B. M. ter Haar Romeny

Multiscale Segmentation of Three-Dimensional MR Brain Images

Segmentation of MR brain images using intensity values is severely limited owing to field inhomogeneities, susceptibility artifacts and partial volume effects. Edge based segmentation methods suffer from spurious edges and gaps in boundaries. A multiscale method to MRI brain segmentation is presented which uses both edge and intensity information. First a multiscale representation of an image is created, which can be made edge dependent to favor intra-tissue diffusion over inter-tissue diffusion. Subsequently a multiscale linking model (the hyperstack) is used to group voxels into a number of objects based on intensity. It is shown that both an improvement in accuracy and a reduction in image post-processing can be achieved if edge dependent diffusion is used instead of linear diffusion. The combination of edge dependent diffusion and intensity based linking facilitates segmentation of grey matter, white matter and cerebrospinal fluid with minimal user interaction. To segment the total brain (white matter plus grey matter) morphological operations are applied to remove small bridges between the brain and cranium. If the total brain is segmented, grey matter, white matter and cerebrospinal fluid can be segmented by joining a small number of segments. Using a supervised segmentation technique and MRI simulations of a brain phantom for validation it is shown that the errors are in the order of or smaller than reported in literature.

A non-linear gray-level appearance model improves active shape model segmentation

Active Shape Models (ASMs), a knowledge-based segmentation algorithm developed by Cootes and Taylor [1995, 1999], have become a standard and popular method for detecting structures in medical images. In ASMs-and various comparable approaches-the model of the objects shape and of its gray-level variations is based the assumption of linear distributions. In this work, we explore a new way to model the gray-level appearance of the objects, using a k-nearest-neighbors (kNN) classifier and a set of selected features for each location and resolution of the Active Shape Model. The construction of the kNN classifier and the selection of features from training images is fully automatic. We compare our approach with the standard ASMs on synthetic data and in four medical segmentation tasks. In all cases, the new method produces significantly better results (p<0.001).

The use of computed tomography to quantitate bone formation after distraction epiphysiolysis in the rabbit

A study of limb lengthening by distraction epiphysiolysis in the rabbit tibia is presented. For this purpose a special external distraction device was developed, which allowed 10 mm lengthening of the leg. Bone formation in the distraction zone was quantified by means of computed tomography. Cross-sectional scan planes at 1.5 mm separation revealed bone formation proceeding for several weeks after the end of the distraction period. A period of bone remodeling followed, resulting in the formation of a solid cortical structure, similar to the diaphysis, in the distraction zone.

Area-based computation of stereo disparity with model-based window size selection

In direct area-based stereo problems occur if there is a significant local deformation between the two images, and at borders of objects. We propose a correlation method with affine deformable windows in which an optimal window size is selected using model-based reasoning. Two criteria for the window size selection are studied and the resulting algorithms are applied to a random dot pair, an autostereogram and Hoffs fruit pair. The results are found to be both accurate and robust.

A complete and irreducible set of local orthogonally invariant features of 2-dimensional images

Presents a method of multi-resolution image analysis that gives the most concise set of local orthogonally invariant features of 2-dimensional input images. Solving the equivalence problem corresponding to a local jet and the group of orthogonal transformations of the cartesian coordinate frame the authors find a complete and irreducible set of local algebraic invariants that may describe any local orthogonally invariant feature of the jet.<<ETX>>

Savings And Costs Of A Picture Archiving And Communication System In The University Hospital Utrecht

The evaluation of the Dutch PACS project comprises amongst other studies a comparison of the direct financial costs of the present conventional system and the PACSystem. This paper shows that the invest-ment costs of a PACSystem are presently substantially higher than of the present system. These higher investment costs will not be compensated for by savings in the area of materials used, floor space needed, and personnel employed. The only cost effective compensation can be found in a shortening of the length of patient stay in the hospital. Preliminary results of the ongoing experiment suggest that compensation is achieved by an average decrease of one third day. Conditions under which a PACSystem can be more cost effective are being discussed.

