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1 All authors: Department of Radiology, Massachusetts General Hospital and Harvard Medical School, 32 Fruit St., Boston, MA 02114.
Received February 26, 2001;
accepted after revision March 28, 2001.
Address correspondence to S. Saini.
Abstract
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MATERIALS AND METHODS. We compared the productivity of two diagnostic CT scanners during the periods January 1 to August 31, 1999 (when both scanners had single-slice CT capability) and January 1 to August 31, 2000 (when one of these scanners was replaced with a multislice CT scanner). The scanners were used primarily for outpatients during the day shift and for inpatients during the evening shift; the demand for CT services was stable. For this analysis, we queried the hospital's radiology information system and identified the number of CT examinations performed during the two analysis periods. We also determined the examination mix, including proportion of enhanced and unenhanced examinations and the anatomic region examined, to ensure comparable patient populations. Statistical analysis was performed.
RESULTS. The number of CT studies performed on the two scanners increased by 1772 (13.1%) from 13,548 (before multislice CT) to 15,320 (when multislice CT was available). The number of examinations enhanced with contrast media increased from 52% to 65%. Between 9:00 A.M. and 5:00 P.M., the number of CT examinations was similar on the single-slice scanners in the two periods (p > 0.05). However, in the period when multislice CT was available, the number of studies performed on the multislice scanner (5919) was 51.9% higher than those performed using the single-slice scanner (3896) (p < 0.0006).
CONCLUSION. Using a multislice CT scanner leads to an increase in CT productivity, even though multislice studies are performed using more complicated protocols than are used on a single-slice CT scanner.
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We hypothesized that these and other technical advances associated with multislice CT could significantly increase patient throughput. In this article, we report our analysis of the effect of multislice CT on scanner productivity.
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At our institution, the operational philosophy has been to empower technologists with all aspects of image acquisition. During both periods studied, two technologists were typically assigned to each diagnostic CT scanner. Their responsibilities included placing of IV lines for administration of contrast agents, monitoring contrast-material injections, and performing initial quality checks of images before removing the patient from the CT scanner, pending final image review by the radiologist. This process allowed technologists to minimize delay between successive patients. Examination protocol was decided by the radiologists and specified at the beginning of each workday.
Our productivity analysis was performed in the outpatient CT suite. Before October 1999, both the scanners had single-slice CT helical capability (Hi-Speed Advantage CTi; General Electric Medical Systems, Milwaukee, WI). Each of the outpatient CT scanners had a schedule template with which patients were given appointments in 30-min slots. However, patients were received at a common location, where a triage technologist managed patient flow with the aim of minimizing patient delays. With this single-queque procedure, an outpatient would be scanned on whichever of the two outpatient scanners was free, not necessarily the one on which the study was scheduled.
A multislice CT scanner (LightSpeed QX/i; General Electric Medical Systems) replaced one of the outpatient scanners in October 1999. During the first 3 months after its installation, the CT technologists were trained in the use of the multislice scanner, and the radiologists modified scanning protocols for multislice CT. For the most part, the changes involved faster injection rates and routine use of breath-hold imaging for all studies, including multiorgan chest—abdomen—pelvis examinations. For routine studies, slice thickness and tube current settings were similar in both single-slice and multislice CT protocols. However, for multislice CT, the detector configuration was selected so that, if necessary, thinner slices could be reconstructed retrospectively. A complete review of scanning protocols is beyond the scope of this article.
To take advantage of the increased capabilities of multislice CT, a third, limited, scheduling template was added to create 16 new patient appointments each weekday. The examination time per appointment was maintained at 30 min. As before, however, the outpatients underwent scanning on either of the two outpatient scanners without regard to which of the three schedules was used to make the appointment. Because multislice CT has enhanced imaging capability, complex contrast-enhanced studies such as dual-phase imaging or thin-slice CT angiographic examinations were performed using the multislice CT scanner.
