We present three years of clinical experience using PACS involving developments on worklists, pre-loading and archiving strategies in a teaching pediatric hospital with all modalities connected to a commercial PACS. A method, allowing to generate and handle different worklists for computed radiography examinations, has been developed in our centre. Worklists and archiving strategies are presented and discussed. We conclude that, with adequate worklists and efficient pre-loading implementation, current PACS could be used successfully in several clinical settings of a multimodality department.

Keywords: PACS, Worklists, Image Pre-Loading, Archiving

Radiology practice in teaching hospitals is highly specialized, being the performance of examinations and reports very selective. Every radiologist performs reports or examinations of a given modality, and/or clinical ward, and/or anatomic region, depending on the organization of the department. Multimodality diagnosis is the usual organization in such environments. Picture archiving and communication systems (PACS) can provide tools that help to manage information in these environments. Many current PACS implementations have been limited, for clinical purposes, by their modality orientation that hampered their clinical impact. This was caused by supporting only cross-sectional imaging, but in other cases by neglecting the methods to mimic traditional and essential practices of a radiology department. In our teaching pediatric hospital, radiology practice is oriented by clinical wards and modalities in a mixed approach: any given radiologist supports the radiology of a clinical ward, an imaging modality, and some fluoroscopy examinations. Since 1991 a PACS (CommView, Philips - ATT) has been progressively installed and incorporated to the daily clinical activity of our hospital, a 250 beds pediatric hospital. Computed radiography, which is connected to the PACS, accounts for 72 % of the imaging procedures performed by our department, because we perform almost all (99 %) radiographic examinations with CR [1-3], leading us to develop several local methods to improve the use of a CommView PACS. One of these methods has been applied, successfully, to build and handle different worklists for computed radiography examinations, an area that many PACS neglect: CR is seldom included in PACS implementations, or, when included, all CR exams are arranged in a single worklist - with hundreds of examinations - that is very challenging to use. To optimize our limited magnetic disc capacity some simple archive strategies have been defined to improve both performance and reliability, and to reduce costs in magnetic and optic media, doing selective archival and deletion from the server and workstations (short-term on-line databases).

CommView PACS has been described elsewhere [4,5]. In our implementation (figure 1), the server (DMS) has 5.4 Gigabytes of unmirrored magnetic disc space, being able to hold 5 days of inpatient activity. The mid-term storage is supported by an optical jukebox of 231 Gbytes (89 disks of 2,6 Gbytes). A fiber-optic proprietary network, with star topology, connects the DMS with the acquisition modules (AM) and workstations (WS). Placed in the reporting rooms we have four main diagnostic workstations (DWS), three of them furnished with four 1Kx1K monitors and one with only two 1Kx1K monitors, and with 1 GByte magnetic disc storage. One of the DWS acts as a laser film-printer server. A gateway provides connection to an ethernet network with 7 PC-based review workstations (RVS, Philips-ATT) for clinical use in the wards: Two RVS, with 2 screens each, are located in the CCU and NCCU (General Pediatric and Neonatal), one in the Emergency Room, and three in the Outpatient Clinic. The last RVS workstation, placed in the radiology department, is devoted to teleradiology experiments using conventional switched phone line and a DQDB MAN. A radiology information system (RIS) to PACS interface will be completed along the first half of 1994.

The main input of our PACS is Computed Radiography (PCR-901 Graphics, Philips), operating since 1988, and to a lesser extent the laser film digitizer (LFD, Lumisys), one digital Fluoroscopy (DF) system (Philips DSI), two Ultrasound Units (US, Acuson, Aloka), one Computed Tomography (CT, Elscint), and two Magnetic Resonance Imaging Units (MRI, Siemens). US, and CT images are digitized by frame-grabbers. DF is connected digitally. MRI will have digital connection in the third quarter of 1994. CR has been a challenge for the system, both in file-size and daily volume (around 1.2 Gbytes/day), but LFD and MRI are also providing high flow of images.
 
 

Figure 1. Configuration of PACS of the University Hospital Materno-Infantil Vall d'Hebron.  AM: Adquisition Modules,  DMS: Data Management System,  DW:Display Workstations, DSI: Digital fluoroscopy,  GW: Ethernet Gateway,  PCR: Computed Radiography,  PIP: PACS-PCR interface,  RT: CR Reception Terminal.

Worklists
A worklist, category in CommView terms, is constituted by a set of exams without diagnostic report, that are assigned to a unique user identification (or interpretation queue). The user may be a physician, a clinical ward, or a modality. Additionally, a given user may be the target of several modalities or wards, in a very flexible way. In any acquisition workstation, worklists are set as the modality by default, but, a physician or ward worklist can be assigned when required.

