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CARDIOVASCULAR ANESTHESIA

A Perioperative Echocardiographic Reporting and Recording System

Department of Anaesthesia, St. George Hospital, Kogarah, Australia

Address correspondence to David A. Pybus, FANZCA, Department of Anaesthesia, St George Hospital, Belgrave St., Kogarah, NSW 2217, Australia. Address e-mail to dpybus{at}bigpond.net.au

	Abstract

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Advances in video capture, compression, and streaming technology, coupled with improvements in central processing unit design and the inclusion of a database engine in the Windows® operating system, have simplified the task of implementing a digital echocardiographic recording system. I describe an application that uses these technologies and runs on a notebook computer.

IMPLICATIONS: The development of inexpensive digital video transcoders and the incorporation of highly efficient video capture, compression, and streaming technology into the Windows® computer operating system has simplified the task of implementing a high-fidelity, real-time, digital, echocardiographic recording system. An application that uses these technologies and runs on a notebook computer is described.

	Introduction

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In their guidelines for describing the performance of an intraoperative multiplane transesophageal echocardiographic examination, Shanewise et al. (1) expressed the hope that the industry would "develop echocardiography systems that allow the quick and easy acquisition, labeling, and storage of images in the operating room."

This perceived need, combined with recent advances in PC-based digital technology, has stimulated the development of inexpensive, high-fidelity, digital echocardiographic reporting and recording systems. Such systems can be used to record either individual frames or video clips from the video port of any echocardiographic machine and to store the images in a highly compressed digital format. Once digitized, the images can be easily integrated into a patient database and are also available for immediate review or for broadcast over 100 megabits (Mbits; 1 million bits [125,000 bytes] of digital data)/s hospital networks. The purpose of this article is to describe the development of one such system ("the application").

	Description

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The application is written in the computer language Delphi 5®. It consists of four related components—a video management system, a patient database, a report generator, and a "knowledgebase"—that are integrated into a single application and controlled through a simple user interface. The system is designed for use on computers running under the Windows 2000® or Windows XP® operating systems.

The Video Management System
The application is designed to acquire the echocardiographic images in real-time from the "S" or "Composite" video port of any echocardiographic machine. The video signal is converted to a digital video stream using a Canopus ADVC-100 transcoder (Fig. 1) and the data are imported via the IEEE 1394 ("Firewire") (an international specification for a high-speed serial bus capable of transmitting data at a rate of 400 Mbits/s) port of the computer. When the ADVC-100 is connected to the computer, it appears as an "AVC Compliant DV Tape Recorder" and is controlled by a capture driver that is an integral part of the operating system.

View larger version (86K): [in this window] [in a new window]   Figure 1. The Canopus ADVC-100 transcoder. The device accepts either "S" or "Composite" video signals and two audio channels. Standard "Mini-DV" format data are outputted through the IEEE 1394 port.

• Preview the echocardiographic image in real-time.
  
• Capture and annotate single frames in compressed (JPEG [Joint Photographic Experts Group]) format.
  
• Capture and annotate video clips in compressed or uncompressed format.
  
• Adjust the frame rate of video capture.
  
• Broadcast the digitized video stream to any location on a broadband (100 Mbits/s) computer network.
  
• View previously recorded frames or clips.
  

The image preview window is set by default to the frame size of the incoming Phase Alternation by Line (PAL) (a television signal standard used in Europe and Australia) or National Television Standards Committee (NTSC) signal (a television signal standard used in North America and Japan). The latency of this preview window is <50 ms. The image can also be viewed "full-screen" and thus allow the computer terminal to function as a slave monitor for the echo machine.

The degree of compression of the captured still frames is adjustable by the user, but is typically in the order of 50–100 Kbytes per image. The data supplement contains the Web address of such images.

Video clips can be recorded in either native, uncompressed format or in any compressed format for which a compressor/decompressor (codec; a system for digital video signals) has been previously installed on the system. When compression is used, it can be performed at the time ("on the fly") or after the event. The load imposed on the central processing unit (CPU) during "on the fly" compression is a function of processor power, available memory, and codec efficiency. As an example, a PAL signal encoded by the Microsoft MPEG¹-4 version 2 codec at a 720*576 frame size and 25 frames per second will use about 75% of the available CPU time of a 2-GHz Pentium IV processor.² In practice, "dropped frames" will start to occur when proportional CPU usage increases more than about 80%. The video management system is based on a software component developed by Datastead software.

The broadcast video stream can be streamed at 15–35 Mbits/s to any specified Internet protocol address that has the viewing application installed. The broadcast stream is an adaptation by Commonwealth Scientific and Industrial Research Organisation of Australia (CSIRO) of the digital video transport stream developed by Ogawa et al. (2). The video stream incorporates a synchronized audio stream and the viewing application a return audio stream. The latency of the complete loop is about 300 ms. This broadcast facility is intended for use either as a teaching aid, or for the purpose of obtaining a second opinion. Main et al. (3) have described another implementation of such a system in some detail.

The Database
The database is written in Microsoft Access® format³ and includes most of the data fields recommended by the combined task force in their report. It uses the 16-segment model of the left ventricle based on the recommendations of the Subcommittee on Quantification of the American Society of Echocardiography Standards Committee (4) and, by default, uses the qualitative grading scale for wall motion advocated by Shanewise et al. (1).

The application interfaces with the database using the Microsoft Jet Engine® which is an integral part of the Windows® operating system. Tools for editing and navigating the database are provided in the application.

The Report Generator
The report generator produces a single-page report that generally complies with the recommendations of the combined task force (5). The report can be printed on a local, network, or virtual printer (in PDF⁴ format) (Fig. 2). The user also has the option of generating a second page of the report which can include up to six static images.

