Kestrel Corporation

ABSTRACT Residues present on circuit boards can cause leakage currents if not controlled and monitored. How “Clean is Clean” is neither easy nor cheap to determine. Most OEMs use analytical methods to assess the risk of harmful residues. The levels that can be associated with clean or dirty are typically determined based on the exposed environment where the part will be deployed. What is acceptably clean for one segment of the industry may be unacceptable for more demanding segments. As circuit assemblies increase in density, understanding cleanliness data becomes more challenging. The risk of premature failure or improper function is typically site specific. The problem is that most do not know how to measure or define cleanliness nor can they recognize process problems related to residues. A new site specific method has been designed to run performance qualifications on boards built with specific soldering materials, reflow settings and cleaning methods. High impedance measurements are performed on break off coupons designed with components geometries used to build the assembly. The test method provides a gauge of potential contamination sources coming from the assembly process that can contribute to electrochemical migration.

Aim: The objective of this project was to evaluate high resolution images from an adaptive optics retinal imager through comparisons with standard film-based and standard digital fundus imagers. Methods: A clinical prototype adaptive optics fundus imager (AOFI) was used to collect retinal images from subjects with various forms of retinopathy to determine whether improved visibility into the disease could be provided to the clinician. The AOFI achieves low-order correction of aberrations through a closed-loop wavefront sensor and an adaptive optics system. The remaining high-order aberrations are removed by direct deconvolution using the point spread function (PSF) or by blind deconvolution when the PSF is not available. An ophthalmologist compared the AOFI images with standard fundus images and provided a clinical evaluation of all the modalities and processing techniques. All images were also analyzed using a quantitative image quality index. Results: This system has been tested on three human subjects (one normal and two with retinopathy). In the diabetic patient vascular abnormalities were detected with the AOFI that cannot be resolved with the standard fundus camera. Very small features, such as the fine vascular structures on the optic disc and the individual nerve fiber bundles are easily resolved by the AOFI. Conclusion: This project demonstrated that adaptive optic images have great potential in providing clinically significant detail of anatomical and pathological structures to the ophthalmologist.

Kestrel Corporation has extensive experience using distorted grating wavefront sensors (DGWFS) in a number of applications. The DGWFS has previously been demonstrated in the visible range (400–700 nm) by Kestrel and others. An experimental system was built in a laboratory environment to show that the DGWFS could recover wavefront characteristics of a midwave infrared (MWIR) laser. This paper describes the theory of the DGWFS and the experimental procedures implemented to run the system with the MWIR laser. The sensitivity to the type of gratings employed will be addressed. The results of sensitivity, dynamic range and thermal noise measurements will be discussed.

This paper presents the effects of image quality, given by the number of pixels used to define the image. A microaneurysm (MA) segmentation algorithm that has been shown to achieve about 90% sensitivity and specificity for clinical classification using high resolution images of those diabetic patients who present with MAs was applied to low resolution images to assess the effects of lower resolution of sensitivity and specificity. The low resolution (640 by 480 pixels) 45/spl deg/ field of view (FOV) was provided by a non-mydriatic camera. High resolutions images from a mydriatic fundus camera were acquired by digitizing 35 mm color film slides to 1400 /spl times/ 1200 pixels for a 30/spl deg/ FOV. The image quality of the digitized 35 mm images was considerably better than those from the non-mydriatic camera. Segmentation of microaneurysms (MAs) was performed using the green channel image of the two modalities. The images were contrast enhanced and corrected for uneven illumination. The images were then filtered using a tophat morphological filter and a threshold applied to segment the candidate MAs. Because the retinal vessels are similar in intensity and contrast to MAs, the retinal vasculature was segmented using matched filters to remove the vessel artifacts from the image. Ground truth, which was provided by an ophthalmic analyst, was used in the tuning step to find the bounds of the different intensity and shape features that characterize the MAs. These features were used to distinguish between MAs from other artifactual objects on the image. The best result that could be achieved with the lower resolution images was 70% sensitivity and specificity. We have found that the effects of pixel resolution on an automated segmentation routine to be of significant in obtaining higher sensitivity and specificity.

