William P. Roach

Comparison of optical coherence tomography imaging of cataracts with histopathology

This paper presents a comparison of in vivo optical coherence tomography (OCT) captured cataract images to subsequent histopathological examination of the lenticular opacities. OCT imaging was performed on anesthetized Rhesus monkeys, known as the delayed effects colony (DEC), with documented cataracts. These monkeys were exposed to several types of radiation during the mid and late 1960s. The radiation and age related cataracts in these animals were closely monitored using a unique grading system developed specifically for the DEC. In addition to this system, a modified version of a common cataract grading scheme for use in humans was applied. Of the original 18 monkeys imaged, lenses were collected at necropsy from seven of these animals, processed, and compared to OCT images. Results showed a direct correlation between the vertical OCT images and the cataractous lesions seen on corresponding histopathologic sections of the lenses. Based on the images obtained and their corresponding documented comparison to histopathology, OCT showed tremendous potential to aid identification and characterization of cataracts. There can be artifactual problems with the images related to movement and shadows produced by opacities. However, with the advent of increased speed in imaging and multiplanar imaging, these disadvantages may easily be overcome.

Argon Laser Retinal Lesions Evaluated In Vivo by Optical Coherence Tomography

PURPOSE To assess the in vivo evolution of argon laser retinal lesions by correlating the cross-sectional structure from sequential optical coherence tomography with histopathologic sectioning. METHODS Argon laser lesions were created in the retinas of Macaca mulatta and evaluated by cross-section optical coherence tomography, which was compared at selected time points with corresponding histopathology. RESULTS Argon laser lesions induced an optical coherence tomography pattern of early outer retinal relative high reflectivity with subsequent surrounding relative low reflectivity that correlated well with histopathologic findings. The in vivo optical coherence tomography images of macular laser lesions clearly demonstrated differences in pathologic response by retinal layer over time. CONCLUSION The novel sequential imaging of rapidly evolving macular lesions with optical coherence tomography provides new insight into the patterns of acute tissue response by cross-sectional layer. This sequential imaging technique will aid in our understanding of the rapid evolution of retinal pathology and response to treatment in the research and clinical setting.

Plasma Membrane Permeabilization by Trains of Ultrashort Electric Pulses

Ultrashort electric pulses (USEP) cause long-lasting increase of cell membrane electrical conductance, and that a single USEP increased cell membrane electrical conductance proportionally to the absorbed dose (AD) with a threshold of about 10 mJ/g. The present study extends quantification of the membrane permeabilization effect to multiple USEP and employed a more accurate protocol that identified USEP effect as the difference between post- and pre-exposure conductance values (Deltag) in individual cells. We showed that Deltag can be increased by either increasing the number of pulses at a constant E-field, or by increasing the E-field at a constant number of pulses. For 60-ns pulses, an E-field threshold of 6 kV/cm for a single pulse was lowered to less than 1.7 kV/cm by applying 100-pulse or longer trains. However, the reduction of the E-field threshold was only achieved at the expense of a higher AD compared to a single pulse exposure. Furthermore, the effect of multiple pulses was not fully determined by AD, suggesting that cells permeabilized by the first pulse(s) in the train become less vulnerable to subsequent pulses. This explanation was corroborated by a model that treated multiple-pulse exposures as a series of single-pulse exposures and assumed an exponential decline of cell susceptibility to USEP as Deltag increased after each pulse during the course of the train.

In vitro investigation of the biological effects associated with human dermal fibroblasts exposed to 2.52 THz radiation

Terahertz (THz) radiation sources are increasingly being used in military, defense, and medical applications. However, the biological effects associated with this type of radiation are not well characterized. In this study, we evaluated the cellular and molecular response of human dermal fibroblasts exposed to THz radiation.

Identification of microRNAs associated with hyperthermia-induced cellular stress response

MicroRNAs (miRNAs) are a class of small RNAs that play a critical role in the coordination of fundamental cellular processes. Recent studies suggest that miRNAs participate in the cellular stress response (CSR), but their specific involvement remains unclear. In this study, we identify a group of thermally regulated miRNAs (TRMs) that are associated with the CSR. Using miRNA microarrays, we show that dermal fibroblasts differentially express 123 miRNAs when exposed to hyperthermia. Interestingly, only 27 of these miRNAs are annotated in the current Sanger registry. We validated the expression of the annotated miRNAs using qPCR techniques, and we found that the qPCR and microarray data was in well agreement. Computational target-prediction studies revealed that putative targets for the TRMs are heat shock proteins and Argonaute-2—the core functional unit of RNA silencing. These results indicate that cells express a specific group of miRNAs when exposed to hyperthermia, and these miRNAs may function in the regulation of the CSR. Future studies will be conducted to determine if other cells lines differentially express these miRNAs when exposed to hyperthermia.

