The effect of virtual reality and training on liver operation planning

OBJECTIVE

The three-dimensional relation of a liver tumour to the intrahepatic vascular trees is basis of operation planning in liver surgery. Yet it has not been proven whether 3D reconstruction and further computerised processing will enhance precision of operation planning in liver surgery which has been based on the liver segment classification of Couinaud up to now.

DESIGN

Our interdisciplinary group (department of Surgery, German Cancer Research Center and Department of Radiology) has developed a new interactive computer-based quantitative 3D operation planning system for liver surgery which is being introduced into the clinical routine. The system quantifies the organ structures semiautomatically, defines resection planes depending on safety margins and the vascular trees, and presents the data in digital movies as well as in quantitative reports. We conducted a clinical trial to evaluate whether 3D reconstruction will lead to an improved operation planning. Data of 7 virtual patients were presented to a total of 81 surgeons in different levels of training. The tumours had to be assigned to a liver segment and subsequently drawn together with the operation proposals into a liver model. The precision of both was measured quantitatively for each surgeon and stratified concerning 2D and different types of 3D presentations.

RESULTS

The 3D anatomy can be visualised in high quality which results in good perception of the third dimension (depth). Tumour assignment to liver segments was significantly correlated to the level of training (p < 0.05). There was a significant increase (p < 0.001) in the precision of tumour localisation by 51% and resection proposal from 2D through 3D reconstructions by 13%-21%. Quantitative differences of the simplified Couinaud's classification of the liver segments compared to the true vascular anatomy of up to 40% were found.

CONCLUSION

The impact of individual 3D-reconstruction on surgical planning has been proven to be significant and increases precision quantitatively. The merit of Couinaud's classification may be enhanced by individualisation of the segment borders in future.

[Evaluation of CHILI teleradiology network 4 years after clinical implementation]

The CHILI teleradiology network has more than 60 installations in Germany and the USA. Radiological images and cardiological multiframe series are exchanged in clinical routine. This article investigates in what way and how often the system is used. This is done by means of accounting files that are produced automatically by the system. User functions, transmission protocols, data quantity, frequencies and time of data transmission and teleconferences are evaluated and discussed in this paper. Different application scenarios have been identified and are described and analyzed as well. An important result is, that the system is not merely an emergency system. Instead, it is used in daily routine as a multifunctional, multimodality workstation with advanced features for teleradiology and telecardiology.

Three-dimensional color Doppler reconstruction of intracardiac blood flow in patients with different heart valve diseases

An improved perception of the magnitude and dynamics of intracardiac flow disturbances has been made possible by the advent of 3-dimensional (3-D) color Doppler, a new diagnostic procedure developed at our institution. This study describes the new insights derived from 3-D reconstruction of color Doppler flow patterns in patients with different heart valve diseases. The color Doppler flow data from 153 multiplanar transesophageal or transthoracic echocardiographic examinations has been obtained from 133 patients with heart valve disease; 73 patients had mitral regurgitation, 15 had mitral stenosis, 18 had aortic regurgitation, 26 had aortic stenosis, and 21 patients had tricuspid regurgitation. Four patients had pulmonary regurgitation associated with mitral valve disease. The 3-D reconstructions of color Doppler flow signals were accomplished by means of the "Heidelberg Raytracing model," developed at our institution. The 3-D color Doppler reconstructions were obtained in all patients. The 3-D images revealed for the first time the complex spatial distribution of the blood flow abnormalities in the heart chambers caused by different heart valve diseases. New patterns of intracardiac blood flow disturbances were observed and classified. Three-dimensional color Doppler provides a unique noninvasive method that can be easily applied for studying intracardiac blood flow disturbances in clinical practice.

The impact of 3-dimensional reconstructions on operation planning in liver surgery

BACKGROUND

Operation planning in liver surgery depends on the precise understanding of the 3-dimensional (D) relation of the tumor to the intrahepatic vascular trees. To our knowledge, the impact of anatomical 3-D reconstructions on precision in operation planning has not yet been studied.

HYPOTHESIS

Three-dimensional reconstruction leads to an improvement of the ability to localize the tumor and an increased precision in operation planning in liver surgery.

DESIGN

We developed a new interactive computer-based quantitative 3-D operation planning system for liver surgery, which is being introduced to the clinical routine. To evaluate whether 3-D reconstruction leads to improved operation planning, we conducted a clinical trial. The data sets of 7 virtual patients were presented to a total of 81 surgeons in different levels of training. The tumors had to be assigned to a liver segment and subsequently drawn together with the operation proposal into a given liver model. The precision of the assignment to a liver segment according to Couinaud classification and the operation proposal were measured quantitatively for each surgeon and stratified concerning 2-D and different types of 3-D presentations.

RESULTS

The ability of correct tumor assignment to a liver segment was significantly correlated to the level of training (P<.05). Compared with 2-D computed tomography scans, 3-D reconstruction leads to a significant increase of precision in tumor localization by 37%. The target area of the resection proposal was improved by up to 31%.

CONCLUSION

Three-dimensional reconstruction leads to a significant improvement of tumor localization ability and to an increased precision of operation planning in liver surgery.

Three-dimensional color Doppler flow reconstruction and its clinical applications

The visualization and quantification of intracardiac blood flow have always been a challenging task for the cardiologist. The advent of color Doppler flow imaging substantially enhanced the clinical diagnosis of heart valve disease. Three-dimensional (3-D) color Doppler, a new diagnostic procedure, refines the diagnostic value of color Doppler by providing unique spatial and temporal information about the actual extension, direction, origin, and size of intracardiac flows. Here, we describe the procedure for 3-D color Doppler reconstruction of intracardiac blood flow velocities and reveal the varied findings in different heart pathologies that cause blood flow disturbances. An automated procedure for the segmentation of turbulent and laminar flows, which allows for the measurement of mitral regurgitant jet volumes, is one of the first 3-D quantitative approaches to the clinical assessment of mitral valve regurgitation. The major technical advances of this procedure include the direct use of digital color Doppler velocity data and an automatic voxel count of the turbulent jet flows. Three-dimensional color Doppler not only can disclose the spatial complex geometry of intracardiac blood flow disturbances but also can quantitatively assess the severity of mitral valve regurgitation.

