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Original Research |
1 Department of Diagnostic Radiology, Inselspital, University of Bern,
Freiburgstrasse 4, Bern, Switzerland.
2 Department of Neuroradiology, Inselspital, University of Bern, Bern,
Switzerland.
Received May 5, 2004;
accepted after revision September 29, 2004.
Address correspondence to J. Gralla.
Abstract
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SUBJECTS AND METHODS. The use of a 16-MDCT scanner for 503 patients in the emergency department of a university clinic was evaluated. For reasons of workflow analysis, seven precise time intervals were recorded during the emergency examinations. A new setting for repositioning multiple-trauma patients after imaging of the head and neck from the head-first position to the feet-first position was introduced.
RESULTS. Six (1.2%) of the 503 patients were excluded because of technical malfunction or patient noncompliance. Image quality in the remaining 497 cases, including CT angiography and CT of multiple-trauma patients, was outstanding. Positioning of the patients took from 3 to 13 min depending on the body region examined, representing 33-67% of the mean room time, which ranged from 8 to 21 min. In multiple-trauma patients, the initial positioning took a mean of 6 min and repositioning took 8 min, representing 19% and 26% of total room time, respectively.
CONCLUSION. The use of a dedicated 16-MDCT scanner in the emergency department resulted in short examination times even for examinations of multiple body regions under emergency conditions. The introduced setting—repositioning of multiple-trauma patients—allowed high image quality to be maintained. The trade-off in multiple-trauma patients was prolonged room time because of patient repositioning.
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The dedicated emergency CT scanner is usually located close to the emergency department, sometimes even in a room prepared specifically for use during a fast intervention. The recent introduction of MDCT with 8 or 16 detector rows has changed CT from a transaxial sectional technique to a 3D imaging technique [4, 5]. Prokop [6] reported that the performance of a 16-MDCT scanner is up to 20 times better than that of a conventional helical CT scanner. This is due to the shorter rotation time, as also reported by other investigators [7-9]. This huge gain in performance reduces scanning time and section collimation and therefore favors MDCT for emergency purposes because it allows high-resolution scans of large areas to be obtained in a short time, fast high-quality reformatting in every orientation, and 3D illustration of the data set [10, 11].
In emergency situations, the patient's room time in the CT suite and the early diagnosis and initiation of treatment have an especially profound influence on the patient's outcome [8, 12]. The correct choice of protocols and optimized workflow in the CT room are therefore of vital importance. Surprisingly, the literature to date contains but scant data on the workflow of MDCT scanners [3, 13].
In this prospective study, we evaluated the reliability and workflow of a dedicated 16-MDCT scanner in the management of patients presenting to the emergency department.
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Data acquisition and planning of examinations and printing of axial images and standardized multiplanar reconstructions were performed by a technologist on a workstation (Volume Navigator, Somaris 5 VA, Siemens Medical Solutions). Two satellite consoles (Volume Wizard and Somaris 5 VA, Siemens Medical Solutions) allowed radiologists immediate access for visualization and further multiplanar and 3D reformatting. Additional reconstructions, necessary to clarify the diagnosis or demanded by the referring clinician (e.g., 2D and 3D reconstructions of complex fractures), were performed and printed by radiologists. The examinations and additional reconstructions were sent via a fast 100-MB/sec local area network-Ethernet to the PACS. All examinations were printed on hard copies including 8-mm axial reconstructions, 2D and 3D reconstructions, and additional images depending on the radiologist. The radiologic evaluation process was based exclusively on image interpretation at the workstation rather than on hard copies or PACS.
An experienced emergency radiologist was present at the examination to confirm the correct choice of protocol, to alter the protocol in response to initial pathologic findings, to administer the contrast agent, and to provide immediate image interpretation for the emergency physician. Because of the study design and concurrent evaluations of emergency patients, a group of experienced emergency radiologists was involved. The emergency examination protocols were standardized for different body regions, and the choice of protocols was up to the radiologist. The scanning protocol for multiple-trauma patients included an examination of the head and neck and scanning of the thorax, abdomen, and pelvis using a multiple bolus application of contrast agent. This allowed evaluation of images in different contrast phases (portal venous and arterial phases) within a single helical scan (Tables 1 and 2).
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In most emergency centers, the examination of multiple-trauma patients is a whole-body scan including the head, cervical spine, and thorax to pelvis. In the conventional setting, the patient is usually examined in the head-first position. This allows fast single-pass scanning but compromises image quality with beam-hardening artifacts due to the position of arms and cables [14].
