Applied Radiology

Mr. DeMaster is Radiology Manager at Mount Auburn Hospital, Cambridge, MA.

As digital technology brings increased efficiencies to diagnostic imaging, pro-viders are faced with significant investment decisions. Both digital radiography (DR) and computed radiography (CR) produce digital radiographs that can be transmitted, viewed, and stored more efficiently than traditional screen-film images. When considering a new system or upgrade, the ability to integrate the images into a Picture Archiving and Communication System (PACS) or other hospital network makes these technologies appealing.

While DR and CR both offer digital formats, it is important to know how they compare with each other in terms of equipment cost, productivity, and patient care. The greater the efficiency in moving patients through the radiology room, the sooner a return on investment for a digital system is realized. Due to the recent introduction of DR technology, however, productivity reports comparing DR and CR are scarce. This article describes results from a recent time-motion study at Mount Auburn Hospital that may assist healthcare providers making these significant investment decisions.

Mount Auburn time-motion study

Mount Auburn Hospital (Cambridge, MA) is a community and teaching hospital affiliated with Harvard Medical School. The radiology department has a staff of 20 radiologists and residents and 50 technologists. Approximately 90,000 exams are performed each year, half of which are conducted in general radiographic rooms or on portable devices. Mount Auburn recently underwent a major renovation, including the replacement of conventional radiographic rooms with digital and computed radiography rooms.

Two conventional radiographic rooms and one chest room were replaced with three new rooms. One ambulatory care room received a GE Monitrol table (GE Medical Systems, Fairfield, CT) modified with a DirectRay selenium digital detector (Hologic, Inc., Bedford, MA). Based on an evaluation of different DR technologies, the selenium flat-panel detector was chosen for its high image resolution and commercial availability. Two other rooms in the ER were equipped with CR digital-ready systems (Philips Medical Systems, Shelton, CT) sharing one CR reader (Agfa, Greenville, SC). With both DR and CR systems available, Mount Auburn conducted a time-motion study to measure productivity differences between these two systems.

The time-motion study evaluated defined intervals for DR and CR exams, from the time the patient entered the exam room to the time the image was available for interpretation. Steps included entering patient data, cassette handling with the CR system, positioning, exposure, image review, CR cassette reading, and quality control (QC). While Mount Auburn did not have a full PACS, they did utilize a network of digital display and review stations that permitted soft-copy reading and remote viewing of radiographic images. Data were collected from 75 consecutive patients on each system. An independent observer (a licensed radiographer) timed each step.

Several different types of examinations were performed on each system, the most common being a two-view chest exam. The time for each step and total examination times were averaged for the same number of views. In this calculation, data from the first two views of a three-, four-, and five-view study were included in the average time of a two-view exam. The same pattern was followed for other multiple-view exam calculations.

DR versus CR: Productivity results

A direct comparison of data from DR and CR systems is shown in Table 1. Overall, DR exams were three times faster than CR exams. In 1 hour, 15 exams could be performed on the DR system, while only five could be completed on the CR system. Productivity gains were consistent across two-, three-, and four-view exams. There were no five-view exams on the CR system available for this comparison.

Other comparisons included average time handling the system, independent of positioning and exposure. This isolated the steps unique to each system and eliminated the intervals that would be directly influenced by patient variability. For example, the longer positioning time for CR patients in a two-view chest exam (Table 2) probably reflects differences in the ER and ambulatory patient populations. With DR, system handling time was only 50 seconds, while it took a total of 8 minutes for CR. Figure 1 shows the individual data points for this analysis to illustrate the low variability in the data for DR and CR. A comparison of time from last exposure to having the image available for interpretation showed a lag time of 16 seconds for DR but 6 minutes for CR. These large differences in productivity are due mainly to the time required to process CR cassettes. For multiple-view exams, all cassettes must be processed before QC. On the other hand, DR does not require cassettes. Within seconds after exposure, DR images are available so the technologist can quickly preview for quality control before completion of the exam.

Time intervals also were compared for each exam step for the same type of exam. A total of 26 patients had a two-view chest exam (PA and lateral), the most common exam type in this study. Table 2 shows the average time required to complete each step of the exam for DR and CR. This comparison concluded that DR was four times faster than CR for the total time to complete a two-view chest exam. Note that the last two steps of the CR exam, reading the cassettes and QC, accounted for 64% of the total exam time. Figure 2 illustrates these major differences, mainly due to steps required with handling CR cassettes.