Worklists are assigned to CommView users and defined over each workstation. In the image server, a decision table is configured, containing pre-loading destinations considering the acquisition module, the modality, the worklist, the user, and the workstation (WS) destination. These procedures have been defined using the CommView tool Tsdecide (Philips - ATT). Each workstation contains its own set of worklists, where all pre-loaded examinations. The different worklists are described in tables 1 and 2.

Preloading
We have developed pre-loading algorithms to support the traditional reporting practice of our radiology department: ward reporting and modality reporting for any radiologist. Pre-loading can be done to several WS for every selected exam or patient. At every WS several user-worklist relationships are defined. By default, the modality is assigned as the worklist, but it can be modified for any given examination. Every display workstation DWS (EGDWS, Philips) handle several worklists. Review workstations (RVS, PC based WS) hold only one worklist. Some computed radiography out-patient examinations are sent to selected RVS. Out-patient CR examinations are not forwarded to any DWS. Some out-patient clinic examinations are not pre-loaded to any WS. Digitized films are pre-loaded to one DWS for quality control or sent to any DWS or RVS following clinical needs. Emergency room examinations (28 % of our daily workload) are only pre-loaded to emergency RVS, after reduction of images to 1024x832x8 bit matrix.
 
 

Worklist-Category	Display Workstation	Daily Volume (Mbyte)
ECO (Ultrasound)	DW2	320
DSI (Digital Fluoroscopy)	DW0	70
CTB (Body CT)	DW3	40
CTN (Neuro CT)	DW3	40
IRM (MRI)	DW3	72
LFD (Laser film digitizer)	DW3	240
PCR1 (Computed Radiography)	DW0, DW1	380

Computed Radiography Worklists:
CR worklists are clinical ward oriented worklists targeted to several workstations where the real worklists are built and presented to the users. Computed radiography worklist implementation is tricky, as the interface between our CR (PCR-901 Graphics, Philips Medical Systems) and the PACS did not support worklists, just WS destinations for CR exams. In our local implementation, marking a CR exam for a category is achieved by adding a two digit code in front of the examination id number. This information is provided automatically by the RIS, using a custom RIS-CR interface [6]. A target WS is also selected. The examinations are performed and processed as usual and pre-loaded to the selected WS. In each DWS, a very simple routine, developed as a script with a proprietary database tool (dmawk, Philips - AT&T), scans the ID numbers in the local database and replaces the default worklist (CR, the modality) by the selected worklist (a clinical ward) following a look-up table, as described in table 2. This routine is scheduled to run every 20 minutes, or can be triggered manually. In each DWS, examinations are grouped as usual by the standard CommView software. To access a worklist, a user logs-in typing a user ID and password, and selects the 'Show worklist' option in the main menu. The list of uninterpreted exams is presented chronologically. Any examination can be selected for review or reporting. When an examination is selected, it is presented in the monitors, and the list of previous examinations is presented allowing the request other exams, from any modality, for comparison. The user may move between the different examinations of the patient freely. When finished with the exam, the user shift to the following exam in the worklist by just taping the 'next' key. After marked as 'dictated', pushing a key the examinations are no longer presented in the worklist, but are still available in the workstation.
 
 

Category Worklist	Radiology  WS	Review WS - RVS	Daily Volume (Mb)	Worklist trigger
UCI (Critical Care Unit)	DW0	UCI	48 Mbyte	(01)
LB (Infants, Unit B)	DW0	-	42	(03)
ESC (Children)	DW0	-	42	(07)
PO (Surgery recovery)	DW0	-	6	(09)
NEO (Neonatal Care)	DW1	NEO	60	(00)
LA (Infants, Unit A)	DW1	-	42	(02)
ES5 (Teenagers)	DW1	-	9	(08)
HEM (Haematology)	DW1	-	21	(05)
ONC (Oncology)	DW1	-	9	(06)
NEF (Nephrology)	DW1	-	35	(04)
CAR  (OC cardiology)	-	CAR	40	-
NEUMO (OC pneumology)	-	NEUMO	20	-
NEURO (OC neurology)	-	NEURO	20	-
URG (Emergency)	-	URG	400	-

Table 2: Computed Radiography Worklists and Categories, and daily volume (Megabytes) per worklist (category), and worklist trigger sequence
 

