Scatter Signatures Research Articles

THE STANDOFF AEROSOL ACTIVE SIGNATURE TESTBED (SAAST) AT MIT LINCOLN LABORATORY

Standoff LIDAR detection of BW agents depends on accurate knowledge of the infrared and ultraviolet optical elastic scatter (ES) and ultraviolet fluorescence (UVF) signatures of bio-agents and interferents. MIT Lincoln Laboratory has developed the Standoff Aerosol Active Signature Testbed (SAAST) for measuring polarization-dependent ES cross sections from aerosol samples at all angles including 180° (direct backscatter) [1]. Measurements of interest include the dependence of the ES and UVF signatures on several spore production parameters including growth medium, sporulation protocol, washing protocol, fluidizing additives, and degree of aggregation. Using SAAST, we have made measurements of the polarization-dependent ES signature of Bacillus globigii (atropheaus, Bg) spores grown under different growth methods. We have also investigated one common interferent (Arizona Test Dust). Future samples will include pollen and diesel exhaust. This paper presents the details of the apparatus along with the results of recent measurements.

High speed classification of individual bacterial cells using a model-based light scatter system and multivariate statistics

We describe a model-based instrument design combined with a statistical classification approach for the development and realization of high speed cell classification systems based on light scatter. In our work, angular light scatter from cells of four bacterial species of interest, Bacillus subtilis, Escherichia coli, Listeria innocua, and Enterococcus faecalis, was modeled using the discrete dipole approximation. We then optimized a scattering detector array design subject to some hardware constraints, configured the instrument, and gathered experimental data from the relevant bacterial cells. Using these models and experiments, it is shown that optimization using a nominal bacteria model (i.e., using a representative size and refractive index) is insufficient for classification of most bacteria in realistic applications. Hence the computational predictions were constituted in the form of scattering-data-vector distributions that accounted for expected variability in the physical properties between individual bacteria within the four species. After the detectors were optimized using the numerical results, they were used to measure scatter from both the known control samples and unknown bacterial cells. A multivariate statistical method based on a support vector machine (SVM) was used to classify the bacteria species based on light scatter signatures. In our final instrument, we realized correct classification of B. subtilis in the presence of E. coli,L. innocua, and E. faecalis using SVM at 99.1%, 99.6%, and 98.5%, respectively, in the optimal detector array configuration. For comparison, the corresponding values for another set of angles were only 69.9%, 71.7%, and 70.2% using SVM, and more importantly, this improved performance is consistent with classification predictions.

A CMOS active pixel sensor system for laboratory- based x-ray diffraction studies of biological tissue

X-ray diffraction studies give material-specific information about biological tissue. Ideally, a large area, low noise, wide dynamic range digital x-ray detector is required for laboratory-based x-ray diffraction studies. The goal of this work is to introduce a novel imaging technology, the CMOS active pixel sensor (APS) that has the potential to fulfil all these requirements, and demonstrate its feasibility for coherent scatter imaging. A prototype CMOS APS has been included in an x-ray diffraction demonstration system. An industrial x-ray source with appropriate beam filtration is used to perform angle dispersive x-ray diffraction (ADXRD). Optimization of the experimental set-up is detailed including collimator options and detector operating parameters. Scatter signatures are measured for 11 different materials, covering three medical applications: breast cancer diagnosis, kidney stone identification and bone mineral density calculations. Scatter signatures are also recorded for three mixed samples of known composition. Results are verified using two independent models for predicting the APS scatter signature: (1) a linear systems model of the APS and (2) a linear superposition integral combining known monochromatic scatter signatures with the input polychromatic spectrum used in this case. Cross validation of experimental, modelled and literature results proves that APS are able to record biologically relevant scatter signatures. Coherent scatter signatures are sensitive to multiple materials present in a sample and provide a means to quantify composition. In the future, production of a bespoke APS imager for x-ray diffraction studies could enable simultaneous collection of the transmitted beam and scattered radiation in a laboratory-based coherent scatter system, making clinical transfer of the technique attainable.For more information on this article, see medicalphysicsweb.org

