Rationale and Objectives
To determine the intraindividual impact of radiation dose reduction in abdominal computed tomography (CT) on diagnostic performance in patients with suspected appendicitis.
Materials and Methods
This study was approved by the institutional review board. Seventy-five patients who underwent standard contrast-enhanced abdominal CT for suspected appendicitis between 2004 and 2009 were retrospectively included. Low-dose CT reconstructions with 75%, 50%, and 25% of the original radiation dose level were generated by applying realistic reduced-dose simulation. Two blinded, independent readers assessed image quality, signal-to-noise ratio, and diagnostic confidence on each dataset. Diagnostic accuracy for detection of appendicitis and complications were calculated for each reader. Paired univariate tests were used to determine intraindividual differences.
Results
Among 75 subjects included in the analysis (57% female, mean age: 41 ± 18 years), the prevalence of histopathologically confirmed appendicitis was 59%. Signal-to-noise ratio and subjective image quality of 50% and 25% reduced-dose CTs were significantly lower than the reference datasets (all P < .005). Appendicitis was correctly identified in all reference and low-dose datasets (sensitivity: 100%, negative predictive value: 100%). Presence of complications was correctly detected in all reference, 75%, and 50% datasets, but was decreased in 25% datasets (sensitivity: 77.8% and negative predictive value: 97.4%). Diagnostic confidence was high for original and 75% datasets, but significantly lower for 50% and 25% datasets ( P < .001).
Conclusions
Our results indicate that diagnostic accuracy in abdominal CT acquisitions acquired at 75% and 50% of radiation dose is maintained in patients with suspected appendicitis, whereas further reduction of radiation exposition is associated with decreased diagnostic performance.
Introduction
Acute appendicitis is one of the most frequent diagnoses in acute nontraumatic abdominal pain, affecting mostly patients in the second and third decade of life, with a cumulative lifetime risk of 9.0% . Established clinical signs, laboratory blood values, and transabdominal ultrasound may help in confirming or excluding the diagnosis of appendicitis; however, several studies underline the predominant benefit of computed tomography (CT) compared to ultrasound in the diagnostic workup, with excellent sensitivity and negative predictive value . Additionally, previous research reported a decline in negative appendectomy rates, which can be attributed to the use of CT in the diagnostic management of appendicitis .
Taking into consideration that patients in whom appendicitis is suspected are often young adults or children, the exposure to ionizing radiation is of particular concern, and CT protocols with reduced radiation exposure are mandatory. Although low-dose CT protocols are often associated with a decrease in image quality and thus potential deterioration of diagnostic accuracy, several studies demonstrated no hampering of diagnostic performance for detection of appendicitis in low-dose CT compared to standard-dose CT . Kim et al. also reported that low-dose CT is noninferior to standard-dose CT with respect to negative appendectomy rates (3.5% vs 3.2%, respectively) . However, these and other studies on low-dose CT in patients with appendicitis are based on between-group comparisons without intraindividual reference and without taking into account associated conditions and complications, which may explain the limited implementation of these low-dose CT protocols in clinical practice.
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Materials and Methods
Subjects and Data Acquisition
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Reference Standard
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Low-dose Simulation
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Qualitative and Quantitative Analyses
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Diagnostic Assessment and Interreader Variability
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Statistical Analysis
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Institutional Review Board Approval
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Results
Subjects and Data Acquisition
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Demographical Information and Diagnoses of the Study Population
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TABLE 1
Patient Demographic Characteristics, Intraoperative Diagnoses, and Presence of Complications of All Patients
Variable Total Patients without Acute Appendicitis Patients with Acute Appendicitis_n_ (%) or Mean (±SD)n (%) or Mean (±SD)n (%) or Mean (±SD)n 75 31 44 Age (y) 40.6 (±17.6) 33.2 (±14.2) 46.2 (±18.0) Male gender 32 (42.7) 9 (29.0) 23 (52.3) Female gender 43 (57.3) 22 (71.0) 21 (47.7) Male-to-female ratio 0.7 0.4 1.1 White cell count ( n /µL) 13,587.7 (±5,424.1) 11,266.8 (±3,766.5) 15,223.0 (±5424.1) C-reactive protein (mg/dL) 6.2 (±8.9) 3.5 (±6.1) 6.2 (±8.9)
Data are arithmetic means and standard deviations (continuous variables) or counts and percentages (categorical variables).
TABLE 2
Intraoperative Diagnoses and Final Diagnoses in Synopsis of Clinical, Intraoperative, and Histopathological Findings
Intraoperative and/or Histopathological Diagnosis, n (%) Acute appendicitis without perforation ( n ) 9 (25.3) Periappendiceal abscess ( n ) 6 (8.0) Perforation ( n ) 17 (22.7) Another cause ( n ) 9 (12.0) Surgical diagnosis missing ( n ) 9 (12.0) No operation ( n ) 13 (17.3) Diagnosis of acute appendicitis 44 (58.7)
Data are counts and percentages (categorical variables).
