Digital Revolution

7 October 2009 (Last Updated October 7th, 2009 18:30)

There has been a gradual transition from conventional analogue film radiographic imaging to digital imaging around the world over the past two decades. But, asks Charlotte Radiology’s Dr Arle Van Moore, does the cost of conversion outweigh the benefits?

Digital Revolution

The transition from the conventional analogue-based radiograph using film screen (FS) techniques to the digital radiograph (DF) has been made in gradual steps, with the cost of conversion from the film-based systems to the digital-based equivalent being the primary impediment when to convert and how the digital conversion is made.

There are multiple drivers that relate to cost, but in order to understand the challenges in moving to a form of digital radiography, one must understand the basics of the two digital radiographic systems that are available to radiology departments that use this technology and their comparison to film screen radiology.

Last century

Film screen radiographic systems for producing radiographs were the standard for much of the last century, employing intensifying screens to produce an exposure on a silver halide film when the radiographic beam passes through the patient and then through X-ray intensifying screens. The primary advantage of these systems is that the cost, relative to digital radiography systems, is relatively low.

When employed correctly the imaging quality can be quite good.

Compared to digital radiographic systems, film screen is highly portable and it has a clear advantage in the degree of latitude with which the film screen cassette can be used to position both the cassette and the patient.

"While film screen has cost advantages, especially in the realm of investment capital outlay, it also has limitations."

Film screen technical disadvantages compared to DR systems are not trivial and have helped spur the gradual transition in many institutions around the world to some form of digital radiographic system, whether it be a computed radiographic system (CR) or DR. Compared to most CR or DR set-ups, FS systems have a relatively limited dynamic range as the combination of the X-ray film and intensification screens determine both the contrast and relative image density levels.

Additionally, once the radiographic film is processed, the image is forever fixed on the film and to enhance it one will either have to use magnification or minification lenses and variable intensity transillumination to obtain the diagnostic information embedded in the radiograph.

Highly portable

Film screen systems produce an analogue film that is highly portable and that does not require a sophisticated picture archiving and communication (PAC) system to display. The analogue film can be viewed in almost any location where the ambient light can be reduced and the developed radiographic film transilluminated.

When investment capital restrictions are a major driving factor, the great advantage that FS has is that the cost of radiographic viewboxes to display radiographic film is substantially less than the cost of high-resolution radiographic monitors. While film screen systems have their cost advantages, especially in the realm of investment capital outlay, they also have their limitations.

In the cost arena, film must be stored both before and after the radiographs are produced. This creates two forms of costs: one the storage cost and the other the cost of administrating the storage.

These are not insignificant costs, especially if there is a large volume of radiographic studies. Attention to detail must be great, requiring sophisticated filing systems that maintain all of the pertinent clinical information and radiographic data.

Highly competent clerical staff are required to satisfactorily manage these storage systems. Additionally, radiographic film must be processed using chemicals and equipment that needs to be maintained in a proper environment to obtain a reproducible image on a day-to-day basis.

"In making any conversion to digital technology, the institution must first see the advantages and the need to migrate away from film screen."

When radiographic volumes are low, compared to digital radiographic systems, the cost analysis both in terms of investment capital outlay and in administrative costs, is clearly in favour of the FS system.

In making any conversion to digital technology the institution must first see the advantages and the need of making the commitment to migrate away from film screen technology. There are two basic types of digital systems: CR and DR. CR uses all of the same radiographic equipment employed by FS systems, the main difference being that instead of using a film cassette to obtain the radiographic image, a photostimulable plate (PSP) – a technology introduced in the 1980s – is employed to obtain the image.

This photostimulable plate is housed in a cassette that is similar to a film cassette and that can be used interchangeably with the film cassette. The logistics are very similar to those used for FS systems in that the images must be loaded and unloaded into the cassette and the cassette must be transported from the X-ray equipment to the image processor.

The DR system has the image capture built directly into the radiographic system and is not portable or transportable from the equipment itself. The receptor system is a sophisticated charge coupled device (CCD) that captures the radiographic image and within seconds directly transmits the digital image into the image display system where it is processed for viewing.

