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Heo, Lee, and Yoon: Effectiveness of Virtual Non-Enhanced Images Acquired by Dual-Energy Computed Tomography in Evaluation of Patients with Suspected Acute Appendicitis
Abdominal Radiology
Original Article

Journal of the Korean Society of Radiology 2016; 75(4): 276-284.

Published online: 29 September 2016

DOI: https://doi.org/10.3348/jksr.2016.75.4.276

Effectiveness of Virtual Non-Enhanced Images Acquired by Dual-Energy Computed Tomography in Evaluation of Patients with Suspected Acute Appendicitis

Taeyeong Heo, MD, Young Hwan Lee, MD, Kwon-Ha Yoon, MD

Department of Radiology, Wonkwang University Hospital, Iksan, Korea.

Corresponding author: Young Hwan Lee, MD. Department of Radiology, Wonkwang University Hospital, 895 Muwang-ro, Iksan 54538, Korea. Tel. 82-63-859-1920, Fax. 82-63-851-4749, yjyh@wonkwang.ac.kr

Received 18 October 2015       Revised 15 December 2015       Accepted 5 March 2016

Copyright © 2016 The Korean Society of Radiology

(open-access):

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose

To determine whether virtual non-enhanced (VNE) images derived from dual-energy computed tomography (DECT) can replace true non-enhanced (TNE) images in patients with suspected acute appendicitis.

Materials and Methods

A total of 195 patients were scanned using DECT. Two radiologists reviewed the VNE set (VNE and portal-phase images) and the TNE set (TNE and portal-phase images), 4 weeks later. Sensitivities and specificities for the diagnosis of acute appendicitis and radiation doses for each set were calculated. Image quality and artifacts in the VNE set were rated on a four point scale (1 = poor–4 = excellent). Size and attenuation of intraperitoneal calcifications were compared in each image.

Results

A total of 114 patients were diagnosed with acute appendicitis by operation. In the VNE set, sensitivity and specificity were 99.1% and 89.9% for reader 1, and 96.6% and 94.8% for reader 2, respectively. In the TNE set, the corresponding values were 96.6% and 94.9% for reader 1, and 94.8% and 92.4% for reader 2, respectively. Among the 87 calcifications detected in the TNE set, 74 calcifications were noted in the VNE set. Mean image quality and artifact were 3.61 and 3.83, respectively. Radiation dose reduction was 48% after excluding the TNE set.

Conclusion

Image quality and diagnostic performance of the VNE set were not inferior to those of the TNE set. Replacing TNE images by VNE images can reduce the radiation dose in evaluation of patients with acute appendicitis.

Keywords: Appendicitis, Radiography, Dual-Energy Scanned Projection, Radiation Dose, Tomography, X-ray Computed

Figures and Tables

Fig. 1

A flow chart of enrollment of patients.

DECT = dual-energy computed tomography, RLQ = right lower quadrant
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Fig. 2

A case with similarly detected cecal hemorrhage on both virtual non-enhanced (VNE) and true non-enhanced (TNE) images. A 28-year-old man presented with RLQ pain.

A. Coronal enhanced image shows markedly hyperattenuated fluid collection (arrow) in the cecum and the ascending colon.
B, C. It was subtracted and it presented as slight hyperattenuation on the VNE image (53 HU, arrow) (B) and also on the TNE image (51 HU, arrow) (C).
HU = Hounsfield unit, RLQ = right lower quadrant
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Fig. 3

A case with a similarly detected appendicolith on both true non-enhanced (TNE) and virtual non-enhanced (VNE) images, but it was not well detected on the enhanced image. A 62-year-old male with acute appendicitis.

A, B. Axial VNE (A) and TNE (B) images show a 0.4 cm sized appendicolith (arrows), dilated bowel lumen and thickened wall of the appendix.
C. Enhanced axial image shows findings compatible with acute appendicitis, but an appendicolith can be mistaken for a small blood vessel (arrow).
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Fig. 4

A case with a similarly detected right-sided urinary stone on both true non-enhanced (TNE) and virtual non-enhanced (VNE) images, but it was not well detected on the enhanced image. A 56-year-old man with a right-sided urinary stone.

