THE DIGITAL ECHO LAB

Purpose and scope
This document describes an overview of a digital echo laboratory. It includes definitions, purpose, history and issues facing those who elect to use digital techniques in echocardiographic practice.  

Digital vs analog
"Digital" is the language of computers where all information is converted into codes of ones and zeros. Since everything is coded into these two numbers, expressed in digits, the word "digital" applies. Even the most complex words, letters, numbers, drawings, sound and pictures can be converted into these strings of ones and zeros. Computers communicate digitally.

Analog is an older, yet standard, method for recording information. It is accomplished using continuous waveforms rather than strings of ones and zeros, thus making it difficult to manage using computers. "Analog" and "digital" are contrasting terms. For example, recording standard video on tape is an analog process. Images degrade and the reviewer is trapped into a slow, linear review of data. By contrast, if such images could be digitally recorded and stored, the original numbers would be preserved (preserving image quality) and a reviewer could access any part of the study at any time (random access).

For echo laboratories, digital methods provide the following benefits over analog:

• More accurate storage and retrieval information with greater speed
• echo information management
• higher quality and reproducibility of image information
• decrease in time and money spent with an increase in accuracy and quality

How do most echo labs run now? Aside from the growing use of word processing programs for report preparation, most echo laboratories today are not digital. Most labs schedule and log patients in by hand, making paper lists. Then notes are taken and images are recorded on analog video tape. After patients are seen, images are reviewed from the video tape and reports are dictated and typed. All these papers and recordings are then kept on shelves or filed away in filing cabinets and have to be distributed and/or retrieved by hand.

Most echo labs have experienced, and thus understand, the problems associated with these conventional methods. Studies are lost, tapes are misplaced, and even the simplest tasks (such as counting the number of inpatients and outpatients) are difficult. Just the recording of echo images onto analog video tape degrades the quality of the echo data from the original and results in an obvious compromise of quality.

    A digital echo lab A digital echo lab is one where all information (including images) is captured in or converted into a digital format for analysis, transmission and storage. A digital lab has the following functions:

• Digital record keeping and reporting
• Digital image recording and storage
• Digital laboratory management (such as billing, education, continuous quality improvement (CQI) functions, etc.)

Historical perspective
The development of digital methods for maintenance of patient log books and reporting of echocardiographic data began in the late 60s and early 70s. Some rudimentary image storage and retrieval systems were in place as early as 1970. These systems allowed for a "snapshot" of a video field from video tape and resultant storage on a floppy disk. Thus the analog images from video tape were digitized. Computer programs were, however, cumbersome and computers were expensive and unreliable. By the onset of the 90s, there were only a handful of laboratories using computerized databases for basic record keeping and reporting.

Digital vs digitized
With the advent of stress echocardiography the ability to digitize loops off video tape was achieved. Although the images were now in a digital format, degradation of image quality had already occurred by first storing the images in a video format. Digital means the direct storing of original data to disk, instead of having to digitize from video. Using this method preserves the original image quality. Now with the recent technological advances in computer storage, decreasing costs of equipment and the explosion of interest in multimedia throughout the world, digital acquisition, storage, retrieval and transmission is a reality. Lower costs for computers and the interest of government and industry (cable, telephone, and cellular companies) in obtaining market share will continue to lower the cost of transmitting digital information.

Changing from video to digital
The main advantage of utilizing video tape is that it is inexpensive and a large amount of real-time data can be stored economically. Because of the difficulty in finding a patient’s study on an old video tape, few echocardiograms are viewed by anyone other than the physician rendering the interpretation. Digital echocardiography allows for the widespread transmission of echocardiographic images directly to the clinician, wherever he or she might be.

There are a number of issues to be faced when deciding to change a lab from video tape (analog) to digital. These issues concern things like how to overcome the technical problems of installing a digital system and who is responsible for the various components (cable, server, workstations, outside links, digital archiving, backing up of the data, etc.). Perhaps the biggest obstacle to overcome is the change in workflow for sonographers, physicians and administrative personnel.

