The transformation from film-based to filmless radiography operations has become more and more demanding as medical imaging studies expand in volume and complexity. Computed radiography (CR) is right now the most common digital radiography system in radiology departments. This digital imaging system eliminates the costs of x-ray film and film processing by recording high-resolution digital images that can be electronically transmitted and displayed. Unfortunately, the high initial cost of this new modality remains a barrier for many healthcare organizations, so computed radiography has yet to be completely adopted by the imaging community.
However, recent advances in technology and manufacturing have started to bring down prices for some computed radiography machines. Systems that once cost more than $150,000 can now be purchased for less than $50,000. Prices may decline even more as the CR market matures and manufacturing processes continue to improve. As prices stabilize in this lower range, CR will become a more realistic option for many healthcare organizations. As a result, health industry leaders are starting to take a closer and more critical look at the basic operational differences between traditional film-based imaging systems and new CR imaging systems.
The fundamental difference between traditional film-based or analog imaging and computed radiography is that the former uses film screens and the latter uses photostimulable phosphor plates. Computed radiography refers to the entire process of creating a diagnostic digital image, which consists of image acquisition, processing, and display. Essential CR equipment includes an imaging plate (IP), reader, computer, monitors, and printer. The IP has a layer of crystals that can store x-ray energy. This plate is placed in a cassette and used instead of film to acquire a latent image. The reader processes the latent image and turns the resultant analog data into a digital signal. Image software provided by the manufacturer is used to manipulate data and view the image.
These pieces of equipment alone do not constitute the full requirement to operate a CR system, however. A major reason for investing in CR imaging is that it is the entry point for general diagnostic imaging into Picture Archiving and Communication Systems (PACS).
Acquiring the CR Image
CR imaging, unlike other systems, uses only one screen type for all studies, so the same cassette is used for portable radiography, bucky radiography, tabletop radiography, and the like. There is no need to stock extremity work cassettes or chest radiography cassettes. These functions are handled by the software performing algorithm functions.
The chronology of the image processing following exposure is as follows: The exposed cassette is placed on the reader where the cassette is mechanically opened and the photostimulable plate is removed. Inside the reader a laser is passed over the plate using a wavelength of 633 nanometers to stimulate luminescence of the phosphors. This stimulated luminescence releases the latent image in the form of light that is filtered and collected onto a photomultiplier tube (PMT). The PMT then converts the light signal to an electrical signal, which is then converted from analog to digital data bits. The raw data are subjected to algorithms that allow for manipulation of digital information. Finally, the image is presented on a monitor for technologist viewing and manipulation. Once the reader scans the plate and digitally displays the image on the workstation, it then erases the imaging plate for reuse. All of this takes place in a matter of seconds rather than the minutes needed for conventional screenfilm image processing.
When considering converting to a computed radiography system, keep the following staffing concerns in mind:
✓ Retraining for physicians and technologists
✓ A demand on radiology departments to increase productivity
✓ Training staff to convert archived films to CR
✓ Fewer staff needed to maintain film library
Things to Consider Before Converting to CR
To make informed decisions about their radiology departments' futures, hospital leaders should take into account four important issues concerning CR: workflow changes, image storage, diagnostic evaluation, and ownership cost.
Workflow changes: The shift from film-based imaging to digital imaging significantly changes the way that images are handled in the diagnostic process. While traditional, film-based projection images are slowly developed in a film processor and managed by hand, CR images are quickly read off of a reusable recording plate and managed electronically. Also, digital imaging allows technologists to quickly check the quality of the image and adjust the display or correct problems before they are transmitted to the radiologist's workstation.
In addition to productivity improvement, digital imaging gets rid of the need for special areas in the hospital or imaging center for developing x-rays. Film-based imaging requires film processors, which contain chemicals and generate waste materials that require special handling and disposal. CR systems display the images on high-resolution monitors and provide functions to write the images to portable media such as a CD or DVD. These capabilities eliminate the need to print the images on film, thus eliminating the need for special processing areas, film processors, and chemicals. Furthermore, digital imaging systems use electronic networks (PACS) to transmit images to multiple locations, and most provide web-based access that allows the display of the images in a standard web browser.
Image storage: Traditional x-rays films are normally stored for many years, but few of the stored films are ever retrieved to be re-examined. Long-term x-ray film storage is expensive because large storage rooms are needed to store the images, and personnel are required to store, retrieve, and deliver the films. CR images can be stored on a PACS server that has the capability of storing millions of images for an indefinite period of time and providing nearly immediate access to any of those images.
Diagnostic evaluation: Old fashioned film-based imaging is limited in its ability to capture low-contrast details and at the same time conserve high spatial resolution. Even though adjusting the illumination of the backlight can expose some additional information, it is not possible to adjust the contrast range of the film once it has been developed. Alternatively, CR images can be electronically improved and thus further aid radiologists to identify potential abnormalities. In up-to-date CR imaging systems, automated post-processing is often used to reduce noise and optimize contrast over the entire image; this is particularly useful when the overall image has been overexposed or underexposed.
