed significant sound speed reductions as early as 4–6 months after tamoxifen initiation (mean (SD): −2.1 (6.8) m/s; p = 0.008). Sound speed reductions were greatest among premenopausal patients (P-interaction = 0.0002) and those in the middle and upper tertiles of baseline sound speed (P-interaction = 0.002). Conclusions: UST can image rapid declines in sound speed following initiation of tamoxifen. Given that sound speed and mammographic density are correlated, we propose that UST breast imaging may capture early responses to tamoxifen, which in turn may have utility in predicting therapeutic efficacy.

We evaluated whole breast stiffness imaging by SoftVue ultrasound tomography (UST), extracted from the bulk modulus, to volumetrically map differences in breast tissues and masses. A total 206 women with either palpable or mammographically/sonographically visible masses underwent UST scanning prior to biopsy as part of a prospective, HIPAA-compliant multicenter cohort study. The volumetric data sets comprised 298 masses (78 cancers, 105 fibroadenomas, 91 cysts and 24 other benign) in 239 breasts. All breast tissues were segmented into six categories, using sound speed to separate fat from fibroglandular tissues, and then subgrouped by stiffness into soft, intermediate and hard components. Ninety percent of women had mammographically dense breasts but only 11.2% of their total breast volume showed hard components while 69% of fibroglandular tissues were softer. All smaller masses (

In this paper we used a new class of special polynomials which satisfy a Sturm Liouville diferential equation of second order. These polynomials form a basis of a polynomial space. Using coefficients of these polynomials we formed a lower triangular matrix which represents a transition matrix from standard polynomial basis to this new basis. Using Matlab for given natural number we obtained a corresponding matrix, found an inverse of this matrix, their eigenvalues and some interesting properties. Using a new class of special polynomials we obtained some interesting and useful summation formulas.

This study explored the relationship between the extent of the fat–glandular interface (FGI) and the presence of malignant vs. benign lesions. Two hundred and eight patients were scanned with ultrasound tomography (UST) as part of a Health Insurance Portability and Accountability Act (HIPAA)-compliant study. Segmentation of the sound speed images, employing the k-means clustering method, was used to help define the extent of the FGI for each patient. The metric, α, was defined as the surface area to volume ratio of the segmented fibroglandular volume and its mean value across patients was determined for cancers, fibroadenomas and cysts. ANOVA tests were used to assess significance. The means and standard deviations of α for cancers, fibroadenomas and cysts were found to be 4.0 ± 2.0 cm−1, 3.1 ± 1.7 cm−1 and 2.3 ± 0.9 cm−1, respectively. The differences were statistically significant (p < 0.001). The separation between the groups increased when α was measured on only the image slice where the finding was most prominent, with values for cancers, fibroadenomas and cysts of 5.4 ± 3.6 cm−1, 3.6 ± 2.3 cm−1 and 2.4 ± 1.5 cm−1, respectively. Of the three types of masses studied, cancer was associated with the most extensive FGIs, suggesting a potential role for the FGI in carcinogenesis, a subject for future studies.

Background: Tamoxifen therapy has been shown to have greater therapeutic benefit among women whose breast density declines subsequent to treatment than among women whose density does not decline. Although limited data suggests that endocrine symptoms after tamoxifen initiation may be associated with improved breast cancer outcomes, it is unknown whether these symptoms are associated with reductions in breast density. We therefore evaluated endocrine symptoms and change in breast density in a 12-month longitudinal study of women undergoing tamoxifen therapy for clinical indications. Methods: Cohort members (N=74) were aged 30-74 years in the Ultrasound Study of Tamoxifen at Karmanos Cancer Institute and Henry Ford Health Systems (Detroit, MI). Endocrine symptoms and breast density were both assessed prior to tamoxifen initiation (T0) and at 1-3 months (T1), 4-6 months (T2), and approximately 12 months (T3) post-tamoxifen initiation. Treatment-associated endocrine symptoms included treatment-emergent or increasing vasomotor and/or joint symptoms. Endocrine symptom severity was also assessed with a Likert scale for symptom frequency and categorized as no symptoms (score=0), low/moderate symptoms (score=1-5), and high symptoms (score=6+). Sound speed (m/s), a surrogate of volumetric breast density, was measured with whole breast ultrasound tomography. Change in breast density was calculated as density at T1-T3 minus density at T0. We used multivariable linear regression to estimate mean change in density by endocrine symptoms adjusting for age, race, menopausal status, body mass index, and baseline sound speed. Generalized estimating equations were used to account for within-subject correlations over time. Results: Women with treatment-associated endocrine symptoms had an overall greater mean reduction in breast density compared with women without symptoms (mean change [95% CI]: -1.97 m/s [-3.80, -0.13]; -0.27 m/s [- 3.50, 2.95], respectively; p=0.22). Longitudinal trends in breast density significantly differed for women with versus without treatment-associated endocrine symptoms (p-interaction=0.02). Significant declines in breast density over time were observed among women with treatment-associated endocrine symptoms (p-trend=0.005), but not among women without symptoms (p-trend=0.16). Similar trends in breast density decline were observed among women with higher symptom severity (p-trends for no symptoms=0.53; low/moderate symptoms=0.04; high symptoms=0.008). Conclusions: These findings suggest that treatment-associated endocrine symptoms may be associated with a significant decline in breast density after tamoxifen initiation. Further studies are needed to assess whether these observations can predict clinical outcome, and if confirmed, both treatment-associated endocrine symptoms and observed reductions in breast density may be useful for patients and providers to improve adherence. Citation Format: Cody Ramin, Ruth Pfeiffer, Shaoqi Fan, Maeve Mullooly, Roni T. Falk, Mark A. Sak, Michael S. Simon, David H. Gorski, Haythem Ali, Peter Littrup, Nebojsa Duric, Mark E. Sherman, Gretchen L. Gierach. Treatment-associated endocrine symptoms and change in ultrasound tomography measures of breast density after tamoxifen therapy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5805.