Our productivity analysis was performed for January 1—August 31, 1999 (using two single-slice CT scanners) and January 1—August 31, 2000 (one single-slice and one multislice CT scanner in use). The hospital's radiology information system (IDXRad; IDX Systems, Burlington, VT) was queried to provide a count of all CT examinations by date, time, and examination type that were performed during the period of analysis. The data reported are for examinations and not patients; for example, CT of the abdomen and CT of the pelvis on a single patient were counted as two separate examinations. Table 1 shows the study mix with regard to type of examinations performed on each scanner and percentage of contrast-enhanced studies for each outpatient scanner during both periods. The proportion of abdominal, chest, and head studies was similar during the two periods, which indicates a comparable patient mix. However, proportionally more contrast-enhanced examinations were performed after the multislice CT scanner was added, which suggests that a more complex examination protocol was used in that period. The demand for outpatient CT services as monitored by the outpatient appointment delay time for both periods was constant and ranged from 5 to 7 days. Statistical analysis was performed using the paired Student's t test.
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Our experience shows that despite modification of CT protocols to take advantage of the greater imaging capabilities of multislice scanners, one of the important benefits of multislice CT technology is greatly increased scanner productivity. Although the overall CT productivity in our outpatient suite increased by only 13%, during the busiest time of the day when the scanners operated at near peak capacity, there was nearly 50% higher productivity on the multislice scanner compared with the single-slice scanner. This finding is particularly noteworthy because the scanning protocols were more complex on the multislice scanner, as can be seen by the greater number of contrast-enhanced examinations that were performed (Table 1). However, during the less busy evening hours, with potentially excess CT capacity, we noticed a shift of work from the single-slice to the multislice scanner, thereby lowering the overall rise in CT productivity. This shift is entirely logical, because examinations are quicker on multislice CT scanners than on single-slice scanners.
Our findings confirm earlier reports that newer CT scanners can decrease examination times [8]. However, increased speed alone cannot account for the striking increase in productivity that we found. One example is the comparison of differences in data acquisition time between a single-slice CT and a multislice CT abdomen—pelvis protocol. On the single-slice scanner, this examination was typically done using two breath-holds with a 1-2 min delay between them to allow for tube cooling, whereas on a multislice scanner the examination was performed on a single breath-hold. Using only one breath-hold decreases examination time by a minute or so, but we think that the main reason for the observed increase in scanner productivity with multislice CT is that delays between patients due to tube heating are largely eliminated. Of the scanners we studied, the X-ray tube in the multislice CT scanner had a higher anode heat storage capacity than the one in the single-slice CT scanner. Therefore, technologists were able to initiate a subsequent examination as soon as the room could be turned over. This observation has also been reported by McCollough and Zink [9].
The main advantage of achieving higher productivity, of course, is to lower the overall cost of a CT examination. However, determining the actual cost requires analysis of the higher costs of new technologies and increased variable operating expenses (e.g., the cost of contrast material, which is used more often with the newer technology). We did not study the impact of higher productivity on CT costs because our CT operation is still evolving toward complete adoption of multislice CT technology.
An important limitation of our analysis is our assumption that any net increase in productivity is due only to adoption of new multislice CT technology. Although our resource allocation was similar in the premultislice CT and the postmultislice CT periods, it is possible that environmental factors may have influenced the results. For example, because of the normal turnover in CT personnel and the on-going training of technologists, we cannot claim that the capabilities of our workforce in the two periods were identical. Certainly, the impact of scheduling a greater number of outpatients through creation of the third out-patients through creation of the third outpatient schedule may have contributed to the observed higher productivity. However, we do not think that the volume of examinations would have been higher if we had scheduled more patients in the premultislice CT period, because peak productivity in the single-slice CT scanners in the two study periods was essentially identical. Furthermore, when annualized, the productivity for the single-slice CT scanners was about twice that of the national norm, indicating that the observed change in productivity could not be explained by underutilization in the first period. Therefore, no significant environmental influence appears to exist, and our conclusion that new technology is the principal explanation for the observed increase in productivity appears to be valid. If not, the single-slice CT scanner should have shown higher productivity in the second period than in the first.
Finally, increases in productivity can be associated with a decrease in the quality of the patient's experience, perhaps because of excessive patient delays when the examinations are not performed at the appointed time, or a feeling of being rushed through the study. Our goal now is to incorporate these quality benchmarks to ensure that examination volume, examination quality, unit study costs, and patient experience are all optimized.
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represents multislice CT. Graphs show examination volume by hour of day in two
outpatient scanners from January 1 to August 31, 1999 (A) and January 1
to August 31, 2000 (B).