Biomedical subjects

A Schlaefke

Publications and source records attributed to A Schlaefke.

6 recordsLinked to original sources

PubMed2004

[Remote access to a web-based image distribution system].

PURPOSE: To assess different network and security technologies for remote access to a web-based image distribution system of a hospital intranet. MATERIALS AND METHODS: Following preparatory testing, the time-to-display (TTD) was measured for three image types (CR, CT, MR). The evaluation included two remote access technologies consisting of direct ISDN-Dial-Up or VPN connection (Virtual Private Network), with three different connection speeds of 64, 128 (ISDN) and 768 Kbit/s (ADSL-Asymmetric Digital Subscriber Line), as well as with lossless and lossy compression. RESULTS: Depending on the image type, the TTD with lossless compression for 64 Kbit/s varied from 1 : 00 to 2 : 40 minutes, for 128 Kbit/s from 0 : 35 to 1 : 15 minutes and for ADSL from 0 : 15 to 0 : 45 minutes. The ISDN-Dial-Up connection was superior to VPN technology at 64 Kbit/s but did not allow higher connection speeds. Lossy compression reduced the TTD by half for all measurements. CONCLUSIONS: VPN technology is preferable to direct Dial-Up connections since it offers higher connection speeds and advantages in usage and security. For occasional usage, 128 Kbit/s (ISDN) can be considered sufficient, especially in conjunction with lossy compression. ADSL should be chosen when a more frequent usage is anticipated, whereby lossy compression may be omitted. Due to higher bandwidths and improved usability, the web-based approach appears superior to conventional teleradiology systems.

Internet↗

PubMed2004

Splanchnic oxygen transport, hepatic function and gastrointestinal barrier after normothermic cardiopulmonary bypass.

BACKGROUND: The effect of non-pulsatile, normothermic cardiopulmonary-bypass (CPB) on the splanchnic blood-flow and oxygen-transport, the hepatic function and the gastrointestinal barrier were observed in a prospective observational study in 31 adults undergoing cardiac valve replacement surgery. METHODS: The splanchnic (i.e. hepatic) blood-flow (HBF) was measured by the constant infusion of indocyanine-green (ICG) using a hepatic-venous catheter. Liver function was examined by calculation of lactate uptake, ICG extraction and the monoethylglycinexylidide (MEGX) test. A day before and after surgery the gastrioduodenal and intestinal permeability was measured by determination of sucrose and lactulose/mannitol excretion. RESULTS: Splanchnic blood flow and oxygen delivery did not decrease during and after surgery while splanchnic oxygen consumption (P < 0.0125) and arterial lactate concentrations increased. The splanchnic lactate uptake paralleled the lactate concentration. After but not during CPB an increase of systemic oxygen consumption was observed. The MEGX test values decreased on the first day after surgery. The ICG extraction was attenuated during the operation. The gastroduodenal and the intestinal permeability increased significantly postoperatively (P < 0.002, respectively, P < 0.001). There was no correlation between these findings and the duration of CPB. There was a significant correlation of the intestinal permeability but not of the gastroduodenal permeability between the prior and after surgery values (P < 0.001). CONCLUSION: Increased oxygen consumption during CPB may indicate an inflammatory reaction due to the pump beginning in the splanchnic area or a redistribution of the splanchinc blood flow during the CPB. Normothermic CPB does not lead to a significant or prolonged reduction of liver function. Normothermic CPB causes an increase of gastrointestinal permeability. The intestinal barrier function prior to surgery was accountable for the degree of loss of intestinal barrier function following surgery.

Adult↗

PubMed2003

Upload capacity and time-to-display of an image Web system during simultaneous up- and download processes.