Purpose: High breast density, as measured by mammography, is associated with increased breast cancer risk, but standard methods of assessment have limitations including 2D representation of breast tissue, distortion due to breast compression, and use of ionizing radiation. Ultrasound tomography (UST) is a novel imaging method that averts these limitations and uses sound speed measures rather than x-ray imaging to estimate breast density. The authors evaluated the reproducibility of measures of speed of sound and changes in this parameter using UST. Methods: One experienced and five newly trained raters measured sound speed in serial UST scans for 22 women (two scans per person) to assess inter-rater reliability. Intrarater reliability was assessed for four raters. A random effects model was used to calculate the percent variation in sound speed and change in sound speed attributable to subject, scan, rater, and repeat reads. The authors estimated the intraclass correlation coefficients (ICCs) for these measures based on data from the authors’ experienced rater. Results: Median (range) time between baseline and follow-up UST scans was five (1–13) months. Contributions of factors to sound speed variance were differences between subjects (86.0%), baseline versus follow-up scans (7.5%), inter-rater evaluations (1.1%), and intrarater reproducibility (∼0%). When evaluatingmore » change in sound speed between scans, 2.7% and ∼0% of variation were attributed to inter- and intrarater variation, respectively. For the experienced rater’s repeat reads, agreement for sound speed was excellent (ICC = 93.4%) and for change in sound speed substantial (ICC = 70.4%), indicating very good reproducibility of these measures. Conclusions: UST provided highly reproducible sound speed measurements, which reflect breast density, suggesting that UST has utility in sensitively assessing change in density.« less

The objective of our study was to determine the clinical display thresholds of an ultrasound tomography prototype relative to MRI for comparable visualization of breast anatomy and tumor rendering.Thirty-six women were imaged with MRI and our ultrasound tomography prototype. The ultrasound tomography scan generated reflection, sound-speed, and attenuation images. The reflection images were fused with the components of the sound-speed and attenuation images that achieved thresholds to represent parenchyma or solid masses using an image arithmetic process. Qualitative and quantitative comparisons of MRI and ultrasound tomography clinical images were used to identify anatomic similarities and optimized thresholds for tumor shapes and volumes.Thresholding techniques generated ultrasound tomography images comparable to MR images for visualizing fibrous stroma, parenchyma, fatty tissues, and tumors. In 25 patients, tumors were cancerous and in 11, benign. Optimized sound-speed thresholds of 1.46±0.1 and 1.52±0.03 km/s were identified to best represent the extent of fibroglandular tissue and solid masses, respectively. An arithmetic combination of attenuation images using a threshold of 0.16±0.04 dB/cm (mean±SD) further characterized benign from malignant masses. No significant difference in tumor volume was noted between benign or malignant masses by ultrasound tomography or MRI (p0.1) using these universal thresholds.Ultrasound tomography is able to image and render breast tissues in a manner comparable to MRI. Using universal ultrasound tomography threshold values for rendering the size and distribution of benign and malignant tissues appears feasible without IV contrast material.

