Cone-beam x-ray luminescence computed tomography (CB-XLCT) prototype development and performance evaluation.

This study developed a prototype for a rotational cone-beam x-ray luminescence computed tomography (CB-XLCT) system, considering its potential application in pre-clinical theranostic imaging. A geometric calibration method applicable to both imaging chains (XL and CT) was also developed to enhance image quality. The results of systematic performance evaluations were presented to assess the feasibility of commercializing XLCT technology. Monte Carlo GATE simulation was performed to determine the optimal imaging conditions for nanophosphor particles (NPs) irradiated by 70 kV x-rays. We acquired a low-dose transmission x-ray tube and designed a prone positioning platform and a rotating gantry, using mice as targets from commercial small animalµ-CT systems. We then employed the image cross-correlation (ICC) automatic geometric calibration method to calibrate XL and CT images. The performance of the system was evaluated through a series of phantom experiments with a linearity of 0.99, and the contrast-to-noise ratio (CNR) between hydroxyl-apatite (HA) and based epoxy resin is 19.5. The XL images of the CB-XLCT prototype achieved a Dice similarity coefficient (DICE) of 0.149 for a distance of 1 mm between the two light sources. Finally, the final XLCT imaging results were demonstrated using the Letter phantoms with NPs. In summary, the CB-XLCT prototype developed in this study showed the potential to achieve high-quality imaging with acceptable radiation doses for small animals. The performance of CT images was comparable to current commercial machines, while the XL images exhibited promising results in phantom imaging, but further efforts are needed for biomedical applications.

Virtual and real-world implementation of deep-learning-based image denoising model on projection domain in digital tomosynthesis and cone-beam computed tomography data.

Reducing the radiation dose will cause severe image noise and artifacts, and degradation of image quality will also affect the accuracy of diagnosis. To find a solution, we comprise a 2D and 3D concatenating convolutional encoder-decoder (CCE-3D) and the structural sensitive loss (SSL), via transfer learning (TL) denoising in the projection domain for low-dose computed tomography (LDCT), radiography, and tomosynthesis. The simulation and real-world practicing results show that many of the figures-of-merit (FOMs) increase in both projections (2-3 times) and CT imaging (1.5-2 times). From the PSNR and structural similarity index of measurement (SSIM), the CCE-3D model is effective in denoising but keeps the shape of the structure. Hence, we have developed a denoising model that can be served as a promising tool to be implemented in the next generation of x-ray radiography, tomosynthesis, and LDCT systems.

Corneal transparency and scleral opacity arises from the nanoarchitecture of the constituent collagen fibrils.

While human scleral and corneal tissues possess similar structural morphology of long parallel cylindrical collagen fibrils, their optical characteristics are markedly different. Using pseudospectral time-domain (PSTD) simulations of Maxwell's equations, we model light propagation through realistic representations of scleral and corneal nanoarchitecture and analyze the transmittance and spatial correlation in the near field. Our simulation results provide differing predictions for scleral opacity and corneal transparency across the vacuum ultraviolet to the mid-infrared spectral region in agreement with experimental data. The simulations reveal that the differences in optical transparency between these tissues arise through differences in light scattering emanating from the specific nanoscale arrangement and polydispersity of the constituent collagen fibrils.

Light extraction efficiency enhancement of flip-chip blue light-emitting diodes by anodic aluminum oxide.

We produced an anodic aluminum oxide (AAO) structure with periodic nanopores on the surface of flip-chip blue light-emitting diodes (FC-BLEDs). The nanopores had diameters ranging from 73 to 85 nm and were separated by distances ranging from approximately 10 to 15 nm. The light extraction efficiency enhancement of the FC-BLEDs subjected to different durations of the second pore-widening process was approximately 1.6-2.9%. The efficiency enhancement may be attributed to the following mechanism: periodic nanopores on the surface of FC-BLEDs reduce the critical angle of total reflection and effective energy transfer from a light emitter into a surface plasmon mode produced by AAO.

Modeling the sub-diffraction focusing phenomenon of light propagation through scattering medium.

Optical techniques are assuming greater importance in biomedical applications, however, due to extreme complexity involved in light propagation through scattering medium, it is very challenging to analyze experimentally. Here we report a two-stage simulation technique to simulate phase-conjugated light propagation through scattering medium with macroscopic dimensions. The reported simulation yields accurate information with flexibility to access research parameters. The proposed simulation method is suitable for finite-difference time-domain (FDTD) technique, pseudospectral time-domain (PSTD) technique, and other simulation techniques based upon numerical solutions of Maxwell's equations. We demonstrate modeling phase-conjugated light propagation through a scattering medium. The reported simulation technique is applicable to model the propagation of continuous-wave (CW) light with specific amplitude and phase through a scattering medium of macroscopic dimensions. More importantly, the flexibility of simulation enables analysis of research factors that are challenging to access experimentally.

