Ballistic Photons Research Articles

Detection and estimation of liquid flow through a pipe in a tissue-like object with ultrasound-assisted diffuse correlation spectroscopy.

Using coherent light interrogating a turbid object perturbed by a focused ultrasound (US) beam, we demonstrate localized measurement of dynamics in the focal region, termed the region-of-interest (ROI), from the decay of the modulation in intensity autocorrelation of light. When the ROI contains a pipe flow, the decay is shown to be sensitive to the average flow velocity from which the mean-squared displacement (MSD) of the scattering centers in the flow can be estimated. While the MSD estimated is seen to be an order of magnitude higher than that obtainable through the usual diffusing wave spectroscopy (DWS) without the US, it is seen to be more accurate as verified by the volume flow estimated from it. It is further observed that, whereas the MSD from the localized measurement grows with time as τ(α) with α≈1.65, without using the US, α is seen to be much less. Moreover, with the local measurement, this super-diffusive nature of the pipe flow is seen to persist longer, i.e., over a wider range of initial τ, than with the unassisted DWS. The reason for the super-diffusivity of flow, i.e., α<2, in the ROI is the presence of a fluctuating (thermodynamically nonequilibrium) component in the dynamics induced by the US forcing. Beyond this initial range, both methods measure MSDs that rise linearly with time, indicating that ballistic and near-ballistic photons hardly capture anything beyond the background Brownian motion.

Evaluation of optical arrangements for ballistic imaging in sprays.

This work investigates the imaging performance, in terms of contrast and resolution, of two different time-gated ballistic imaging setups commonly used in spray research. It is shown that the two setups generate similar spatial resolution in the presence of scattering media. The simpler (2f) setup, however, is less sensitive to component misalignments and time-gate induced aberrations than the commonly used (4f) system. Measurements comparing both arrangements indicated slightly higher contrast for the 2f system under the densest conditions for small scatterers. Subsequent computational modeling confirmed the observed tolerance of the 2f system to misalignment and gate effects. The best performing setup was also compared experimentally to its non-time-gated shadow-imaging equivalent, to establish when the time-gate enhances imaging performance. It is shown that the time-gated setup generates higher contrast under almost all of the scattering conditions tested, while the non-time-gated setup generates higher spatial resolution only in the lower scatterer size range at the lowest scatterer concentrations.

Quantitative phase imaging through scattering media by means of coherence-controlled holographic microscope.

A coherence-controlled holographic microscope (CCHM) enables quantitative phase imaging with coherent as well as incoherent illumination. The low spatially coherent light induces a coherence gating effect, which makes observation of samples possible also through scattering media. The paper describes theoretically and simulates numerically imaging of a two-dimensional object through a static scattering layer by means of CCHM, with the main focus on the quantitative phase imaging quality. The authors have investigated both strongly and weakly scattering media characterized by different amounts of ballistic and diffuse light. It is demonstrated that the phase information can be revealed also for the case of the static, strongly scattering layer. The dependence of the quality of imaging process on the spatial light coherence is demonstrated. The theoretical calculations and numerical simulations are supported by experimental data gained with a model phase object, as well as living carcinoma cells treated in an optically turbid emulsion.

Ballistic imaging of biological media with collimated illumination and focal plane detection.

A simple, affordable method for imaging through biological tissue is investigated. The method consists of (1) imaging with a wavelength that has a relatively small scattering coefficient (1310 nm in this case) and (2) collimated illumination together with (3) focal plane detection to enhance the detection of the ballistic photons relative to the diffusive light. We demonstrate ballistic detection of an object immersed in a 1-cm-thick cuvette filled with 4% Intralipid, which is equivalent to ∼1 to 2 cm of skin tissue. With the same technology, a ballistic image of a 1-mm-wide object in 10-mm-thick chicken breast is also presented.

Looking deeper: multimodal and contrast-enhanced photoacoustic imaging offer a clearer view within tissues for more accurate diagnosis.

Optical imaging modalities such as fluorescence (FL) microscopy, multiphoton microscopy, and optical coherence tomography (OCT) have been well established for high optical contrast and high spatial resolution imaging of biological tissues. However, as they are dependent on ballistic photons, these methods fail to image beyond ~1 mm or so inside biological tissue. In contrast, diffuse optical imaging (DOI), which uses multiple scattered photons for imaging, can image much deeper (up to a several centimeters) into the tissue. Unfortunately, due to strong light scattering in tissues, it fails to maintain the high resolution at the deeper imaging depth. Photoacoustic imaging (PAI) bridges this gap of imaging deeper with high resolution and contrast by combining optical excitation with acoustic detection [1].

