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Published online before print May 20, 2004, 10.1148/radiol.2321031115
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(Radiology 2004;232:164-172.)
© RSNA, 2004

Gastrointestinal Imaging

Acute Appendicitis: Comparison of Low-Dose and Standard-Dose Unenhanced Multi–Detector Row CT1

Caroline Keyzer, MD, Denis Tack, MD, Viviane de Maertelaer, PhD, Pascale Bohy, MD, Pierre Alain Gevenois, MD, PhD and Daniel Van Gansbeke, MD

1 From the Department of Radiology, Hôpital Erasme, Université Libre de Bruxelles, Route de Lennik 808, B-1070 Brussels, Belgium (C.K., P.B., P.A.G., D.V.G.); Department of Radiology, Centre Hospitalier Universitaire de Charleroi, Belgium (D.T.); and Statistical Unit, Institut de Recherche Interdisciplinaire en Biologie Humaine et Moléculaire, Université Libre de Bruxelles, Belgium (V.d.M.). Received July 16, 2003; revision requested September 29; final revision received December 29; accepted January 16, 2004. Address correspondence to C.K.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
PURPOSE: To prospectively compare low- and standard-dose unenhanced multi–detector row computed tomography (CT) in patients suspected of having acute appendicitis.

MATERIALS AND METHODS: Ninety-five consecutive patients underwent two unenhanced multi–detector row CT examinations with 4 x 2.5-mm collimation, 120 kVp, and 30 and 100 effective mAs. Two radiologists independently read the images obtained at each dose during two sessions. Readers recorded visualization of the appendix and presence of gas in its lumen, appendicolith, periappendiceal fat stranding, cecal wall thickening, and abscess or phlegmon to measure the diameter of the appendix and to propose diagnosis (appendicitis or alternative). Data were compared according to dose and reader, with definite diagnosis established on basis of surgical findings (n = 37) or clinical follow-up. {chi}2 tests and logistic regression were used. Measurement agreements were assessed with Cohen {kappa} statistics.

RESULTS: Twenty-nine patients had a definite diagnosis of appendicitis. No difference was observed between the frequency of visualization of the appendix (P = .874) neither in its mean diameter (P = .101–.696, according to readers and sessions) nor in the readers’ overall diagnosis (P = .788) at each dose. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of each sign were not different between doses. Fat stranding, appendicolith, and diameter were the most predictive signs, regardless of dose, yielding approximately 90% of correct diagnoses. The ability to propose a correct alternative diagnosis was not influenced by the dose.

CONCLUSION: Low-dose unenhanced multi–detector row CT has similar diagnostic performance as standard-dose unenhanced multi–detector row CT for the diagnosis of acute appendicitis.

© RSNA, 2004

Index terms: Appendicitis, 751.291 • Appendix, CT, 751.12111, 751.12117 • Computed tomography (CT), multi–detector row • Computed tomography (CT), radiation exposure


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Acute appendicitis is the most common cause of acute abdominal pain that requires surgical intervention in the Western world (1). However, the clinical diagnosis of appendicitis is accurate in only 80% of the cases (1–3). To increase diagnostic accuracy, computed tomography (CT) has been used more frequently during the past decade because it is reproducible, sensitive, specific, easy to perform, and causes little discomfort to the patient (1,2). Even without oral or intravenous administration of contrast material, diagnostic performances of greater than 95% have been reported (4,5). CT, however, also delivers ionizing radiation to patients. Since many individuals suspected of having acute appendicitis are young, with a mean age of 30 years (2), radiation dose is of particular concern. Reduction of the radiation dose has already been successfully used in conditions characterized by intrinsic high contrast between structures, that is, in pulmonary nodule screening, in diagnosis of nephrolithiasis and ureterolithiasis, and with CT colonography (6–11). It has not yet been used in conditions with low contrast between structures, such as acute appendicitis.

The aim of this study, therefore, was to prospectively compare low- and standard-dose unenhanced multi–detector row CT in patients suspected of having acute appendicitis.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
Consecutive patients seen in the emergency room of Academic Erasme Hospital between March and December 2002 were asked to participate in this prospective study. The inclusion criteria were age of older than 15 years and acute right lower quadrant abdominal pain for which CT examination was requested by the emergency room physician to evaluate for acute appendicitis. Exclusion criteria were prior appendectomy or pregnancy. The study group consisted of 95 (58 female and 37 male) patients aged 16–74 years (mean, 37 years). The mean age of female patients was 38 years (range, 16–74 years) and that of male patients was 36 years (range, 17–73 years). Body mass index (BMI) was calculated from the data available in the medical chart (12). The institutional review board approved our research protocol, and written informed consent was obtained from all patients; for those who were adolescents, consent was obtained from the parents.

