Roughly two thirds of the resources of diagnostic imaging departments are tied up in conventional radiography. No other modality consumes as much staff, front-line management time, or as much physical space. That prompts many department administrators to seek solutions that allow those resources to be reallocated to other, more productive (and profitable) uses. The solution they often embrace now is direct digital radiography (ddR). Small wonder: the introduction of a single ddR machine typically increases the efficiency of a department’s radiography service by up to 400% and reduces associated costs by a factor of three.
How that is possible has much to do with the fact that ddR is electronic. There is no film to generate (or, potentially, to lose); there are no cassettes to handle and no effluent to capture and treat. There also is no guesswork involved in making an image, which means fewer steps.
An imaging department will not necessarily be any more productive or profitable just because it has swapped analog radiography for digital. Realizing the benefits of digital radiography requires much more than just digital image production. The first thing to consider when evaluating the merits of one digital radiography technology over another is the way in which the digital image is produced. For many radiology enterprises, the entry level to digital radiography is computed radiography (CR). The primary attraction of CR is its portability. The major drawback is that it creates the digital image via Rube Goldberg-style methodology that first exposes a light-sensitive plate within a cassette. This cassette is removed from the bucky and walked some distance to a processor unit where the stored contents of the plate can be scanned. The scanner reads the images and converts them to digital form. At that point, the images are routed to a soft-copy workstation, a hard-copy printer, an electronic archive, or all three.
The simplicity of ddR stands in contrast to this method. No cassette is needed because the images are recorded directly, in digital format. The concept is not much different from that of the digital camera used at home: the technologist positions, makes an exposure, and a digital image appears on the screen moments later without further effort. The absence of a cassette is a primary reason that ddR affords greater productivity. No need to handle cassettes translates into faster throughput. Cassette-free radiography means faster patient throughput. The average radiography procedure-with all steps considered, beginning when the patient walks into the room-normally takes 7.5 minutes using cassette-based methods. With cassette-free ddR, however, the same procedure is completed in less than 3 minutes and, in a best-case scenario, in just over 1 minute.
The 4.5-minute difference between CR and ddR procedure times gives rise to some rather intriguing benefits for ddR users. A single technologist full-time equivalent is able to do the work of two or three, and the workload normally requiring three rooms can be consolidated into one. These freed resources can be reallocated to other, more profitable, demand-satisfying services, both existing and new. Examples include CT, MRI, and even positron emission tomography (PET).
Digital radiography minus the cassette does not, by itself, tell the entire story of why the right kind of ddR system permits greater productivity and economy. High productivity also requires a ddR system that can take exposures at short intervals; not all systems do. Some digital detectors require technologists to wait 10 seconds for the detector to charge before an exposure can be made and as long as 60 seconds for the detector to relax before it can charge again to take the second exposure.
Another factor in the productivity equation for a ddR system is the ability of the technologist to view the image in full resolution quickly after exposure. This makes it possible to promptly QC the image and release the patient.
Image production must be self-contained. The technologist should not be obliged to leave the procedure room to view the image. Any production task that causes the technologist to walk away from the ddR system will use valuable minutes.
The productivity gained by using a ddR system is further enhanced by multiaxis detector positioning, which permits facile imaging for every possible procedure and in many creative ways. Without this capability, the system is limited to upright and supine imaging; it is not possible, for example, to take decubitus images involving exposures shot cross-table and requiring compound angles.
The table itself should be multidirectional and not limited by being anchored to the floor. Such a configuration will let the technologist easily move the patient as necessary for optimum positioning, regardless of the angle at which the detector must be set. In the same way, productivity increases when the ddR system incorporates a motorized C-arm. Positioning entails very little effort, especially if the C-arm is programmable. The technologist needs only to hit a preset key for, say, a chest radiograph, and the detector would then automatically drive into the correct position for that particular imaging procedure. This saves time because the C-arm could be positioning itself while the techologist is escorting the patient into the room. Beyond motorization, the C-arm should also be isocentric. That way the x-ray tube is always automatically centered any time the detector is moved. No adjusting by the technologist is necessary. Without isocentric design, the technologist must make a series of manual adjustments involving tedious checking and rechecking of the tube-to-detector alignment. Decubitus images invariably are the hardest to align and often entail extensive maneuvering because improper alignment may yield grid artifact on the image. A related factor is the quality of the stand on which the detector rests. It must be sturdy enough to resist flexing when a patient is placed against or upon it. A stand that bends, even slightly, will result in alignment problems, which, naturally, ties up technologist time by necessitating corrective measures and image retakes.