Purpose: To explore the feasibility of improving cross-sectional reflection imaging of the breast using refractive and attenuation corrections derived from ultrasound tomography data. Methods: The authors have adapted the planar Kirchhoff migration method, commonly used in geophysics to reconstruct reflection images, for use in ultrasound tomography imaging of the breast. Furthermore, the authors extended this method to allow for refractive and attenuative corrections. Using clinical data obtained with a breast imaging prototype, the authors applied this method to generate cross-sectional reflection images of the breast that were corrected using known distributions of sound speed and attenuation obtained from the same data. Results: A comparison of imagesreconstructed with and without the corrections showed varying degrees of improvement. The sound speed correction resulted in sharpening of detail, while the attenuation correction reduced the central darkening caused by path length dependent losses. The improvements appeared to be greatest when dense tissue was involved and the least for fatty tissue. These results are consistent with the expectation that denser tissues lead to both greater refractive effects and greater attenuation. Conclusions: Although conventional ultrasound techniques use time-gain control to correct for attenuation gradients, these corrections lead to artifacts because the true attenuation distribution is not known. The use of constant sound speed leads to additional artifacts that arise from not knowing the sound speed distribution. The authors show that in the context of ultrasound tomography, it is possible to construct reflection images of the breast that correct for inhomogeneous distributions of both sound speed and attenuation.

Although mammography is the gold standard for breast imaging, its limitations result in a high rate of biopsies of benign lesions and a significant false negative rate for women with dense breasts. In response to this imaging performance gap we have been developing a clinical breast imaging methodology based on the principles of ultrasound tomography. The Computed Ultrasound Risk Evaluation (CURE) system has been designed with the clinical goals of whole breast, operator-independent imaging, and differentiation of breast masses. This paper describes the first clinical prototype, summarizes our initial image reconstruction techniques, and presents phantom and preliminary in vivo results. In an initial assessment of its in vivo performance, we have examined 50 women with the CURE prototype and obtained the following results. (1) Tomographic imaging of breast architecture is demonstrated in both CURE modes of reflection and transmission imaging. (2) In-plane spatial resolution of 0.5 mm in reflection and 4 mm in transmission is achieved. (3) Masses > 15 mm in size are routinely detected. (4) Reflection, sound speed, and attenuation imaging of breast masses are demonstrated. These initial results indicate that operator-independent, whole-breast imaging and the detection of breast masses are feasible. Future studies will focus on improved detection and differentiation of masses in support of our long-term goal of increasing the specificity of breast exams, thereby reducing the number of biopsies of benign masses.

Women with high mammographic breast density have a four- to fivefold increased risk of developing breast cancer compared to women with fatty breasts. Many preventative strategies have attempted to correlate changes in breast density with response to interventions including drugs and diet. The purpose of this work is to investigate the feasibility of assessing breast density with acoustic velocity measurements with ultrasoundtomography, and to compare the results with existing measures of mammographic breast density. An anthropomorphic breast tissue phantom was first imaged with our computed ultrasoundtomography clinical prototype. Strong positive correlations were observed between sound speed and material density, and sound speed and computed tomography number (Pearson correlation coefficients = 0.87 and 0.91, respectively). A cohort of 48 women was then imaged. Whole breast acoustic velocity was determined by creating image stacks and evaluating the sound speed frequency distribution. The acoustic measures of breast density were evaluated by comparing these results to two mammographic density measures: (1) qualitative estimates determined by a certified radiologist using the BI-RADS Categorical Assessment based on a 1 (fatty) to 4 (dense) scale, and (2) quantitative measurements via digitization and computerized analysis of archival mammograms. A one-way analysis of variance showed that a significant difference existed between the mean values of sound speed according to BI-RADS category, while post hoc analyses using the Scheffe criterion for significance indicated that BI-RADS 4 (dense) patients had a significantly higher sound speed than BI-RADS 1, 2, and 3 at an alpha level of 0.05. Using quantitative measures of breast density, a direct correlation between the mean acoustic velocity and calculated mammographic percent breast density was demonstrated with correlation coefficients ranging from 0.75 to 0.89. The results presented here support the hypothesis that sound speed can be used as an indicator of breast tissue density. Noninvasive, nonionizing monitoring of dietary and chemoprevention interventions that affect breast density are now possible.

High breast density, as measured by mammography, is associated with increased breast cancer risk, but standard methods of assessment have limitations including 2D representation of breast tissue, distortion due to breast compression, and use of ionizing radiation. Ultrasound tomography (UST) is a novel imaging method that averts these limitations and uses sound speed measures rather than x-ray imaging to estimate breast density. The authors evaluated the reproducibility of measures of speed of sound and changes in this parameter using UST.One experienced and five newly trained raters measured sound speed in serial UST scans for 22 women (two scans per person) to assess inter-rater reliability. Intrarater reliability was assessed for four raters. A random effects model was used to calculate the percent variation in sound speed and change in sound speed attributable to subject, scan, rater, and repeat reads. The authors estimated the intraclass correlation coefficients (ICCs) for these measures based on data from the authors' experienced rater.Median (range) time between baseline and follow-up UST scans was five (1-13) months. Contributions of factors to sound speed variance were differences between subjects (86.0%), baseline versus follow-up scans (7.5%), inter-rater evaluations (1.1%), and intrarater reproducibility (∼0%). When evaluating change in sound speed between scans, 2.7% and ∼0% of variation were attributed to inter- and intrarater variation, respectively. For the experienced rater's repeat reads, agreement for sound speed was excellent (ICC = 93.4%) and for change in sound speed substantial (ICC = 70.4%), indicating very good reproducibility of these measures.UST provided highly reproducible sound speed measurements, which reflect breast density, suggesting that UST has utility in sensitively assessing change in density.

