Biomedical subjects

Hans-Peter Meinzer

Publications and source records attributed to Hans-Peter Meinzer.

26 records · Page 2Linked to original sources

PubMed2002

Navigation and image-guided HBP surgery: a review and preview.

Image-guided surgery and navigation have resulted from convergent developments in radiology, teletransmission, and computer science. Patient selection and preoperative planning in hepatobiliary-pancreatic (HBP) surgery rely on preoperative imaging. The operative procedure is finally led by the fusion of additional information gained by the palpating hand and intraoperative ultrasound. Despite advances in reducing morbidity and mortality, decisions are often hardly quantifiable and are restricted to super-specialists in HBP surgery. New developments in computed tomography (CT) and magnetic resonance imaging (MRI) technology have led to the possibility of the volumetric prediction of liver resections. These data can be shared via telemedicine and used for simulation and training. Three-dimensional (3D) reconstructions have led to a better topologic understanding of tumor-vascular tree relations in the individual patient. With the increasing use of ablative procedures and laparoscopy, intraoperative imaging and navigation will hold increasing significance for the HBP surgeon. Flat screen monitors adjacent to the surgical field present computer-generated 3D virtual liver resection proposals which can be transferred into the real liver. The main obstacles in HBP navigation are the flexibility and mobility of the target organ. Intrahepatic and surface markers seem to be mandatory for computer-navigated surgery. The first feasibility studies are promising.

Bile Ducts↗

PubMed2002

ROPES: a semiautomated segmentation method for accelerated analysis of three-dimensional echocardiographic data.

Echocardiography (cardiac ultrasound) is today the predominant technique for quantitative assessment of cardiac function and valvular heart lesions. Segmentation of cardiac structures is required to determine many important diagnostic parameters. As the heart is a moving organ, reliable information can be obtained only from three-dimensional (3-D) data over time (3-D + time = 4-D). Due to their size, the resulting four-dimensional (4-D) data sets are not reasonably accessible to simple manual segmentation methods. Automatic segmentation often yields unsatisfactory results in a clinical environment, especially for ultrasonic images. We describe a semiautomated segmentation algorithm (ROPES) that is able to greatly reduce the time necessary for user interaction and its application to extract various parameters from 4-D echocardiographic data. After searching for candidate contour points, which have to fulfill a multiscale edge criterion, the candidates are connected by minimizing a cost function to line segments that then are connected to form a closed contour. The contour is automatically checked for plausibility. If necessary, two correction methods that can also be used interactively are applied (fitting of other line segments into the contour and searching for additional candidates with a relaxed criterion). The method is validated using in vivo transesophageal echocardiographic data sets.

Algorithms↗

PubMed2002

Visualization and attributation of vascular structures for diagnostics and therapy planning.

In various medical fields vascular structures have to be examined with usually two-dimensional views which present imaging techniques produce. The interpretation of the data can be supported by 3-dimensional visualization techniques. The further analysis requires often the attributation of the particular functional or anatomical entities. To attribute these interactively we developed two different visualization strategies. In the first one the shape of the structures is modelled with OpenGL achieving very fast response times, most notably during the navigation. The second strategy, the direct rendering of the volume, benefits from the accurate reproduction of the vascular structures. Although the rendering needs much more time, the strategy provides similar response times for the attributation. Thus, the strategies complement one another.

Computer Simulation↗

PubMed2002

Evaluation of visualization techniques for image-guided navigation in liver surgery.

A substantial component of an image-guided surgery system (IGSS) is the kind of three-dimensional (3D) presentation to the surgeon because the visual depth perception of the complex anatomy is of significant relevance for orientation. Therefore, we examined in this contribution four different visualization techniques, which were evaluated by eight surgeons. The IGSS developed by our group supports the intraoperative orientation of the surgeon by depicting a visualization of the spatially tracked surgical instruments with respect to intrahepatic vessels that have to be conserved vitally, the tumor, and preoperatively calculated resection planes. In the prelimenary trial presented here we examined the human ability to percept an intraoperative virtual scene and to solve given navigation tasks. The focus of the experiments was to measure the ability of eight surgeons to orientate intrahepaticaly and to transfer the percepted spatial relation to movements in real space. An autostereoscopic visualization with a prism-based display yielded that the navigation can be performed faster and more accurately than with the other visualization techniques.

Anatomy, Regional↗

PubMed2002

Virtual reality in 3D echocardiography: dynamic visualization of atrioventricular annuli surface models and volume rendered Doppler-ultrasound.