ABSTRACT Earlier research reported a comparison of the wavefronts recorded simultaneously by a Shack-Hartmann and a Distorted Grating Wavefront Sensor (DGWFS). In this paper we present the results of a continuation of this earlier work where we have now closed an adaptive optics loop under simulated propagation conditions using the Advanced Concept Laboratory (ACL) at Lincoln Laboratory. For these measurements only one wavefront sensor controlled the deformable mirror at a time. To make direct comparisons between the sensors we took advantage of the ACL’s ability to exactly replicate a time varying propagation simulation. Time varying and static comparisons of the two sensors controlling the ACL adaptive system under conditions that ranged from a benign path, D/r 0 = 2, to a propagation condition with significant scintillation, D/r 0 =9, will be shown using the corrected far field spot as a measure of performance. The paper includes a description of the DGWFS used for these tests and describes the procedure used to align and calibrate the sensor. Keywords: distorted grating wavefront sensing, closed loop compensation, atmospheric wavefront measurement

The fusion of multi-modal medical images provides a new diagnostic tool with clinical applications. Over the years, image fusion has been used in a number of medical disciplines. However, little fusion work in ophthalmic imaging appears in the literature. With the advent of multi-modal digital information of the retina and advanced image registration programs, the possibility of displaying complementary information in one fused retinal image becomes visually and clinically exciting. The objective of this research was to demonstrate that through fusion of multi-modal retinal information one could increase the information content of retinal pathologies on a fused image. Two aspects of image fusion were addressed in this study: image registration and image fusion of two distinctly different modalities, Fluorescein Angiography (FA) videos and standard color photography. Quantitative analysis of the fusion results was performed using entropy and image noise index. Qualitative analysis was performed by simultaneous visual comparison of two modalities (FA and color) of all registered unfused modes and the fused modes.

Age-Related Macular Degeneration (ARMD) is the leading cause of irreversible visual loss among the elderly in the US and Europe. A computer-based system has been developed to provide the ability to track the position and margin of the ARMD associated lesion; drusen. Variations in the subject's retinal pigmentation, size and profusion of the lesions, and differences in image illumination and quality present significant challenges to most segmentation algorithms. An algorithm is presented that first classifies the image to optimize the variables of a mathematical morphology algorithm. A binary image is found by applying Otsu's method to the reconstructed image. Lesion size and area distribution statistics are then calculated. For training and validation, the University of Wisconsin provided longitudinal images of 22 subjects from their 10 year Beaver Dam Study. Using the Wisconsin Age-Related Maculopathy Grading System, three graders classified the retinal images according to drusen size and area of involvement. The percentages within the acceptable error between the three graders and the computer are as follows: Grader-A: Area: 84% Size: 81%; Grader-B: Area: 63% Size: 76%; Grader-C: Area: 81% Size: 88%. To validate the segmented position and boundary one grader was asked to digitally outline the drusen boundary. The average accuracy based on sensitivity and specificity was 0.87 for thirty four marked regions.

The major limitations of precise evaluation of retinal structures in present clinical situations are the lack of standardization, the inherent subjectivity involved in the interpretation of retinal images, and intra- as well as interobserver variability. While evaluating optic disc deformation in glaucoma, these limitations could be overcome by using advanced digital image analysis techniques to generate precise metrics from stereo optic disc image pairs. A digital stereovision system for visualizing the topography of the optic nerve head from stereo optic disc images is presented. We have developed an algorithm, combining power cepstrum and zero-mean-normalized cross correlation techniques, which extracts depth information using coarse-to-fine disparity between corresponding windows in a stereo pair. The gray level encoded sparse disparity matrix is subjected to a cubic B-spline operation to generate smooth representations of the optic cup/disc surfaces and new three-dimensional (3-D) metrics from isodisparity contours. Despite the challenges involved in 3-D surface recovery, the robustness of our algorithm in finding disparities within the constraints used has been validated using stereo pairs with known disparities. In a preliminary longitudinal study of glaucoma patients, a strong correlation is found between the computer-generated quantitative cup/disc volume metrics and manual metrics commonly used in a clinic. The computer generated new metrics, however, eliminate the subjective variability and greatly reduce the time and cost involved in manual metric generation in follow-up studies of glaucoma.

In our analysis, each image is partitioned into a number of non-overlapping, spatial regions. Each spatial region is viewed as a Region of Interest (ROI). A grade is assigned to each ROI from a set of independent raters. The model is applied in lung image analysis, where a grade of 0/1 is assigned to each ROI. Here, I represents success, while 0 represents failure to detect a hypothesized pattern in the region. Methods for establishing spatial symmetry and spatial growth analysis are presented. In addition, a Bayes and a novel summation classifier are used for classifying the entire lung based on their regional grades. When compared against the readers, the two classifiers have a total misclassification error of the order of inter-rater variability error.