This paper examines relations between the radio surface brightness £ and the diameter D (also known as Σ-D relations) for a sample of extragalactic supernova remnants (SNRs) as constructed from a combination of published data and data from our own surveys. Our sample of extragalactic SNRs is the largest ever devised for the purpose of analyzing Σ-D relations. The main results of this paper may be summarized as follows: (i) the empirical relations for SNRs in 10 of the 11 nearby galaxies studied have the approximately trivial Σ D -2 form, therefore limiting their interpretation as physically meaningful relations. In addition, these relations are subject to selection effects rendering them even less useful. Further Monte Carlo simulations suggest that the effect of survey sensitivity has the opposite effect of volume selection (e.g. Malinquist bias, a volume selection effect that shapes the Galactic sample) by tending to flatten the slopes toward a trivial relation. In this case, the true slopes may be steeper than the observed slopes; (ii) compact M 82 SNRs appear to follow a uniquely different Σ-D relation in comparison to the larger, older SNRs in the other 10 galaxies. Monte Carlo simulations suggest that the probability of this difference arising by chance is 1% to 10%, depending on what is assumed regarding the underlying SNR population; (iii) three candidate hypernova remnants were identified in our sample of 11 nearby galaxies.

We present a wide field, sub-arcminute resolution VLA image of the Galactic Center region at 330 MHz. With a resolution of ~ 7" X 12" and an RMS noise of 1.6 mJy/beam, this image represents a significant increase in resolution and sensitivity over the previously published VLA image at this frequency. The improved sensitivity has more than tripled the census of small diameter sources in the region, has resulted in the detection of two new Non Thermal Filaments (NTFs), 18 NTF candidates, 30 pulsar candidates, reveals previously known extended sources in greater detail, and has resulted in the first detection of Sagittarius A* in this frequency range. A version of this paper containing full resolution images may be found at http://lwa.nrl.navy.mil/nord/AAAB.pdf., Astronomical Journal, Accepted 62 Pages, 21 Figures

We present a multi-frequency study of supernova remnants (SNRs) and $\ion{H}{ii }$ regions in the nearby Sculptor Group Sd galaxy NGC 300, based on new ATCA observations at the wavelengths of 13 and 20 cm, XMM-Newton observations, newly-processed ROSAT (PSPC/HRI; Read & Pietsch 2001) and VLA (20/6 cm) images of this galaxy. We have investigated the physical properties at the X-ray and radio wavelengths of the 28 optical SNRs found by Blair & Long (1997) and have expanded on the multi-wavelength work by Pannuti et al. (2000) on this same galaxy. From a total of 54 radio sources and 11 X-ray sources, we report 18 SNRs and three (3) SNR candidates (classified by spectral index alone) in NGC 300. Five of these 18 SNRs are associated with reported optical SNRs and three have X-ray counterparts. An additional 12 radio SNRs are seen in the Blair & Long (1997) [S II] images. We also investigate the luminosity function of our SNRs. Three background radio sources are confirmed and 12 other sources could represent additional background objects. Twenty two radio correlations with OB associations within NGC 300 correspond to either $\ion{H}{ii }$ regions or SNRs making them a good tracer of SNRs near star-forming regions. Additionally, two radio sources coincide with potential globular clusters of NGC 300 reported by Kim et al. (2002).

We report the detection of Sagittarius A*, the radio source associated with our Galaxy's central massive black hole, at 330 MHz with the Very Large Array. Implications for the spectrum and emission processes of Sagittarius A* are discussed and several hypothetical geometries of the central region are considered., Astrophysical Journal Letters, Accepted

Continued improvements in existing low frequency radio interferometers are expected, but limits of sensitivity, angular resolution, and frequency range impose fundamental restrictions which cannot easily be overcome. This has inspired the development of the Low Frequency ARray (LOFAR) which will provide significantly increased imaging power over present low frequency systems. In light of advantages offered by recent low frequency observations of the Galactic center, we consider how LOFAR might impact the field by the end of this decade.

