Angiographic investigation using high-resolution CT images has become a useful tool for the sensitive examination of vascular diseases. However, CT angiography (CTA) does not allow a straightforward understanding of vascular structure, since some of interesting parts can be located near the high intensity skull base region. In this paper, a novel method for fast and automatic 3D digital subtraction CT angiography (DS-CTA) is presented to generate artifact-free angiograms. The proposed method consists of 3D registration to align a CT image to the CTA image, and subtraction and refinement to extract blood vessels. For efficient and accurate 3D registration, an NMI (normalized mutual information) based algorithm is adopted and its fast version is developed by introducing a new measure. The speed-up ratio of the proposed fast registration algorithm is about 1.74~3.01 compared with the conventional registration method. And to improve the subtracted image quality in the second step, a novel 3D refinement algorithm is suggested to effectively remove unwanted residuals. Experimental results of seven clinical CT/CTA head datasets demonstrate that cerebral vessels are well extracted from CTA images with almost no loss. The typical processing time is about 3~9 minutes depending on the image size in a PC with a 2.4GHz CPU.
Recent progress toward wavelength-scale photonic crystal lasers is summarized. Lasing characteristics of two possible configurations of the unit-cell photonic crystal laser that has a central node through which current could be supplied. The very high quality factor in excess of 100,000 is theoretically expected from a square lattice unit-cell photonic crystal resonator. Applications of photonic crystals to other forms of active devices are also briefly discussed.
A new surgical simulator is developed for spine needle biopsy, that provides realistic visual and force feedback to a trainee in the PC environment. This system is composed of four parts: a 3D human model, visual feedback tool, force feedback device, and an evaluation section. The 3D human model includes multi-slice XCT images, segmentation results, and force-feedback parameters. A block-based technique is adopted for efficient handling of large amounts of data and for easy control of rendering parameters such as opacity. For visual feedback, we implement a virtual CT console box and a 3D visualization tool providing MIP, MPR, summed voxel projection, and realistic 3D color volume rendering view. The visualization tool is for interactive 3D path planning. A haptic device is used to provide force feedback to the biopsy needle during simulation. The interactive force is generated in a voxel-based manner. After each simulation, the evaluation section provides a performance analysis to the trainee. We implemented the system by attaching a 3DOF PHANToMTM device to a PC with 600MHz Pentium III Dual CPUs and 512Mbyte RAM.
Volume rendering is a visualizing technique for 3D volume data. The pixel values of a rendered image are determined by accumulating sampled values form volume data. Usually, the product of opacity and shading values is used as a sampled value. However, the size of the volume data is usually too big to handle in real time. Therefore, a control measure, which changes the level of detail (LOD) of the rendered image, may be introduced for obtaining a reasonable rendering speed. In this paper, we introduce a new criterion for controlling the LOD of the rendered image, and a new octree-based rendering method using this criterion efficiently. As the new criterion, the variance of the opacity and normal vector product is adopted and used to classify volume blocks into an octree structure. In the rendering stage, normal blocks are rendered by using the shear-warp factorization and single-valued blocks by using a template, while zero blocks are skipped. By performing in this fashion, the prosed scheme can reduce the overall rendering time. The scheme is evaluated by rendering a skull volume data ste obtained from an x-ray CT system.