Interactive realtime Doppler-ultrasound visualization of the heart

Heart valve insufficiencies can optimally be assessed using transesophageal, triggered, three-dimensional ultrasound imaging. The dynamic ultrasound data contain morphological as well as functional components which are recorded and displayed simultaneously. It allows the visualization of intracardiac motion which is an important parameter to detect abnormal flow caused by defect valves. A realtime reconstruction is desired to get a spatial impression on the one hand and to interactively clip parts of the volume on the other hand. Therefore, we use the OpenGL Volumizer API. Scalability of the visualization was tested with respect to different workstations and graphics resources using a Multipipe Utility library. The combination of both APIs enables a visualization of volumetric and functional data with frame rates up to 10 frames per second. By using the proposed method, it is possible to visualize the jet in the original color-coding which is employed during a conventional two-dimensional examination for displaying the velocity values. The morphological and the functional data are handled as two independent data channels. A good scalability from low cost up to high end graphic workstations is given by the use of the MPU. The quality of the resulting 3D images allows exact differentiation of heart valve insufficiencies to support the diagnostic procedure.

[Computer-assisted oral, maxillary and facial surgery]

BACKGROUND

Methods from the area of virtual reality are used in oral and maxillofacial surgery for the planning and three-dimensional individual simulation of surgeries. SIMULATION: In order to simulate complex surgeries with the aid of a computer, the diagnostic image data and especially various imaging modalities (CT, MRT, US) must be arranged in relation to each other, thus enabling rapid switching between the various modalities as well as the viewing of mixed images. Segmenting techniques for the reconstruction of three-dimensional representations of soft-tissue and osseous areas are required. We must develop ergonomic and intuitively useable interaction methods for the surgeon, thus allowing for precise and fast entry of the planned surgical intervention in the planning and simulation phase.

SURGERY

During the surgical phase, instrument navigation tools offer the surgeon interactive support through operation guidance and control of potential dangers. This feature is already available today. Future intraoperative assistance will take the form of such passive tools for the support of intraoperative orientation as well as so-called tracking systems (semi-active systems) which accompany and support the surgeons' work. The final form are robots which execute specific steps completely autonomously.

DISCUSSION

The techniques of virtual reality keep gaining in importance for medical applications. Many applications are still being developed or are still in the form of a prototype. However, it is already clear that developments in this area will have a considerable effect on the surgeon's routine work.

[Use of virtual reality for MRI data of complex vascular structures]

During the last years because of the progress in magnetic resonance imaging (MRI) magnetic resonance angiography (MRA) has become a serious alternative to conventional X-ray angiography. The potential of MRA in combination with methods for three-dimensional reconstruction will be presented and different methods for image post-processing are discussed based on a number of cases. The examinations were performed on a clinical 1.5 T magnetic resonance tomograph (Siemens Vision, Erlangen) using conventional MR angiography sequences. The different options of post-processing were carried out online on the console and offline using dedicated workstations (Siemens Virtuoso and CHILI).

DISCUSSION

Complex post-processing procedures are applied to different areas like pulmonary vasculature, thoracic aorta, abdominal aorta, and renal transplant arteries. Different diagnostic values can be seen for the variety of three-dimensional reconstruction methods. According to our experience volume rendering has been selected as the method of choice due to the time needed for reconstruction and the information content of the resulting image.

[Volumetric analysis and visualization of cardiologic ultrasound data]

BACKGROUND

Echocardiography is a standard imaging technique for the assessment of heart valve disease. The good spatial and temporal resolution is the basis for different methods which provide information about the severity of such defects. Dynamic colour visualisation and volumetric measurements of regurgitant jets are a new evaluating tool for the assessment of heart valve insufficiencies.

METHODS

The regurgitant jet volume of 58 patients was evaluated on an external work-station after segmentation of the left atrium and compared to regurgitant volume; the correlation was good. This result is valid for central jets as well as for eccentric jets.

CONCLUSIONS

Measurement of regurgitant jet volume is a method which considers the three-dimensional shape of the examined volume. Real-time visualisation techniques which support the interactive clipping of morphological structures provide dynamic visualisation of intracardiac flow during the heart cycle. Dynamic colour visualisation of jets together with myocardial structures allows the assignment of intracardiac flow to morphological structures.

Design of a distributed CORBA based image processing server

This paper presents the design and implementation of a distributed image processing server based on CORBA. Existing image processing tools were encapsulated in a common way with this server. Data exchange and conversion is done automatically inside the server, hiding these tasks from the user. The different image processing tools are visible as one large collection of algorithms and due to the use of CORBA are accessible via intra-/internet.