CT Examinations
CT images were obtained by using a commercially available four–detector row scanner (Somatom Plus Volume Zoom; Siemens Medical Systems, Forchheim, Germany). Patients were examined in the supine position. A frontal 52-cm scout view was first obtained at 120 kVp and 50 mA, followed by acquisition of two helical scans at the top of the liver to the symphysis pubis with a 4 x 2.5-mm collimation, 120 kVp, and 30 and 100 effective mAs. The effective milliampere second, as defined by Mahesh et al (13), corresponds to milliampere second divided by the pitch, where pitch is defined by Silverman et al (14) as the ratio between the table feed per rotation and the x-ray beam width. Table feed was 15 mm per 0.5 second of scanner rotation (30 mm/sec), resulting in a pitch of 1.5:1.0. From the raw data of each acquisition, 3-mm-thick transverse sections were reconstructed with 1.5-mm increments. No patient received oral, rectal, or intravenous contrast material.

If the CT diagnosis remained uncertain, the radiologist conducting the examination was authorized to acquire additional scans with intravenous injection of iodinated contrast material (Ultravist 370; Schering, Berlin, Germany). These scans were obtained in 11 patients. Results of the CT examination were immediately interpreted and reported to the referring clinician, who integrated the results into the final case management decision. This interpretation was not taken into consideration for the present study.

Image Analysis
Reconstructed images were stored on compact disks and read, for the purpose of the present study, on a clinical workstation with three-dimensional functionalities (Wizard; Siemens Medical Systems). These images were read independently by a board-certified radiologist (D.T.) with 15 years experience in reading CT scans of the abdomen (reader A) and a 3-year radiology resident (P.B.) who had no specific coaching or training prior to the study (reader B). The readers were aware that the patient had presented with acute right lower quadrant pain but they were blinded to the interpretation by the radiologist who had conducted the examination, the results obtained from any other diagnostic technique (eg, laboratory results), and the definite diagnosis. They were not blinded to the radiation dose.

Reconstructions obtained from low-dose scans were read prior to those obtained from standard-dose scans in two independent reading sessions, with a minimum 2-week interval between the two sessions, and were presented to readers in the same patient order. One month later, reconstructions from low- and standard-dose scans were read again, also with a 2-week interval between each reading session. At each session, readers were asked to record whether the appendix was visible, to measure its largest outer transverse diameter (if seen) by using electronic calipers, and to code the following signs as present or absent: gas in the appendiceal lumen, appendicolith, periappendiceal fat stranding, cecal wall thickening, and abscess or phlegmon in the right iliac fossa. The presence of gas was considered to be a possible negative criterion for appendicitis, while the other signs were considered to be positive criteria suggestive of appendicitis. After separately coding each sign, readers were asked to propose an overall diagnosis of appendicitis or an alternative disease that could explain the acute right lower quadrant pain.

Effective Dose Calculations
The effective dose was computer simulated with commercially available software (CT-Expo; G. Stamm, Medizinische Hochschule, Hanover, Germany) installed on a personal computer. This software does not require any phantom measurements. CT acquisition parameters, patient sex, and the scanned region as represented on a graph of the Monte Carlo phantom model were entered into the program. The effective dose was then computed according to the Monte Carlo simulations for anthropomorphic phantoms, as recommended by Nagel (15); and conversion factors, as reported by Zankl et al (16,17). The calculated effective doses were expressed according to the International Commission on Radiological Protection recommendations (IRCP report no. 60). We also used this software to calculate the effective dose delivered in previously published studies in which CT acquisition parameters were available (4,5,18–20).

Definite Diagnosis
The definite diagnosis was based on surgical findings (n = 37) or findings from other diagnostic techniques (n = 58) consisting of ultrasonography (US), contrast material–enhanced standard-dose CT, barium enema, vaginal smear, colonoscopy with biopsy, and laboratory analysis. For all patients who did not undergo surgery, information from the clinical follow-up was obtained by reviewing the medical charts and telephone calls 1 month after the acute episode.