The scientific need for a homogenous remote telescope image request system is rapidly escalating as more remote or robotic telescopes are brought to function and scientific programs are created or adapted to use such powerful telescopes. To respond to this need, we have drafted a protocol - "Remote Telescope Markup Language" (Version 2.1) - which has enabled us to implement a non-homogeneous network of imaging telescopes capable of processing requests for the acquisition and retrieval of simple astronomical images. This protocol is designed to be independent of the specific instrumentation and software that control the remote and/or robotic telescopes. It embeds traditional astronomical features such as coordinates and exposure times, and allows for prioritized queue scheduling of telescopes while protecting the telescope operating system. The prioritization supports high-stakes interruption of other observations - "Targets of Opportunity" like optical detection of gamma-ray bursts or other transient events. Some generality in this definition and flexibility is desirable, so that a broad variety of objects and observations can be accommodated within this standard. A number of professional observatories, telescope hardware/software companies, and amateur astronomers are already working with this version of RTML and a large body of additional professional and amateur users willing to share observing time and/or provide observations for scientific or educational use could easily adopt this protocol. The next generation mark-up language (RTML 3) will include elements necessary to schedule more complex observations, enabling its use in practically all ground-based and satellite observatories.

We present a study of 35 radio-selected supernova remnant (SNR) candidates in the nearby spiral galaxy NGC 6946. In this study, an optically selected sample of 27 SNRs from Matonick & Fesen is compared to our sample of radio-selected SNRs. The optically selected SNRs are found to have almost no overlap with the radio-selected sample. This dichotomy is further enhanced by the observation that the optically selected SNRs favor the interarm regions, while the radio-emitting SNRs lie predominately on the spiral arms in or near regions of high star formation. The separation of the two samples of SNRs is discussed in terms of selection effects and differences in cosmic-ray production. The optical sample of SNRs is probably biased toward those SNRs located in areas of NGC 6946 where the confusion of Hα emission by H II regions is relatively low and the SNRs are easier to identify by their emission-line signatures. The radio-selected sample is also subject to selection biases such that these SNRs favor the arms. However, the absence of radio emission from the optically selected, largely interarm SNRs and the relatively large number of radio-detected SNRs in the arms require additional explanation. The properties of the radio-selected SNRs are discussed in the context of diffusive shock acceleration theory. We find that the theory can account for the range in radio flux densities and the nondetection of the optically selected SNRs. The differences in the radio properties between the arm and interarm population of SNRs can be explained by differences in the average gas densities and magnetic fields since the latter affect both the cosmic-ray yield and the radio properties of the SNRs. The possibility that the arm and interarm SNRs arise from different stellar populations is also addressed.

The most common stars in the Galaxy are the main-sequence M dwarfs, yet current techniques are not optimized for detecting companions around the lowest mass M dwarfs, those with spectral designations ranging from M6 to M10. Described in this paper is a search for companions around such stars using a newly designed differential spectrophotometric technique. This novel method combines the strengths of the photometric and spectroscopic techniques, while it minimizes their inherent limitations. The scientific goal of this project is to search for short-period systems containing brown dwarfs and giant planets. The detection of or placing limits on such systems will help discriminate among competing theories of planetary formation.

We present Hα images of four edge-on galaxies: NGC 5775, NGC 3044, NGC 4183, and NGC 3556. Our goals are twofold: first, to continue the study of the occurrence and physical properties of extraplanar diffuse ionized gas (DIG), and second, to compare extraplanar Hα, H I, and radio continuum emission. The DIG of NGC 5775 is found to be concentrated in numerous bright filaments extending as high as 6 kpc off the midplane. NGC 3044, on the other hand, has a bright, smooth region of DIG above the central part of the disk with some faint filaments at higher galactocentric radius. Vertical profile fits to the extraplanar emission show that both NGC 5775 and NGC 3044 have DIG layers more extended than the Reynolds layer. In contrast, NGC 4183 shows very little extraplanar DIG. Profile fits suggest that it is very unlikely that the DIG layer of NGC 4183 is as extended as the Reynolds layer. The correlation between levels of star formation and prominence of DIG layers for these galaxies is consistent with previous observations. A prediction of the "chimney model" of the ISM is that extraplanar Hα features should have H I and radio continuum counterparts. Comparisons among these three tracers have revealed, for the first time, correlations on the scale of individual extraplanar filaments in a galactic disk. NGC 5775 shows correlations between Hα filaments, H I shells, and radio continuum spurs that are consistent with a chimney model. However, features identified as possible chimneys in NGC 5775 show radio spectral indices steeper than would be expected if cosmic rays were swept into the halo via galactic winds. Calculations of cosmic-ray propagation scale lengths within the DIG filaments demonstrate that diffusion may indeed be responsible for transporting cosmic rays through chimneys marked by DIG filaments. Correlated emission in these three tracers is also seen in NGC 3044, where extraplanar H I and radio continuum features appear to be associated with the galaxy's central region of extraplanar DIG, as well as filaments above the disk. Such correlations are not as prominent in NGC 3556, where extraplanar DIG detection is hampered by the galaxy's relatively low inclination.