Innovative software features also play a role in making a ddR system useful as a productivity enhancer. One example is size-wise collimation capability. With many ddR systems, every image that is generated becomes a 15MB data file, regardless of whether the image fills the entire frame (as does a chest view) or fills only a portion of it (as does a view of a finger). A well-engineered ddR system, on the other hand, will electronically collimate the image as the technologist collimates the exposure field so that the captured image contains no unused frame. This is not image compression; it is simply the elimination of unneeded frame. At first glance, that might not seem to have much bearing on productivity, but it clearly can. The collimated image of a finger, instead of being a 15MB file, slims down to a mere 1MB or less of data. Because it is one fifteenth the size that it would otherwise be, that image can travel more rapidly across a PACS network. Since it arrives at its destination sooner and loads onto the viewstation monitor screen more quickly, the radiologist (or, perhaps, the orthopedist or emergency surgeon) on the receiving end can get straight to work on the patient.
A very important Digital Imaging and Communications in Medicine (DICOM) protocol is Worklist, which automatically populates patient-demographics fields with data supplied by either the imaging department’s radiology information system (RIS) or the larger enterprise’s hospital information system (HIS). This can save the technologist additional time (1 to 3 minutes per examination). A desirable ingredient on the software side of the ddR system is a program to ensure examination-to-examination consistency by storing the precise algorithms, positioning angles, and x-ray exposure parameters used for a specific patient’s most recent procedure. This allows the technologist to pull up the patient’s most recent ddR examination, press two keys, and stand back as the system automatically drives to the exact position that it was in for the previous examination.
Considering the TECHNOLOGY
The most expensive component in a ddR system is, of course, the digital imaging technology. Therefore it is very important that the system is configured to efficiently perform all radiography procedures with a single detector. Conventional two-detector arrangements require twice the investment to purchase and maintain and will never be financially viable in the real world of modern health care.
The imaging technology must be proven to provide high quality images in a variety of demanding environments and serve a large, diverse market. Even the largest company will have difficulty justifying the ongoing expense of supporting technology that can only be used for radiography applications.
If there is one lesson to be learned from the evolution of medical equipment, it is the realization that there is no ultimate medical imaging system. Continuous scientific advancement yields ever better components. It is very important that the digital detector be modular in design so that new technology can be readily adapted as it becomes available without requiring a complete detector replacement. On the same note, any detector that does not allow component level repairs will prove prohibitively expensive to own.
Finally, let the clinical image quality itself be the most important ddR system selection criteria. Subjective as it may be, there is no specification that better defines successful performance than the satisfaction of your physicians.
OFFSETTING INVESTMENT COSTS
Economic benefits also are realized when the ddR system offers connectivity. For that reason, an enterprise planning to acquire a ddR system should investigate whether the candidate product contains a proven interface to the PACS, RIS, and HIS so that images can be transmitted across networks to radiologists, referring physicians, and system archives immediately, simultaneously, and without manual intervention. Similarly, a good system must be built around architecture that is as open as possible and wholly compliant with DICOM and the Integrating the Healthcare Enterprise project.
The system must accommodate the special requirements of orthopedic radiography; otherwise, cost savings will be lost when film is printed for these procedures. Revenue can be lost, as well, should it turn out that patients must be sent elsewhere because the system does not have (for example) the capability of producing a single, seamless scoliosis image by combining upper and lower spine images, or because the system does not have a weight-bearing stand that allows images to be taken of the feet while the patient is standing.
There is another economic benefit that is gained when a ddR system permits room consolidation. When radiographic procedure rooms are consolidated, the enterprise can dispense with the need to own and maintain the radiographic equipment housed therein. This, however, requires the introduction of a ddR system that is multifunctional: capable of accommodating whatever type of radiography imaging need must be met at any given moment. Such flexibility allows the system to handle higher workloads, which, in turn, serves to offset the higher up-front investment cost of ddR.
In conclusion, gaining the full benefits of ddR-image quality improvement, productivity gain, and cost savings-requires high quality direct-to-digital imaging technology, packaged as an integral part of a well-designed, complete system. It is important that the imaging department planning to acquire such equipment understand the performance impact of all components and avoid viewing a ddR acquisition as an isolated purchase of a digital image capture device.
Rex Harmon is vice president of marketing for Swissray America, Inc, Elmsford, NY.