Statistical Analysis
Quantitative variables are expressed as mean ± standard error of the mean. Intrareader and interreader agreements in the assessment of the coded signs were investigated by calculating Cohen {kappa} statistics with their asymptotic standard error (21). Interreader agreements were assessed for both reading sessions. The null hypothesis of no agreement between the two observers was tested, and the associated P values were calculated (22). All {kappa} values were interpreted as proposed in the literature (23). A {kappa} value lower than 0.20 indicated poor agreement; 0.21–0.40, fair agreement; 0.41–0.60, moderate agreement; 0.61–0.80, good agreement; and 0.81–1.00, excellent agreement.

We created receiver operating characteristic (ROC) curves and determined the threshold of appendiceal diameter that led to the optimal values of probabilities in correctly predicting the presence or absence of appendicitis. This optimal threshold was defined as the intersection of the ROC curve with the bisecting line at which sensitivity equated specificity (24).

To evaluate the performance of multi–detector row CT at each radiation dose, the number of misclassifications compared with the number of definite diagnoses of appendicitis was summed according to readers and reading sessions for both low and standard radiation doses. The {chi}2 test was used to compare the number of misclassifications with the number of reading sessions according to doses. A similar procedure was used to compare the performance of readers.

At each dose and for each reader, stepwise logistic regression was used to predict the probability of correctly diagnosing appendicitis as a function of the different CT signs. The effect of sex, age, and BMI on the probability of appendix visualization was investigated with logistic regression for each dose and for each reader.

Statistical significance was defined as a P value of less than .05. Statistical software (SPSS for Windows, release 11.0; SPSS, Chicago, Ill) was used.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Definite Diagnosis
Twenty-nine (13 female and 16 male) of the 95 patients were classified as definitely having acute appendicitis. There were more male (16 of 37) than female (13 of 58) patients (P = .032). The diagnosis was confirmed with microscopic examination of the surgical specimens in all patients. Thirty-five (26 female and nine male) patients had an alternative diagnosis (Table 1). Thirty-one (19 female and 12 male) patients were considered as having nonspecific abdominal pain because their symptoms were not elucidated with any diagnostic technique and had resolved without any specific treatment. Consequently, 66 (45 female and 21 male) patients were thus classified as definitely not having acute appendicitis.


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  		TABLE 1. Frequency of Alternative Diagnosis from Each Reader during Each Reading Session at Standard-Dose and Low-Dose Multi-Detector Row CT

 
Visualization and Diameter of the Appendix
The number of patients in whom the appendix was visualized is listed in Tables 2 and 3 according to each reader, each interpretation session, and each radiation dose. No statistically significant difference was observed between readers (P = .425) or between radiation doses (P = .874). More important, the appendix was visualized in all 29 patients with a definite appendicitis, regardless of the reader, the interpretation session, or the radiation dose.


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  		TABLE 2. Frequency of Signs and Overall Diagnosis in 29 Patients with a Definite Diagnosis of Appendicitis

 

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  		TABLE 3. Frequency of Signs and Overall Diagnosis in 66 Patients with a Definite Diagnosis of No Appendicitis

 
Measurements of the appendiceal diameter are summarized in Table 4. The mean appendiceal diameters were 11.7 mm ± 0.2 and 6.3 mm ± 0.3 in patients with and those without definite appendicitis, respectively, (P < .001). Mean appendiceal diameters were also compared between reading sessions, readers, and radiation doses. No statistically significant difference was observed between reading sessions (P = .351–.792) except for reader B at low-dose CT (P = .020). The mean appendiceal diameter measured at the first reading session was compared between readers at each radiation dose. No statistically significant difference was observed with use of the standard dose (P = .550), but a difference between readers was detected with use of a low dose (P = .015). Last, the mean appendiceal diameter was compared between radiation doses for each reader and each reading session. No statistically significant difference was observed (P = .101–.696).


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  		TABLE 4. Measurements of Appendicular Diameter

 
Intrareader and Interreader Agreements
The frequency of signs and the overall diagnosis from both readers during reading sessions at standard dose and low dose are shown in Tables 2 and 3. The {kappa} values (±asymptotic standard error) for intrareader and interreader agreements at low dose and at standard dose are shown in Figures 1 and 2, respectively.