Borderless teleradiology with CHILI

Teleradiology is one of the most evolved areas of telemedicine, but one of the basic problems which remains unsolved concerns system compatibility. The DICOM (Digital Imaging and Communications in Medicine) standard is a prerequisite, but it is not sufficient in all aspects. Examples of other currently open issues are security and cooperative work in synchronous teleconferences. Users without a DICOM radiological workstation would benefit from the ability to join a teleradiology network without any special tools. Drawbacks of many teleradiology systems are that they are monolithic in their software design and cannot be adapted to the actual user's environment. Existing radiological systems currently cannot be extended with additional software components. Consequently, every new application usually needs a new workstation with a different look and feel, which must be connected and integrated into the existing infrastructure. This paper introduces the second generation teleradiology system CHILI. The system has been designed to match both the teleradiology requirements of the American College of Radiology (ACR), and the functionality and usability needs of the users. The experiences of software developers and teleradiology users who participated in the first years of the clinical use of CHILI's predecessor MEDICUS have been integrated into a new design. The system has been designed as a component-based architecture. The most powerful communication protocol for data exchange and teleconferencing is the CHILI protocol, which includes a strong data security concept. The system offers, in addition to its own secure protocol, several different communication Methods: DICOM, classic e-mail, Remote Copy functions (RCP), File Transfer Protocol (FTP), the internet protocols HTTP (HyperText Transfer Protocol) and HTTPS (HyperText Transfer Protocol Secure),and CD-ROMs for off-line communication. These transfer METHODS allow the user to send images to nearly anyone with a computer and a network. The drawbacks of the non-CHILI protocols are that teleconferences are not possible, and that the user must take reasonable precautions for data privacy and security. The CHILI PlugIn mechanism enables the users or third parties to extend the system capabilities by adding powerful image postprocessing functions or interfaces to other information systems. Suitable PlugIns can be either existing programs, or dedicated applications programmed with interfaces to the CHILI components. The developer may freely choose programming languages and interface toolkits. The CHILI architecture is a powerful and flexible environment for Picture Archiving and Communications Systems (PACS)and teleradiology. More than 40 systems are currently running in clinical routine in Germany. More than 300,000 images have been distributed among the communication partners in the last two years. Feedback and suggestions from the users influenced the system architecture by a great extent. The proposed and implemented system has been optimized to be as platform independent, open, and secure as possible.

A new diagnostic procedure for assessing intracardiac flow disturbances in patients with heart valve disease

BACKGROUND

Until now no diagnostic technique was available for the three-dimensional (3D) study of intracardiac blood flow abnormalities in patients with heart valve disease. 3D color Doppler is a new diagnostic technique first developed at our institution.

METHODS

The 3D reconstructions of the blood flow velocity data have been obtained from conventional multiplanar transesophageal or transthoracic Doppler echocardiographic examinations. We analyzed 111 reconstructions of color Doppler data obtained from 85 patients with different heart valve diseases who underwent intraoperative transesophageal echocardiography. Sixty-nine patients had a significant mitral regurgitation, 7 mitral stenosis, 9 aortic regurgitation, 12 aortic stenosis, 14 tricuspid regurgitation. Three patients had pulmonary regurgitation associated with mitral valve disease.

RESULTS

3D color Doppler disclosed the complex spatial spreading of the blood flow abnormalities caused by heart valve disease. New patterns of intracardiac blood flow disturbances could be observed and classified.

CONCLUSIONS

This paper shows the first clinical applications of 3D color Doppler in patients with heart valve disease. The new insights derived from the 3D study of intracardiac blood flow dynamics revealed a great impact of this technique on the clinical management of patients with heart valve disease.

Virtual surgery in a (tele-)radiology framework

This paper presents telemedicine as an extension of a teleradiology framework through tools for virtual surgery. To classify the described methods and applications, the research field of virtual reality (VR) is broadly reviewed. Differences with respect to technical equipment, methodological requirements and areas of application are pointed out. Desktop VR, augmented reality, and virtual reality are differentiated and discussed in some typical contexts of diagnostic support, surgical planning, therapeutic procedures, simulation and training. Visualization techniques are compared as a prerequisite for virtual reality and assigned to distinct levels of immersion. The advantage of a hybrid visualization kernel is emphasized with respect to the desktop VR applications that are subsequently shown. Moreover, software design aspects are considered by outlining functional openness in the architecture of the host system. Here, a teleradiology workstation was extended by dedicated tools for surgical planning through a plug-in mechanism. Examples of recent areas of application are introduced such as liver tumor resection planning, diagnostic support in heart surgery, and craniofacial surgery planning. In the future, surgical planning systems will become more important. They will benefit from improvements in image acquisition and communication, new image processing approaches, and techniques for data presentation. This will facilitate preoperative planning and intraoperative applications.

The evolution of a German teleradiology system

This paper describes the evolution of a german teleradiology system. The development started from simple image file transfer, continued with a dedicated teleradiology system and ended up with a general radiology workstation with teleradiology features. The main features, advantages and drawbacks of the different generations are described. The own developments are compared with developments at other places. The influence by standards is also included in this investigation. The latest systems are mainly used by the radiologists and the image transfer for scientific cooperation is nowadays just one of several application fields of teleradiology.

Extending a teleradiology system by tools for 3D-visualization and volumetric analysis through a plug-in mechanism

This paper describes ongoing research concerning interactive volume visualization coupled with tools for volumetric analysis. To establish an easy to use application, the 3D-visualization has been embedded in a state of the art teleradiology system, where additional functionality is often desired beyond basic image transfer and management. Major clinical requirements for deriving spatial measures are covered by the tools, in order to realize extended diagnosis support and therapy planning. Introducing the general plug-in mechanism this work exemplarily describes the useful extension of an approved application. Interactive visualization was achieved by a hybrid approach taking advantage of both the precise volume visualization based on the Heidelberg Raytracing Model and the graphics acceleration of modern workstations. Several tools for volumetric analysis extend the 3D-viewing. They offer 3D-pointing devices to select locations in the data volume, measure anatomical structures or control segmentation processes. A haptic interface provides a realistic perception while navigating within the 3D-reconstruction. The work is closely related to research work in the field of heart, liver and head surgery. In cooperation with our medical partners the development of tools as presented proceed the integration of image analysis into clinical routine.