While there are a lot of technical differences in how the image is produced, it is similar to that obtained by CR.

It is also ready to be electronically transported to the picture archiving and communication system.

Displayed images

Whether one is considering moving to a DR or CR system, the common thread in migrating to either is the use of a different means of displaying the images obtained. A PAC system will need to be developed and deployed.

The first cost analysis that needs to be made is the investment in the PAC system.

PAC requires high-resolution monitors coupled to a single computer workstation,
a high-speed data networking system, a high-capacity server to service the workstations placed onto the network being built, and a high-capacity data storage system with redundancy. There are a lot of resources available to assist one with analysing which PACs might be right for you and which will work best in one’s specific situation.

There are different purchase options, too, with the ability to lease or buy equipment and to use PAC software based on the level of use of the technology.

There are advantages of digital technology compared to FS techniques. The radiographs are stored centrally in a digital format, and anyone who has the proper credentials and need to access the data may do so, with multiple individual healthcare providers able to access the images simultaneously.

Once archived in the PAC, there should be no more "lost" images or even entire X-ray folders. The digital archives are usually backed up frequently so that there is almost no potential for a complete loss of these image data.

While the cost of the PAC systems and system maintenance is an important factor in continuing administrative and maintenance cost, there are reduced costs in the physical storage of large volumes of radiographic film as well as the administrative costs involved in administering and maintaining that file. These cost reductions are not trivial and in many instances can more than pay for the new digital administrative costs.

One disadvantage of the digital system is that the film cannot be viewed in almost any location, with or without a viewbox; it must now be viewed on some type of computer imaging or PAC system.

Additionally, images may be electronically sent from institution to institution, making it easier to access specialised radiologists in other geographic areas, tapping into their expertise. In order to be able to do this, however, one must have a relatively robust wide or local area network to facilitate the exchange of these relatively large data sets.

There are plenty of lists of advantages and disadvantages available to the interested party in the literature, from system vendors and on the internet. It is relatively easy to take advantage of these resources.

Volume

"The cost of DR technology is gradually decreasing, making it more accessible to situations where it makes economic sense."

Once the decision is made that one can financially support a PAC system, then the next decision to make is whether or not there is enough volume to support DR as opposed to CR. DR systems tend to be more expensive, with the cost savings justified by high volume procedures.

Having a dedicated DR system to perform a high volume of chest radiographs is one example where cost efficiencies may be found. The DR cost savings are in the form of fewer manual steps being required in obtaining the image and reduced imaging processing times needed.

Perhaps the greatest time saving is in the elimination of PSP cassette handling with the elimination of loading and unloading the cassette and the need to transport the cassette between the cassette processing equipment and the X-ray machine.

There are a few other intangible advantages that digital inherently has over FS systems, with one being the greater dynamic range of the digital detectors in these systems. This reduces radiation exposure because of fewer repeat exposures in order to get it right.

Additionally, in this environmentally conscious world the need to dispose of the chemicals used to develop radiographic film is no longer an issue.

By and large, most radiology departments making a conversion to a digital system take a slow and incremental approach because of the nature of the associated costs. In situations where the volume is low, migrating to a digital world initially may not make sense on purely a cost basis.

However, as the world changes about us, migrating to a digital imaging system makes increasing sense in our efforts as physicians to provide our patients with the best care available. This conversion will open new vistas for our patients in getting them access to radiologists outside of their local areas.

This can extend into perhaps a larger regional or international presence. As this slow process occurs and the digital image becomes more the expectation than the exception, then an increased focus on the advantages that the typically more expensive DR systems have over the CR systems makes sense.

These advantages are increased productivity with faster work flow, shorter turnaround time for image viewing and the potential for improved image quality with lower radiation doses.

For the long term

It is our opinion that DR is here to stay. The cost of the technology is gradually decreasing, making it more accessible to situations where it makes economic sense. With increasing demands for institutions to be more productive, to do more with less and with the gradually declining costs of these technologies, DR will gradually assume its place in the digital armamentarium of the radiologist and the radiology department.