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  		Figure 1. Graph shows Cohen {kappa} coefficients used to assess intrareader agreements for each CT sign and for overall reader diagnosis of acute appendicitis. {circ} = low-dose unenhanced multi-detector row CT, {bullet} = standard-dose unenhanced multi-detector row CT. For each sign, the first two circles refer to Reader A and the last two circles refer to Reader B.

 


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  		Figure 2. Graph shows Cohen {kappa} coefficients used to assess interreader agreements for each CT sign and for overall reader diagnosis of acute appendicitis. {circ} = low-dose unenhanced multi-detector row CT, {bullet} = standard-dose unenhanced multi-detector row CT. For each sign and each radiation dose, the first open and closed circles refer to the first reading session and the second open and closed circles refer to the second reading session.

 
Misclassifications Compared with Definite Diagnosis
Differences in misclassified signs between low-dose and standard-dose examinations and between readers were compared (Table 5). We did not observe any statistically significant difference in these comparisons except between readers for the overall diagnosis of appendicitis, where the number of misclassified overall diagnoses was lower for reader A than for reader B (P = .031). No difference was observed between radiation doses (P = .788).


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  		TABLE 5. Frequency of Misclassified Signs for Each CT Finding

 
The frequency of each alternative diagnosis proposed by each reader at each reading session and for each radiation dose compared with the frequency of definite alternative diagnosis is listed in Table 1.

Diagnostic Performance
For each CT sign and overall diagnosis, we calculated the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy. This was done for each reader and each reading session at low dose and at standard dose (Table 6). No statistically significant difference between low dose and standard dose was observed in diagnostic performances (P values .387 to .99).


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  		TABLE 6. Minimum and Maximum Parameters in Evaluation of Diagnostic Performance of Each CT Sign

 
For the appendiceal diameter, ROC curves were drawn. The sensitivity was equated to the specificity for each reader and each radiation dose (Fig 3). These values ranged from 88% to 91% and corresponded to an appendiceal diameter ranging from 7.7 to 8.6 mm. For standard dose, the area under the curve was 0.925 (95% CI: 0.857, 0.993) and 0.905 (95% CI: 0.838, 0.972) for readers A and B, respectively. For low dose, the area under the curve was 0.921 (95% CI: 0.852, 0.990) and 0.928 (95% CI: 0.873, 0.984) for readers A and B, respectively. The overlap between the 95% CIs indicates no significant difference in measurements of appendiceal diameter between radiation doses or between readers.



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  		Figure 3. Graphs show ROC curves used to describe test characteristics of appendiceal diameter in the diagnosis of acute appendicitis by readers A and B. Areas below dashed and bold lines refer to low- and standard-dose unenhanced multi-detector row CT, respectively, and are not significantly different.

 
Logistic regression models showed that at low dose, the most predictive sign was periappendiceal fat stranding and the second (and only other) sign was appendicolith, together yielding 89% correct classification for the diagnosis of appendicitis by reader A. For reader B, the most predictive sign was appendiceal diameter and periappendiceal fat stranding, together yielding 88% correct classification. At standard dose, the most predictive sign was periappendiceal fat stranding and the second and last sign was appendiceal diameter, together yielding 94% correct classification for reader A. For reader B, the most predictive sign again was appendiceal diameter and periappendiceal fat stranding, this time yielding 92% correct classification.

Effect of Sex, Age, and BMI
In the entire study group, the mean BMI was 24.0 kg/m2 ± 4.6 (range, 16.4–40.7 kg/m2). Sex, age, and BMI were not found to influence the probability of appendix visualization, neither for dose nor for reader (P = .111–.788). We also did not elicit any lower or upper threshold of BMI where the appendix was not visible.

We assigned patients into the following three categories, which were adapted from the five BMI categories proposed by the World Health Organization (12): underweight (BMI range, 16.4–18.4 kg/m2; n = 9; included two patients with a definite diagnosis of appendicitis), normal to overweight (BMI range, 18.6–29.7 kg/m2; n = 76; included 24 patients with a definite diagnosis of appendicitis), and obese to extremely obese (BMI range 30.1–40.7 kg/m2; n = 10; included three patients with a definite diagnosis of appendicitis). Figures 4 and 5 illustrate findings from low- and standard-dose CT in an underweight and an extremely obese patient, respectively. Comparisons of sensitivity and specificity of each CT sign, as well as the overall reader diagnosis between BMI subgroups, did not reveal a statistically significant difference (P values from .051 to .99).