Impediments to the Effective Use of Ballistics Imaging Information In Criminal Investigations: Lessons from the Use of IBIS in a Developing Nation

We use a case study approach to explore the facilitators and impediments to effectively using forensics ballistics imaging technology to improve police investigations in a developing country. The study site, Trinidad and Tobago, a nation located in the Caribbean basin, was experiencing a homicide epidemic during the time of this study. The homicide epidemic involved the repeated use of a limited number of firearms, conditions that are ideal for ballistics imaging technology. This nation also possessed a professionalized forensic crime lab and advanced ballistic imaging technology. The analysis reveals that the effective use of ballistics imaging was impeded by inefficient processes and backlogs at the national crime lab, time delays in identifying ballistics hits, and an inefficient system of transmitting hit reports to police investigators. In sum, organizational arrangements in the forensic crime lab and police in the focal country blunted the effectiveness of a proven forensic technology.

Picosecond ballistic imaging of diesel injection in high-temperature and high-pressure air

The first successful demonstration of picosecond ballistic imaging using a 15-ps-pulse-duration laser in diesel sprays at temperature and pressure is reported. This technique uses an optical Kerr effect shutter constructed from a CS2 liquid cell and a 15-ps pulse at 532 nm. The optical shutter can be adjusted to produce effective imaging pulses between 7 and 16 ps. This technique is used to image the near-orifice region (first 3 mm) of diesel sprays from a high-pressure single-hole fuel injector. Ballistic imaging of dodecane and methyl oleate sprays injected into ambient air and diesel injection at preignition engine-like conditions are reported. Dodecane was injected into air heated to 600 °C and pressurized to 20 atm. The resulting images of the near-orifice region at these conditions reveal dramatic shedding of the liquid near the nozzle, an effect that has been predicted, but to our knowledge never before imaged. These shedding structures have an approximate spatial frequency of 10 mm−1 with lengths from 50 to 200 μm. Several parameters are explored including injection pressure, liquid fuel temperature, air temperature and pressure, and fuel type. Resulting trends are summarized with accompanying images.

Modeling focusing Gaussian beams in a turbid medium with Monte Carlo simulations.

Monte Carlo techniques are the gold standard for studying light propagation in turbid media. Traditional Monte Carlo techniques are unable to include wave effects, such as diffraction; thus, these methods are unsuitable for exploring focusing geometries where a significant ballistic component remains at the focal plane. Here, a method is presented for accurately simulating photon propagation at the focal plane, in the context of a traditional Monte Carlo simulation. This is accomplished by propagating ballistic photons along trajectories predicted by Gaussian optics until they undergo an initial scattering event, after which, they are propagated through the medium by a traditional Monte Carlo technique. Solving a known problem by building upon an existing Monte Carlo implementation allows this method to be easily implemented in a wide variety of existing Monte Carlo simulations, greatly improving the accuracy of those models for studying dynamics in a focusing geometry.

Improved Arterial Tissue Differentiation by Spectroscopic Optical Coherence Tomography

University of Toronto, 610 University Avenue, Toronto, Ontario, M5G 2M9, CanadaOptical coherence tomography (OCT) is a relatively new imaging modality similar with ultrasound where the sound waves are replaced by ballistic photons. OCT provides images at high spatial resolution which allow for the identification of micron size morphological tissue structures. A high impact application is visualization of arterial wall and atherosclerotic plaques. Despite high spatial resolution to complete the transfer of this imaging modality into clinical environment there is a need for markers which would quantify the physiological condition of the sample. Finding the proper markers is a topic of high interest for many research groups. A potential marker suggested by the OCT community is the optical attenuation coefficient. Although OCT image itself provides important diagnostic and structural information there are also new methods of tissue characterization that have been developed through spectroscopic OCT and quantitative OCT. Spectroscopic OCT investigates the spectral response while the quantitative OCT extends the investigation to non-spectral parameters. Here we investigate two procedures for calculation of optical attenuation coefficient dependence versus wavelength. The wavelength analysis will provide new insight into the chemical nature of the sample, because the spectral backreflected signal depends on sample absorption and scattering properties. In this study we demonstrate the application of OCT for quantitative and spectral analysis of vulnerable plaque morphology on Watanabe heritable hyperlipidemic – myocardial infarction (WHHLMI) rabbit model. The results suggest that the spectral dependence of the derived OCT attenuation coefficient can be used for tissue differentiation. We demonstrated that differences and the spectral dependence of the optical attenuation coefficient are linked to the macrophage content of the region of interest.Key words: optical coherence tomography; quantitative and spectral analysis; WHHLMI rabbits.Corresponding author: Costel Flueraru, e-mail: costel.flueraru@nrc-cnrc.gc.ca