Technical aspects of virtual liver resection planning

Operability of a liver tumor is depending on its three dimensional relation to the intrahepatic vascular trees which define autonomously functioning liver (sub-)segments. Precise operation planning is complicated by anatomic variability, distortion of the vascular trees by the tumor or preceding liver resections. Because of the missing possibility to track the deformation of the liver during the operation an integration of the resection planning system into an intra-operative navigation system is not feasible. So the main task of an operation planning system in this domain is a quantifiable patient selection by exact prediction of post-operative liver function and a quantifiable resection proposal. The system quantifies the organ structures and resection volumes by means of absolute and relative values. It defines resection planes depending on security margins and the vascular trees and presents the data in visualized form as a 3D movie. The new 3D operation planning system offers quantifiable liver resection proposals based on individualized liver anatomy. The results are visualized in digital movies as well as in quantitative reports.

An architecture for implementing customizable medical image processing systems

Monolithic image processing systems containing a superset of imaging algorithms are difficult to use and require specialized knowledge of image processing. Thus they increase the workload of medical personnel instead of making the work situation easier. Customizable medical image processing systems on the other hand may be easily adapted to address various problems in the medical image processing domain integrating only the necessary subset of image processing functionality presented in on intuitive way. In this work we present an architecture for creating customizable image processing systems for the medical domain. We address three major topics: 1.) easy, goal-oriented customization of imaging systems by using a generalized algorithm model and repository, 2.) dynamic, data-oriented parameterization of the selected algorithms and 3.) semi-automated generation of user interface components for each new algorithm to be inserted in an imaging system based on cognitive ergonomics. We conclude with the presentation of an initial implementation of the architecture in form of an object-oriented framework for the creation of components for customizable medical imaging systems.

Three-dimensional color Doppler: a clinical study in patients with mitral regurgitation

OBJECTIVES

The purpose of this study was to assess the clinical feasibility of three-dimensional (3D) reconstruction of color Doppler signals in patients with mitral regurgitation.

BACKGROUND

Two-dimensional (2D) color Doppler has limited value in visualizing and quantifying asymmetric mitral regurgitation. Clinical studies on 3D reconstruction of Doppler signals in original color coding have not yet been performed in patients. We have developed a new procedure for 3D reconstruction of color Doppler.

METHODS

We studied 58 patients by transesophageal 3D echocardiography. The jet area was assessed by planimetry and the jet volumes by 3D Doppler. The regurgitant fractions, the volumes, and the angiographic degree of mitral regurgitation were assessed in 28 patients with central jets and compared with those of 30 patients with eccentric jets.

RESULTS

In all patients, jet areas and jet volumes significantly correlated with the angiographic grading (r = 0.73 and r = 0.90), the regurgitant fraction (r = 0.68 and r = 0.80) and the regurgitant volume (r = 0.66 and r = 0.90). In patients with central jets, significant correlations were found between jet area and angiography (r = 0.86), regurgitant fraction (r = 0.64) and regurgitant volume (r = 0.78). No significant correlations were found between jet area and angiography (r = 0.53), regurgitant fraction (r = 0.52) and regurgitant volume (r = 0.53) in the group of patients with eccentric jets. In contrast, jet volumes significantly correlated with angiography (r = 0.90), regurgitant fraction (r = 0.75) and regurgitant volume (r = 0.88) in the group of patients with eccentric jets.

CONCLUSIONS

Three-dimensional Doppler revealed new images of the complex jet geometry. In addition, jet volumes, assessed by an automated voxel count, independent of manual planimetry or subjective estimation, showed that 3D Doppler is also capable of quantifying asymmetric jets.

Three-dimensional Doppler. Techniques and clinical applications

AIMS

Colour Doppler is the most widely used technique for assessing valve disease, but eccentric regurgitant jets cannot be visualized and measured by conventional 2D techniques. We have developed a new procedure for three-dimensional (3D) reconstruction of colour Doppler signals.

METHODS AND RESULTS

Fifty patients with mitral regurgitation underwent transoesophageal echocardiography and 3D acquisition. The severity of mitral regurgitation was assessed by angiography and the regurgitant volumes were measured by pulsed Doppler. The jet areas were calculated by planimetry from conventional colour Doppler; the jet volumes were obtained by 3D Doppler. A higher degree of mitral regurgitation was found in the patients with eccentric jets. While jet areas showed poor correlation with regurgitant volumes (r = 0.61), jet volumes correlated significantly with regurgitant volumes (r = 0.93; P < 0.001). While jet areas failed to identify patients with different grades of regurgitation, jet volumes could so discriminate.

CONCLUSIONS

3D Doppler revealed new patterns of regurgitant flow and allowed a more accurate semiquantitative assessment of complex asymmetrical regurgitant jets. Three-dimensional colour Doppler has a great potential for becoming a reference method for the assessment of patients with heart valve disease.

[Virtual surgical planning in liver surgery]

The operability of a liver tumour depends on its three-dimensional relation to the intrahepatic vascular trees which define autonomously functioning liver (sub-)segments. The aim of our study was to establish a computer-based three-dimensional volumetric operation planning system for the liver.

METHODS

Using data from routine helical CT scans the three tissue subclasses of liver parenchyma, liver vessels and liver tumour were segmented semiautomatically. A dedicated segmenting tool was established using region growing algorithms in combination with an "intelligent" border finder. Visualisation is performed by the "Heidelberg Raytracer". The vascular trees are visualised as 3D graphs. Pseudoconnections between portal and hepatic venous trees are separated automatically. Security margins are calculated and the system presents a virtual resection proposal.

RESULTS

The 3D anatomy of the liver can be visualised in high quality resulting in good depth perception. Security margins are demonstrated. Dependent liver parenchyma can be recognized automatically on the basis of the vascular trees. The system offers a individualised resection proposal including the tumour, security margin and dependent liver parenchyma.