Using radio data to identify and optical data to confirm, we have established the largest and most complete sample of extragalactic radio-bright supernova remnants (SNRs) in the nearby spiral galaxy M33. We have identified 53 radio SNRs, doubling the size of the earlier survey by Duric et al. The increased sample size provides more insight into the nature of SNRs and provides an extensive informational database about SNRs for future studies. The SNR sample was analyzed for statistical trends that relate to the evolution of their radio emission. We report no significant correlation between the radio flux densities and diameters of SNRs in our sample. The absence of a statistically meaningful Σ-D relation is consistent with the view that environmental factors govern the radio evolution of SNRs. A new radio luminosity function for SNRs is presented. Although there appears to be a break in the function, the break is the result of selection effects and not intrinsic to the sample. A comparison of the radio luminosity function with the integrated radio continuum properties of M33 suggests that SNRs may well be the primary source of the relativistic electrons in M33. A histogram of synchrotron spectral indices of the SNRs is presented. Statistical analysis of the spectral index distribution indicates that the mean spectral index of SNRs in M33 is steeper than the mean in samples of SNRs in the Galaxy or the LMC and is consistent with a particle spectrum expected from a diffusive shock acceleration process.

We report on multi-epoch millimeter observations of variable radio sources that were identified through the 6-cm Galactic plane survey by Gregory and Taylor. Although the aim of the original survey was to search for exotic galactic radio sources such as Cyg X-3, our multifrequency study in the past suggested that the majority of these sources are extragalactic. To explore intrinsic variability of these sources, we carried out monitoring observations at short millimeter wavelengths where the interstellar scintillation effects become less significant and stronger intrinsic variability is expected as the millimeter emission arises from deeper in the cores. Most of the observed sources show moderate degrees of millimeter variability indicating they are intrinsically variable. The spectra for some observed sources are flat out to millimeter wavelengths — similar to that of blazars. Thus the survey sample is likely to contain many unidentified radio-loud AGN behind the Milky Way.

We present a new and larger sample of supernova remnants in the nearby spiral galaxy M33. The sample is based upon CCD interference filter observations obtained with the Kitt Peak 4 m telescope and spectroscopic observations obtained with the Multiple Mirror Telescope. Using optical emission-line ratios, supplemented by a radio continuum map of M33 (Duric et al.; Gordon et al.), we have identified 98 supernova remnant (SNR) candidates, of which 53 were previously unknown. We have obtained spectra of 27 SNR candidates, bringing the total number of M33 SNRs for which spectra are available to 72. All the spectra show the characteristic signature of shock-heated gas, which leads us to believe that the rest of the candidates are also supernova remnants. The large sample provides a useful database to investigate the global properties of SNRs. In this paper, we present a new cumulative number-diameter [N(

We report observational results of a VLA 20 cm and 6 cm survey of the nearby spiral galaxy NGC 6946. The purpose of the survey is to identify compact radio sources in NGC 6946. We report the detection of 118 such sources. Using the spectral index to discriminate between thermal and nonthermal emission, 37 candidate sources have been identified as possible supernova remnants or background objects, 31 candidate sources have been identified as possible H II regions, and six sources have been identified with inverted spectra. The remaining sources were detected only at 20 cm. A catalog summarizing the properties of the radio sources is presented. The source positions, flux densities, and spectral indices are listed in the catalog. An atlas consisting of contour maps of all detected sources is presented.

Breast density is an important indicator for a woman's lifetime risk of breast cancer. A 3D model of breast density can be obtained by taking 3D tomographic ultrasound and then identifying tissue distribution in the breast with 3D medical image segmentation. In this paper, we compare two segmentation algorithms, EM-MPM (Expectation Maximization with Maximization of Posterior Marginals) and K-means clustering using simulated phantoms. The computational phantoms cover various tissue density patterns. A total of twenty volumes of three dimensional synthetic ultrasound breast images were compared. We found that EM-MPM performs better than K-means Clustering on segmentation accuracy because the segmentation result fits the ground truth data very well. The EM-MPM is able to use a Bayesian prior assumption, which takes advantage of the 3D structure and finds a better localized segmentation. EM-MPM performs significantly better especially for the highly dense tissue scattered within low density tissue and for volumes with low contrast between high and low density tissues.