Ballistic imaging of diesel sprays using a picosecond laser: characterization and demonstration

Ballistic imaging using a 15 ps pulse laser in high-injection-pressure diesel sprays is reported. An optical Kerr effect shutter, constructed from a CS2 liquid cell and activated by a 15 ps pulse at 1064 nm, produces effective 532 nm imaging pulses between 7 and 15 ps. The performance of the imaging system is characterized using an Air Force target positioned before an optical cell filled with polystyrene spheres in a water suspension. The impact of spatial filtering, temporal filtering, and scattering path length on image resolution are reported. The technique is demonstrated by imaging the near-orifice region of methyl oleate and methyl butyrate sprays injected using a high-pressure single-hole fuel injector with direct comparison against simultaneous orthogonal shadowgraphy.

Optimum heterodyning angle for heterodyned optical Kerr gated ballistic imaging.

We perform heterodyned optical Kerr gated (HOKG) ballistic imaging of an object hidden behind a turbid medium using a femtosecond laser. The experimental results show that an optimum heterodyning angle should be selected to acquire the highest spatial resolution of the HOKG imaging system. The optimum heterodyning angle depends on the scattering parameters of the turbid media, and it decreases with increasing optical density or decreasing thickness of the turbid medium.

Tissue characterization with ballistic photons: counting scattering and/or absorption centres

AbstractWe describe a new method to separate ballistic from the scattered photons for optical tissue characterization. It is based on the hypothesis that the scattered photons acquire a phase delay. The photons passing through the sample without scattering or absorption preserve their coherence so they may participate in interference. We implement a Mach−Zehnder experimental setup where the ballistic photons pass through the sample with the delay caused uniquely by the sample indices of refraction. We incorporate a movable mirror on the piezoelectric actuator in the sample arm to detect the amplitude of the modulation term. We present the theory that predicts the path−integrated (or total) concentration of the scattering and absorption centres. The proposed technique may characterize samples with transmission attenuation of ballistic photons by a factor of 10

He-Ne Laser Imaging Probes Premature Diabetes Mellitus

An empirical approach to develop a comprehensive monitoring framework to track progress of ballistic photons through glucose doped aqueous humor by two dimensional sixteen Mueller polarization matrix element images for deepening efforts in polarimetry reported. The glucose doped aqueous humor has been illuminated with a He-Ne (632.8 nm) laser in vitro measurement. The obtained transmitted Mueller polarization matrix images are strong evidence to discriminate normal glucose level, impaired fasting glycaemia (IFG), impaired glucose tolerance (IGT) and diabetes mellitus.

Deep Tissue Wavefront Estimation for Sensorless Aberration Correction

The multiple light scattering in biological tissues limits the measurement depth for traditional wavefront sensor. The attenuated ballistic light and the background noise caused by the diffuse light give low signal to noise ratio for wavefront measurement. To overcome this issue, we introduced a wavefront estimation method based on a ray tracing algorithm to overcome this issue. With the knowledge of the refractive index of the medium, the wavefront is estimated by calculating optical path length of rays from the target inside of the samples. This method can provide not only the information of spherical aberration from the refractive-index mismatch between the medium and biological sample but also other aberrations caused by the irregular interface between them. Simulations based on different configurations are demonstrated in this paper.

The reference ballistic imaging database revisited

A reference ballistic image database (RBID) contains images of cartridge cases fired in firearms that are in circulation: a ballistic fingerprint database. The performance of an RBID was investigated a decade ago by De Kinder et al. using IBIS® Heritage™ technology. The results of that study were published in this journal, issue 214. Since then, technologies have evolved quite significantly and novel apparatus have become available on the market. The current research article investigates the efficiency of another automated ballistic imaging system, Evofinder® using the same database as used by De Kinder et al. The results demonstrate a significant increase in correlation efficiency: 38% of all matches were on first position of the Evofinder correlation list in comparison to IBIS® Heritage™ where only 19% were on the first position. Average correlation times are comparable to the IBIS® Heritage™ system. While Evofinder® demonstrates specific improvement for mutually correlating different ammunition brands, ammunition dependence of the markings is still strongly influencing the correlation result because the markings may vary considerably. As a consequence a great deal of potential hits (36%) was still far down in the correlation lists (positions 31 and lower). The large database was used to examine the probability of finding a match as a function of correlation list verification. As an example, the RBID study on Evofinder® demonstrates that to find at least 90% of all potential matches, at least 43% of the items in the database need to be compared on screen and this for breech face markings and firing pin impression separately. These results, although a clear improvement to the original RBID study, indicate that the implementation of such a database should still not be considered nowadays.

