Dual-Energy Spectral in CT Aids Diagnosis of Acute Gangrenous Appendicitis

Leesburg, VA, November 19, 2018—In cases of suspected appendicitis, dual-energy CT that includes virtual monoenergetic and iodine overlay imaging is accurate for confirming and excluding the presence of gangrenous appendicitis with high sensitivity and specificity, according to an article in the December 2018 issue of the American Journal of Roentgenology (AJR).

In dual-energy, or spectral, CT (DECT) two photon spectra are used, allowing gathering of information from two absorption measurements. It can be used to differentiate tissue or materials on the basis of changes in x-ray attenuation at different photon spectra, providing spectral information based on the chemical composition of materials. Several postprocessing algorithms are available for displaying clinically relevant spectral information, such as virtual unenhanced, color-coded iodine overlay, and virtual monochromatic datasets.

The study included 209 patients with a pathologic diagnosis of appendicitis. Two abdominal radiologists reviewed 120-kV simulated images, 40-keV virtual monoenergetic images, and color-coded iodine overlay images. Sensitivity, specificity, positive and negative predictive values (PPV and NPV), accuracy, and interobserver agreement were calculated for each set of images.

The results showed 44 patients (21.0%) had histopathologic results positive for gangrenous appendicitis. The sensitivity of 40-kV virtual monoenergetic imaging was 100% (44/44); specificity, 81.2% (134/165); PPV, 58.7% (44/75); NPV, 100% (134/134); accuracy, 85.2%; and interobserver agreement, 0.99. The corresponding values for the iodine overlay imaging datasets were 100% (44/44), 80.0% (132/165), 57.1% (44/77), 100% (132/132), 84.2%, and 0.99 and for 120-kV simulated imaging were 22.7% (10/44), 96.4% (159/165), 62.5% (10/16), 82.4% (159/193), 77.5%, and 0.93. All cases of gangrenous appendicitis had true-positive results of virtual monoenergetic and iodine overlay imaging. There were no false-negative results of virtual monoenergetic or iodine overlay imaging.

Researchers assessed the role of DECT, or spectral, imaging in the diagnosis of gangrenous appendicitis by detecting the presence of transmural necrosis on 40-keV virtual monoenergetic and iodine overlay images. This is facilitated in low-kilovoltage virtual monoenergetic and iodine overlay reconstructions by accentuating subtle differences in the enhancement of normally perfused mucosa and hypoperfused gangrenous mucosa. As a result, gangrene is easily visualized as an area of markedly decreased enhancement or reduced iodine uptake.

Founded in 1900, ARRS is the first and oldest radiology society in the United States, and is an international forum for progress in radiology. The Society's mission is to improve health through a community committed to advancing knowledge and skills in radiology. ARRS achieves its mission through an annual scientific and educational meeting, publication of the American Journal of Roentgenology (AJR) and InPractice magazine, topical symposia and webinars, and print and online educational materials. ARRS is located in Leesburg, VA.