CONCLUSION

Three-dimensional presentation of the individual liver anatomy of a given patient facilitates the perception of the pathology. Virtual reality combined with artificial intelligence allows calculation of complete resection protocols, which can be quantified and modified interactively. This will make operation planning more objective; patient selection may be improved, and in cases of difficult tumour localisation different resection strategies may be tested. Thus virtual reality in liver surgery will improve teaching, surgical training and planning. It may lead to improved surgical care.

High performance medical image processing in client/server-environments

As 3D scanning devices like computer tomography (CT) or magnetic resonance imaging (MRI) become more widespread, there is also an increasing need for powerful computers that can handle the enormous amounts of data with acceptable response times. We describe an approach to parallelize some of the more frequently used image processing operators on distributed memory architectures. It is desirable to make such specialized machines accessible on a network, in order to save costs by sharing resources. We present a client/server approach that is specifically tailored to the interactive work with volume data. Our image processing server implements a volume visualization method that allows the user to assess the segmentation of anatomical structures. We can enhance the presentation by combining the volume visualizations on a viewing station with additional graphical elements, which can be manipulated in real-time. The methods presented were verified on two applications for different domains.

Three-dimensional color Doppler: a new approach for quantitative assessment of mitral regurgitant jets

Color Doppler echocardiography does not provide adequate information about the severity of mitral regurgitation in patients with eccentric mitral regurgitation. We have developed a new procedure for 3-dimensional (3D) color Doppler reconstruction and for segmentation of regurgitant jets. The volume of regurgitant jets was compared with jet area in 63 patients with mitral regurgitation. Mitral regurgitation was assessed by angiography, regurgitant fraction and volume by pulsed Doppler, JA by planimetry, and JV by 3-dimensional Doppler. Twenty-eight patients with central jets were compared with 35 patients with eccentric jets. In the patients with eccentric jets, JV showed significant correlations with regurgitant volume (r = 0.90; P <.01) and regurgitant fraction (r = 0.76; P < .01) and was able to separate groups with different degrees of mitral regurgitation (P <.01). Three-dimensional Doppler revealed origin, direction, and spatial spreading of complex jet geometry. JV, a new parameter of mitral regurgitation, was also capable of quantifying asymmetrical jets.

Three-dimensional color Doppler for assessing mitral regurgitation during valvuloplasty

OBJECTIVE

Transesophageal color Doppler (or 2D Doppler) is the most widely used technique for intraoperative assessment of mitral valve repair. However, the most severe mitral regurgitations produce eccentric jet flows which cannot be assessed by 2D imaging. Up to now the indications for surgical intervention and intraoperative decisions after valve repair have been based on 2D Doppler examinations. Aim of this study was to compare conventional 2D Doppler to three-dimensional (3D) Doppler for assessing residual regurgitation in patients after mitral valvuloplasty.

METHODS

Twenty-four patients were referred to surgery for mitral valve repair. They underwent transesophageal echocardiography and 3D data acquisition during mitral valve reconstruction. Conventional assessment of mitral valve regurgitation, measured by color Doppler jet area, was compared to the volume of regurgitant jets obtained by 3D Doppler. Regurgitant volume and fraction were measured by pulsed Doppler and two-dimensional echocardiography. The 3D reconstructions of color Doppler data were accomplished by means of the 'Heidelberg Raytracing Algorithm' developed at our institution.

RESULTS

The jet areas did not show any significant correlation to the regurgitant fraction (r = 45; P = NS) or regurgitant volumes (r = 0.40; P = NS). In contrast the jet volumes correlated significantly to regurgitant fraction (r = 0.71; P < 0.01) and regurgitant volume (r = 0.85; P < 0.01). The reproducibility analysis of repeated jet volume and jet area measurements also showed that the parameter jet volume has a lower variability and higher agreement of repeated measurements than jet area.

CONCLUSIONS

Three-dimensional color Doppler flow imaging revealed the complex geometry of eccentric regurgitant jets and showed that the assessment of mitral regurgitation, based on conventional 2D Doppler, can be misleading. This new technique has a great potential for becoming a reference method for assessing mitral valve repair.

Virtual planning of liver resections: image processing, visualization and volumetric evaluation

Operability of a liver tumor depends on its three dimensional relation to the intrahepatic vascular trees as well as the volume ratio of healthy to tumorous tissue. Precise operation planning is complicated by anatomic variability and distortion of the vascular trees by the tumor or preceding liver resections. We have developed a computer based 3D virtual operation planning system which is ready to go in routine use. The main task of a system in this domain is a quantifiable patient selection by exact prediction of post-operative liver function. It provides the means to measure absolute and relative volumes of the organ structures and resected parenchyma. Another important step in the pre-operative phase is to visualize the relation between the tumor, the liver and the vessel trees for each patient. The new 3D operation planning system offers quantifiable liver resection proposals based on individualized liver anatomy. The results are presented as 3D movies or as interactive visualizations as well as in quantitative reports.

Extending a teleradiology system by tools for visualization and volumetric analysis through a plug-in mechanism

This paper describes ongoing research concerning interactive volume visualization coupled with tools for volumetric analysis. To establish an easy to use application, the three-dimensional-visualization has been embedded in a state of the art teleradiology system, where additional functionality is often desired beyond basic image transfer and management. Major clinical requirements for deriving spatial measures are covered by the tools, in order to realize extended diagnosis support and therapy planning. Introducing a general plug-in mechanism, this work exemplarily describes the useful extension of an approved application. Interactive visualization was achieved by a hybrid approach taking advantage of both the precise volume visualization based on the Heidelberg ray-tracing model and the graphics acceleration capabilities of modern workstations. Several tools for volumetric analysis extend the three-dimensional-viewing. They are controlled by adequate input devices to select locations in the data volume, measure anatomical structures or initiate a segmentation process. Moreover, a haptic interface can be connected to provide a more realistic feedback while navigating within the three-dimensional-reconstruction. The work is closely related to research in the field of heart, liver and head surgery. In cooperation with our medical partners the development of tools as presented facilitates the integration of image analysis into the clinical routine.

