• Detection of the Normal Appendix with Low-Dose Unenhanced CT: Use of the Sliding Slab Averaging Technique

    Seung-Moon Joo, MD Kyoung Ho Lee, MD Young Hoon Kim, MD SoYeon Kim, MD Kyuseok Kim, MD Kil Joong Kim, MS Bohyoung Kim, PhD

    Purpose: To determine the frequency of normal appendix visualiza­tion at low-dose (LD) unenhanced computed tomography (CT) performed with a 16- or 64-detector row scanner when images are reviewed by using the sliding slab averag­ing technique

    Materials and Methods: The institutional review board approved the study and waived the informed consent requirement. A total of 259 patients, 37 (14.3%) of whom had previously undergone appendectomy, underwent LD unenhanced CT (mean ef­fective dose, 1.7 mSv) performed with a 16- or 64-detec-tor row scanner to assess urinary colic. Three readers used the sliding slab averaging technique to retrospectively review the thin-section (0.67- or 2.00-mm section thick­ness) images and grade the appendix as absent, unsurely or partly visualized, or clearly and entirely visualized. In-terobserver agreement was measured with weighted k statistics. McNemar tests were used to compare sensitivity between the readers. Logistic regression analysis was per­formed to assess the effects of body mass index, patient, sex, and type of CT scanner on appendiceal visualization.

    Results: : The k statistics for each reader pair were as follows: 0.97 for agreement between readers 1 and 2, 0.93 for agree­ment between readers 2 and 3, and 0.92 for agreement between readers 1 and 3. Each reader clearly identified the entire appendix in 213 (96.0%), 209 (94.1%), and 205 (92.3%) of the 222 patients without a history of appendec­tomy. When unsurely or partly visualized appendices were included, the frequencies increased to 99.1% (n = 220), 98.7% (n = 219), and 97.3% (n = 216), respectively, for readers 1, 2, and 3. These frequencies rarely differed between the readers. (P values ranged from .021 to greater than .99.) The three readers consistently reported that the appendix was not visualized in the 37 patients who had undergone appendectomy. None of the tested vari ables significantly affected appendix visualization.

    Conclusion: Most normal appendices are visualized on thin-section LD unenhanced CT images reviewed with the sliding slab av­eraging technique.