A, B. Axial VNE (A) and TNE (B) images show a 0.3 cm sized right-sided urinary stone (arrows).
C. Enhanced axial image also shows a tiny hyperattenuated lesion adjacent to the right ureterovesical junction, but it can be mistaken for a small blood vessel (arrow).
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Table 1

Final Diagnosis of Patients

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Surgical Treatment Groups (n = 123) Follow Up Groups (n = 72)
Acute appendicitis 114 Enterocolitis 24
Appendiceal tumor 2 Miscellaneous 10
Uterine leiomyoma 2 Urinary stone 9
Ovarian cyst 1 Diverticulitis 4
Acute cholecystitis 1 Mesenteric lymphadenitis 5
Chronic cholecystitis 1 Pelvic inflammatory disease 5
Ischemic enteritis 1 Complicated ovarian cyst 3
Duodenal ulcer perforation 1 Irritable bowel syndrome 2
Acute pyelonephritis 2
Periappendiceal abscess 2
Others* 6

*Others including Crohn's disease, Leiomyoma, acute cholangitis, Henoch-Scheonlein purpura, appendiceal mucocele, obstuctive ileus.

Table 2

CT Parameters

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TNE DE Portal TNE
Detector A Detector B
Tube voltage (kVp) 120 140 100
Tube current (mAs) 210 135 350
Configuration (mm) 128 × 0.6 64 × 0.6 64 × 0.6
Pitch 0.8 0.6 0.6
Scanning delay time (s) - 100 100
Rotation time (s) 0.33 0.33 0.33

DE portal = dual energy portal phase image, TNE = true non-enhanced image

Table 3

Diagnostic Value of Each Data Set for Detection of Acute Appendicitis

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Data Set Sensitivity Specificity PPV NPV Diagnostic Accuracy AUC
Reader 1 VNE + CE 99.1 89.9 93.5 98.6 95.4 0.941 (p = 0.021)
TNE + CE 96.6 94.9 96.6 94.9 95.9 0.930 (p = 0.021)
Reader 2 VNE + CE 96.6 91.1 94.1 94.7 94.4 0.936 (p = 0.021)
TNE + CE 94.8 92.4 94.8 92.4 94.8 0.917 (p = 0.023)
Diagnostic performance btw VNE + CE and TNE + CE in reader 1 p = 1.000
Diagnostic performance btw VNE + CE and TNE + CE in reader 2 p = 1.000
Interobserver agreement between reader 1 and 2 in “VNE + CE” set κ = 0.873

AUC = area under the curve, CE = contrast enhanced image, NPV = negative predictive value, PPV = positive predictive value, VNE = virtual non-enhanced image

Table 4

Analysis of Image Quality and Artifact of VNE Images

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Quality* Artifact†
Reader 1 Reader 2 Reader 1
Mean grade 3.61 ± 0.49 3.83 ± 0.48 3.36 ± 0.51

*Grade 1–4; 1 = poor, 2 = fair, 3 = good, 4 = excellent.

†Grade 1–4; 1 = severe, 2 = moderate, 3 = minimal, 4 = no artifact.

VNE = virtual non-enhanced image

Table 5

Quantitative Analysis of the Lesions Detected on Each Images

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Appendicolith (n = 27) Biliary Stone (n = 8) Lower Ureteral Stone (n = 9)
VNE TNE p Value VNE TNE p Value VNE TNE p Value
Mean size (mm) 7.73 8.50 0.093 9.5 9.75 0.17 3.1 3.5 0.08
Mean attenuation (HU) 128.4 208.6 0.001 91.6 131.5 0.127 114.7 199.5 0.004

HU = Hounsfield unit, TNE = true non-enhanced image, VNE = virtual non-enhanced image

Table 6

Radiation Dose Analysis

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Total TNE Portal Phase TNE × 100/Total
Mean DLP (mGycm) 879.01 ± 289.05 461.44 ± 149.31 422.09 ± 137.59 48%
Mean ERD (mSv) 13.19 ± 4.33 6.33 ± 2.06 6.92 ± 2.24 48%

DLP = dose length product, ERD = effective radiation dose, TNE = true non-enhanced image

Acknowledgments

This study was supported by Institute of Wonkwang Medical Science in 2015.

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