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  		Figure 4a. Oblique unenhanced CT reformation at (a) 30 and (b) 100 effective mAs obtained in a 36-year-old woman with definite diagnosis of acute appendicitis shows enlarged appendix (short arrow) containing appendicolith (long arrow) and periappendiceal fat stranding (arrowhead). Her BMI was 18.4 kg/m2.

 


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  		Figure 4b. Oblique unenhanced CT reformation at (a) 30 and (b) 100 effective mAs obtained in a 36-year-old woman with definite diagnosis of acute appendicitis shows enlarged appendix (short arrow) containing appendicolith (long arrow) and periappendiceal fat stranding (arrowhead). Her BMI was 18.4 kg/m2.

 


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  		Figure 5a. Oblique unenhanced CT reformation at (a) 30 and (b) 100 effective mAs obtained in a 44-year-old man with definite diagnosis of acute appendicitis shows enlarged appendix (short arrow) containing appendicolith (long arrow) and periappendiceal fat stranding (arrowhead). His BMI was 40.7 kg/m2.

 


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  		Figure 5b. Oblique unenhanced CT reformation at (a) 30 and (b) 100 effective mAs obtained in a 44-year-old man with definite diagnosis of acute appendicitis shows enlarged appendix (short arrow) containing appendicolith (long arrow) and periappendiceal fat stranding (arrowhead). His BMI was 40.7 kg/m2.

 
Effective Radiation Dose
The mean height of the scanned region was 39.0 cm ± 3.1 (range, 32.4–44.7 cm) for male patients and 37.6 cm ± 3.2 (range, 29.5–44.8 cm) for female patients. At 100 effective mAs, the calculated mean effective radiation dose was 5.2 mSv for male and 7.1 mSv for female patients. At 30 effective mAs, the calculated mean effective radiation dose was 1.4 mSv for male and 2.2 mSv for female patients. These radiation doses are compared with those delivered in previously published studies in Table 7.


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  		TABLE 7. Comparisons of Effective Radiation Doses for Helical CT Protocols

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
REFERENCES
 
Appendicitis is a potentially life-threatening condition but one that can be treated with simple and efficient surgical procedures. Consequently, it is imperative that diagnostic tests be highly sensitive with a very high negative predictive value (25). Unenhanced multi–detector row CT achieves this with sensitivity and a negative predictive value of 98% or more, even with a decrease in radiation dose. This value is even higher than previously reported, although there was a slightly lower specificity and positive predictive value (4,5,20). In addition, our study findings show that in patients suspected of having acute appendicitis, low-dose unenhanced multi–detector row CT provides the same diagnostic performance as does standard-dose unenhanced multi–detector row CT.

In all patients with appendicitis, both readers at both radiation doses visualized the appendix. Further, even in patients without appendicitis, the appendix was seen with the same frequency (~80%) at both radiation doses. This frequency is consistent with that in previous studies of unenhanced standard-dose single–detector row spiral CT (4,5,26).

Approximately one-third of our patients had a definite alternative diagnosis, which is similar to previously published studies (4,18–20,27–30). However, because of the small number of patients included in each of the various alternative diagnosis categories, we were unable to statistically compare the diagnostic performances of low- and standard-dose CT for each diagnostic category. Nevertheless, performance was similar regardless of the radiation dose.

In a previous study in which standard-dose single–detector row CT was used with oral and/or colonic contrast material, Rao et al (27) showed that the sensitivity and specificity of various CT signs vary. These previously reported values are comparable to the ones we obtained using unenhanced low-dose multi–detector row CT. Because CT signs can be more or less redundant to predict the diagnosis of appendicitis, and because this possible redundancy could differ according to radiation dose and reader’s experience, we classified the value of CT signs by using stepwise logistic regression for each radiation dose and for each reader. Periappendiceal fat stranding and appendiceal diameter are the two most predictive signs, that is, the signs with the highest probability of a correct diagnosis, at both radiation doses. For one reader, appendicolith was the second most important sign at low dose. More important, these signs are also the most reproducible.

When the two most predictive signs are positive, no other sign yields any additional information that could significantly contribute to the diagnosis of acute appendicitis. This is true regardless of the radiation dose or reader’s experience. Also, when CT signs were considered separately, misclassification was not different between readers with different levels of expertise. However, the more experienced reader makes a correct overall diagnosis more frequently than does the less experienced reader. This suggests that experience in reading abdominal CT scans helps in the integration of signs in the overall diagnosis.