To explore the feasibility of improving cross-sectional reflection imaging of the breast using refractive and attenuation corrections derived from ultrasound tomography data.The authors have adapted the planar Kirchhoff migration method, commonly used in geophysics to reconstruct reflection images, for use in ultrasound tomography imaging of the breast. Furthermore, the authors extended this method to allow for refractive and attenuative corrections. Using clinical data obtained with a breast imaging prototype, the authors applied this method to generate cross-sectional reflection images of the breast that were corrected using known distributions of sound speed and attenuation obtained from the same data.A comparison of images reconstructed with and without the corrections showed varying degrees of improvement. The sound speed correction resulted in sharpening of detail, while the attenuation correction reduced the central darkening caused by path length dependent losses. The improvements appeared to be greatest when dense tissue was involved and the least for fatty tissue. These results are consistent with the expectation that denser tissues lead to both greater refractive effects and greater attenuation.Although conventional ultrasound techniques use time-gain control to correct for attenuation gradients, these corrections lead to artifacts because the true attenuation distribution is not known. The use of constant sound speed leads to additional artifacts that arise from not knowing the sound speed distribution. The authors show that in the context of ultrasound tomography, it is possible to construct reflection images of the breast that correct for inhomogeneous distributions of both sound speed and attenuation.

Despite some shortcomings, mammography is currently the standard of care for breast cancer screening and diagnosis. However, breast ultrasound tomography is a rapidly developing imaging modality that has the potential to overcome the drawbacks of mammography. It is known that women with high breast densities have a greater risk of developing breast cancer. Measuring breast density is accomplished through the use of mammographic percent density, defined as the ratio of fibroglandular to total breast area. Using an ultrasound tomography (UST) prototype, we created sound speed images of the patient's breast, motivated by the fact that sound speed in a tissue is proportional to the density of the tissue. The purpose of this work is to compare the acoustic performance of the UST system with the measurement of mammographic percent density. A cohort of 251 patients was studied using both imaging modalities and the results suggest that the volume averaged breast sound speed is significantly related to mammographic percent density. The Spearman correlation coefficient was found to be 0.73 for the 175 film mammograms and 0.69 for the 76 digital mammograms obtained. Since sound speed measurements do not require ionizing radiation or physical compression, they have the potential to form the basis of a safe, more accurate surrogate marker of breast density.

Breast density descriptors were estimated from ultrasound tomography (UST) and digital mammogram (DM) images of 46 anthropomorphic software breast phantoms. Each phantom simulated a 450 ml or 700 ml breast with volumetric percent density (PD) values between 10% and 50%. The UST based volumetric breast density (VBD) estimates were calculated by thresholding the reconstructed UST images. Percent density (PD) values from DM images were estimated interactively by a clinical breast radiologist using Cumulus software. Such obtained UST VBD and Cumulus PD estimates were compared with the ground truth VBD values available from phantoms. The UST VBD values showed a high correlation with the ground truth, as evidenced by the Pearson correlation coefficient of r=0.93. The Cumulus PD values also showed a high correlation with the ground truth (r=0.84), as well as with the UST VBD values (r=0.78). The consistency in measuring the UST VBD and Cumulus PD values was analyzed using the standard error of the estimation by linear regression (σ E ). The σ E value for Cumulus PD was 1.5 times higher compared to the UST VBD (6.54 vs. 4.21). The σ E calculated from two repeated Cumulus estimation sessions (σ E =4.66) was comparable with the UST. Potential sources of the observed errors in density measurement are the use of global thresholding and (for Cumulus) the human observer variability. This preliminary study of simulated phantom UST images showed promise for non-invasive estimation of breast density.

Conventional ultrasound techniques use beam-formed, constant sound speed ray models for fast image reconstruction. However, these techniques are inadequate for the emerging new field of ultrasound tomography (UST). We present a new technique for the reconstruction of reflection images from UST data. We have extended the planar Kirchhoff migration method used in geophysics, and combined it with sound speed and attenuation data obtained from the transmission signals to create reflection ultrasound images that are corrected for refractive and attenuative effects. The resulting technique was applied to in-vivo breast data obtained with an experimental prototype. The results indicate that sound speed and attenuation corrections lead to considerable improvements in image quality, particularly in dense tissues where the refractive and scattering effects are the greatest.

