Data Flow and Network Infrastructure

West Long

Approximately 95% of all mammograms remain film based today, but demand for the digital procedure is growing. The ability to offer patients digital mammograms, however, requires more than the acquisition equipment needed to obtain them and make them available for interpretation. The amount of electronic data generated by a single digital mammogram (that is, one view) far exceeds the amount generated by its counterparts in other modalities like CT, MRI, or digital radiography/fluoroscop (see Figure 1). One digital mammographic image can be as large as 50 MB. It is important to note that it is not only the individual file size of FFDM that causes concern, but rather the number of files an FFDM system can produce in a day. A typical system can image more than six patients an hour. Multiplied by 8 hours, that equals 48 patients times the size of the data set. The sheer volume of data in digitized mammography can overwhelm the information systems of the unprepared.

INTEGRATING FFDM IMAGES INTO PACS

Figure 1. Workflow graph illustrates department information flow. (Click the image for a larger version.)

Until now, digital mammography systems have generally been designed as stand-alone, isolated image delivery systems. The pattern has been for digital mammography to be stored and transmitted to independent mammography workstations via a special, isolated mini picture archiving and communications system (PACS) with its own separate storage system. This isolation of mammography from the general flow of imaging data in an enterprise has had negative workflow effects on radiology, as well as on patient care and patient throughput. Physicians studying comparison examinations in modalities like CT, MRI, and ultrasound have needed to go from one workstation to another to compare images. Mammographic studies have not been integrated with other studies and reports so that all data for a given patient could be available from a single source.

With the introduction of multimodality digital mammography workstations such as Agfa’s IMPAX for Digital Mammography (IMPAX MA3000), it is entirely possible to integrate digital mammograms into an enterprise PACS. Integrating mammographic images into an enterprise PACS has several advantages over stand-alone digital mammography mini-PACS: economies of scale on storage, improvement of diagnostic reading workflow, clinical advantages of a multimodality workstation, and greater access to images for referring and consulting physicians. Giving these referring physicians the proper clearance and access can potentially eliminate the necessity to print film.

PLANNING THE INSTALLATION

Prior to adding digital mammography to an organization’s imaging services portfolio and incorporating the images into the enterprise PACS, the health care organization must undergo a comprehensive workflow analysis to determine where the new data-rich studies will add stress to a network. If this step in the implementation process is overlooked, the sheer size of the mammographic digital data sets can cause delays in the delivery of all images. This is where consultation with a Professional Services team or consultant is critical.

Table 1. Comparative chart of data generated by each modality. (Click the image for a larger version.)

One of the benefits of digital mammography is the ability to offer faster diagnostic review, but a poorly planned network can greatly lengthen the time it takes to move the image from the scanner to the diagnostic workstation. One challenge is that mammography data do not flow in an evenly spaced progression. Instead, they come in large clusters, all at once, usually with one sizeable data set of as much as 200 MB representing four views in a screeniong mammogram being sent every 5 to 10 minutes (the typical interval between screening procedures). If a facility has multiple digital mammography rooms, as many are now planning, plus active digital stereotactic, biopsy, and ultrasound imaging in progress, the multiple transmissions of these large data clusters has the potential to make images move even more slowly to the workstation. A facility’s challenge is to analyze patient/imaging workflow carefully, incorporating data storage and network image distribution limitations. This is, of course, in addition to other digital modalities, such as ultrasound, MRI, nuclear medicine, CT, and perhaps other modalities that share a common network and/or archive. A trusted consultant can help with workflow analysis and network analysis, design, implementation, and validation. A consultant can also help with any temptation to overspend and overbuild a facility’s future data capacity.

STORAGE AND RETRIEVAL

The storage needs of digital mammography files can exceed the current storage infrastructure of the existing PACS, so the size of the archive may need to be boosted to handle the additional data. If the facility is operating a storage-area network, expanding the archive is not a major issue, but in other configurations, it can be. Many decisions must be made concerning where the stored mammographic data will reside and how it will be archived. A decision also has to be made as to how long the images will be archived and what the retrieval expectations of clinicians and diagnostic radiologists will be. Local regulatory/legal requirements will also come into play as it pertains to storage and retrieval. Because they will impact storage requirements, retrieval volume, and frequency, all of these choices will have bearing on the ultimate design of the storage and network infrastucture. Digital mammography has special requirements in the areas of storage and security, not the least of which are long-term image retention and expedient image recall. Consultants can help with the selection of the proper archive for cost-effective deep storage, as well as with obtaining transmission speeds sufficient to expedite image retrieval (see Table 2).

Table 2. Network transfer time in seconds (assuming no compression). (Click the image for a larger version.)

Image retrieval is of crucial importance since, in mammography, current and prior examinations must nearly always be compared. Often, these comparisons span a period of 2 to 4 years. Therefore, the rate and timing of breast-image recall has a decisive impact on the type of storage equipment needed and could, in some cases, necessitate an upgraded storage/management system. Fortunately, because most screening mammography is scheduled well in advance, a facility can arrange to retrieve priors when network activity is low.

The handling of digital mammographic data takes on added importance when they are to be combined with other imaging studies and information flows in an enterprise PACS (see Figure 1). If a hospital has a stand-alone radiology network and the major connections are all of gigabit capacity, then handling the additional digital mammographic studies should not be a problem. If, though, the hospital PACS is sharing a network with clinical laboratories, pharmacy, admissions, and billing, and a 30% traffic increase due to digital mammography is added to all this, it could slow network transmission. In some instances, network connections and design will need to be altered or enhanced to accommodate digital mammographic studies. Additional challenges are encountered when transmitting mammographic data from a remote site to a central reading site, as the expense, bandwidth, and availability of wide area network (WAN) options must be taken into consideration when planning workflow. Facilities are advised to seek expert assistance on how to avoid such pitfalls, through careful workflow/network design that makes optimum use of WAN connectivity (see Table 2). Another aspect of this analysis is calculating peak image-flow times during the day and planning for them.

All of this planning has the objective of maintaining throughput from both the patients’ and the diagnostic radiologists’ perspectives. Because patients will be scheduled for mammography every 15 minutes or so as the facility takes advantage of the speed of digital mammography, it is particularly important that bottlenecks or bad designs in network connectivity not be permitted to slow down patient flow and productivity.

West Long is sales manager, professional services, Agfa Corporation, Greenville, SC.