Validating baseball bat compliance

Professional baseball players have attempted to illegally modify baseball bats in the hopes of increasing bat speed and thus the distance travelled by batted balls. To date, no low-cost, non-invasive, real-time solution exists to this problem. Previously proposed solutions to this problem that involved using radar to measure the scatter signature of a scanned baseball bat were found to be extremely expensive. Ultrasound technology offers the ability to provide equivalent scatter signature measurements as compared to radar technology at a much lower cost and level of complexity while still operating in real time. We therefore present an ultrasound-based implementation of a prototype for a hand-held scanner unit designed to detect illegally modified baseball bats. A detailed discussion of the performance enhancements resulting from illegally modifying a baseball bat will be provided and an analysis of the attenuative properties of wood will be presented to determine appropriate sample rates for the ultrasound unit. Data acquisition issues encountered in prototyping the scanner will be examined and measurement data for both solid wood bats and modified bats will be evaluated to determine the effectiveness of the ultrasound-based data acquisition unit and the prototype’s ability to distinguish between both types of scatter signatures.

Polyhedral Silver Nanocrystals with Distinct Scattering Signatures

An Silber gestreut: Polyedrische Silbernanokristalle liefern komplexe und charakteristische Streusignale, die von ihrer Form und Größe bestimmt sind (siehe Bild). Die Fähigkeit, spezifische Plasmon-Moden zu erzeugen, sollte wichtige Auswirkungen für die oberflächenverstärkte Raman-Spektroskopie, die Subwellenlängenoptik und den Transport mithilfe von Plasmonen haben.

Polyhedral Silver Nanocrystals with Distinct Scattering Signatures

Silver nanoparticles are ideal building blocks for opticalmaterials that seek to manipulate, transport, or amplify light becausethey support surface plasmons with frequencies in the visible and near-IRregime. We demonstrate that polyhedral silvernanocrystals displaycomplex and distinct scattering signatures dictated by shape and size.The ability to engineer specific plasmon modes should have profoundconsequences for surface-enhanced Raman spectroscopy, sub-wavelengthoptics, and plasmonic transport.

Measurements of X-ray scatter signatures for some tissue-equivalent materials

In this work, we have measured the angular distribution of photons scattered (scattering signature) by five tissue-equivalent materials used in mammography and conventional radiology and four samples used in bone densitometry at the photon energy 17.44 keV using a X-ray tube equipped with a graphite monochromator, a goniometer system and a NaI detector. Results from the tissue-equivalent materials scattering signatures have been compared with previous results for human tissues (adipose, glandular, muscle and bone). The scattering profiles obtained with tissue-equivalent materials are different from those obtained with human tissue. These differences are due to intermolecular correlation on the elastic scattering. Some tissue-equivalent materials present some very sharp peaks, absent in real soft human tissue. These results suggest that a careful analysis of the scattering properties must be done in order to use tissue-equivalent material to simulate human tissues.

Predicting Urinary Stone Composition Using X-Ray Coherent Scatter: A Novel Technique With Potential Clinical Applications

Coherent scatter properties depend on the molecular structure of the scattering medium and measured scatter patterns are often characteristic of a chemical species. We explored the usefulness of coherent scatter analysis as a basis for identifying urinary calculus composition. A laboratory system for collecting coherent scatter signals from biological specimens was developed. This technique uses a diagnostic x-ray tube and image intensifier, and measures coherent scatter from intact renal stones. The coherent scatter signatures of 6 common stone components (calcium oxalate monohydrate, calcium phosphate, calcium phosphate dihydrate, cystine, magnesium ammonium phosphate and uric acid) were acquired from pure chemical samples and stones identified by infrared spectroscopy as having a uniform composition. In addition, a sample of calculus identified as containing only calcium oxalate dihydrate was examined. The same fragmented stone samples analyzed by infrared spectroscopy were scanned using coherent scatter. In each case the scatter patterns from powdered chemicals and fragmented stones showed circular symmetry and consisted of a series of broad rings of various intensities. Each pure chemical sample produced a distinct coherent scatter pattern. The signatures of the stone specimens closely agreed with those of the chemical samples. These initial results indicate that coherent scatter analysis using diagnostic x-rays has potential as a tool for urinary calculous composition identification. Further developments in this technique may have the potential for determining the composition of a calculus in vivo before therapy, thus, aiding in therapy planning.

