Bridging the gap: linking a legacy hospital information system with a filmless radiology picture archiving and communications system within a nonhomogeneous environment.

A health level 7 (HL7)-conformant data link to exchange information between the mainframe hospital information system (HIS) of our hospital and our home-grown picture archiving and communications system (PACS) is a result of a collaborative effort between the HIS department and the PACS development team. Based of the ability to link examination requisitions and image studies, applications have been generated to optimise workflow and to improve the reliability and distribution of radiology information. Now, images can be routed to individual radiologists and clinicians; worklists facilitate radiology reporting; applications exist to create, edit, and view reports and images via the internet; and automated quality control now limits the incidence of "lost" cases and errors in image routing. By following the HL7 standard to develop the gateway to the legacy system, the development of a radiology information system for booking, reading, reporting, and billing remains universal and does not preclude the option to integrate off-the-shelf commercial products.

Transparent image access in a distributed picture archiving and communications system: the Master Database broker.

A distributed design is the most cost-effective system for small-to medium-scale picture archiving and communications systems (PACS) implementations. However, the design presents an interesting challenge to developers and implementers: to make stored image data, distributed throughout the PACS network, appear to be centralized with a single access point for users. A key component for the distributed system is a central or master database, containing all the studies that have been scanned into the PACS. Each study includes a list of one or more locations for that particular dataset so that applications can easily find it. Non-Digital Imaging and Communications in Medicine (DICOM) clients, such as our worldwide web (WWW)-based PACS browser, query the master database directly to find the images, then jump to the most appropriate location via a distributed web-based viewing system. The Master Database Broker provides DICOM clients with the same functionality by translating DICOM queries to master database searches and distributing retrieval requests transparently to the appropriate source. The Broker also acts as a storage service class provider, allowing users to store selected image subsets and reformatted images with the original study, without having to know on which server the original data are stored.

Evolution of a filmless digital imaging and communications in medicine-conformant picture archiving and communications system: design issues and lessons learned over the last 3 years.

This presentation describes our experience and lessons learned over the first 3 years of developing and operating a filmless picture archiving and communications system (PACS) for all computed tomography (CT), magnetic resonance (MR), ultrasound, and nuclear medicine studies in our hospital. The PACS conforms to the Digital Imaging and Communications in Medicine (DICOM) standard and includes a sophisticated Worldwide Web (WWW)-based interface to complement the regular DICOM services. The PACS has undergone many design modifications from its inception, which have addressed performance, functionality, support, and maintenance issues. The lessons we have learned through making these modifications are described here and may prove to be helpful to anyone planning to deploy a PACS of their own.

Design and implementation of World Wide Web-based tools for image management in computed tomography, magnetic resonance imaging, and ultrasonography.

This article describes our experience in developing and using several web-based tools to facilitate access to and management of images from inside and outside of our department. Having recently eliminated film in ultrasound, computed tomography (CT) and magnetic resonance imaging (MRI), a simple method was required to access imaging from computers already existing throughout the hospital. The success of the World Wide Web (WWW), the familiarity of endusers with web browsers, and the relative ease of developing user interfaces virtually dictated that such an approach be pursued in our case. The resulting web-based tools allow validated users to search our Digital Imaging and Communications in Medicine (DICOM)-compliant archive servers for specific exams; to download image data from a remote site; to request the retrieval of data from long-term storage; to view images, and to perform certain DICOM routing operations. The existing infrastructure of the internet has allowed us to develop a low-cost system capable of being used for teleradiology. Since low-level, machine-specific interface programming was avoided, these tools were developed rapidly and are easily adapted. The familiarity of browser-based interfaces has facilitated user acceptance, and the benefit of platform independence minimizes software portability concerns.

Implementation of a filmless mini picture archiving and communication system in ultrasonography: experience after one year of use.

