A study has been conducted to determine the effects of mechanical stresses induced from the coefficient of thermal
expansion (CTE) differential between a light emitting diode (LED) chip, and various substrate materials to which the
LEDs were mounted. The LEDs were bonded to typical packaging materials including ceramics, copper and metal
matrix composites. The objective of this investigation was to determine the viability of implementing alternate
substrate materials for packaging of LED power chips. In particular, thermally induced stresses resulting from the CTE
differentials between the alternate substrate materials and the LED sub-mount material were analyzed and compared
against the stresses resulting from the nearly ideal CTE match that is realized with traditional ceramic substrates.
We describe what is, to the best of our knowledge, the first pilot study of coregistered tomographic x-ray and optical breast imaging. The purpose of this pilot study is to develop both hardware and data processing algorithms for a multimodality imaging method that provides information that neither x-ray nor diffuse optical tomography (DOT) can provide alone. We present in detail the instrumentation and algorithms developed for this multimodality imaging. We also present results from our initial pilot clinical tests. These results demonstrate that strictly coregistered x-ray and optical images enable a detailed comparison of the two images. This comparison will ultimately lead to a better understanding of the relationship between the functional contrast afforded by optical imaging and the structural contrast provided by x-ray imaging.
Critical requirements including high brightness, high color rendering, and high wall plug efficiency for the most demanding LED applications such as surgical illumination and industrial and dental sealant curing are difficult to meet with the limitations posed by commercially available LED packages.
The importance of optimizing an illumination system from the system-level perspective is presented. It is necessary to integrate efficient die, electrical drive conditions, heat dissipation, LED out-coupling optics and auxiliary optics. It is not sufficient to collect the maximum amount of light from an LED package; the light must be captured into a minimum aperture while maintaining maximal brightness. Commercially available LED packages, including the recently available 1 and 5 Watt emitters, suffer by varying degrees, in their applicability to today's most demanding applications. An optimized LED package is described that outperforms commercially available packages. Specific medical, commercial and industrial LED applications are described that can meet many of the most demanding requirements with today’s technology.
A visible-near IR (500-1,000nm) fiber optic sensor is under development that is intended to non-invasively assess muscle metabolism through the measurement of tissue pH and oxygen partial pressure. These parameters are calculated from the spectra of hemoglobin and myoglobin in muscle. The sensor consists of transmit (illumination) fibers and receive (detection) fibers that are coupled to a spectrometer. Light from the probe must penetrate below the surface of the skin and into a 5-10mm thick layer of muscle. A study was conducted to quantify the relationship between transmit and receive fiber separation and sensor penetration depth below the surface of the skin. A liquid phantom was created to replicate the absorption (μa) and reduced scatter coefficient (μs') profiles typically found in human blood and tissue. The phantom consisted of a solution of Intralipid and India ink in the appropriate concentrations to achieve desired reduced scatter coefficient and absorption profiles. The reduced scatter coefficient of the liquid phantom was achieved to an accuracy of +/-10% compared to previously published data. A fixed illumination fiber and translatable detector fiber were placed in the liquid phantom, and the fiber separation was varied from 3-40mm. Values of μa and μs' varied from 0.03-0.40 cm-1 and 5.0-15.0 cm-1 respectively. Results from the experiment demonstrate a strong correlation between penetration depth and fiber separation. Additionally, it was found that penetration depth was not substantially influenced by absorption and scatter concentration. As signal-to-noise is an important parameter in many non-invasive biomedical applications, the relative signal as a function of fiber separation was determined to follow an exponential relationship.
Optimization of the systems and reconstruction techniques is important for good optical breast imaging. Quantitative and objective assessments of the quality of the reconstructed image and the detection sensitivity are required to optimize single projection optical imaging. In this paper, the detection sensitivity was estimated by the contrast to noise ratio, and the quality of an image is evaluated using resolution, image noise, positional error, and quantitative accuracy. The expressions of these evaluating parameters were set up and analyzed by simulation. Using the quantitative assessment parameters we developed, we present a sensitivity and accuracy analysis of the Truncated Singular Value Decomposition (TSVD) method applied to optical breast imaging in transmission mode. The results indicate that the higher spatial resolution and improved quantitative accuracy obtained by decreasing the TSVD regularization parameter (i.e. the number of singular values used in the matrix inversion) must be balanced against the concomitant increase in image noise. Other parameters needs to be optimized including probe geometry, voxel size were also analyzed.
Diffuse optical tomographic imaging has broad application to the field of clinical diagnosis of diseased tissue states. In particular, there has been considerable interest in applying diffuse optical imaging to breast cancer detection. We explore the effects of such parameters as regularization, source-to-source and detector-to-detector spacing, voxel size and source modulation frequency on characteristics of the point spread function (PSF) of the reconstructed image. An understanding of these effects is critical to the optimization of diffuse optical tomographic imaging techniques. We also present a figure of merit that can be used to compare various reconstruction techniques and parameters when considering the effects of noise on quantitative accuracy and resolution. In all cases we look at heterogeneities with changes in absorption only and limit the analysis to the linear approximation of the diffusion equation. We show that the resolution and quantitative accuracy are fundamentally limited by the degree of regularization required to achieve images of acceptable contrast in the presence of representative noise levels. All simulations are based on Tikhonov regularization and truncated singular value decomposition (TSVD) reconstruction techniques for which we have generally achieved best results.
Continuous-Wave (CW) and Frequency-Domain (RF) methods of diffuse optical imaging are compared to identify the optimal approach for a clinical system. The CW Imager features fast imaging with 9 frequency-encoded sources and 16 detectors. The homodyne RF imager has 40 sources modulated at a frequency of 70 MHz and 9 detectors. Both systems incorporate two wavelengths. The features and characterization of both system are discussed and compared. A versatile phantom box design is presented that offered flexibility in experimental design and facilitated optimization of probe geometry. A 3D absorption image reconstruction phantom experiment is carried out to test the performance of the RF system. Noise models are set up and experimentally verified, and a signal-to-noise ratio analysis is presented. The heterogeneity detection sensitivity of the CW method and the RF method are compared, using both simulation and phantom experiments. The comparison results are discussed in the context of the most suitable approach to the design of a clinical breast cancer detection system.
A novel mid infrared patented (IR) endoscopic imaging system is described with applications as both a medical and industrial diagnostic tool. The endoscopic and borescopic IR imaging systems can be configured to work in the range of 2 to 15 microns, according to the application.
A novel mid infrared (IR) endoscopic imaging system (patent pending) is described with applications as both a medical and industrial diagnostic tool. The endoscopic and borescopic IR imaging systems can be configured to work in the range of 2 to 15 microns, according to the application.
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