Up Close: Laser vs. CCD film scanning
PACS users deserve a closer look at the cost/benefit trade-offs of laser vs. charged couple device (CCD) film scanning technologies, both of which are very effective for scanning images into and across PACS networks.
In your October article titled Inside Image Digitizers, a CCD marketer stated when you get down to the nuts and bolts [between CCDs and lasers], theres not a lot of difference from a radiologists perspective, in image quality. We respectfully disagree! As a manufacturer of laser-based systems, we wish to offer a rebuttal and a brief comparison of these very different technologies.
For years, the laser film digitizers coupling of advanced laser and optic technologies has surpassed the image quality of CCD. This is a proven fact: Most CCD models see no more than a useful optical density range of 2.5, while some laser film digitizers can see up to 4.0 optical densities and deliver it in accuracies of .002.
Do radiologists really want to make conclusions from useful density ranges, or from a wide dynamic range offering the full spectrum of meticulous diagnostic-quality image densities? (Lumisys has responded to claims of no real difference between technologies: see this at Kodak URL: www1.lumisys.com/support/techref/Laser_vs_CCD.pdf for full details.)
A lower cost CCD digitizer does make sense when strictly used for teleradiology, where the level of image quality is unwarranted, but not for diagnoses. When asked if a higher level of scan image quality is of value in making the correct diagnosis, any radiologist would naturally say, Yes! No reliable radiologist will forgo the ability to make the most accurate patient diagnoses possible due to an initial price difference. Take the case of chest images, among the largest pool of images to be scanned: seeing even the most minute differences in density is crucial. Any scanner that doesnt accurately reproduce the full density spectrum does not offer the radiologist the real attributes of the image.
The CCD marketer also stated that CCD scanners offer more features for less money. In actuality, users would need several CCD models to meet varying application needs, whereas a single, flexible laser-based film digitizer offering variable sampling pitches capable of changing spot size from 50 to 500 microns in 1 micron steps, among other features not combined in a CCD offering covers a departments complete spectrum of image applications. Furthermore, with laser-based technology software applications, radiologists can compare patient studies captured directly from modalities and the relevant prior films using softcopy workstations stack and cine modes – not possible with CCD. A lasers optical density and speed also surpass those of CCD: hands down, for comparable resolution values, laser is up to 3 times faster than CCD systems.
The same CCD marketer stated that CCD scanners require no service beyond installation, and that when a problem occurs, they can be hot-swapped, while the service model for the lasers was pretty complex.
Service of laser digitizers is not at all complex: Technicians normally are onsite within hours. Equipment service and support are what any savvy consumer looks for in the world of radiology, where a same-day service response is not a foreign concept. Having quick access to trained support is crucial when the digitizer is a key element of the radiologists primary interpretation – not part of convenience-based teleradiology, but a critical segment of the imaging chain. Rather than merely hot swapping, laser support specialists provide personalized service to address issues and further streamline users specific, customized applications. If the film digitizer is used as part of the interpretive process (comparisons), the loss/downtime of that device could impact the departments ability to appropriately treat patients and support the referral base, as well as its financial affairs.
Afterall, is hot swapping really more beneficial than onsite service? What do hot swaps really cost? What about routine cleanings or maintenance? Does a technician come onsite to annually check the internal lookup tables to ensure the system provides accurate density values? Who deinstalls and reinstalls, what does this cost and who pays? How long does a hot swap take and who pays the freight? What happens after the warranty expires? Does the user really want to go through this again and again, each time a CCD unit crashes?
It makes little sense to believe there is no need for some type of maintenance for CCDs and lasers to ensure quality results and long equipment life.
In addition, from a technical perspective, one of the primary enemies of all film digitizers is dust and dirt. The slightest introduction of debris can appear in an image scan as a positive density artifact. Scanners should be cleaned periodically to prevent dust build-up and ensure optimal image quality in the scan. No responsible manufacturer wants untrained individuals to enter the equipment to resolve this issue: Safety, liability and the equipment investment all are at risk. We maintain that cleaning a film digitizer annually costs very little when compared to the potential liability of having an artifact on film interpreted as disease.
Looking closer at the design features of some CCD models versus lasers, the feed approach of CCD is gravity that is, a top down feed of the film to be scanned – with an entrance cavity open and susceptible to dust collection. A lasers feed entrance is below the optics and covered to eliminate dust.
In summary, we agree that CCD digitizers do have a place in Radiology and have made improvements in their basic technology. However, they are not equal to laser, especially when considering all of the factors comprising a reason to purchase. It is simply not a matter of cost.
Thomas J. Nardozzi, President
Array Corporation USA