We report on the use of ultrasound tomography (UST) to characterize breast cancer and study the local and distant tumor environments. We have imaged the tumor and its environment in 3 cases of breast cancer using a UST prototype and its associated image reconstruction algorithms. After generating images of reflection, sound speed and attenuation, the images were fused in combinations that allowed visualization and characterization of the interior of the tumor as well as the tissue immediate to the tumor and beyond. The reflection UST images demonstrated the presence of spiculation, and architectural distortion, indicators of both local tumor invasion and distant involvement with surrounding tissues. Furthermore, the sound speed images showed halos of elevated sound speed surrounding the tumors, indicating a local environment characterized by stiff tissues. The combination of sound speed and attenuation images revealed that the tumor interiors were the stiffest tissues in the region studied. These features and characteristics are commensurate with the known biomechanical properties of cancer and may be manifestations of the desmoplastic process that is associated with tumor invasion. We propose that UST imaging may prove to be a valuable tool for characterizing cancers and studying the tumor invasion process.

Our laboratory has focused on the development of ultrasound tomography (UST) for breast imaging. To that end we have been developing and testing a clinical prototype in the Karmanos Cancer Institute's (KCI) breast center. The development of our prototype has been guided by clinical feedback from data accumulated from over 300 patients recruited over the last 4 years. Our techniques generate whole breast reflection images as well as images of the acoustic parameters of sound speed and attenuation. The combination of these images reveals major breast anatomy, including fat, parenchyma, fibrous stroma and masses. Fusion imaging, utilizing thresholding, is shown to visualize mass characterization and facilitates separation of cancer from benign masses. These results indicate that operator-independent whole-breast imaging and the detection and characterization of cancerous breast masses are feasible using acoustic tomography techniques. Analyses of the prototype images suggests that we can detect the variety of mass attributes noted by current ultrasound-BIRADS criteria, such as mass shape, acoustic mass properties and architecture of the tumor environment. These attributes help quantify current BIRADS criteria (e.g. "shadowing" or high attenuation) and provide greater possibilities for defining a unique signature of cancer. The potential for UST to detect and characterize breast masses was quantified using UST measurements of 86 masses from the most recent cohort of patients imaged with the latest version of our prototype. Our preliminary results suggest that the development of a formal predictive model, in support of larger future trials, is warranted.

We discuss a bent-ray ultrasound tomography algorithm with total-variation (TV) regularization. We have applied this algorithm to 61 in vivo breast datasets collected with our in-house clinical prototype for imaging sound-speed distributions in the breast. Our analysis showed that TV regularization could preserve sharper lesion edges than the classic Tikhonov regularization. Furthermore, the image quality of our TV bent-ray sound-speed tomograms was superior to that of the straight-ray counterparts for all types of breasts within BI-RADS density categories 1 through 4. Our analysis showed that the improvements for average sharpness (in the unit of (m x s)(-1)) of lesion edges in our TV bent-ray tomograms are between 2.1 to 3.4-fold compared with the straight ray tomograms. Reconstructed sound-speed tomograms illustrated that our algorithm could successfully image fatty and glandular tissues within the breast. We calculated the mean sound-speed values for fatty tissue and breast parenchyma as 1422 +/- 9 m/s (mean +/- SD) and 1487 +/- 21 m/s, respectively. Based on 32 lesions in a cohort of 61 patients, we also found that the mean sound-speed for malignant breast lesions (1548 +/- 17 m/s) was higher, on average, than that of benign ones (1513 +/- 27 m/s) (one-sided p

The behavior of charged particles near X-type magnetic neutral lines is investigated. The magnetic field is taken to be hyperbolic and time stationary, with a uniform electric field perpendicular to the magnetic field. The general properties of the orbits of noninteracting particles in that field geometry are examined. Approximate analytic solutions to the orbit equations are derived by considering a magnetic-insulation picture where there is a hole in the magnetic insulation around the neutral line. Scaling laws for the dependence of the energy gain on strengths of the magnetic and electric fields are derived. The kinetic-energy distribution function for accelerated particles is derived for particles flowing past the neutral line. These analytic derivations are supported by computer simulations, in which the relativistic equations of motion for single test particles are numerically solved and the orbits and kinetic-energy gains of the particles are obtained. A number of simulations were performed and one parameter at a time was varied. Applications of the results to magnetic-neutral-line regions in space physics and astrophysics are possible.

We report and discuss clinical breast imaging results obtained with operator independent ultrasound tomography. A series of in-vivo experiments were carried out using a recently upgraded clinical prototype based on the principles of ultrasound tomography. The in-vivo performance of the prototype was assessed by imaging patients at the Karmanos Cancer Institute. Our techniques successfully demonstrated in-vivo tomographic imaging of breast architecture in both reflection and transmission imaging modes. Masses as small as 6 mm in size were detected. These initial results indicate that operator- independent whole-breast imaging and the detection of cancerous breast masses are feasible using ultrasound tomography techniques. This approach has the potential to provide a low cost, non-invasive, and non-ionizing means of evaluating breast masses. Future work will concentrate on extending these results to larger trials.