The aim of this study was to assess the up- and download performance of an image Web system (IWS) during simultaneous up- and download procedures. Following preparatory tests, the upload capacity (UC) with and without simultaneous download and the time-to-display (TTD) with and without simultaneous upload were determined for different image, server and compression types, and with up to 16 concurrent clients. The UC varied between 1.7-5.5 Gigabyte per hour (GB/h) and was slightly influenced by a simultaneous download; however, the TTDs were substantially prolonged during an upload and only below 5 s with up to four to six concurrent clients. The choice of image and server type had a strong impact on UC and TTD. Lossy primary compression proved slightly superior. An effective UC of approximately 4.0 GB/h or 96 Gigabyte per day (GB/day) can be achieved, which appears suitable even for large institutions. Because of its substantial influence on UC and TTD during simultaneous up- and download, the server hardware should be equipped with two processors and 1 GB RAM. Lossy primary compression may be used with slight performance benefits when full-resolution images are not required. The upload is a time-demanding process, and it is possible that during peak hours the waiting times are unacceptable for clinicians.

Data Compression↗

PubMed2003

Performance of Web-based image distribution: server-oriented measurements.

The aim of this study was to assess the performance of Web-based image distribution when multiple personal computers (PCs) are downloading images simultaneously for different server hardware configurations. Using specially developed software, the time-to-display (TTD) of different image types was measured with up to 16 concurrent PCs for various combinations of processor, random access memory (RAM), network connection and image compression. The TTD increased linearly with the number of concurrent PCs but remained under 5 s in most of the cases, even with 16 concurrent PCs. Only with a 10-Mbit/s network connection or with lossy compression were TTDs above 5 s obtained. Two processors instead of one led to a slight and constant improvement of the TTD. Reducing the amount of RAM increased the TTD mainly for computed radiography (CR) images. There was no difference between a 200- and 100-Mbit/s network, but 10 Mbit/s proved significantly worse. When increasing the number of clients lossless compression performed substantially better than lossy. A standard off-the-shelf server provides an appropriate download performance even with 16 concurrent clients. Processor speed and RAM amount are of minor importance, but it is highly recommended to use a 100-Mbit/s network connection and to avoid the application of on-demand lossy compression in a local area network.

Internet↗

PubMed2003

Performance of Web-based image distribution: client-oriented measurements.

The aim of this study was to define a clinically suitable personal computer (PC) configuration for Web-based image distribution and to assess the influence of different hard- and software configurations on the performance. Through specially developed software the time-to-display (TTD) for various PC configurations was measured. Different processor speeds, random access memory (RAM), screen resolutions, graphic adapters, network speeds, operating systems and examination types (computed radiography, CT, MRI) were evaluated, providing more than half a million measurements. Processor speed was the most relevant factor for the TTD; doubling the speed halved the TTD. Under processor speeds of 350 MHz, TTD mostly remained above 5 s for 1 CR or 16 CT images. Here Windows NT with lossy compression were superior. Processor speeds of 350 MHz and over delivered TTD <5 s. In this case Windows 2000 and lossless compression were preferable. Screen resolutions above 1280 x 1024 pixels increased the TTD mainly for CR images. The RAM amount, network speed and graphic adapter did not have a significant influence. The minimum threshold for clinical routine is any standard off-the-shelf PC better than Pentium II 350 MHz, 128 MB RAM; hence, high-end PC hardware is not required.

Computers↗

PubMed2002

Evaluation of a "no-cost" Internet technology-based system for teleradiology and co-operative work.

The aim of this study was to assess the suitability of a no-cost system based on standard Internet technology components for teleradiology. The system was composed of free software (communication, DICOM viewer, compression) and standard off-the-shelf hardware components. For different image (CR, CT, MR) and network types (LAN and ISDN) the File Transfer, Audio and Video Conference, and Co-operative Work properties were examined and compared with the literature referring to standard complete packages and dedicated teleradiology systems. The main advantages of the no-cost system are: price; ease of use; independence from specific hardware; and potential connection to any possible partner. The performance of the File Transfer and the Audio and Video Conference was comparable to the other system groups with slight disadvantages in the usability. For Co-operative Work the employed "application sharing" technology does not meet the clinical requirements, which applies identically to the standard complete packages. Here the specialized systems prove superior, although they are proprietary. With minimal restraints the evaluated no-cost solution can be used for File Transfer and Conference scenarios. The usage for Co-operative Work with ISDN is not recommended, unless for the purpose of gaining experience or when dealing with small amounts of cases or images.

Computer Systems↗