[A method of computer-assisted, 3-dimensional subtraction angiography using spiral roentgen computerized tomography]

[A fast procedure of patient set-up verification in pelvic radiotherapy]

Accuracy of patient positioning is an important aspect in radiation therapy. The present paper presents a new procedure for the determination of set-up errors in radiotherapy, which is based on a special form of the Fast Fourier Transform (FFT), i.e., the Fast Hartley Transform (FHT). The use of this method allows to compare in short time verification and simulator films, and to calculate the translation vector or the in-plane rotation of the patient. Standard deviations < 1 mm for shifting measurements and < 1 degree for measurements of the rotation were detected, provided that the positioning remained within the common clinical range. The present results were in good agreement with data obtained using a landmark-based method.

CT angiography of the circle of Willis and intracranial internal carotid arteries: maximum intensity projection with matched mask bone elimination-feasibility study

Results are reported of a feasibility study in which bone pixels are eliminated from computed tomographic (CT) angiographic images with a method that enables the construction of maximum intensity projection (MIP) images without interference by bone. The method proved to be successful in six patients. Two observers blinded to the bone elimination method judged the image quality of MIP images to be considerably higher than that of standard subtraction MIP images. This method is an effective means to remove bone from CT angiographic images with only a slight increase in radiation dose.

Enhanced image detail using continuity in the MIP Z-buffer: applications to magnetic resonance angiography

In this paper a new algorithm is presented for the segmentation and display of blood vessels from images obtained with magnetic resonance angiography (MRA) and other three-dimensional (3D) angiographic imaging techniques. The algorithm developed is based on the observation that vessels are strongly evident in the maximum intensity projection (MIP) Z-buffer as regions of high continuity and low local roughness. Roughness is measured here by the minimum chi2 value of a low-order local least-squares fit in the principal directions through each point in the MIP Z-buffer. Although some background pixels in the Z-buffer exhibit low local roughness, the size of the connected region is nearly always much smaller than even the very smallest vessels that appear in the MIP image. It is shown that by applying connectivity to the regions of low roughness, there is nearly complete separation between vascular detail and background. When connectivity is further applied in the original 3D image, vascular bed segmentation becomes nearly complete. The algorithm consists of three basic steps: a) determination of the minimum local roughness at each point in the MIP Z-buffer; b) connection of all neighboring points of low local roughness; and c) connection of all points in the original 3D image matrix that are connected to the points determined in the MIP Z-buffer and that are above an intensity threshold. The algorithm as presented is not optimized but demonstrates a very strong potential for improved portrayal of vascular detail.

Virtual reality in medicine-computer graphics and interaction techniques

This paper describes several new visualization and interaction techniques that enable the use of virtual environments for routine medical purposes. A new volume-rendering method supports shaded and transparent visualization of medical image sequences in real-time with an interactive threshold definition. Based on these rendering algorithms two complementary segmentation approaches offer an intuitive assistance for a wide range of requirements in diagnosis and therapy planning. In addition, a hierarchical data representation for geometric surface descriptions guarantees an optimal use of available hardware resources and prevents inaccurate visualization. The combination of the presented techniques empowers the improved human-machine interface of virtual reality to support every interactive task in medical three-dimensional (3-D) image processing, from visualization of unsegmented data volumes up to the simulation of surgical procedures.