Figure 1 is a diagram of the workflow in a typical video-based echo lab. Figure 2 is a diagram of the workflow in Duke’s digital echo lab. While the tasks are similar in all labs, the order may differ. It is obvious that not only are there less steps in the digital lab but the final reports are available much earlier than in the video-based lab. Of course, neither of these figures takes into account the time spent by both sonographers and physicians on the telephone, responding to stat studies, dealing with patient transportation problems, consulting with referring physicians and other issues.

For physicians, there are many benefits in a digital echo lab. Having previous studies on-line for comparison at the time of interpretation saves time and improves quality control. Being able to view the preliminary echo report, make changes, finalize and electronically send the report to required destinations (referring physicians, medical records, in-patient units, out-patient clinics) expedites the review/reporting process. The final report can be sent as E-mail (either in-house or via the Internet), faxed or printed at a remote site (such as doctors offices or medical records) or viewed on remote workstations.

In labs where sonographers do the scanning and interpreting physicians are not always available for consultation there will be greater reliance on the sonographer’s ability to document the presence or absence of abnormalities in multiple beat loops instead of long video runs. Thus, a major challenge in converting from video to digital is in adjusting the way in which sonographers scan. Some of the newer ultrasound systems allow the storage of long loops (up to 10 beats or 10 seconds). However, these longer loops require more time to store and retrieve in addition to taking up more storage space. An effective and practical method for recording digital studies is to record one or two beat loops for each of the standard views. The short loops provide the fastest storage and retrieval times as well as requiring less archival space. Longer loops should be used only when needed to document things like complex congenital pathology where a sweep through various planes is critical.  

EIMS / DNI
Using the combination of EIMS (Echo Image Management Solution) and DNI (Digital Network Interface) eases the transition to a digital echo lab. EIMS is the HP network solution for the echocardiography lab. DNI is an expansion of the digital storage and transferring capabilities of the SONOS ultrasound system. Transforming a lab from analog to digital requires that the clinician, especially the individual performing the echo exam, use a new work-flow model to perform the echo exam. As discussed previously, instead of recording long segments of a given anatomic view onto videotape, the sonographer (or MD) must acquire a looped or still image in digital memory, review the image on SONOS, store the loop/frame onto DNI or MOD and ultimately send the image to EIMS via the network. DNI is crucial to the successful transition to a digital lab since its features offer the most effective way to acquire and store images to the EIMS. DNI will fit the new work-flow model in a unique way that will enable the clinician to most effectively and efficiently "go digital".  

Advantages of the Digital Lab
One of the principle advantages of digitally storing images is improved image quality. Recording echocardiographic images on video tape causes marked degradation on playback. Using Super VHS tapes has slightly improved recording quality but requires the purchase of SVHS monitors, recorders, cabling and more expensive video tapes. Even using SVHS equipment still does not prevent degradation of the recording over time, as the coating on the tape oxidizes just sitting on the shelf. With digital storage, there is no issue with the storage medium degrading over time. An image will retain it’s originally recorded image quality indefinitely. Other advantages for the digital echo lab include:

• Random access to any image at any time. Displaying the entire study as small "thumbnail" icons allows for quick review of the most important views.

• Reproduction of studies with no degradation of image quality. Unlimited dubs and edits are possible.

• Side-by-side comparison of the current study with prior studies. This allows for easy follow-up on the efficacy of treatment, progression of disease or for teaching purposes.

• Installation of remote viewing stations to provide access to a patient’s study at in-patient units, out-patient clinics or even in the physician’s office and at home.

• Transmission of images to another institution or site for consultation or telediagnosis.

• Off-line quantitation, analysis and even some image post-processing can be performed (when images are stored with the proper calibration information).

• A variety of display formats for image review: single, dual or quad screen. Integration of the digital images with an echo report and patient demographics would provide a major advance towards an electronic or digital patient record.

  Disadvantages of a digital lab Even though the cost of computers is decreasing every six months, starting a digital echo lab still requires high initial investment. The technology is evolving and there remains proprietary equipment from various vendors that does not easily interface together. This current lack of standardization makes the installation of a digital network a very technical endeavor. With the move towards adopting DICOM 3 standards (see below) it will become easier to combine ultrasound systems from a variety of vendors in one digital network.

