FAQs for PACS

Aniruddha Nene

PACS is an acronym for Picture Archival and Communication System for medical imaging. Imaging has become critically important in diagnostics with rapidly advancing technology, improving accuracy of the diagnosis and turn around time. Ever increasing number of diagnostic equipments (also called modalities) provide images in the form of digital data that adheres to universal standards. Naturally, forming a common pool of images as digital archival becomes immediately possible, despite the diverse nature of manufacturers of the equipment. This centralised repository is PACS.

Simplistic view : Archival is meaningless without addressing efficient retrieval at right time and at right place in a convenient manner. The images are viewed on workstations which have special functionality in terms of viewing and processing the image before the consultants arrive at diagnostic conclusions.

As regards the retrieval part PACS, data is retrieved obviously for viewing (also called 'reading' the images) by viewing stations/workstations. As the films (called 'hardcopy') are not totally eliminated as of date, PACS data can also be retrieved to print a film on machines called thermal/ laser imagers (formerly called camera )

It is important to note that modalities are source of the image. Workstations/hardcopy imagers are the destination. These are essentially the external components and in principal all these components are not the part of core PACS. Core activity of PACS is, however, to manage the link between the components and not the components themselves. So, choice of PACS should rest on the single point of how the storage is managed, how the retrievals are facilitated. In the simplistic view, it may appear that it's all only about the movement of a digital image across the hospital, but it's not! Holistic view in the next section depicts what else really matters.

It will be worthwhile to know a few basics of the external components. As the digital imagers will slowly give a way to filmless environment, we have a look only at viewing /processing workstation. Owing to specific nature of images and clinical aspect of diagnosis, workstations can be classified into:

Standard diagnostic viewing : That offers typical processing such as arranging images in the format most suitable for a particular diagnosis, applying grey level enhancement such as Window -Level Window - Width etc.

Special processing: This is modality specific processing such as 3D reconstruction of coronary arteries in case of cardiac CT scan or treatment planning in orthopaedics superimposing layout of metallic implant onto the bone image.

Summary viewers : This viewing facility benefits consultants or surgeons to co-relate the report with extent of the pathology diagnosed in a vivid manner. Such viewers do not require high-end processing as it a summary viewer is expected to get only filtered and pre-processed data in 'ready-to-view' mode.

What is DICOM?

DICOM is a standard for exchanging digital images between different modalities, PACS, workstations / imagers etc. Prevalent version of DICOM currently 3.0. This standard was developed by jointly American College of Radiology (ACR) and NEMA where the radiologist and the modality manufacturers jointly architectured mechanism to enable data sharing between different modalities. This was a very important mile stone in the advancement of medical imaging.

DICOM standard defines structure of the file as well as certain medical work flow specific, higher level, communication protocol between the modalities. So, once basic definitions to identify DICOM counterpart and qualify certain DICOM service requests is completed on either sides; all needed is to connect the DICOM modalities by standard ethernet network and data exchange begins.

Examples of DICOM communications:

A DICOM CT issues a command to print a film on a DICOM Imager:

1. Here the CT scan console defines necessary parameters of the imager to identity the service counterpart (provider) in DICOM communication setting menu and enables DICOM services that are needed for availing filming.

2. DICOM imager console defines identification parameters of the DICOM service counterpart ie CT scan to allow access of the filming services and enables DICOM services that are needed for offering the filming.

Benefits of PACS

The main advantage of PACS which is common to all departments is directly impacting better and faster diagnostics with improved workflow and advanced processing. It has a very stronger impact on therapeutic side as well. With suitable work stations and integration of PACS with EMR, Cardiology, Neurology, Orthopaedics benefits because the consultants and the surgeons get to see the summary view during consultation and handy references for procedures / surgeries. Key issue to be addressed here is that summary viewing must not offer the all images in PACS that are needed for diagnostic viewing. PACS workflow should facilitate filtering of key positive images and add value to it in terms of highlighting the findings to add value for summary viewing.

It is a known fact that unlike DICOM standard, which has to address fixed set of services, the exchange of transactional data has numerous aspects to be taken into account before such integration takes place. And it involves mapping process of messages to be done by each system to be able to be integrated for the transaction. Therefore, it is important to register the fact that such integrations are not 'plug and play'. Needless to say, functional knowledge of all key systems is essential in order holistic PACS is the target.

Holistic picture of PACS

How is it different from an HIS? Does PACS come under HIS?

• Ideally speaking, there is no reason why we have to deal with different IT systems in a hospital. One may argue that why can't there be an all encompassing HIS that uses a common data base and common software backbone to store.
• All clinical data captured during all patient encounters such as OPD, wards, ICU, OT etc conventionally EMR.
• All specialised diagnostic departments say radiology or cardiology or pathology where examination status is monitored; workflow within the department is automated; images / test results ( numbers / graphs ) are captured, stored, diagnosed on Viewing station, finally reports and key images are made available for viewing (conventionally RIS, CIS, LIS and PACS ).
• The reason is not limitation of technology. Conventionally, all the systems were developed with restricted domain knowledge. And were promoted with as islands of efficiency. For example, PACS for a long time had been a strong hold of equipment manufacturers. Therefore there was no focus on promoting holistic view as it probably made no business sense. It is only because of truly domain oriented and Information Technology-driven vendors who look at it without artificial boundaries of each segment of the healthcare a genuine holistic solution can emerge.
• IT in healthcare is young as compared to counterparts in other verticals. And standards like HL7 is just a means of facilitating integration.

Investing in PACS

• It is difficult to put a price tag to something like PACS unless the data load, archival policy, workflow specifications, integration requirements are specified.
• Some of the items which external components to PACS are workstations are costly. It is necessary to evaluate them separately on merits and cost.
• Typical cost of imported systems with simplistic PACS will cover PACS server with a couple of diagnostic workstations will range from Rs 50,00,000 to a multi-crore budget.
• The holistic indigenous PACS can cover archival diagnostic and summary distribution, along with in-built workflow systems such as RIS and complete clinical EMR including HIS integration as a sub crore budget. A typical cost for the first phase addressing immediate archival and departmental workflow requirement such as in built RIS/ CIS will range from Rs 25,00,000 onwards.

The writer is Principal Consultant, Imaging Director, 21st Century Health Solutions, Mumbai