The PACS Workstation: A Theory of Evolution

David Weiss, MD

Disclosures

Appl Radiol. 2008;37(8):24-29. 

In This Article

Descended from monkeys? My dear, let us hope it isn't true! But if it is, let us pray it doesn't become widely known!
Quote attributed to the wife of the Bishop of Worchester

Introduction and Workstation Evolution

Introduction

The picture archiving and communication system (PACS) workstation has been an object of radiologist desire and derision for the past 20 years. Softcopy viewing functionality has developed synergistically and in parallel with mega-slice computed tomography (CT) and multiseries magnetic resonance (MR). Along with technology advances, radiologist training and experience have necessarily evolved as well, with the implementations of tile mode, to stack mode, to 3-dimensional, and 4-dimensional image interpretation. Increasingly complex image analysis capabilities are raising the bar for even rudimentary workstation requirements. Moreover, the need for interoperability with a multitude of other systems is becoming pervasive. Vendors of PACS are well aware of these challenges and are taking steps to meet them.

Workstation Evolution

The PACS workstation evolved from 2 requirements–radiologists' need to view an increasing number of anatomically related CT and MR images, and the yearning for freedom from the geographic tyranny of proximity to the film library. At the same time, computed radiography technology for projection radiographs allowed softcopy viewing of these images. Pre-existing digital modalities, such as ultrasound and nuclear medicine, were naturally suited for PACS viewing. Rudimentary workstations were developed initially for off-site viewing to ease the burden of night call. Current workstations retain some DNA from these PACS precursors. In-house, many radiologists initially used a modality workstation to scroll through CT data. This was marginally satisfactory, but more functionality–both in image viewing and areas such as worklist control and image display–was desperately needed.[1]

Enter the full-function PACS workstation. These developed in an era before the availability of the Windows platform. Early PACS vendors often relied on UNIX software and were held hostage by low-bandwidth networks. With these thick clients and the limitations of transmission speed, complex routing algorithms were developed to send image data sets to predefined workstations where the appropriate radiologist subspecialists would be working. Sometimes called distributed architecture, this workflow, born of necessity, had its limitations. If studies that were not resident on the local hard drive were needed, an ad hoc query of the database often took many minutes.

Second-generation PACS were able to utilize the then-novel Windows technology as well as higher bandwidth for what many calledcentralized PACS architecture–a philosophy of any image, anywhere, anytime. Images were pulled from a centralized server only when needed. This advancement allowed a move toward thin-client workstations with more server-side computation. Radiologists were released from the yoke of having to sit at a prechosen workstation and were no longer at the mercy of an overmatched network for ad hoc queries.

Later PACS vendors took the thin-client workstation concept even further. Rather than upload 1 full case at a time, these workstations worked on a just-in-time delivery principle in which images and resolution were dependent on real-time user requests. This ultra-thin-client architecture had high bandwidth requirements and worked extremely well in a hospital environment. Challenges arose when the increased demands of off-site reading, an increasingly common workflow, became more pervasive.

Currently, most vendors are moving toward a hybrid environment that combines the best features of distributed and centralized architecture to accommodate all reading patterns. Newer vendors have perhaps had an easier time of this, standing on the shoulders of the early designers. Several of the original PACS vendors have had more difficulty making these rapid changes because of the need to accommodate legacy customers with backward compatibility.

In addition to architectural changes, the phenotype of the workstation itself has also evolved. Early monitor configurations emulated the 4-over-4 lightbox, assuming that radiologist reading patterns would remain the same. The number of monitors decreased rapidly in the early PACS years to 4 and then to 2 as users realized that reading in softcopy was radically different from reading film.[2](Almost all workstations now have a third monitor, sometimes of lesser resolution, for text and other non–image-related information.) Early investigators confirmed the 2-monitor workstation as satisfactorily efficient,[3]but some radiologists are now returning to a greater number of diagnostic monitors as studies and comparisons become more complex.

Dr. Rubin Mezrich, University of Maryland, is fond of reminding us that the C in PACS stands for communication, a concept seemingly forgotten by some software designers. Dr. Steve Hori, University of Pennsylvania, was perhaps one of the first to introduce the concept of a single–point-of-contact (SPOC) workstation that would accommodate all functions needed by the radiologist. These 2 requirements are facing a moving target as more is being asked of workstation functionality.

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