This article details our experience in developing and operating an ultrasound mini-picture archiving and communication system (PACS). Using software developed in-house, low-end Macintosh computers (Apple Computer Co. Cupertino, CA) equipped with framegrabbers coordinate the entry of patient demographic information, image acquisition, and viewing on each ultrasound scanner. After each exam, the data are transmitted to a central archive server where they can be accessed from anywhere on the network. The archive server also provides web-based access to the data and manages pre-fetch and other requests for data that may no longer be on-line. Archival is fully automatic and is performed on recordable compact disk (CD) without compression. The system has been filmless now for over 18 months. In the meantime, one film processor has been eliminated and the position of one film clerk has been reallocated. Previously, nine ultrasound machines produced approximately 150 sheets of laser film per day (at 14 images per sheet). The same quantity of data are now archived without compression onto a single CD. Start-up costs were recovered within six months, and the project has been extended to include computed tomography (CT) and magnetic resonance imaging (MRI).

CD-based image archival and management on a hybrid radiology intranet.

This article describes the design and implementation of a low-cost image archival and management solution on a radiology network consisting of UNIX, IBM personal computer-compatible (IBM, Purchase, NY) and Macintosh (Apple Computer, Cupertino, CA) workstations. The picture archiving and communications system (PACS) is modular, scaleable and conforms to the Digital Imaging and Communications in Medicine (DICOM) 3.0 standard for image transfer, storage and retrieval. Image data is made available on soft-copy reporting workstations by a work-flow management scheme and on desktop computers through a World Wide Web (WWW) interface. Data archival is based on recordable compact disc (CD) technology and is automated. The project has allowed the radiology department to eliminate the use of film in magnetic resonance (MR) imaging, computed tomography (CT) and ultrasonography.

Three-dimensional reconstruction of vascular trees: experimental evaluation.

This paper is the second of two that together present a novel approach to the problem of reconstructing vascular trees from a small number of projections. Previously, we described the reconstruction algorithm and how it effectively circumvents the matching or "correspondence problem" found in most photogrammetric or computer-vision-based approaches. The algorithm is fully automatic and assumes that the imaging geometry is known, the vascular tree is a connected structure, and that its center-lines have been identified in three or more images. It employs consistency and connectivity constraints and comprises three steps: The first generates a connected structure representing the multiplicity of solutions that are consistent with the first two views; the second assigns a measure of agreement to each branch in this structure based on one or more additional projections; and the third step employs this measure to distinguish between those branches comprising the vasculature and the accompanying artifacts. This paper addresses the issue of validation via simulations and experiments. In addition to a clinical case, we examine the performance of the algorithm when applied to simulated projections of two 3-D vascular models, both representative of the complexity faced in coronary and cerebral angiography. The results in each instance are impressive and demonstrate that adequate reconstructions may be obtained with as few as three distinct views.

Development and preliminary evaluation of VISLAN, a surgical planning and guidance system using intra-operative video imaging.

VISLAN is an integrated neurosurgical planning and guidance system. New segmentation and rendering techniques have been incorporated. A stereo video system is used intra-operatively and fulfils four roles. First, the video display is overlaid with graphical outlines showing the position of the planned craniotomy or the target (enhanced reality displays). Second, a skin surface patch is reconstructed from the stereo video images using patterned light (mean errors of surface point location are < 0.15 mm). Third, a freely mobile, hand-held localizer is tracked in real time (position errors are < 0.5 mm and with improved calibration < 0.2 mm), with its position superimposed on the pre-operative patient representation to assist surgical guidance. Fourth, markers fixed to the skull bone next to the cranial opening are used to detect intra-operative movement and to update registration. Initial results from phantom experiments show an overall system accuracy of better than 0.9 mm for intra-operative localization of features defined in pre-operative images. The prototype system has been tested during six neurosurgical operations with very good results.

Three-dimensional reconstruction of vascular trees. Theory and methodology.

In this paper we examine the few-view reconstruction problem as it applies to imaging vascular trees. A fully automated reconstruction algorithm is described that circumvents the traditional "correspondence problem," using only notions of consistency and connectivity. It is assumed that the vascular tree is a connected structure and that its centerlines have been identified in three or more images. The first of three steps in the procedure involves generating a connected structure that represents the multiplicity of solutions that are consistent with any two (different) projections. The second step assigns to each branch in this structure a measure of agreement based on its relationship with one or more additional views of the vasculature. The problem then becomes one of propagating this information, via connectivity relationships and consistency checks, throughout the above structure to distinguish between the branches comprising the imaged structure and the accompanying artifacts. In this paper we present the theory and methodology of the technique, while in a companion paper we address the issue of validation via simulations and experiments. Together, these papers shed some light on why ambiguities arise and often lead to errors in the few-view reconstruction problem. Strategies to handle these errors are described and results are presented that demonstrate the ability to obtain adequate reconstructions with as few as three distinct views.