Ballistic Properties of Hybrid Thermoplastic Composites with Silica Nanoparticles

Multi-axial aramid fabrics have a wide range of applications in the construction of composite structures for body armor. Nanoparticles, which include nanosilica, are one of the most common nanofillers for these structures. The particles of nanosilica possess nanometer dimensions with high specific surface area. Silane coupling agents are mostly used for modifying nanosilica surface in order to prevent silica agglomeration. Incorporation of nanosilica treated with silane adhesion promoter, in the matrix part of the hybrid composite form, leads to increased resistance to the bullet shock impact. In this study, the resistance to penetration of a shot bullet was tested for four samples of the aramid fabric composite forms. All fabrics were coated with γ-aminopropyl triethoxysilane (AMEO silane)/ethanol solution. Two samples were impregnated with poly (vinyl butyral) (PVB)/ethanol solution, while the other two were impregnated with the same solution, but with the addition of the 30 wt.% AMEO silane modified silica nanoparticles as reinforcement. The samples were both hard and flexible options. The bullet-shooting test was applied to all the composites by two different bullet types. The structural design of the samples improved the ballistic resistance after the bullets were shot. Some ballistic image analyses for print and penetration depth of the samples were performed using Image Pro-Plus software.

The Second National Ballistics Imaging Comparison (NBIC-2).

In response to the guidelines issued by the American Society of Crime Laboratory Directors/Laboratory Accreditation Board (ASCLD/LAB-International) to establish traceability and quality assurance in U.S. crime laboratories, NIST and the ATF initiated a joint project, entitled the National Ballistics Imaging Comparison (NBIC). The NBIC project aims to establish a national traceability and quality system for ballistics identifications in crime laboratories utilizing ATF’s National Integrated Ballistics Information Network (NIBIN). The original NBIC was completed in 2010. In the second NBIC, NIST Standard Reference Material (SRM) 2461 Cartridge Cases were used as reference standards, and 14 experts from 11 U.S. crime laboratories each performed 17 image acquisitions and correlations of the SRM cartridge cases over the course of about half a year. Resulting correlation scores were collected by NIST for statistical analyses, from which control charts and control limits were developed for the proposed quality system and for promoting future assessments and accreditations for firearm evidence in U.S. forensic laboratories in accordance with the ISO 17025 Standard.

Fired Cartridge Case Identification Using Optical Images and the Congruent Matching Cells (CMC) Method.

The Congruent Matching Cells (CMC) method for ballistics identification was invented at the National Institute of Standards and Technology (NIST). The CMC method is based on the correlation of pairs of small correlation cells instead of the correlation of entire images. Four identification parameters – TCCF, Tθ, Tx and Ty are proposed for identifying correlated cell pairs originating from the same firearm. The correlation conclusion (matching or non-matching) is determined by whether the number of CMC is ≥ 6. This method has been previously validated using a set of 780 pair-wise 3D topography images. However, most ballistic images stored in current local and national databases are in an optical intensity (grayscale) format. As a result, the reliability of applying the CMC method on optical intensity images is an important issue. In this paper, optical intensity images of breech face impressions captured on the same set of 40 cartridge cases are correlated and analyzed for the validation test of CMC method using optical images. This includes correlations of 63 pairs of matching images and 717 pairs of non-matching images under top ring lighting. Tests of the method do not produce any false identification (false positive) or false exclusion (false negative) results, which support the CMC method and the proposed identification criterion, C = 6, for firearm breech face identifications using optical intensity images.

Comparative study of two ballistic imaging methods based on the femtosecond optical Kerr gate and spatial filtering

We demonstrated two ballistic imaging for an object hidden behind turbid media using the optical Kerr gate (OKG) and spatial filtering (SF), respectively. The influence of the scattering parameters of the turbid media on the image contrast was investigated. The experimental results showed that the image contrast of the SF imaging decreased significantly with increasing optical density and scattering particle size of the turbid media. Compared to the SF imaging, the OKG imaging showed a higher and more stable image contrast as scattering photons in the optical gated imaging case were more effectively eliminated.

Enhancement of optical coherence microscopy in turbid media by an optical parametric amplifier.

We report the enhancement in imaging performance of a spectral-domain optical coherence microscope (OCM) in turbid media by incorporating an optical parametric amplifier (OPA). The OPA provides a high level of optical gain to the sample arm, thereby improving the signal-to-noise ratio of the OCM by a factor of up to 15 dB. A unique nonlinear confocal gate is automatically formed in the OPA, which enables selective amplification of singly scattered (ballistic) photons against the multiply-scattered light background. Simultaneous enhancement in both imaging depth and spatial resolution in imaging microstructures in highly light-scattering media are demonstrated with the combined OPA-OCM setup. Typical OCM inteferograms (left) and images (right) without and with OPA.