Assessment of mitral regurgitant jets by three-dimensional color Doppler

BACKGROUND

Color Doppler echocardiography is a standard technique for assessing mitral regurgitation before and after mitral valvuloplasty. Mitral valve prolapse produces complex eccentric jet flows that cannot be visualized and measured by two-dimensional color Doppler echocardiography. The aim of this study was to evaluate the clinical impact of three-dimensional color Doppler echocardiography, a new technique developed at our institution, for assessing mitral regurgitation.

METHODS

Forty-five patients with mitral regurgitation underwent intraoperative transesophageal echocardiography and three-dimensional Doppler data acquisition. The grade of mitral regurgitation was assessed by angiography. The jet areas were calculated by planimetry from conventional color Doppler; the jet volumes were obtained by three-dimensional Doppler data.

RESULTS

New patterns of mitral regurgitant flows were recognized according to the origin, direction, and spatial spreading into the left atrium. Conventional jet areas failed to separate the groups of patients with different degrees of regurgitation, whereas the jet volumes were able to divide patients with different regurgitation grades. No significant correlation was found between jet area and angiographic grading (r = 0.63, p = NS). Jet volumes were significantly correlated to angiography (r = 0.89, p < 0.001).

CONCLUSIONS

Three-dimensional color Doppler echocardiography revealed new patterns of regurgitant flow and allowed a more accurate semiquantitative assessment of complex asymmetrical regurgitant jets.

Applying computer modeling to examine complex dynamics and pattern formation of tissue growth

For research in areas such as developmental biology and cancer, understanding the formation and regrowth of tissue is of great importance. Since complex system behavior makes it difficult to interpret dynamics and pattern formation of tissue growth, it is helpful to have a way to simulate the cell systems and test hypotheses about the mechanisms by which the system is responding. Computer "modeling experiments" can serve this purpose, as we show with an example of the small intestine epithelial cells' response to cytosine arabinoside. This example demonstrates that nonhomogeneities in the cell population can play an important role and emphasizes the need to use a modeling approach, like our spatial modeling, that addresses the differences within the tissue structure. These types of "modeling experiments" can guide researchers with further experiments and provide clues as to how complex cell proliferation behavior is linked to underlying molecular phenomena.

[Integration of functional and morphologic MRI data for preoperative 3D visualization of tumors. Example: cervical carcinoma]

PURPOSE

The goal of this exemplary study was to integrate morphological and functional MRI to establish computer-based, pre-operative therapy planning for tumors, instancing cervical carcinoma.

METHODS

For morphological representation T1-weighted, filtered 3D sequences were investigated within a hierarchical segmentation approach. Using a method for image registration, segmented structures were combined and overlaid with functional information of contrast medium-enhanced, dynamic MRI. After assigning colour attributes to the segmented structures, they were presented using a method for direct volume visualisation.

RESULTS

Segmentation of organs and vessels as well as tissue differentiation yielded a morphological visualisation of anatomical structures that were overlaid with pharmacokinetic parameters derived from dynamic MRI, subsequently. Thereby, three-dimensional, arbitrary views on the functional data were displayed.

CONCLUSIONS

Image analysis and visualisation of the acquired MR data establishes both a morphologic and functional evaluation of suspect lesions and adjacent organs. By integrating morphologic and functional MRI additional information can be gathered that possibly impinge on preoperative planning.

Heterogeneity of myocardial edema in isolated pig hearts after perfusion with different types of cardioprotective solutions

The extent and distribution of myocardial edema induced by perfusion with cardioprotective solutions is of great interest. Domestic pig hearts (n = 12) were perfused in situ after aortic cross clamping either with Bretschneider's cardioplegic solution (HTK, 4 degrees C, n = 3), with a heparinized Krebs-Henseleit solution containing 30 mmol/L 2,3 Butanedionemonoxime (BDM, 4 degrees C, n = 3) or with heparinized pig blood (HPB, 24 degrees C, n = 3). After a three-hours storage period, magnetic resonance tomography (MRI) was carried out. The acquired T1-weighted data were used for the subsequent three-dimensional reconstruction based on the "Heidelberg ray-tracing technique". The small myocardial tissue blocks (n = 216) were excised from these hearts for dry weight measurements for 9 preselected regions in duplicate including ventricular papillary muscle, ventricular free wall, ventricular septum, apex, and atrial tissue. In control hearts (n = 3), dry weight was measured immediately after explantation (no MRI). The results of dry-weight measurements and three dimensional visualization were compared. Dry-weight measurements revealed that considerable myocardial edema is induced by any of the experimental procedures. The effects were most pronounced after BDM perfusion. Regardless how the edema was induced, there were significant differences of the water content within the heart: the water content in the heads of the papillary muscles and in the interventricular septum was always smaller than that of the free left- and right-ventricular walls. The heterogeneity of myocardial edema and its spatial distribution pattern could be qualitatively visualized. The experimental data (biophysical data and 3D visualization) clearly show a heterogeneity of myocardial edema induced by different types of cardioprotective solutions. As the presence of myocardial edema represents one of the crucial events in the pathophysiology of myocardial dysfunction occurring during myocardial infarction, ischemia, heart transplantation, and extracorporeal circulation, the present study represents an interesting contribution towards intravital detection and distribution of myocardial edema.

A three-generation model for teleradiology

This paper proceeds from the definition of teleradiology. It identifies three different generations of teleradiology systems and includes those systems that are not regarded as teleradiology systems by the authors. A list of requirements pertinent to users of first-generation teleradiology systems is introduced. Most of the requirements have been realized in a new generation teleradiology system called CHILI.