Integration of stereoscopic DSA and 3D MRI for image-guided neurosurgery.

We demonstrate the feasibility and utility of using anatomical/vascular correlation in image-guided surgery, by interfacing a PC-based stereoscopic Digital Subtraction Angiography (DSA) analysis system to a three-dimensional (3D) image based surgical workstation that has been modified to allow presentation of stereoscopic images. Numerical values representing the position and angulation of a hand-held probe are transmitted to both systems simultaneously, enabling the probe to be visualized stereoscopically in both anatomical and vascular images during the surgical procedure. The integration of the patient's vascular and anatomical data in this way provides the surgeon with a complete overview of brain structures through which he is passing the electrode-guiding cannulas, enabling him to avoid critical vessels en route to the targets.

Analysis of projection geometry for few-view reconstruction of sparse objects.

In this paper certain projections are examined as to why they are better than others when used to reconstruct sparse objects from a small number of projections. At the heart of this discussion is the notion of "consistency," which is defined as the agreement between the object's 3-D structure and its appearance in each image. It is hypothesized that after two or more projections have been obtained, it is possible to predict how well as subsequent view will perform in terms of resolving ambiguities in the object reconstructed from only the first few views. The prediction is based on a step where views of the partial reconstruction are simulated and the use of consistency to estimate the effectiveness of a given projection is exploited. Here some freedom is presumed to acquire arbitrary as opposed to predetermined views of the object. The principles underlying this approach are outlined, and experiments are performed to illustrate its use in reconstructing a realistic 3-D model. Reflecting an interest in reconstructing cerebral vasculature from angiographic projections, the experiments employ simulations based on a 3-D wireframe model derived from an internal carotid arteriogram. It is found that for such an object, the predictions can be improved significantly by introducing a correction to account for the degree to which the object possesses some symmetry in shape. For objects sufficiently sparse, this correction is less important. It is concluded that when the number of projections is limited, it may be possible to favorably affect the reconstruction process in this manner.

Multimodality image integration for stereotactic surgical planning.

A method is presented for integrating stereotactic projection and tomographic image data to give composite 3-D images (stereo pairs) of cerebral anatomy and vasculature. The technique serves to combine complementary information from each modality and allows the imaged volume to be viewed directly. The procedure is largely automated and requires no additional apparatus or information beyond that which is ordinarily employed during stereotactic surgical planning. The two types of data are combined by superimposing the projection angiogram (DSA) onto a translucent volume rendered CT or MR image. Since the rendering algorithm employs an orthographic projection technique, the tomographic volume must first be reshaped and oriented to yield a perspective view that matches the DSA projection. During this process, the data undergo various interpolations which consequently affect the accuracy of target identification based on the resulting images. The integrity of the matching procedure was assessed using simulated data sets. Also, calculations were performed to estimate the resolution of measurements made from digitized stereoscopic images. The resulting sub-pixel accuracy of the matched images suggests that the technique has potential for stereotactic applications. Preliminary results are presented illustrating combined CT-DSA and MR-DSA data sets.

Three-dimensional display of cortical anatomy and vasculature: magnetic resonance angiography versus multimodality integration.

We present two methods for acquiring and viewing integrated three-dimensional (3D) images of cerebral vasculature and cortical anatomy. The aim of each technique is to provide the neurosurgeon or radiologist with a 3D image containing information which cannot ordinarily be obtained from a single imaging modality. The first approach employs recent developments in MR which is now capable of imaging flowing blood as well as static tissue. Here, true 3D data are acquired and displayed using volume or surface rendering techniques. The second approach is based on the integration of x-ray projection angiograms and tomographic image data, allowing a composite image of anatomy and vasculature to be viewed in 3D. This is accomplished by superimposing an angiographic stereo-pair onto volume rendered images of either CT or MR data created with matched viewing geometries. The two approaches are outlined and compared. Results are presented for each technique and potential clinical applications discussed.