There are a few hurdles that hospitals may have to face when replacing conventional radiographic screen-film systems. Not all radiologists and referring physicians are immediately comfortable with digital technology. One advantage of film-based imaging is that doctors are accustomed to it and some prefer to physically hold a piece of film. Digital imaging requires doctors to use computers and to learn to interpret images displayed on electronic monitors rather than images printed on film. If a doctor refuses to embrace digital technology, it may be difficult for healthcare managers to persuade them to adopt new digital imaging technologies such as CR into their workflow.
Ownership costs: As the up-front costs of purchasing CR equipment decrease, CR is becoming more affordable for the majority of healthcare organizations. After an initial investment is made, the CR system begins to pay for itself quickly through the elimination of film and film processing costs, reduced file room storage costs, and a reduction in the number of support staff required to run the facility.
Overall improvements in efficiency and economy of the project can only be achieved if an entire imaging area (or an entire department) switches from film-based to digital radiography. Also, the organization will need to gradually convert its film library to digital imaging after it makes the switch to CR. This can be accomplished by installing digitizers in the film library and retraining film librarians to scan x-rays films and convert them into digital images. Once this is completed, the digitized studies can be electronically transmitted to the facility's PACS as needed.
The birth of computed radiography can be traced back as early as 1975, when the Eastman Kodak company patented a device that was capable of releasing a stored image by using thermoluminescent infrared stimulable phosphors. The FUJI Photo Film Company recognized the far-reaching possibilities of this new discovery and in 1980 patented the first process that made use of photostimulable phosphors to record a reproducible radiographic image. The basic common finding of both applications was that some phosphors (called storage phosphors, also known as photostimulable phosphors) could capture an image from absorbed electromagnetic or particulate radiation. Part of the energy stored in the phosphor was released when stimulated by a high-frequency helium-neon laser. The phosphor's luminescence was detected using a photomultiplier tube (PMT), thus generating an electrical signal that was ultimately reconstructed into a digital radiographic image.
Common Problems and Solutions
According to ECRI, one frequently reported problem is associated with the imaging plates. For all practical purposes, these plates should not wear out. However, they often become damaged due to mishandling. Although reusable, these plates have a unit replacement cost that ranges from $650 to $1,800. In addition to using caution when managing these plates, one should also keep them clean and free of any defects such as scrape or cracks. It is further recommended that the light guide should always be dirt free for best image quality.
A quality control program for CR inspection includes a set of test objects and analysis of the obtained image data. Several manufactures established guidelines for acceptance testing (Kodak 2001, Agfa 1999), but there are no industry standards for specifying the performance of these devices. This causes a lack of uniformity in measurement procedures among different manufactures. O. Rampado, P. Isoardi, and R. Ropolo completed and published their work regarding this matter. They successfully developed a set of software processing tools that can be used to make a complete quantitative assessment of CR quality control parameters. They claim that these tools should reduce the time needed to perform the CR quantity tests and avoid any biased influence in quality parameters evaluation.
The following list of several available standards and guidelines for CR was complied by ECRI. Visit www.ecri.org for a larger directory.
American College of Radiology/National Electrical Manufacturers Association. Digital imaging and communications in medicine (DICOM) part 1: introduction and overview [standard]. 1999 (revised 2004). (There are now 18 parts to this standard.)
American National Standards Institute/Association for the Advancement of Medical Instrumentation. Safe current limits for electromedical apparatus [standard]. 3rd ed. ANSI/AAMI ES1-1993. 1985 (revised 1993).
American Society for Testing and Materials. Guide for computed radiology (photostimulable luminescence [PSL] method) [standard]. ASTM Committee E7 on Nondestructive Testing. BSR/ASTM E2007-00. 1998 (revised 2000).
Canadian Standards Association. Diagnostic imaging and radiation therapy equipment [standard]. C22.2 No.114-M90 (R1996). 1990 (reaffirmed 2000).
Health Level Seven. Application protocol for electronic data exchange in healthcare: version 2.5. 1987 (revised 2003).
Future Development of CR
Future advances in CR technologies are aimed at improving signal collection and acquisition speed to make CR competitive with Direct Digital Radiography (DDR). DDR is similar to CR except the image is obtained directly, instead of using an IP and reader.
DDR systems tend to be much more expensive than CR systems. However, some argue that the productivity gains from DDR can offset the higher cost. Such proponents claim that while the gap in acquisition time between them is closing, DDR is still better and faster since technologists do not have to handle and process cassettes as with CR. Also, with DDR, the image is seen immediately. Due to all these claims, many people in the healthcare industry predicted that DDR would quickly overtake CR, but that has yet to happen.
However, even when considering all of these valid claims, customers still show a preference for CR systems, especially smaller imaging centers and private physicians who cannot make the larger financial investment in DDR. Additionally, CR units are more attractive because of their mobility. One currently available plate reader weighs only about 35 pounds and runs on 110 volt power or can be operated from a power inverter. Combine this with a laptop and portable printer and the entire system can be taken on the road.
CR image quality continues to improve from one generation to the next. With its superior image quality, speed, and ease of storage, the increased cost of a system is a sound investment.
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Sofia Iddir completed her undergraduate studies in December 2005 at the University of Connecticut, where she obtained a double major in biomedical engineering and materials science and engineering. She is presently working toward an MS in biomedical engineering with a concentration in clinical engineering. As part of her studies, she is serving as an intern at Baystate Health System in Springfield, MA. She is expected to graduate in December 2007. Her e-mail address is email@example.com.