Computed tomography use in a tertiary care university hospital

Abstract

Purpose: Improvements in computed tomography (CT) technology, with shorter scan times and better image quality, have contributed to an increase in the use of CT in the United States in recent years. This increased use has implications for health policy and radiation risk assessment. The purpose of this study was to evaluate trends in CT use.

Methods: The CT performance records at a university-based, tertiary care, level 1 trauma center hospital were evaluated from 1998 to 2005. The hospital's decision support infrastructure was used to track overall patient visits and stays. From these data sets, the age and sex dependency of CT use rates were evaluated for outpatients, inpatients, and emergency department (ED) patients.

Results: Outpatient use rates averaged over the age groups of 21 to 30 years, 41 to 50 years, and 61 to 70 years were 20, 59, and 87 CT scans per 1,000 outpatient visits, respectively. Inpatient use rates for these same age groups were 88, 148, and 162 CT scans per 1,000 inpatient days, respectively. ED patient use rates for these same age groups were 705, 687, and 394 CT scans per 1,000 ED patient visits, respectively. Male patients outnumbered female patients for both ED and inpatient CT use from the early teens to the mid-40s age range.

Conclusion: The overall CT use increased 27% and 48% from 2000 to 2004 for outpatient and inpatient visits, respectively. CT use in the hospital's high-volume ED increased 131% from 2000 to 2004, which may be partly attributable to the installation of 2 CT scanners near the ED.

Figure 1

The number of CT scans performed at our institution over the timeframe 1998–2005 is illustrated as a function of the age of the patient. Male patients (solid line) are shown separately from female patients (dashed line). Figure 1A shows these data for out-patient CT examinations, and Figure 1B illustrates these data for in-patient CTs. Figure 1C illustrates Emergency Room CT utilization. Figure 1D: The age distributions for both male and female patients (and total) are illustrated. These data were acquired from the hospital’s decision support system. Each curve was smoothed slightly using a boxcar average.

Figure 2

Figure 2A illustrates the total number of CT scans as a function of patient age for both sexes, normalized to the 2004 calendar year, for out patients. Figure 2B illustrates the CT utilization in terms of the number of CT scans per 1,000 visits as a function of age for our out-patient population. In Figure 2C, the number of CT scans performed per 1,000 patient visits is illustrated for both female (broken line) and male (solid line) patients as a function of age.

Figure 3

The in-patient CT statistics are shown in this figure. Figure 3A illustrates the age distribution of CT scans performed in the calendar year 2004. Figure 3B illustrates the number of CT scans per 1,000 patient days as a function of age. The number of CT scans per 1,000 patient days is illustrated in Figure 3C for inpatients, broken down by sex.

Figure 4

The Emergency Room CT utilization is illustrated in this figure. Figure 4A shows CT scans as a function of age for ER patients, while Figure 4B illustrates the CT scans per 1,000 visits as a function of age. Figure 4C shows the number of CT scans per 1,000 visits for Emergency Room patients as a function of age, by sex.

Figure 5

Figure 5A: The raw (unnormalized) CT scan use is shown as a function of year. Figure 5B: The number of out-patient and ER-patient visits are illustrated, along with the number of In-patient patient-days. Figure 5C: The CT utilization rates are illustrated for out-patients, in-patients, and ER-patients. Figure 5D: an expansion of the in-patient and out-patient data shown in Figure 5C. The metric for out-patients and ER-patients is CT scans per 1000 visits, whereas the metric for in-patients is CT scans per 1000 Patient-Days.

Figure 6

The number of hospital visits (including in-, out-, and ER patients) as a function of age, per 1000 residents (of the same age group) in the 4 county catchment area of the medical center (population 1.93 million) is illustrated. The linear fit (dashed line) corresponds to Y = 297.66 + 19.173 X (r² = 0.940).

Figure 7

A histogram showing the frequency distribution of the number of CT scans per patient undergoing CT is shown. The average CT patient received 2.88 CT studies. The ordinate axis is logarithmic, which is necessary to show the large range of data. Fifty percent of patients received 4 CT scans or less, while 80% of patients had 9 scans or less. Five percent of patients had more than 20 CT studies.

Figure 8

The average number of CT studies performed, per patient who had a CT scan, is illustrated as a function of patient age.