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Quantitative and Qualitative Analyses of the CT Datasets
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TABLE 3
Summary of the Evaluation of Subjective Quality of the Original Standard-dose CT and the Generated Low-dose CT Datasets in Terms of Subjective Quality
Reference CT 75% Low-dose CT 50% Low-dose CT 25% Low-dose CT 100% vs 75% Low-dose CT 100% vs 50% Low-dose CT 100% vs 25% Low-dose CT Subjective image quality Overall quality Reader A 2 (1–3) 2 (2–4) 3 (2–5) 4 (3–5) 0.003 0.001 0.001 Reader B 1 (1–3) 2 (2–4) 3 (2–5) 4 (3–5) 0.001 0.001 0.001 Image noise Reader A 2 (1–3) 2 (2–4) 3 (2–5) 4 (3–5) 0.001 0.000 0.001 Reader B 1 (1–3) 2 (2–4) 3 (2–5) 4 (3–5) 0.001 0.001 0.001 Sharpness Reader A 2 (1–3) 3 (2–4) 3 (2–5) 4 (3–5) 0.001 0.000 0.001 Reader B 1 (1–3) 3 (2–4) 3 (2–5) 4 (3–5) 0.001 0.001 0.001 Artefacts Reader A 1 (1–3) 2 (1–3) 3 (2–5) 4 (3–5) 0.006 0.001 0.001 Reader B 1 (1–3) 2 (1–3) 3 (2–5) 4 (3–5) 0.060 0.001 0.001 Diagnostic confidence Overall Reader A 1 (1–2) 2 (1–4) 3 (2–5) 4 (3–5) 0.001 0.001 0.001 Reader B 1 (1–3) 2 (1–4) 3 (2–5) 4 (3–5) 0.001 0.001 0.001 Appendicitis-specific Reader A 1 (1–3) 2 (1–4) 2 (1–5) 2 (1–5) 0.698 0.011 0.001 Reader B 1 (1–3) 1 (1–4) 1 (1–5) 2 (1–5) 0.309 0.003 0.000
CT, computed tomography.
Data are median with minimum and maximum. Subjective quality was evaluated on a five-point Likert scale (1 = excellent to 5 = very poor).
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Diagnostic Performance
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TABLE 4
Diagnostic Accuracy of Detection of Complications in the 25% Reduced-dose CT Datasets in Comparison to Original-dose CT
Complications Overall Abscess Formation Free Intraabdominal Air Reader A Reader B Reader A Reader B Reader A Reader B Sensitivity 77.78 (52.36–93.59) 96.21 (91.38–98.75) 81.82 (48.22–97.72) 72.73 (39.03–93.98) 71.43 (29.04–96.33) 71.43 (29.04–96.33) Specificity 97.40 (93.48–99.29) 96.77 (92.63–98.94) 100.00 (49.4–100.00) 100.00 (94.4–100.0) 94.12 (85.62–98.37) 92.65 (83.67–97.57) PPV 77.78 (56.33–90.47) 96.21 (91.47–98.37) 100.00 100.00 55.56 (30.22–78.30) 50.00 (27.59-27.41) NPV 97.40 (94.05–98.89) 96.77 (92.70–98.61) 96.97 (90.13–99.12) 95.52 (89.04–98.25) 96.97 (90.83–99.04) 96.92 (90.69–99.03)
NPV, negative predictive value; PPV, positive predictive value.
Data are indicated in percentage with 95% confidence interval.
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Interreader Variability
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TABLE 5
Interreader Agreement Between Reader A vs Reader B Within the Low-dose Generated CT Dataset and the Original Dataset in Terms of Subjective Analyses
Interreader Agreement, Cohen Kappa (±Asymptotic Standard Error) 25% Low-dose CT 50% Low-dose CT 75% Low-dose CT 100% Low-dose CT Wall thickening of the appendix 0.899 (±0.047) 1 (±0) 0.974 (±0.026) 0.917 (±0.04) Appendicolith 1 (±0) 0.927 (±0.072) 0.938 (±0.058) 0.798 (±0.077) Periappendiceal phlegmon 0.974 (±0.026) 0.975 (±0.025) 0,973 (±0.026) 0.901 (±0.042) Free intraabdominal fluid 0.882 (±0.053) 1 (±0) 1 (±0) 0.932 (±0.038) Free intraabdominal air 0.94 (±0.06) 1 (±0) 1 (±0) 1 (±0) Abscess formation 0.934 (±0.066) 1 (±0) 1 (±0) 1 (±0) Confidence in diagnosis of acute appendicitis 0.862 (±0.049) 0.842 (±0.054) 0.922 (±0.043) 0.756 (±0.136) Diagnosis of an acute appendicitis 1 (±0) 1 (±0) 1 (±0) 1 (±0)
Data are indicated in Cohen κ values (±asymptotic standard error), respectively. Interreader agreement indicated as κ values ranging from 0.0 to 1.0, overall (depicted: 0.4–0.59 = weak, 0.6–0.79 = moderate, 0.8–0.9 = strong and above 0.90 = almost perfect).
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Discussion
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Acknowledgement
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