Implications for radiology departments

This study shows that DR offers major productivity gains over CR, independent of a PACS system, in a typical clinical setting. The cost and time implementing a PACS need not stand in the way of converting radiography rooms to digital, since productivity benefits can be realized within any existing IT structure. This is not to say that there are not significant advantages of having a PACS, including more efficient viewing, storage, retrieval, and transmission of images. However, these benefits are realized after the exam, once the image is available for interpretation.

With better throughput using DR (15 exams per hour with DR versus 5 with CR), fewer radiographic rooms are necessary to process the same number of patients. This translates into savings in terms of the area required for new building or renovation projects, or reducing the number of existing radiographic rooms to free space for other needs. For radiology departments experiencing growth in patient volume, the increased efficiency of DR rooms allows for more patient volume with the same amount of square footage.

Increased productivity also allows technologists to use time more efficiently. DR allows radiology departments to handle more patients with the same number of staff. This is especially important now, with the shortage of technologists and an increasing patient volume. Time gained with DR can allow for more time with the patient (e.g., taking a history or answering questions). During a CR exam, the technologist must leave the room to process cassettes, and the patient must wait for the technologist to return after reviewing the images. This is not necessary in a DR room. DR images are available immediately after exposure, so the technologist is always in the room during the exam. As a result, the patient experiences greater comfort in addition to a shorter exam time. Physicians also benefit from decreased turnaround time to receive images for interpretation. The benefits of greater patient interaction with healthcare pro-viders and decreased time waiting for results are particularly important in this age of consumerism and competition between healthcare systems. These outcomes benefit not only the patient, but also the work environment of the staff.

The productivity advantage seen for DR can lead to cost savings through more efficient use of space and the ability to accommodate volume growth with existing staff. There is also an operating cost advantage for DR. The CR plates and cassettes have a finite life and a relatively high replacement cost. In addition, the life of a typical radiographic room is considerably longer than the life of a typical CR reader. Since one multi-plate reader usually supports more than one radiographic room, there is a potential for a single point of failure to impact several rooms, unless a backup reader is purchased. On the other hand, in certain low-volume applications these issues become less important. Also, current DR technology cannot accommodate portable exams, so both DR and CR will have a place in the digital radiology department.

The results of this study can help radiology professionals take into account the space, full-time equivalent, and equipment costs associated with DR and CR systems. A cost comparison model based on this study is being developed for radiologists and administrators by Hologic, Inc. to evaluate the economic impact of each technology, as defined by the needs of the individual institution. Such models can be very useful when considering such a long-term investment.

The future of radiographic technologies

While productivity is an important investment consideration, image quality is another critical factor in selecting a new technology. Both DR and CR offer advantages over traditional screen-film systems. Images can be corrected for over- or underexposure, de-creasing the need for repeated exposures. Both technologies also provide a digital image format for better processing, communication, and storage compared with conventional film radiography. However there are significant differences between DR and CR technology and among different DR technologies, especially in the way that the x-ray image is captured.

The DR system in this study employs direct-to-digital technology, using an amorphous selenium flat-panel detector. This detector directly converts x-rays to digital images, with no intermediate steps to compromise image quality. On the other hand, screen-film, CR, and some DR systems (charge-coupled devices and cesium iodide detectors) use indirect conversion. These systems rely on an intermediate step to convert x-ray energy to light, which scatters and blurs the image. A more detailed discussion of these technologies can be found elsewhere. ¹

Selenium detectors have been used to upgrade conventional radiography systems (as in this study) or included as part of integrated digital radiography systems. Mount Auburn hospital has recently replaced its retrofit DR unit with the EPEX radiography system (Hologic, Inc., Bedford, MA), which includes the DirectRay selenium detector and operator console. The console interfaces with the detector and the x-ray exposure equipment, and it allows for digital connectivity to receive patient information and transmit results. Mount Auburn has planned another time-motion study comparing this system with CR.

Conclusion

Overall, DR systems improve productivity of radiographic exams three times over CR systems. For a typical two-view chest exam, the productivity gain over CR is 4:1. The gains in productivity are due mainly to the absence of cassettes with DR systems. CR cassette handling, processing, and quality control steps increase exam time substantially. The efficiency gains realized with DR systems translate into cost savings in terms of room space requirements, technician time, and patient volume. As healthcare institutions continue to experience increased pressure to contain costs while providing quality care, this study shows that DR systems are positioned to meet these demands. AR

Acknowledgment

The author thanks Ms. Kelly Reith for assistance in the preparation of this manuscript.