Development of a compact terahertz time-domain spectrometer for the measurement of the optical properties of biological tissues

Terahertz spectrometers and imaging systems are currently being evaluated as biomedical tools for skin burn assessment. These systems show promise, but due to their size and weight, they have restricted portability, and are impractical for military and battlefield settings where space is limited. In this study, we developed and tested the performance of a compact, light, and portable THz time-domain spectroscopy (THz-TDS) device. Optical properties were collected with this system from 0.1 to 1.6 THz for water, ethanol, and several ex vivo porcine tissues (muscle, adipose, skin). For all samples tested, we found that the index of refraction (n) decreases with frequency, while the absorption coefficient (μ(a)) increases with frequency. Muscle, adipose, and frozen/thawed skin samples exhibited comparable n values ranging between 2.5 and 2.0, whereas the n values for freshly harvested skin were roughly 40% lower. Additionally, we found that the freshly harvested samples exhibited higher μ(a) values than the frozen/thawed skin samples. Overall, for all liquids and tissues tested, we found that our system measured optical property values that were consistent with those reported in the literature. These results suggest that our compact THz spectrometer performed comparable to its larger counterparts, and therefore may be a useful and practical tool for skin health assessment.

Retinal damage and laser-induced breakdown produced by ultrashort-pulse lasers

Abstract• Background: In vivo retinal injury studies using ultrashort-pulse lasers at visible wavelengths for both rabbit and primate eyes have shown that the degree of injury to the retina is not proportional to the pulse energy, especially at suprathreshold levels. In this paper we present results of calculations and measurements for laser-induced breakdown (LIB), bubble generation, and self-focusing within the eye. • Methods: We recorded on video and measured the first in vivo LIB and bubble generation thresholds within the vitreous in rabbit and primate eyes, using external optics and femtosecond pulses. These thresholds were then compared with calculations from our LIB model, and calculations were made for self-focusing effects within the vitreous for the high peak power pulses. • Results: Results of our nonlinear modeling and calculations for self-focusing and LIB within the eye were compared with experimental results. The LIB ED50 bubble threshold for the monkey eye was measured and found to be 0.56 μJ at 120 fs, compared with the minimum visible lesion (MVL) threshold of 0.43 μJ at 90 fs. Self-focusing effects were found to be possible for pulsewidths below 1 ps and are probably a contributing factor in femtosecond-pulse LIB in the eye. • Conclusions: Based on our measurements for the MVL thresholds and LIB bubble generation thresholds in the monkey eye, we conclude that in the femtosecond pulsewidth regime for visible laser pulses, LIB and self-focusing are contributing factors in the lesion thresholds measured. Our results may also explain why it is so difficult to produce hemorrhagic lesions in either the rabbit or primate eye with visible 100-fs laser pulses even at 100 μJ of energy.

CUDA Implementation of

This letter presents the graphic processor unit (GPU) implementation of the finite-difference time domain (FDTD) method for the solution of the two-dimensional electromagnetic fields inside dispersive media. The FDTD is truncated by the convolutional perfectly matched layer (CPML) and the piecewise-linear recursive-convolution (PLRC) formulation is used for modeling dispersive media. By using the newly introduced Compute Unified Device Architecture (CUDA) technology, we illustrate the efficacy of GPUs in accelerating the FDTD computations by achieving significant speedup factors with great ease and at no extra hardware/software cost. We validate our approach by comparison to exact and other simulated results, which show favorable agreements. The effect of the GPU-CPU memory transfers on the speedup factor will be also studied.

{\rm TE}^{z}

In recent years, numerous security, military, and medical applications have been developed which use Terahertz (THz) radiation. These developments have heightened concerns in regards to the potential health risks that are associated with this type of radiation. To determine the cellular and molecular effects caused by THz radiation, we exposed several human cell lines to high-power THz radiation, and then we determined death thresholds and gene expression profiles. Necrotic and apoptotic death thresholds were determined for Jurkat cells using an optically-pumped molecular gas THz source (υ = 2.52 THz, H = 227 mW/cm2), MTT viability assays, and flow cytometric techniques. In addition, we used confocal microscopic techniques to demarcate lethal spatial regions in a monolayer of dermal fibroblasts exposed to THz radiation. Then, to determine if cells exhibit a THz-specific gene expression signature, we exposed dermal fibroblasts to THz radiation and analyzed their transcriptional response using microarray gene chips. We found that 60% of the Jurkat cells survived the 30-minute THz exposure, whereas only 20% survived the 40-minute exposure. The flow data confirmed these results and provided evidence that THz-induced cell death was mediated using both nectrotic and apoptotic processes. The preliminary microscopy studies provided convincing evidence warranting future efforts using these techniques. Lastly, we found that dermal fibroblasts up-regulated several genes when exposed to THz radiation. Overall, these results provide evidence for the cellular and molecular effects associated with THz radiation, and we speculate that the identified up-regulated genes may serve as excellent candidate biomarkers for THz exposures.

-FDTD Solution of Maxwell's Equations in Dispersive Media

Recent studies of retinal damage due to ultrashort laser pulses have shown that less energy is required for retinal damage for pulses shorter than 1 ns than that for longer pulses. It has also been shown that more energy is required for near-infrared (NIR) wavelengths than in the visible because the light focuses behind the retina, requiring more energy to produce a damaging fluence on the retina. We review the progress made in determining the trends in retinal damage from laser pulses of 1 ns to 100 fs in the visible and NIR wavelength regimes. We have determined the most likely damage mechanism(s) operative in this pulse width regime.