X-ray scatter signatures for normal and neoplastic breast tissues

Measurements of breast tissue scattering properties have been made in an energy dispersive x-ray diffraction system over the momentum transfer range of 0.70 to 3.50 nm-1. One hundred samples of excised tissue have been used. Results from the diffraction system have been compared with the histological analysis for each individual sample. It has been found that tissue types can be characterized on the basis of the shape of the scatter spectrum and on its relative intensity. The shapes are significantly different between tissue types in the range 1.0 to 1.8 nm-1 and suggest that if particular values of momentum transfer are monitored, a discriminating signal could be obtained. Analysis of the maximum intensity in the signature also reveals a change of up to a factor of 2 between adipose and fat-free tissues.

Three‐body scattering produces precipitation signature of special diagnostic value

Examples are given of three‐body scatter signatures produced by high reflectivity cores in thunderstorms. The process consists of (1) scattering by the hydrometeors, (2) backscattering by the ground to the hydrometeors and (3) scattering by the hydrometeors to the radar. When viewed on radar displays, the signatures have an elongated shape, radially aligned behind strong (60 dBZ) reflectivity cores. A radar equation for echo power is developed and predicted r−3 dependence of the echo power on the range between the center of scattering volume and a reflecting ground ring is confirmed by a least squares fit to actual data. It is shown theoretically that mean Doppler shifts associated with three‐body scatter signatures are caused by the vertical and radial components of hydrometeor velocities; this is also verified from least square fits of range profiles of measured Doppler velocities to theoretical curves based on geometrical considerations.

Microwave and Laser Facilities to Determine Scattering and Colour Signatures Related to the Physical Properties of Dust Particles

AbstractAt Bochum there exist three experimental setups for measurements of the scattering properties of dust particles. The microwave analog experiment is the best choice for systematic studies of particles in the size range between 0.5 and 10 times the wavelength (correspondig to about 0.25 to 5 μm in the optical region). The multicolour laser experiment providing electrodynamic suspension of single dust particles is optimized for studies of particles in the size range between 20 and 150 μm. Another laser experiment is designed for rapid analysis of particle mixtures in view of in-situ applications. The measuring principles of all instruments are shortly summarized.

High‐latitude F region irregularities observed simultaneously with ISIS 1 and the Chatanika radar

Simultaneous measurements of the high‐latitude ionosphere were made by the Chatanika radar and the ISIS 1 topside sounder and cylindrical electrostatic probe (CEP) when the satellite was at a height of about 700 km. The variation of enhancements and valleys of electron density with invariant latitude at the satellite, on the scale of a few hundred kilometers, agrees reasonably well with the radar results, even though the satellite displacement changed from almost coincident to about 500 km magnetic west of the radar scan path. These density enhancements comprise a collection of large‐scale (tens of kilometers) irregularities or ‘blobs.’ Evidence for the formation of these blobs was obtained from the sounder. Natural, intense radio noise (hiss) was observed on the sounder ionograms recorded on the poleward side of the auroral zone, indicating the presence of precipitating kiloelectron volt electrons. A few minutes after these ionograms were recorded the radar scanned the same invariant latitude region and a large‐scale ionization enhancement, or ‘blob,’ not present 13 minutes earlier, had developed in the bottomside F layer. ISIS 1 telemetry dropouts resulting from medium‐scale irregularities, and enhanced irregularities down to about 200 m, observed with the CEP, are observed in association with blobs. Scatter signatures observed on the ISIS ionograms may be associated with large‐scale irregularities that can be identified in the radar data. The scattering detected by the sounder is caused by 30‐ to 60‐m wavelength irregularities (small‐scale) that presumably are created by instabilities operating on the edges of the large‐scale irregularities. The small‐scale irregularities, however, are observed on both poleward and equatorward directed gradients. If the gradient‐drift instability is responsible for these irregularities, then they either convect to the point of observation, are due to zonal gradients, or are field‐aligned extensions of irregularities generated at lower heights.