The German teleradiology system MEDICUS: system description and experiences in a German field test

MEDICUS is a teleradiology system which has been developed in a joint project of the German Cancer Research Center (Deutsches Krebsforschungszentrum) and the Transfer Center Medical Informatics (Steinbeis-Transferzentrum Medizinische Informatik) in Heidelberg, Germany. The system is designed to work on ISDN lines as well as in a local area network. Special attention has been given to the design of the user interface and data security, integrity, and authentication. The software is in use in 13 radiology departments in university clinics, small hospitals, private practices, and research institutes. More than 25 thousand images have been processed in 6 months. The system is in use in six different application scenarios. MEDICUS is running under the UNIX operating system. The connection of the modalities could in most cases not be realized with the DICOM protocol as older machines were not equipped with this standard protocol. Clinical experiences show that the MEDICUS system provides a very high degree of functionality. The system has an efficient and user friendly graphical user interface. The result of a comparison with other systems shows that MEDICUS is currently the best known teleradiology system. Cost reductions are already obvious, but additional research has to be performed in this field. An even more powerful commercial successor is currently under construction at the Steinbeis-Transferzentrum Medizinische Informatik in Heidelberg.

Cognition-based development and evaluation of ergonomic user interfaces for medical image processing and archiving systems

Whether or not a computerized system enhances the conditions of work in the application domain, very much demands on the user interface. Graphical user interfaces seem to attract the interest of the users but mostly ignore some basic rules of visual information processing thus leading to systems which are difficult to use, lowering productivity and increasing working stress (cognitive and work load). In this work we present some fundamental ergonomic considerations and their application to the medical image processing and archiving domain. We introduce the extensions to an existing concept needed to control and guide the development of GUIs with respect to domain specific ergonomics. The suggested concept, called Model-View-Controller Constraints (MVCC), can be used to programmatically implement ergonomic constraints, and thus has some advantages over written style guides. We conclude with the presentation of existing norms and methods to evaluate user interfaces.

Experiences with the german teleradiology system MEDICUS

This paper introduces the teleradiology system, MEDICUS, which has been developed at the Deutsches Krebsforschungszentrum (German Cancer Research Center) in Heidelberg, Germany. The system is designed to work on ISDN lines as well as in a local area network. The global software architecture is explained in the article. Special attention has been given to the design of the user interface and data security, integrity and authentication. The software has been evaluated in a German field test at 13 radiology departments in university clinics, small hospitals, private practices and research institutes. More than 30 thousand images have been transmitted using this system during a 9 month period. Realized application scenarios are: in-house communication, image and report delivery to referring hospitals, remote reporting, radiotherapy treatment planning and research cooperation. Experience has shown that the system is easy to use and saves time. It obviates the need for patient transport and reduces film costs. Experiences of individuals while using the system during the field test helped define the functionality of the second generation teleradiology system which is even more flexible and is also available as a commercial product.

How to deal with security issues in teleradiology

The use of teleradiological systems for medical image communication is increasing significantly. Digital images can be transferred over public telephone (e.g. ISDN) lines to colleagues for interpretation and/or consultation. Thus, a new quality is being introduced into the process of radiological diagnostics. However, technical implementation of such systems is accompanied by little consideration of legal, i.e. data protection and security, issues. In this paper we describe a concept for data protection in teleradiology which unites aspects of privacy and security as well as user aspects. After highlighting the legal situation in Germany we describe the methodology used for deriving the security profile for teleradiology in Germany. As a result the set of security measures which have to be employed with a teleradiology system is listed. A detailed description follows of how the software requirements are implemented in the teleradiology software MEDICUS.

[Requirements for a teleradiology system. Experiences with the MEDICUS-2 field test]

During the Medicus field test we gained experience using the teleradiology system for almost daily teleconferences between a radiology department and clinics for internal medicine, urology, and gynecology. The existing system has a high degree of functionality. The full 12-bit data format is available using the DICOM protocol. A data security concept is implemented, ensuring data integrity, privacy and authentication of communication partners. This concept covers the areas of organization, technique, user training, and software implementation. A future system should be a general purpose radiology workstation covering viewing functionality, image manipulation, and digital archive access. Dedicated teleradiology features have to be a part. Specialized evaluation software, e.g. for dynamic MRI, should be integratable in a modular way. For data exchange with other systems and for the synchronization of teleconference sessions, the protocols should be independent of the network standard used (ISDN, Ethernet, ATM) and based on the DICOM protocol. Extensions of the existing standard are therefore necessary. Besides future technical developments, reimbursement for teleradiology must be accomplished.

[Calibration of clinical databanks with "virtual patients"]

The scientific value of multicenter studies is still questionable, as there are no methods available that allow to determine whether in fact identical items are recorded in the same way in different centers. Subjective classifications (for example according to the New York Heart Association (NYHA)), definitions of items, documentation habits and procedures may not be comparable in different hospitals. For that reason the concept of a "virtual patient" for calibration of database systems was developed as a new methodological approach. The "virtual patients" describes a computer program that includes and uses multimedia-tools to represent an exactly defined patient. A sound card enables a patient to talk and to represent intracardial and intrapulmonary sounds. Additional information including echocardiographic sequences, perioperative video sequences, x-ray analysis, angiograms, etc. is represented in the program. Thus during the perioperative course of a patient the complete relevant pre-, intra- and postoperative information regarding the patient is provided. Any physician participating in a multicenter study is asked to record the data of this virtual patient and to store it in a database system using the sheets applied in a multicenter study. As the patient is exactly defined (virtual patient) incorrect classifications and incomplete recordings, etc. can easily be detected and discussed. The virtual patient is a tool that allows calibration of database systems by direct comparison of the documentation technique between different physicians and different hospitals participating in multicenter studies. It is thus a multimedia-instrument to support standardization and quality assurance of database systems.

