CTA-based angle selection for diagnostic and interventionalangiography of saccular intracranial aneurysms

Coil embolization is a safe treatment for cerebral aneurysms only if the width of the neck in relation to the fundus of the aneurysm is small. Therefore, accurate visualization of the aneurysmal neck is required both in the diagnostic process and during the intervention. Conventional digital subtraction angiography (DSA) is still the preferred modality for the examination of cerebrovascular abnormalities like aneurysms, but it often does not provide the required morphological characteristics due to the suboptimal selection of projection angles and resulting overprojections of surrounding vasculature. This paper presents a method for performing a computer-assisted calculation of the optimal projection angles for DSA by post-processing computed tomographic angiography (CTA) volume data using ray-casting techniques and a combination of image processing algorithms. By means of phantom studies, retrospective simulations of angiograms, and in vivo applications of calculated optimal viewing angles, it is demonstrated that the proposed method results in better angiographic projections of the neck of saccular aneurysms with small neck-fundus ratio than those acquired at standard angles prescribed by clinical protocols     

Development of an intravascular impedance catheter for detection offatty lesions in arteries

Recent studies show that the presence of fatty lesions in the atherosclerotic vessel wall is a risk factor for acute occlusion of blood vessels. Although fat has a high electrical resistivity, existing impedance catheter systems cannot be used for detection of these lesions because artifacts owing to impedance variations in the extravascular surroundings have a major and irretraceable effect on the measurement. Standard algorithms used in attempt to compensate for these artifacts suffer from severe instability problems. The authors defined design guidelines to be met by a new impedance catheter system in order to make a robust reconstruction algorithm possible and have built an experimental in travascular impedance catheter (IIC) system according to these guidelines, using a normalized differential measurement procedure. With this IIC, the authors performed experiments on human iliac arteries from the section ward (fixed specimens), showing that plastic models of arterial fatty lesions (8 mm³) can be detected reliably     

Efficient and reliable schemes for nonlinear diffusion filtering

Nonlinear diffusion filtering in image processing is usually performed with explicit schemes. They are only stable for very small time steps, which leads to poor efficiency and limits their practical use. Based on a discrete nonlinear diffusion scale-space framework we present semi-implicit schemes which are stable for all time steps. These novel schemes use an additive operator splitting (AOS), which guarantees equal treatment of all coordinate axes. They can be implemented easily in arbitrary dimensions, have good rotational invariance and reveal a computational complexity and memory requirement which is linear in the number of pixels. Examples demonstrate that, under typical accuracy requirements, AOS schemes are at least ten times more efficient than the widely used explicit schemes.     

Temperature dependence of the magnetic volume susceptibility of human breast fat tissue: an NMR study

Object  

Proton resonance frequency shift (PRFS)-based MR thermometry (MRT) is hampered by heat-induced susceptibility changes when applied in tissues containing fat, e.g., the human breast. In order to assess the impact of fat susceptibility changes on PRFS-based MRT during thermal therapy in the human breast, reliable knowledge of the temperature dependence of the magnetic volume susceptibility of fat, dχ_fat/dT, is a prerequisite. In this work we have measured dχ_fat/dT of human breast fat tissue, using a double-reference method to ensure invariance to temperature-induced changes in the proton electron screening constant.     

Evaluation of ridge seeking operators for multimodality medicalimage matching

Ridge-like structures in digital images may be extracted by convolving the images with derivatives of Gaussians. The choice of the convolution operator and of the parameters involved defines a specific ridge image. In this paper, various ridge measures related to isophote curvature are constructed, reviewed, and evaluated with respect to their usability in CT/MRI matching of human brain scans. Construction is initially done using heuristics in two-dimensional images, and then established firmly in a mathematical framework. Attention is paid to the necessity of operator invariance, scale of the operator, extension to three-dimensional images, and relations to isophote and principal curvature. It is shown that one of the ridge measures appears well suited for the purpose of matching, despite the fact that the measure fails to detect ridges in a number of stylized scenes     

Multimodality visualization of medical volume data

New developments in 3-D volume acquisitions are creating a rapidly increasing demand for integrating multimodality 3-D visualization. In order to accomplish routine clinical multimodality visualization, many issues have to be dealt with, such as techniques for accurate spatial registration, integrated representation, suitable graphical user interfaces, and obtaining adequate rendering speeds. The aim of this experience paper is 2-fold. First, it presents various results from our research on multimodality visualization/registration. Second, this paper explicitly addresses practical problems and findings related to software development and multimodality registration/visualization. We hope that this will give colleagues a better understanding in some of these issues based on our experience, including notably our mistakes.     

A discrete dynamic contour model

A discrete dynamic model for defining contours in 2-D images is developed. The structure of this model is a set of connected vertices. With a minimum of interaction, an initial contour model can be defined, which is then automatically modified by an energy minimizing process. The internal energy of the model depends on local contour curvature, while the external energy is derived from image features. Solutions are presented to avoid undesirable deformation effects, like shrinking and vertex clustering, which are common in existing active contour models. The deformation process stops when a local minimum of the energy function is reached. The final shape of the model is a reproducible approximation of the desired contour. Results of applying the method to computer-generated images, as well as clinical images, are presented.     

Improved tomographic reconstruction in seven-pinhole imaging

Cardiac emission tomography using a seven-pinhole collimator has received only little appreciation as a diagnostic imaging technique. The main reasons are the limited angular sampling of the seven-pinhole device and the difficulties encountered in properly positioning the patient relative to the collimator/camera system. In order to overcome these problems, we have developed a modified ART3 algorithm for reconstruction of the radioactivity distribution in the heart. The method is very appropriate for seven-pinhole tomography, as demonstrated by the quality of the reconstructions, by the excellent point source resolution of the system response, and by a comparison to two other suitable reconstruction techniques, viz., SMART and SIRT.     

Brain shift estimation in image-guided neurosurgery using 3-D ultrasound

Intraoperative brain deformation is one of the most important causes affecting the overall accuracy of image-guided neurosurgical procedures. One option for correcting for this deformation is to acquire three-dimensional (3-D) ultrasound data during the operation and use this data to update the information provided by the preoperatively acquired MR data. For 12 patients 3-D ultrasound images have been reconstructed from freehand sweeps acquired during neurosurgical procedures. Ultrasound data acquired prior to and after opening the dura, but prior to surgery, have been quantitatively compared to the preoperatively acquired MR data to estimate the rigid component of brain shift at the first stages of surgery. Prior to opening the dura the average brain shift measured was 3.0 mm parallel to the direction of gravity, with a maximum of 7.5 mm, and 3.9 mm perpendicular to the direction of gravity, with a maximum of 8.2 mm. After opening the dura the shift increased on average 0.2 mm parallel to the direction of gravity and 1.4 mm perpendicular to the direction of gravity. Brain shift can be detected by acquiring 3-D ultrasound data during image-guided neurosurgery. Therefore, it can be used as a basis for correcting image data and preoperative planning for intraoperative deformations.