Archive Policy
Archive methods are developed using existing CommView tools, with minor script procedures to automate some CR 'archive after delete', procedures. Archiving is scheduled with different approaches related to patient origin or modality. Archiving by CommView tools means to copy the examination folder to an optical disc and to delete -always- the examination from the magnetic media of the DMS. We can recover the folder back from the optical archive, but with a significant amount of time and system resources. Nevertheless, the softcopies of the exams distributed over the DWS' or RVS' are not deleted by these archive procedures. A second routine deletes reported exams from each DWS after a scheduled period. Computed radiography from in-patient examinations are archived 77 hours after acquisition. The remaining CR studies from out-patients, older than 77 hours, are removed completely from the PACS, but softcopies were previously archived in the CR optical disk subsystem just after acquisition. In-patient and out-patient examinations from other modalities are archived on PACS optical disk and deleted 5 days after acquisition. In-patient images of all modalities last in the DMS of the PACS for at least 5 days before being archived and erased from magnetic media on the DMS. In the DWS and RVS examinations may last longer. All these archiving procedures are done during nighttime. Digitized films are pre-loaded and deleted after quality control on a DWS. The jukebox provides slightly more than 2 years of on-line activity, fitting the more frequent retrieval period. The compression ration used by CommView is 3:1, bit-preserving.

The original design of the CommView system dates from 1986, and, it is proprietary, slow for current standards, and its future growing is uncertain. Nevertheless, we have exploited its provided services and functions - worklists, pre-loading and archiving - bypassing the constrains of the system and providing enhanced functions to our clinical users. CommView worklist implementation is suitable. It supports transparent pre-loading, and easy reviewing and reporting, allowing to mimic alternator use. The users log-in, by typing a CommView user name at the assigned workstation. Moving between examinations of the same patient, or to the next patient in the worklist, is done easily by a couple of keystrokes. When the examinations are available locally in any DWS, the display of an exam is done in 15-60 sec. for CR exams and digitized films, and in 4-15 sec. for US, MRI, CT, or fluoroscopy exams. The first image appears in 15 or 4 seconds, respectively. If we need to recall images from the central database the longer delay makes the system response exceedingly slow for clinical reporting falling between 30 to 120 seconds. Display times are even longer when we need to de-archive from optical discs; thus, our strategy has been to pre-load as many exams as possible. The daily volume of new examinations loaded in each DWS is the interval of 250-470 Mb. (Tables 1-2).

Our solution for CR worklists provides a functional and unique solution to a problem ignored by many PACS implementations. This CR worklist system is a development that has not been implemented, or described before in the literature, or applied to a CommView PACS. By dividing the CR workload generated in worklists we can handle the most frequent type of examinations in any radiology department. Without CR worklists, some functional advantages of PACS image handling are lost. This implementation allows to run the radiology-clinical sessions much more easily, because patients are grouped by wards, and can be retrieved sequentially. We are working in other submodality approaches: as new subcoding system that will allow to review all patients with bone and joint radiology refered from any ward.

On-screen reporting is greatly assisted by using worklists, especially when dictation is the reporting method. This procedure is compelling in CommView PACS, as worklist management does not accept direct typing of reports from the image reviewing mode. In some cases, as CT, a single modality has different worklists (Body CT, Neuroradiology CT). Technicians can perform their quality control very quickly using modality worklists, as in ultrasound or fluoroscopy. Our implementation in the ultrasound unit, has been very successful, allowing to work for the last 20 months completely filmless. Critical care unit reporting improved after moving to dictation and quick transcription. The initial availability of WS and previous reporting habits hampered their implementation in some wards or modalities.

Our archiving strategy allows to use efficiently our storage capacity, by spreading exams between the central database and the DWS' and RVS'. The phased folder archiving and deletion allows to keep locally most images and to free enough disc space for incoming images. Optical archive allows to have about two years of activity on-line. In our experience a period of 10 days is advisable for critically ill patients of the CCU or NCCU, we are investigating methods to expand the availability of in-patient examinations in the DMS and DWS. We archive along the night, being the jukebox free along daytime for dearchiving or rearchiving. This approach helps to reduce traffic over the network and avoid load bottlenecks in the server. We digitize conventional previous films of inpatients and archive them in optical disc as a prospective archive, an archive that will include digital copies of previous examinations only when the patients are readmitted in the hospital, and to include in the PACS all images of the current clinical event not generated by digital methods. We are using the PACS as the main archiving and retrieval system with satisfactory results as other authors have found [7-8].

Pre-loading helps to smooth the peaks of activity and computer load along daytime. Worklists allow to mimic traditional reporting routines and incorporates new possibilities. CR worklists allow a practical approach to PACS radiography management, still the most frequent imaging procedure. The technical limitations of the CommView hardware are an obstacle when dealing with multiple CR images, but are barely noticed reporting cross-sectional or fluoroscopy examinations. Developers of PACS should consider the influence of worklists in PACS' organizative impact, that ultimately will endorse PACS for clinical practice.

References
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