Modeling of carrier transport in organic light emitting diode with random dopant effects by two-dimensional simulation.

To model the carrier transport in organic light-emitting diodes (OLEDs) with random dopant effects in the emitting layer, two-dimensional simulation was used. By including the Gaussian shape density of states and field-dependent mobility in the Poisson and drift-diffusion solver, the carrier transport, trapping in the dopant state, and radiative recombination were accurately modeled. To examine the model, the current-voltage characteristics of organic light-emitting devices were compared. The host material in the emitting layer was 2,2-bis(1-phenyl-1H-benzo[d]imidazol-2-yl)biphenyl (BImBP), which was doped with bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic) at various concentrations. By including the random doping model, the trend of mobility was altered and the radiative efficiency fitted experimental values well.

2-D PSTD Simulation of focusing monochromatic light through a macroscopic scattering medium via optical phase conjugation.

By employing the pseudospectral time-domain (PSTD) simulation technique, we analyze the propagation of monochromatic light through a macroscopic scattering medium. Simulation results show that, monochromatic light can be directed through a scattering medium and focus into a narrow peak; a range of wavelengths has been simulated. Furthermore, we compare: i) focusing monochromatic light through a macroscopic scattering medium, and, ii) focusing monochromatic light through vacuum. Based upon numerical solutions of Maxwell's equations, we demonstrate: with a fully-surrounding wavefront of specific amplitude and phase, sub-diffraction focusing can be achieved with monochromatic light, with or without the presence of a scattering medium.

2-D PSTD Simulation of the time-reversed ultrasound-encoded deep-tissue imaging technique.

We present a robust simulation technique to model the time-reversed ultrasonically encoded (TRUE) technique for deep-tissue imaging. The pseudospectral time-domain (PSTD) algorithm is employed to rigorously model the electromagnetic wave interaction of light propagating through a macroscopic scattering medium. Based upon numerical solutions of Maxwell's equations, the amplitude and phase are accurately accounted for to analyze factors that affect the TRUE propagation of light through scattering media. More generally, we demonstrate the feasibility of modeling light propagation through a virtual tissue model of macroscopic dimensions with numerical solutions of Maxwell's equations.

PSTD Simulation of optical phase conjugation of light propagating long optical paths.

The phenomenon of Optical Phase Conjugation (OPC) can be rigorously simulated using the pseudospectral time-domain (PSTD) technique. However, with finite computational memory, it is infeasible to simulate light propagating long optical paths. We report a robust OPC simulation technique that can account for long optical path lengths by sequentially inverting the electromagnetic fields. Specifically, the ideal efficiency of OPC refocusing of light through scattering medium can be accurately determined.

2-D PSTD Simulation of optical phase conjugation for turbidity suppression.

Turbidity Suppression via Optical Phase Conjugation (TS-OPC) is an optical phenomenon that uses the back propagation nature of optical phase conjugate light field to undo the effect of tissue scattering. We use the computationally efficient and accurate pseudospectral time-domain (PSTD) simulation method to study this phenomenon; a key adaptation is the volumetric inversion of the optical wavefront E-field as a means for simulating a phase conjugate mirror. We simulate a number of scenarios and demonstrate that TS-OPC deteriorates with increased scattering in the medium, or increased mismatch between the random medium and the phase conjugate wave during reconstruction.

Exact solution of Maxwell's equations for optical interactions with a macroscopic random medium: addendum.

This Addendum provides a revised set of figures containing converged numerical data for total scattering cross section (TSCS), replacing the figures in our recent publication [Opt. Lett. 29, 1393 (2004)]. Due to the use of an overly large time step, our original TSCS data exhibited a systematic, nonphysical diminution above 150 THz for all cases studied. We have determined that numerical convergence in the temporal sense for the pseudospectral time-domain (PSTD) algorithm employed previously requires limiting the time step to no more than 1/60th of the sinusoidal period at the maximum frequency of interest, which in the previous case was 300 THz. This is an important point that we hereby report to future users of PSTD simulations in electrodynamics and optics. Note that all our original conclusions remain valid.

Exact solution of Maxwell's equations for optical interactions with a macroscopic random medium.

We report what we believe to be the first rigorous numerical solution of the two-dimensional Maxwell equations for optical propagation within, and scattering by, a random medium of macroscopic dimensions. Our solution is based on the pseudospectral time-domain technique, which provides essentially exact results for electromagnetic field spatial modes sampled at the Nyquist rate or better. The results point toward the emerging feasibility of direct, exact Maxwell equations modeling of light propagation through many millimeters of biological tissues. More generally, our results have a wider implication: Namely, the study of electromagnetic wave propagation within random media is moving toward exact rather than approximate solutions of Maxwell's equations.