To maintain the high quality of imaging, we introduced a new setting for this study. Multiple-trauma patients were studied as follows: for examination of the head, skull base, and cervical spine, the patient was positioned head-first in the scanner. For subsequent thoracic and abdominal imaging, the patient was then turned to the feet-first position. This procedure is time-consuming, but it is likely to improve the imaging quality because it reduces to a minimum possible artifacts caused by the positioning of arms, electrodes, and cables in the scan field.
Data Acquisition
For reliable and high-quality acquisition of data, the workflow intervals
were measured by staff members not involved in the emergency treatment. The
data were entered into a database (Excel 2000, Microsoft) using the program's
autoformat function to avoid typing mistakes. The internal computed time was,
because of the expected length of time intervals, entered in full minutes.
This setup allowed precise recording of time intervals during emergency
examinations.
Seven time intervals were recorded. Interval 1, which we referred to as the "positioning interval," was the time from the patient's entrance into the MDCT room until the start of the first measurement (scout). Interval 2, the "acquisition interval," was measured from the start of the first measurement until the radiologist's decision to conclude the examination (including all unenhanced and contrast-enhanced studies). Interval 3, the "repositioning interval," was a subdivision of the acquisition interval in multitrauma cases during which the patient was rotated from the head-first position to the feet-first position. Interval 4, the "reformatting interval," was from the end of the examination until all the data, including reconstructions, were available at the satellite console. Interval 5, the "evaluation interval," was from the end of the fourth interval (the reformatting interval) until the radiologist's final diagnosis. Interval 6, "room time," was from the patient's entrance into the scanner room until completion of the examination—that is, the sum of intervals 1, 2, and 3 in multitrauma patients. Interval 7, "diagnostic time," was from the patient's entrance into the scanner room to the final diagnosis (i.e., the sum of intervals 1-5). By that time, the radiologist had evaluated all images and had reported all diagnoses, including secondary findings, and was therefore no longer occupied by that case. Of course, initial findings such as life-threatening injuries were immediately reported to the referring clinician sometimes even before the end of the CT examination to facilitate optimal patient care (Fig. 1).
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Patients
Five hundred three patients from the surgical and medical emergency
admissions were studied. Patients from the clinical wards experiencing
emergency situations were not included in this study. The patients were
recorded consecutively within a period of 6 weeks.
The patient population and their age distribution, ranging from 1.8 to 97.3 years (SD, 22.3 years), were representative of the spectrum of patients in the emergency unit. Thirty-nine of the patients had multiple traumas requiring MDCT of more than two body regions (e.g., head and thorax-abdomen). These patients were admitted in critical condition and underwent CT after initial stabilization of circulation. Scanning was not performed within the first 6 min after admission, corresponding to phases alpha and beta of the advanced trauma life-support concept [8, 15]. The study design (Fig. 2 and Table 3) is in accord with the guidelines of the institute's ethics committee and was performed according to the revised Declaration of Helsinki of 1998 [16].
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The low compliance of two restless patients (0.4%) did not allow CT, and anesthesiologic problems in another patient (0.2%) forced interruption of the examination. A total of six patients (1.2%) therefore were excluded from the study, leaving 497 emergency patients who completed the study. In three (0.6%) of these 497 patients, a CT malfunction caused a delay in the examination; in these cases, scans from the second examination were evaluated. Scanning in four patients (0.8%) with minor injuries was delayed to give priority to a multiple-trauma patient. In another three cases (0.6%), immediate intervention in the scanner room led to a prolongation of room time.
Time Evaluation and Reformatting
In 350 (70.4%) of the 497 cases, only one body region was scanned. The mean
room times for these most frequent types of CT examination were 8 min for
imaging the neck and cervical spine and 21 min for CT angiography. CT
angiography was performed in 56 patients (11.3%); in 36 of these 56 patients,
CT angiography was performed to search for pulmonary embolism. The
bolus-tracking protocol of the scanner was successful in all cases.
The mean number of images for single-region examinations ranged from 161 for head imaging to 674 for the extremities. Table 4 summarizes the results for the time intervals for single-region CT.
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Multiplanar reformatting was routinely performed after examinations of the spine, neck, extremities, and vessels. Three-dimensional reconstructions were often performed in bone imaging (72%) and CT angiography (30%). The positioning interval for these single-region examinations, including preparation of the examination (interval 1), accounted for 37% of the room time for spinal imaging and for up to 67% for CT angiography (Fig. 3).
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The mean positioning time for multiple-trauma patients was 6 min, representing 19% of the room time. Patients were turned after head and spine imaging to the feet-first position to reduce artifacts. This repositioning required a mean of 8 min, representing 26% of the room time. Because of the fast scanning time and low collimation, especially for trauma protocols, the number of images ranged from a minimum of 88 in head imaging to 4,637 in multiple-trauma patients. However, the reformatting interval, including calculation and reconstruction of thin sections and transfer to the satellite console, was low (mean, 3-7 min) (Table 5).