Our study findings also showed no difference in the appendiceal diameter between either radiation dose. However, in the low-dose reading sessions, there were some differences between reading sessions by the less experienced reader and between both readers for their first reading session. Even if significant, these differences were small and they could be explained, at least in part, by the vermicular shape of the appendix, whereby measuring its diameter at different levels can produce a wide range of values. In our study, the mean diameters of a normal and an abnormal appendix are ~6 and ~12 mm, respectively. The intersection of ROC curves with the bisecting line identifies an optimal threshold of ~8 mm for the appendiceal diameter, with no difference in the area under the ROC curve between radiation doses or between readers. This threshold for distinguishing a normal from an abnormal appendix at unenhanced CT is higher than previously reported—6 mm measured in the short axis of the organ (27–30). As shown by the area under ROC curve of more than 0.9, the appendiceal diameter is a valuable sign. But as was revealed with the logistic regression models, associated signs should simultaneously be taken into consideration.

Since noise on a CT image increases with the body size, we investigated the possible effects of BMI on the visualization of the appendix and on the diagnostic performance of unenhanced low-dose multi–detector row CT. Our results do not reveal any difference in visualization between BMI subgroups and do not indicate any upper or lower threshold in BMI for which the appendix would not be visible. We could speculate that the negative effect of an increase in BMI on the performance of low-dose CT could be, at least in part, balanced by the accumulation of peritoneal and retroperitoneal fat around the appendix.

In the present study, the radiation dose was reduced by lowering the effective mAs. At 30 effective mAs, the dose is approximately one-third of that delivered by single–detector row CT. This dose is similar to that obtained with a single-detector row CT technique with 5-mm collimation, 200–220 mAs, and a pitch of 1.5 focused on the pericecal region (19). Focusing the CT acquisition on the lower abdomen can indeed reduce the dose, but it introduces the risk of obscuring possible alternative diagnoses in adjacent abdominal regions. Increasing the pitch could also reduce the dose, but this is associated with a decreased image quality, principally as a result of increased volume-averaging artifacts related to the broadened section profile. Consequently, small structures such as the appendix itself and periappendiceal fat stranding—one of the most predictive signs of appendicitis—could be missed.

Our study did have several limitations. First, in patients who were not treated surgically, we had no absolute confirmation that they truly had no acute appendicitis. However, because this applied equally to low- and standard-dose CT, there is no risk for bias. Second, we did not evaluate the possible influence of the amount of peritoneal fat on the visualization of the appendix. This has been evaluated by Benjaminov et al (26), and they reported an increased rate of identification of the appendix when an adequate amount of fat was present. Third, we have not evaluated the possible effect that dose reduction had on a reader’s confidence in the proposed diagnosis. Fourth, patients were seen in the same order, but because 95 patients were included in our study group, the probability for a reader to remember the successive order of the results would be very low, certainly lower than recognizing particular CT appearances.

In conclusion, our study results showed that for the detection of both acute appendicitis and alternative diseases, low-dose unenhanced multi–detector row CT has the same diagnostic performance as does standard-dose unenhanced multi–detector row CT. Low-dose unenhanced multi–detector row CT can be recommended for evaluation of adult patients suspected of having acute appendicitis.


   ACKNOWLEDGMENTS
 
The authors thank A. M. Bali, MD, E. Coppens, MD, and M. Zalcman, MD, who helped to make this research possible by their assistance in data acquisition. The authors also thank A. Van Muylem, PhD, for figure preparation.


   FOOTNOTES
 
Abbreviations: BMI = body mass index, ROC = receiver operating characteristic

Author contributions: Guarantor of integrity of entire study, C.K.; study concepts and design, C.K., D.V.G., D.T.; literature research, C.K., D.V.G., D.T.; clinical studies, C.K., P.B., D.T.; data acquisition, C.K., P.B., D.T.; data analysis/interpretation, C.K., D.T., P.A.G., V.d.M.; statistical analysis, V.d.M.; manuscript preparation, C.K., V.d.M., P.A.G.; manuscript definition of intellectual content, C.K., D.T., P.A.G.; manuscript editing, C.K.; manuscript revision/review and final version approval, all authors


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 

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