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Original Research |
1 Center for Evidence-Based Imaging, Brigham and Women's Hospital, Harvard
Medical School, 75 Francis St., Boston, MA 02115.
2 Division of General Medicine and Primary Care, Brigham and Women's Hospital,
Harvard Medical School, Boston, MA 02115.
3 Department of Radiology, Brigham and Women's Hospital, Harvard Medical School,
Boston, MA 02115.
Received April 22, 2004;
accepted after revision January 5, 2005.
Address correspondence to R. Khorasani.
Abstract
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MATERIALS AND METHODS. We retrospectively reviewed the administrative data about adult inpatients for fiscal years 1993-2002 in a 721-bed tertiary care institution. Examinations were coded according to imaging technique: conventional (plain films and fluoroscopy), sonography, nuclear medicine, CT, or MRI. We assessed workload trends using relative value units (RVUs). Linear regression analysis was used to assess the significance of trends for the number of examinations and RVUs per case-mix-adjusted admission (CMAA).
RESULTS. There was a significant decrease in the total number of examinations per CMAA (p < 0.001). This was due to significant decreases in the use of conventional studies (p < 0.001) and sonograms (p < 0.001), despite significant increases in the number of nuclear medicine (p = 0.046), CT (p < 0.001), and MRI (p < 0.002) examinations per CMAA. The RVUs per CMAA increased significantly (p < 0.01) during the study period.
CONCLUSION. Newer imaging technologies (nuclear medicine, CT, and MRI) are replacing older ones in the evaluation of inpatients. Despite the significant decrease in the total number of imaging examinations per CMAA, we observed a significant increase in RVUs per CMAA during the 10-year study period. Understanding the impact of this change in practice on the quality of care would be useful in justifying the increasing use of these new technologies, and decreasing their inappropriate use should be a priority in efforts that focus on controlling imaging expenditures.
Keywords: health care costs • imaging utilization • inpatient imaging • radiology services • radiology workload
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Several studies about trends in imaging utilization and radiology workload have been published in the past decade [1-7]. All found increases in raw utilization, relative value unit (RVU) rates, or both over time. Most of these studies were conducted over a period of only 3-6 years, and only two studies calculated imaging rates adjusted for changes in disease severity among the patient population over the study interval [1, 2]. Henley et al. [2] found that the increase in inpatient imaging RVUs between 1993 and 1998 at Harborview Medical Center was no longer significant after accounting for changes in case mix and that only the increase in MRI RVUs was significant. Khorasani et al. [1] found that total imaging per patient admission actually declined over a 10-year period, from 1984 through 1993, once an adjustment for the severity of illness was made. In contrast to the results of the study by Henley et al., the results of the study by Khorasani et al. were a significant increase in total inpatient imaging RVUs even after adjustment for case mix because of increases in CT and MRI rates. Khorasani et al. concluded that these newer imaging technologies were replacing conventional studies. This conclusion was supported by Maitino et al. [3], who showed that the rate of utilization of conventional studies among the Medicare population declined significantly nationwide between 1993 and 1999, whereas the use of all other imaging techniques increased.
The objective of the present study was to assess the use of radiology services over the past decade at our institution and to determine whether the decreasing trend in total imaging found in the prior 10-year period [1] has continued or whether the expanding capacity to perform high-tech imaging has resulted in increasing use. We analyzed 10-year trends in the use of diagnostic radiology services among inpatients at our institution, specifically looking at the annual utilization rate of conventional studies (plain films and fluoroscopy), sonography, nuclear medicine, CT, and MRI and adjusting for yearly changes in case mix among the inpatient population. To assess changes in radiology workload and charges during this period, we followed trends in RVUs for these examinations.
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To account for changes in severity of disease among the inpatient population during the study period, the number of admissions per year was adjusted using the Centers for Medicare & Medicaid Services' case-mix index (CMI) based on diagnosis-related groups. The number of case-mix-adjusted admissions (CMAAs) was calculated for each year by multiplying the unadjusted number of admissions by the average CMI of inpatients in that year. Trends in imaging utilization were then assessed in terms of the number of studies per CMAA.
To measure changes in radiologist workload, we also analyzed case-mix-adjusted trends in the RVUs of the Centers for Medicare & Medicaid Services. We retrospectively applied the latest published RVUs for each type of imaging study to the data from all 10 years to have a consistent scale for assessing relative changes throughout the study period. Trends for global, professional, and technical RVUs were then analyzed.
Linear regression analysis was used to determine whether time was a significant predictor for the number of radiology studies and the number of RVUs in each year. A significant p value implies that the observed trend was significant over time.
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Although the annual number of conventional studies (70,000) and sonograms (14,000) remained relatively stable, their utilization per CMAA per year decreased significantly (Figs. 2 and 3) (p < 0.001, from 1.05 to 0.78; p < 0.001, from 0.21 to 0.14, respectively). The rate of use of nuclear medicine studies increased in the latter half of the study period by 37% (p = 0.046), from 0.038 to 0.052 examinations per CMAA per year (Fig. 3). This increase in the rate of utilization represents a twofold increase in the number of nuclear medicine studies, from approximately 2,500 studies in 1993 to roughly 5,000 studies in 2002. The number of CT examinations per CMAA increased from 0.122 to 0.223 (p = 0.001), or by 83%, during the study period (Fig. 4), mostly in the latter half of the decade, while utilization of MRI per CMAA increased from 0.025 to 0.067 (p = 0.002), or by 167%, during the same time period (Fig. 4). These increases in the rate of use of CT and MRI represent an even larger increase in the unadjusted number of studies: from 8,402 CT studies in 1993 to 20,715 in 2002 and from 1,728 MRI studies in 1993 to 6,209 in 2002.