Differential structure of images: accuracy of representation

Differentiation is known to be ill-posed in the sense of Hadamard. The theory of regular tempered distributions and the concept of Gaussian convolution filters open the way to a well-posed differentiation process, thereby introducing the notion of scale (or: inverse resolution). There is no a priori fundamental limit to the order of differentiation of images provided they are calculated on a sufficiently high scale (relative to pixel scale and noise correlation width), and provided we have a sufficient dynamic range of intensity values. Constraints in resolution (both in the spatial and in the intensity domain) enforce a scale-dependent restriction to the accuracy with which Gaussian kernels G/sub n/(x; /spl sigma/) can be represented in a physical sense. So at a given scale /spl sigma/ (e.g. in units of the sampling scale) and a given measure of inaccuracy /spl alpha/ there is a maximal order n above which the margin /spl alpha/ is exceeded. In this paper we quantify this relation.<<ETX>>

First results of the diagnostic evaluation studies and the clinical efficacy evaluation in the Dutch PACS project

The objective of the studies was to evaluate the diagnostic performance of the image digitizing distribution and display equipment of the installed PACS (Philips) in the Utrecht University Hospital (see also procee-dings SPIE 914, 1988). The diagnostic accuracy was evaluated by means of observer performance studies, using ROC analysis. Three series of films were used: chest phantom radiographs, clinical mammographic films, and clinical head CTs. We compared: original films versus images digitized with a video scanner, and/or original films versus images digitized with a laser scanner. Both scanners have 1024x1024x8 bits output resolution. Four radiologists scored the presence on a 5-point scale. The results of the mammographic and head CT series will be presented in this paper. The results of the diagnostic accuracy studies of the chest radiographs and their specific methodology will be presented in a companion SPIE paper. Goal of the clinical efficacy study is to see if the use of a PACS multimodality viewing station at an internal ward has clinical advantages as compared to the conventional situation. Using PACS integrated with a HIS (including a RIS) more easier and faster information is accessible to the clinicians. In this paper we will describe: the procedures which are needed to evaluate the use of the workstation installed at the internal ward, the development of the user interface with four layers of the Image Management System, and the methodology of evaluation the clinical advantages.

PACS Efficiency : A Detailed Quantitative Study Of The Distribution Process Of Films In A Clinical Environment In The Utrecht University Hospital

One of the goals of the Dutch PACS-project (a collaborative effort of the Utrecht University Hospital (UUH), Philips Medical Systems and BAZIS Central Development and Support Group Hospital Information Systems) is to perform a clinical evaluation and equipment testing at the UUH. In earlier publications a setup for this clinical evaluation is presented. A target ward, a subdivision of the department of Internal Medicine (IM) with a total number of 15 beds, is selected to be treated fully digital. Two other wards, similar to the target ward, were not digitally treated and served as control group. To exploit the efficiency potential of PACS, a comparison will be made between current procedures and PACS procedures. From February 1st until June 1st 1988, a detailed timing and logistic study of examinations and folder tracking has been carried out for all patients of the 3 wards of Internal Medicine, mentioned above. The first part of the study regarding the conventional distribution process is now completed. For this purpose time-registration forms were added to the patients application-forms for radiological examinations. These forms were required to be filled in by all personnel involved (receptionist, archive, technologist, radiologist, etc.). A total number of 500 usable time-registration forms were gathered. One of the results, indicated that the mean time interval for examinations to cover the total conventional distribu-tion process comes to 53.9 hours. An analysis of the number of disturbances in the conventional distribution process indicated that in 24.1 % of all examinations, some exponent was lacking (missing, loaned, delayed, etc.). These disturbances are analyzed in relation to time-intervals. Data were analyzed statistically by means of the SPSS statistical package. This paper describes and explains in detail: - frequencies and means of the total distribution time and different parts of the current distribution process - total number of disturbances in the current distribution process - disturbances analyzed in relation to time intervals The three wards were statistically not significantly different, so they can be compared with each other. This analysis shows clearly the possibilities for efficiency of the PACS distribution process and the consequences of this innovation for the organization and organizational communication.

First experiences with the modelling and simulation packagemiracles applied to a picture archiving and communication system (PACS) in a clinical environment

Since the construction of picture archiving and communication systems (PACS) appears to be extremely difficult, computer modelling and simulation are used as decision support tools. The package MIRACLES (Medical Image Representation, Archiving and Communication Learned from Extensive Simulation) has been developed at BAZIS in order to support the construction of simulation models of image information systems. This article discusses the application of MIRACLES to a prototypical PACS as being installed in a clinical environment. Attention is focussed to the required system analysis and difficulties which arose during the construction of the simulation model. The emphasis is on the presentation of the results of the simulation study, which show that simulation can be fruitfully used to predict, to analyse and to assist in solving performance problems. The simulation study confirmed assumptions and suppositions concerning both the system performance itself and strategies to improve the performance. The study also resulted in a number of concrete recommendations which might be useful for the set-up of the prototypical PACS.