View larger version (50K): [in this window] [in a new window]   Figure 2. An example of the printed report.

Tools for editing and adding to the knowledgebase are provided in the application. At the time of writing, the knowledgebase contained about 250 text entries, including about 200 static images and 40 video clips.

A separate table in the knowledgebase contains standard "comments" that can be used to make entries in the various free text data fields of the patient data record using a single key stroke.

	Discussion

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Recent advances in digital video technology have brought the goal of high-fidelity digital recording of echocardiographic images on notebook computers within the realm of possibility.

Four specific advances have made the achievement of this objective a reality:

1. The development of high-resolution, inexpensive video transcoders such as the Canopus ADVC-100 which are able to convert any "S" or "Composite" video signal to standard "Mini-DV" digital format within one frame acquisition time.⁵
   
2. The incorporation of the IEEE 1394 port (which will accept the "Mini-DV" signal) onto the motherboard of many notebook and desktop computers.
   
3. The development of powerful CPUs which are optimized for video management.
   
4. The development of high-fidelity, high compression-ratio codecs which are able to compress a single frame within one frame acquisition time.
   

The ability to compress the incoming signal is essential in any digital echocardiographic recording system because of the extremely large size of uncompressed Audio Video Interleave (AVI) files. As an example, in uncompressed format, 1 minute of a 720*576 pixel video recorded at 25 frames per second requires about 1250 Mb of storage space. The same video clip processed by an MPEG-4 codec can be compressed by a ratio of about 250:1 (and thus occupy about 5 Mb) with little discernible loss in image quality.

The quality of data compression achieved by the application has not yet been formally examined. However, Spencer et al. (6) concluded that MPEG-1 compression of echocardiographic video signals at a ratio of 200:1 produced no degradation of diagnostic content. Given that the MPEG-4 compressor is recognized to be a superior compressor, it is hardly surprising that 250:1 compression is associated with little loss of image quality.

In this context, it is worth noting that the typical echocardiographic image contains large areas of relatively homogenous information (the regions of the screen outside the sector display). It is possibly for this reason that the signal is amenable to such extreme data compression.

The application’s database is in Microsoft Access® format. This format was chosen because it is the most popular PC database format and is often used by physicians. The data fields in the database are largely those suggested for inclusion by the combined task force, except that data relating to left ventricular diastolic function are included and some demographic data such as ICD-9 codes have been omitted.

It should be noted that the database engine which is used to control this database is an integral component of the Windows 2000® and Windows XP® operating systems and, as such, the use of this format does not incur any additional licensing fees from Microsoft.

The digital video quality achieved by interfacing the Canopus transcoder to a notebook computer is so impressive that it is easy to imagine other perioperative applications of such a system. In particular, it would be relatively easy to implement endoscopic (anesthetic or surgical) recording, reporting, and broadcasting applications.

	Data Supplements

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A freeware version of the program (which does not include the broadcast facility and has a limit on the number of cases per database) can be downloaded from www.manbit.com.

Examples of the patient report, typical images, and public domain codecs are available from the same site.

A database of about 350 echocardiographic images recorded with the system can be found at http://www.manbit.com/ERS/ERSindex.asp.

The video capture component used in the video management system can be obtained from www. datastead.com and can be used with either Delphi or C++ compilers.

	Footnotes

 
The author is a director of Manbit PL.

¹Moving Picture Experts Group. A group that develops standards for digital video and digital audio compression. It operates under the auspices of the International Organization for Standardization.

²Equipped with 384 megabytes (Mb) of RAM running under the Windows 2000® operating system.

³Other database formats such as Foxpro, Paradox, or SQL can be made available on request.

⁴Portable Document Format. A document file format that can be read on most computer platforms.

⁵1/25 of a second for a PAL signal, 1/30 of a second for an NTSC signal.

	References

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1. Shanewise JS, Cheung AT, Aronson S, et al. ASE/SCA guidelines for performing a comprehensive intraoperative multiplane transesophageal echocardiography examination: recommendations of the American Society of Echocardiography Council for Intraoperative Echocardiography and the Society of Cardiovascular Anesthesiologists Task Force for Certification in Perioperative Transesophageal Echocardiography. Anesth Analg 1999; 89: 870–84.[Free Full Text]
2. Ogawa A, Kobayashi K, SugiuraK, et al. Design and implementation of DV stream over Internet. In: Proceedings of the Internet workshop ’99. IEEE, 2000.
3. Main ML, Foltz D, Firstenberg MS, et al. Real-time transmission of full-motion echocardiography over a high-speed data network: impact of data rate and network quality of service. J Am Soc Echocardiogr 2000; 13: 764–70.[Medline]
4. Schiller NB, Shah PM, Crawford M, et al. Recommendations for quantitation of the left ventricle by two-dimensional echocardiography. American Society of Echocardiography Committee on Standards, Subcommittee on Quantitation of Two-Dimensional Echocardiograms. J Am Soc Echocardiogr 1989; 2: 358–67.[Medline]
5. Savage R, Hillel Z, London M, et al. Recommendations for a standardized report for adult perioperative echocardiography from the Society of Cardiovascular Anesthesiologists/American Society of Echocardiography Task Force for a Standardized Perioperative Echocardiography Report [Society of Cardiovascular Anesthesiologists Web site]. Available at: www.scahq.org/sca3/teereport.shtml. Accessed August 11, 2004.
6. Spencer K, Solomon L, Mor-Avi V, et al. Effects of MPEG compression on the quality and diagnostic accuracy of digital echocardiography studies. J Am Soc Echocardiogr 2000; 13: 51–7.[Medline]

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