Knowledge about annuli shape and blood flow patterns, both optimally assessed by transesophageal 3D Doppler echocardiography, can be used in computer assisted surgical planning of heart valve reconstruction. Moreover, information about the individual shape of the annulus anatomy can guide the design of annular prostheses. The problem is that the annulus cannot be easily differentiated from the valve and the myocardium with standard visualization methods. We have developed a nearly automatic method for annulus segmentation. The algorithm provides the annulus shape in a symbolic description, which can be used for surface visualization. Best results to visualize the blood flow from the Doppler signal and the myocardial morphology are obtained by volume rendering. A hybrid visualization technique combining surface rendering and volume rendering enables to dynamically visualize the surface rendered annulus combined with a volume rendered 3D (plus time) reconstruction of either backscatter (morphology) and Doppler information (in original color coding), or together with backscatter only or Doppler only. Visualization of annuli structures combined with blood flow and general myocardial morphology provides a new tool to analyze heart diseases.

Blood Flow Velocity↗

PubMedDate not supplied

Limits of Couinaud's liver segment classification: a quantitative computer-based three-dimensional analysis.

PURPOSE: Traditionally, liver surgery relies on Couinaud's liver segment classification. As the position and shape of these segments are variable and their borders are hidden within the homogeneous liver mass, the accuracy of segment identification methods needs computer-aided reevaluation. METHOD: The segmental liver anatomy of 23 patients receiving diagnostic helical CT scans because of suspected intrahepatic lesion was analyzed with the aid of a computer-based operation-planning system. We compared the standard Couinaud classification, which depends particularly on the main stems of portal and hepatic veins, with a method that calculates the segment borders by analyzing the complete portal venous tree. Volume, shape, and position of the liver segments found by each method were compared. RESULTS: With reference to the portal vein-based method, segmental volumes were overestimated by the classic Couinaud method by up to 24% and underestimated to 13%. Volumes of Couinaud segments 4a, 7, and 8 were generally larger compared with those obtained by the portal vein-based method, whereas segments 3 and 6 were smaller. Gross variations were found in segments 5, 7, and 8. When shape and position were considered, poor correlation was found for five segments (median kappa = 0.35-0.45). Only segments 2, 7, and 8 had kappa values clearly above 0.45 in the majority of cases. The plane that divides the two hemilivers along the middle hepatic vein and the border between the left sector (segments 2 and 3) and the medial sector (4a and 4b) were found in both methods with very good conformity (kappa > 0.75). CONCLUSION: Couinaud's method of dividing the liver into eight autonomous liver segments has to be accepted as a good approximation. Nevertheless, the volume, position, and shape of these segments and their segmental borders show significant variability.

Adult↗

PubMedDate not supplied

DICOM structured reporting: Part 1. Overview and characteristics.

Supplement 23 to Digital Imaging and Communications in Medicine (DICOM) is an introduction to the structured reporting (SR) classes, which are used for transmission and storage of clinical documents. The SR classes fully support both conventional free-text reports and structured information, thus enhancing the precision, clarity, and value of clinical documentation. In addition, the SR standard provides the capability to link text and other data to particular images or waveforms and to store the coordinates of findings. In other words, SR documents not only describe the specific features contained in images or waveforms but can also refer to any number of images or waveforms. Accordingly, SR bridges the traditional gap between imaging systems and information systems. Furthermore, SR plays an essential role in Integrating the Healthcare Enterprise by providing healthcare practitioners with an effective tool that encompasses a variety of clinical contexts. Harmonization of DICOM SR and the Health Level Seven clinical document architecture standard is under way.

Abstracting and Indexing↗

PubMedDate not supplied

DICOM structured reporting: Part 2. Problems and challenges in implementation for PACS workstations.

Structured reporting (SR) was recently added to the Digital Imaging and Communications in Medicine (DICOM) standard to provide an efficient mechanism for the generation, distribution, and management of clinical reports. The main advantage of SR is the ability to link clinical documents with the referenced images for simultaneous retrieval and display. A generic SR toolkit that covers the different clinical reports used in today's healthcare enterprises was developed for picture archiving and communication system (PACS) workstations. The modules of the SR toolkit collaborate to automatically construct the DICOM SR files from the free-text input presented in hypertext markup language (HTML) by using the associated SR trees. The DICOM toolkit is reused for SR encoding and DICOM services. A setup module was required for creating both the standard and private SR templates used in different healthcare specialties. The SR manager transparently converts between the different SR document presentations, that is, DICOM SR files and HTML documents, to provide the end users with an easy-to-use toolkit. To evaluate and demonstrate the effectiveness of the SR toolkit in a pragmatic setting, the toolkit was integrated into PACS workstations.

Data Display↗