Medical Images in Integrated Health Care Workstations

The difference between an invention and a discovery is discussed, before turning to the sources of medical images. Next, the ongoing integration of image modalities in clinical routine is reviewed, as well as improvements in diagnosis and therapy planning with the help of better images in inter-connected distributed systems. Current shortcomings of image processing, and the attempts to overcome these shortcomings are presented. Examples of image processing are given, together with a vision on future systems and procedures.

Integration of a European image processing component with an American HIS: the advantage of open standards

This paper describes the integration of a European Image Processing System with an existing American Hospital Information System. Both systems were built independently (with no knowledge of each other), but on open systems standards. The easy integration of these systems demonstrates the major benefit of open standards-based software design.

The image related services of the HELIOS software engineering environment

This paper describes the approach of the European HELIOS project to integrate image processing tools into ward information systems. The image processing tools are the result of the basic research in image analysis in the Department Medical and Biological Informatics at the German Cancer Research Center. These tools for the analysis of two-dimensional images and three-dimensional data volumes with 3D reconstruction and visualization ae part of the Image Related Services of HELIOS. The HELIOS software engineering environment allows to use the image processing functionality in integrated applications.

The component-based architecture of the HELIOS medical software engineering environment

The constitution of highly integrated health information networks and the growth of multimedia technologies raise new challenges for the development of medical applications. We describe in this paper the general architecture of the HELIOS medical software engineering environment devoted to the development and maintenance of multimedia distributed medical applications. HELIOS is made of a set of software components, federated by a communication channel called the HELIOS Unification Bus. The HELIOS kernel includes three main components, the Analysis-Design and Environment, the Object Information System and the Interface Manager. HELIOS services consist in a collection of toolkits providing the necessary facilities to medical application developers. They include Image Related services, a Natural Language Processor, a Decision Support System and Connection services. The project gives special attention to both object-oriented approaches and software re-usability that are considered crucial steps towards the development of more reliable, coherent and integrated applications.

The HELIOS Image Related Services

The HELIOS Software Engineering Environment is a tool for the construction of medical ward information systems. This paper describes the image processing tools which are a part of this system. The Image Related Services can be used both as ready-to-use end-user tools and as software modules for the construction of integrated multimedia applications. The tasks and architecture of the end-user tools and their integration into the HELIOS architecture are described. It is shown how the available image processing functionality can be used to build up new applications.

The HELIOS medical software engineering environment

The aim of the HELIOS project is to create an integrated Software Engineering Environment (SEE) to facilitate the development and maintenance of medical applications. HELIOS is made of a set of software components, communicating through a software bus called the HELIOS Unification Bus. The object oriented paradigm is used both as the basic structure for building the software components and as the methodology for modelling, storing and retrieving the entities and procedures used in an application. Development standards include UNIX as operating system and X Window/MOTIF as windowing environment. One of the target applications for the HELIOS prototype is the development of a multimedia medical workstation as a front end to a hospital information system.

Integration of HIS components through open standards: an American HIS and a European Image Processing System

This paper describes the integration of an existing American Hospital Information System with a European Image Processing System. Both systems were built independently (with no knowledge of each other), but on open systems standards. The easy integration of these systems demonstrates the major benefit of open standards-based software design.

Generation-dependent control mechanisms in cell proliferation and differentiation--the power of two

There is evidence that the proliferation of cells is controlled by the number of divisions after leaving a multi-potent (stem) cell. A detailed study of the growth of tissue in the small intestinal tract, more precisely the growth of crypts and villi, suggests that not only the proliferation but also the differentiation of cells obey the same biological law. We postulate a theory of a cellular internal control mechanism: the cell-generation control of differentiation and proliferation. This basic mechanism, together with external influences, determines the kinetic behaviour of the crypt-villus system.

Modelling and simulation of complex control structures in cell biology

Biological and biomedical tissues and organs represent very complex and highly dynamic systems. The problem to model such complex systems is twofold. First, it is necessary to identify and describe the biological properties and the connecting control mechanisms of the studied system and its subparts. Here, biological knowledge is often missing. Secondly, we are confronted with the problem to formulate the model of the control structure in a form that allows model analysis. Here, a normal mathematical formalism is often inadequate. To solve these modelling problems and to develop methods for building models of complex control structures that will enable the formulation of dynamic systems in biology, a framework for building such models is presented. The model framework is here mainly used for studies of dynamic cell structures, but the possible application areas are more general. An example is given for modelling cell structures of epithelial tissues in the intestine.

The growth and life of a monoclonal crypt

A computer simulation of a highly dynamic model for the birth, growth and adult life of a monoclonal crypt in the intestine was developed starting with a single precursor stem cell. The intestinal epithelial system was studied and observed in analogy to 'in vivo' experiments. The model output, e.g. the geometric shape of a crypt, mitotic index, labelling index and the crypt length distribution in adult state, was compared with experimental data. There was evidence from the simulation that a certain steady state in the adult life could be reached regardless of some harmless influences in post-natal life, e.g. the influence of being weaned or non-weaned. The model is based on our hypothesis of the generation-controlled proliferation mechanism and at the same time is a confirmation of it.

The cell cycle time in intestinal crypts by simulation of FLM experiments

A computer program is developed that permits simulation of the dynamic behaviour of cells in intestinal crypts (Meinzer & Sandblad, 1985). Here we present the simulation of FLM data which is compared with the experimental findings of Al-Dewachi et al. (1974). The phase durations and total cycle times of cells in the jejunal crypts of rats were calculated. Additionally, the influence of various control parameters on the simulation output is discussed, e.g. the standard errors of phase times and the grain dilution at mitosis.