Another potential limitation is the retraining of sonographers on how they perform echocardiographic studies. As mentioned before, there will be a greater reliance on the ability of the sonographer to record the pertinent information since a study will be comprised of a set of loops and stills. Sonographers will no longer be able to rely on letting the video tape run as they obtain their images, hoping to capture all necessary information. In the Duke Echo Lab this challenge to the sonographers was met with little resistance as everyone quickly saw that the benefits of recording in a digital format far outweighed the disadvantages.

DICOM
DICOM stands for Digital Imaging and Communications in Medicine. DICOM is an emerging set of communications standards which specify how medical images are stored and exchanged over networks between different manufacturers. Adherence to DICOM file formats will allow easier sharing of digital images (open system) between different manufacturers who otherwise would use proprietary formats (closed systems). These rules for a common digital format are the result of over 10 years of negotiating between the National Electrical Manufacturer’s Association (NEMA) and medical organizations such as the American College of Radiology, American Society of Echocardiography and the American College of Cardiology.

The current standard, DICOM 3.0, emerged from this workgroup in 1994. This latest standard removed many of the final image format restrictions so that people can build an imaging network using equipment from different manufacturers. This allows laboratories and physicians to create integrated systems which can communicate with each other. However, the current DICOM standard does not address the sharing of all digital data (such as measurements and patient demographics), only for images.

Things to consider when setting up a network: -

• What do I want to store (number of loops, heartbeats, or views?)
• What and who will be included in the network (echo lab only, hospital wide, or multiple sites)?
• Who does the work (data entry, acquisition, report generating, etc.)?
• Who maintains the network? How accessible do the images need to be?
• What is the current workflow model and how will it change?
• Who will want to access the data and for what purpose?
• What will be the archival storage medium?
• How will the images be transferred from the echo machine?
• How will the images and data be combined?

The Duke echo lab (past to present)

The recording of echocardiographic images at Duke Medical Center has changed constantly over the past 20 years. These changes reflect the improvement in recording media. Figure 3 shows a chronological listing of the types of media used at Duke, ultimately arriving at an all digital lab on May 8th, 1995. Since that time video has only been used as backup for the digital studies.  

  The transformation to an all-digital lab required much more than just changing the recording media however. Other steps towards the complete digital lab are detailed below.

• June 1990 -One computer for starting an electronic logbook and report generation program.
• Sept. 1990 -10 computer network for the logbook and report generation program.
• June 1991 -20 computer network.
• Aug.1993 -File server connected to Duke MCIS (Medical Center Information Systems)
• May 1995 -Digital imaging system operational  

The transformation to digital at Duke
The decision was made to convert from a video recording format to a digital format. But, long before the actual transformation took place there were questions that needed to be answered. First, could we do a complete study just storing the images in loops? The answer was "Yes, we could", except in those few patients who had arrhythmias, were undergoing microcavitation studies or had congenital heart disease, in which sweeps from one view to another were essential for diagnosis. In the vast majority of patients, we were able to record complete digital studies with one beat loops and still frames.

Next, how many loops were necessary to record a complete study and how many cycles per loop should be stored? To determine how many loops comprise a complete study we decided to follow our regular imaging protocol for the standard sequence of views. But instead of recording 20 seconds of the long axis we would record one or two loops lasting one cardiac cycle. We would then repeat these loops with color flow and progress through our protocol. In order to establish the "digital protocol", we spent six months practicing obtaining loops and recording them on video tape.

Thus, when the digital system became operational, sonographers and physicians were accustomed to storing and viewing loops instead of long runs on video tape. At first, the transition to recording loops required approximately 50% more time for scanning (storing to MOD and also video tape). With practice, this was decreased to less than an additional 10% of time added to each study. We have found that this increase in scan time has been more than made up in time saved dealing with video tapes (queuing up tapes, searching for old studies, filing tapes, etc.).  

The Future Converting from analog to digital echo is the first step in integrating information and images throughout a cardiology department. Indeed, while this conversion within the echo lab is a significant step, one can see the possibilities for expansion in the areas of patient billing, inventory management, CQI (Continuous Quality Improvement), scheduling and other administrative tasks. Once the echo lab is fully digital, it may be just a small piece of an ultimately big pie which will be driven by the need for an electronic patient record containing not only reports from various tests, but also the images acquired during those tests.