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Technical Aspects
Even scanning of large body segments—as is necessary, for example, in
CT angiography of the chest and abdomen—was possible under emergency
conditions without major artifacts. Moreover, the short scanning time allowed
older patients or patients in serious condition to hold their breath during
the examination and thus minimized artifacts. The 56 CT angiography
examinations that we performed in a relatively short period may suggest that
the high temporal resolution and nearly isotropic imaging expanded the
indications for CT and made it applicable to emergency examinations
[3,
7] (Figs.
4A, and
4B).
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The presence of two satellite consoles providing access to the images is useful in emergency imaging because it permits the presentation of previous patients to the treating physicians without disturbing current examinations. The ability to perform surface-rendered 3D reformatting in a reasonable time allows often superior imaging of fractures and dislocations (Fig. 5).
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The relatively long room time for CT angiography may be caused by two factors: First, the often poor clinical condition of patients demands multiple methods of patient monitoring. This may lead to a more complicated and time-consuming positioning and explains the findings of a prolonged positioning interval of 13 min, compared with 6 min for a regular thoracic scan (Table 4). Second, the triggering of the bolus needs additional preparations by technicians and also may explain the prolonged acquisition interval compared with a regular thoracic scan (Table 4).
For all scan regions, a mean interval of 4-13 min was needed for positioning the patient and preparing for the scan (Table 4). This represents a mean of 32% of the room time, a finding that accords with the 7.34 min reported in the only other data available on the time distribution in routine MDCT examinations [13].
Multiple-trauma patients—Emergency patients with multiple traumas generally arrived in critical condition and were difficult to transport. Surprisingly, the mean positioning interval for these patients was equal to the total CT examination time for emergency patients and was significantly shorter than that for patients undergoing CT angiography. This is probably due to the transportation technique used by our center: All multiple-trauma patients remain in a vacuum cushion until the end of the CT examination and are therefore relatively easy to move to the scanner table.
The setting for multiple-trauma patients described here was designed to maximize image quality. The patients were therefore rotated to the feet-first position after head and cervical spine imaging. This study is, to our knowledge, the first one to report experiences using this setting for multiple-trauma patients. The main advantage is to scan a body region in an optimal position and exclude artifacts from arms and cables. Furthermore, this protocol allows the anesthesiologist to use regular equipment without extensions for tubes and cables.
In all examinations of multiple-trauma patients, the image quality was sufficient with low artifacts, especially on the thoracic scans. However, the present study does not directly compare the image quality between the conventional setting with a rigid head-first position and the presented setting with rotating the patient. It remains to further investigations to quantify the effect of rotating the patient on artifact reduction.
The time evaluation shows that turning the multiple-trauma patient caused a mean delay of 8 min (interval 3, the repositioning interval) or 26% of room time, which is disputable in multiple-trauma patients.
The only previous study on examination times for multiple-trauma patients in an emergency CT unit reports a room time of 16 min using a 4-MDCT scanner and head-first single-pass positioning of the patient for the total examination [17]. The mean room time in our study was significantly longer (32 min). This difference is only partially due to repositioning the patient. Another important factor is that in every case the radiologist in our study had to decide whether imaging of the head and cervical spine was sufficient and the patient could be turned to the feet-first position. Therefore, part of the evaluation was already performed during the repositioning interval, which extended room time. This also explains the relatively short evaluation interval of 13 min for an average of 2,588 images (3.3 images/sec) in multiple-trauma patients compared with 8 min for an average of 664 images (1.4 images/sec) in the entire emergency group.
The room time is an especially critical factor for multiple-trauma patients because no additional diagnostic procedure is performed and gaining access to the patient is complicated. On the other hand, the fast-scanning technique time of approximately 90 sec for multiple-trauma patients comprised a negligible part of the total room time. Further optimization of patient transport and positioning in multiple-trauma cases may contribute to a reduction of the room time in the future without compromising image quality by beam-hardening artifacts due to the position of arms and cables.
It is up to further studies to examine the time gain and effects on quality of such changes (Fig. 6).
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In conclusion, the new generation of 16-MDCT scanners are suited for application as dedicated emergency scanners and their low rate of technical malfunction favors them as a reliable imaging technique. Their high level of performance reduces movement artifacts and allows fast scanning with high spatial resolution under emergency conditions.
The protocol described here for emergency scanning of multiple-trauma patients helped to avoid beam-hardening artifacts but prolonged room time because of the repositioning procedure. Based on the present findings, further advances in emergency CT should focus on the development of transportation and positioning equipment because scanner performance is already of sufficient quality for emergency use.
Acknowledgments
We are grateful to G. von Allmen, Department of Diagnostic Radiology,
University of Berne, for technical support.
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