A comprehensive threat detection system is needed to protect critical assets and infrastructure in the nation's harbors. Such a system must necessarily rely on a variety of sensor technologies to provide protection against airborne, submerged, and surface threats. Although many threats can be detected with current technology, which include sonar, radar, visible light, and infrared sensors, there is a substantive gap in harbor defense against quiet surface intruders such as swimmers. This threat cannot be reliably detected with current sensors. Waves and chop occlude visual detection and render sonar blind to relatively small surface objects. The dark of night is also sufficient to defeat visible light detection methods. Wetsuit materials are available that minimize the infrared signature, matching the surrounding water temperature while cloaking the body's heat. However, a range-gated lidar sensor can be used to detect the signature of the swimmer's shadow, which appears impossible to conceal because it depends only on the opaqueness of the swimmer’s body to visible light. A spatially diffuse laser pulse of short duration is used to illuminate an area of interest. The photons are forward scattered in the water, and effectively illuminate the water to an appreciable depth. By range-gated imaging of the water column beneath the swimmer, the absence of backscattered photons is manifested as a shadow in the sensor image and easily detected with existing image processing algorithms. Lidar technology can therefore close the sensor gap, complementing existing systems and providing greater security coverage. The technology has been successfully demonstrated in the detection of moored and floating sea mines, and is readily scaled to a harbor defense system consisting of a network of imaging lidars.
Catheter ablation has emerged as a highly effective treatment for arrhythmias that are constrained by known, easily located, anatomic landmarks. However, this treatment has enjoyed limited success for arrhythmias that are characterized by complex activation patterns or are not anatomically constrained. This class of arrhythmias, which includes atrial fibrillation and ventricular tachycardia resulting from ischemic heart disease, demands improved mapping tools. Current technology forces the cardiologist to view cardiac anatomy independently from the functional information contained in the electrical activation patterns. This leads to difficulties in interpreting the large volumes of data provided by high-density recording catheters and in mapping patients with abnormal anatomy (e.g., patients with congenital heart disease). The goal of this is work is development of new data processing and display algorithms that will permit the clinician to view activation sequences superimposed onto existing fluoroscopic images depicting the location of recording catheters within the heart. In cases where biplane fluoroscopic images and x-ray camera position data are available, the position of the catheters can be reconstructed in three-dimensions.
Clinical procedures that rely on biplane x-ray images for three-dimensional (3-D) information may be enhanced by three-dimensional reconstructions. However, the accuracy of reconstructed images is dependent on the uncertainty associated with the parameters that define the geometry of the camera system. In this paper, we use a numerical simulation to examine the effect of these uncertainties and to determine the limits required for adequate three-dimensional reconstruction. We then test our conclusions with images of a calibration phantom recorded using a clinical system. A set of reconstruction routines, developed for a cardiac mapping system, were used in this evaluation. The routines include procedures for correcting image distortion and for automatically locating catheter electrodes. Test images were created using a numerical simulation of a biplane x-ray projection system. The reconstruction routines were then applied using accurate and perturbed camera geometries and error maps were produced. Our results indicate that useful catheter reconstructions are possible with reasonable bounds on the uncertainty of camera geometry provided the locations of the camera isocenters are accurate. The results of this study provide a guide for the specification of camera geometry display systems and for researchers evaluating possible methodologies for determining camera geometry.