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When compared with figures from 1993, the fraction of global imaging RVUs accounted for by CT, MRI, and nuclear medicine studies has increased by nearly 62%. The increasing demand for these and other new imaging techniques is not surprising in light of the rapidly advancing clinical uses for these techniques [8-10] along with changes in practice patterns, patient complexity, and societal expectations [2]. However, given the high cost of these studies, efforts at controlling expenditures should begin with identifying areas of highest use, followed by implementation of strategies for minimizing the inappropriate use of imaging resources. These strategies will need to be informed by research on the yield of different imaging techniques in specific clinical scenarios and the impact of imaging practices on clinical decision making, therapy, and patient outcomes [11-13]. Recent examples from the literature of such studies include the analysis by Ginsberg et al. [14] of the clinical usefulness of imaging performed after negative CT angiography for pulmonary embolus and the assessment of Rothschild et al. [15] of the yield and utility of abdominal cross-sectional imaging for inpatients with abnormal liver function test results. There are many other examples of such studies in the literature [16-19], and this will be an area of rapid growth in radiology research in coming years as improved databases are created that can support these important endeavors [20-22]. Although continuing research will help close the knowledge gap on what is appropriate testing, experiments using existing guidelines such as those developed by the American College of Radiology may show a reduction in inappropriate testing [23].
With rising health care costs and general concerns regarding overuse of imaging services, the first step in devising cost-containment strategies is to study utilization patterns and to ensure that costly radiologic studies are used in the appropriate clinical scenarios. Although this study did not assess the appropriateness of imaging practices, it did show that total adjusted imaging rates among inpatients were decreasing during the 10-year study period (and over two decades when taken together with a prior study [1]) and that the increasing use of newer techniques has been associated with a marked decline in the use of conventional studies. This trend is reassuring because it debunks the notion that high-tech imaging has merely been added to the diagnostic workup rather than replacing inferior imaging tools. However, our study looked only at overall trends and did not analyze imaging patterns for specific clinical indications. There have been reports that the increased use of newer radiologic techniques in neuroimaging [24] and cardiac imaging [25] has not resulted in decreased reliance on more conventional studies. Further studies will be required in these and other areas identified as sources of high resource utilization to better understand the usage patterns and to develop guidelines for appropriate imaging use [23, 26-28].
The utilization of imaging resources is determined in large part by the practices of referring physicians who request these procedures. Radiologists have the greatest expertise regarding the utility of different imaging techniques for depicting disease, but they are infrequently consulted before the placement of requisitions for imaging tests. Although consultation with radiologists would seem to result in improved imaging choices and decreased inappropriate use, there are little data to support this notion. To the contrary, there is evidence that radiologic consultation does not significantly alter imaging use in the inpatient setting [29, 30]. Furthermore, agreement among radiologists regarding the appropriateness of requests for imaging procedures was shown in one study to be only slightly greater than that expected by chance [31]. Clearly, better data regarding the appropriateness and impact of various imaging strategies are needed to inform guidelines and decision-support tools. Computer-based decision-support systems for helping physicians select radiology procedures may be helpful [32], but will necessarily rely on the results of further research on the impact and outcomes of imaging [11-13]. These efforts will require new methodologies for overcoming barriers particular to outcomes research in imaging [33] and are essential for the practice of evidence-based radiology [34].
Our study has several limitations. First, we studied inpatient data only and therefore cannot comment on outpatient or emergency department imaging utilization and workload, as Henley et al. [2] did at their institution. Second, we did not have access to databases on imaging examinations performed by nonradiologists. This could potentially result in an underestimation of true utilization of imaging resources; however, we believe that most inpatient noncardiac imaging is being performed by radiologists at our institution. Third, our study may not have accurately measured the true utilization rate of imaging studies per hospitalization, because we analyzed data on only those imaging examinations performed between the dates of admission and discharge. Any imaging workup before admission or examinations scheduled after discharge were not captured in this study. This limitation would be expected to primarily affect measurement of the more readily available conventional studies and sonography; however, our hospital is a major referral center and more extensive workup is also frequently done on patients before transfer to our institution. Fourth, we studied data from only one tertiary care hospital, and the results may not be generalizable to other institutions or regions [35]. Fifth, the inclusion of inpatient interventional procedures with the technique used to perform them prevented us from assessing trends in the use of interventional procedures separately. Sixth, we retrospectively applied the most recent RVUs for each imaging CPT (current procedural terminology) code to data from all years in the study. Although this is admittedly suboptimal, it was necessary for establishing a consistent scale with which we could assess changes in the relative amount of work. Finally, the purpose of this study was not to evaluate appropriateness of imaging practices or to determine which factors affect utilization of imaging studies. As discussed, these are important areas of research and must be addressed in future studies.
We conclude that the total number of imaging procedures per CMAA at our institution decreased over the past two decades, whereas the use of nuclear medicine, CT, and MRI studies rose. Use of the more advanced cross-sectional imaging techniques may partly explain the decreasing utilization of sonography [6]. The rising complexity and severity of illness among inpatients, combined with the increasing clinical utility of newer imaging techniques, may explain the progressive substitution of these newer studies for conventional studies. These data may be useful in directing future research efforts and in developing strategies for improving the use of imaging studies.
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) and number of
total imaging studies (
) and conventional studies (
) per
case-mix-adjusted admission, per year. Note decrease in all categories over
time, although decrease in length of stay occurred predominantly during first
half of study period and was not statistically significant over the 10-year
study period.
