308 Discussion An automatic method of detecting and assessing the completeness of fissural surfaces has been described and tested. The completeness of pulmonary fissures may be important in the correct selection of patients for novel therapeutic techniques including BLVR treatment [4] and is commonly assessed by radiologists from a chest CT. Visual assessment of fissural completeness is time-consuming and tedious on large thin section reconstructed chest CT. In addition, visual assessment of fissural surface completeness is challenging given the anatomy of the fissures and the need to assess them on multiple planes of reconstruction. Several previous studies have attempted to evaluate fissural completeness in the last decade and their results are provided in Table 2. These studies were based on visual assessments in cohorts of relatively normal subjects. Interestingly, despite our study being performed on patients with severe COPD and differing definitions of complete- ness, our findings were within the range published. The results of Mahmut and Nishitani [6] differ most from all other studies listed and the present study. This is probably caused by their definition of incomplete fissures—more than 1 cm missing—as well as their cohort of normal subjects. Volumetric thin-section CT data allow for precise delineation of the interlobar fissures and allow automatic methods of recognising the fissures with high accuracy (e.g. [9–12]). Precise quantification is difficult using the eye alone. Gülsün et al. [2] visually determined the percentage of incompleteness of the major fissures in five categories: 0%, 1–25%, 26–50%, 51–75% and 76–99%. In their study population of 144 CT studies of disease-free patients they found that most incomplete major fissures were between 1 and 25% incomplete (around 70%), and that most of the remaining incomplete fissures were scored to be 26–50% incomplete; no fissures were found to be more than 75% incomplete. More recently, Ozmen et al. [7] used a similar visual quantification score for all lobar fissures. For the major fissures similar results were found as in Gülsün et al. [2]. For the right minor fissure, they found the extent of incompleteness to be almost equally divided over the different categories. Advantages of computer-based schemes are that quantification is more robust, precise, and reproducible. The descriptive statistics provided in Fig. 3 show a similar trend to that described in Ozmen et al. [7]: if the major fissures are incomplete the percentage of incompleteness is mostly between 10% and 30%; for the right minor fissure the percentages are more spread out. It is interesting that there was a difference in the agreement between the right major and minor fissures and the left major fissure, with better agreement seen on the right. A possible explanation for this is that the degree of incompleteness in the left major fissure is often less than in Eur Radiol (2012) 22:302–309 the right major and minor fissures as reported by Aziz et al. [1], and therefore the readers tended to have more variation in the ability to recognise completeness. We suggest that the best use of the proposed method is as a support aid for a visual read by a radiologist. The method indicates incomplete parts of the fissure and provides the exact quantification. The reader can quickly assess if he/she agrees with the method and only in cases where the reader disagrees with the method is another strategy or a complete visual read necessary. Most disagreement between the readers in this study occurred in the area of fissures visually thought to be complete or incomplete to a small degree; out of the 36 discordant fissure reads, 27 (75%) were scored by the automatic method to be between 86% and 97% complete. This is exactly where the automatic method would be beneficial; the readers agree that there might be a gap in the fissure, but the exact quantification of the size of the gap is difficult for humans to judge and is assessed much more accurately by computers. The limitations of our study include the use of a truth panel as the gold standard and the use of a trichotomous scale for the visual read. This protocol was used for the visual read as it is the current standard for visual fissure completeness assessment in several BLVR trials [4]. To conclude, a fully automatic, quantitative method is able to quantify fissural completeness in a manner comparable to expert radiologists in a cohort of subjects with severe emphysema. Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which per- mits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. References 1. Aziz A, Ashizawa K, Nagaoki K, Hayashi K (2004) High resolution CT anatomy of the pulmonary fissures. J Thorac Imaging 19:189–191 2. Gülsün M, Ariyürek OM, Cömert RB, Karabulut N (2006) Variability of the pulmonary oblique fissures presented by high-resolution computed tomography. Surg Radiol Anat 28:293–299 3. Cronin P, Gross BH, Kelly AM, Patel S, Kazerooni EA, Carlos RC (2010) Normal and accessory fissures of the lung: evaluation with contiguous volumetric thin-section multidetector CT. Eur J Radiol 75:1–8 4. Sciurba FC, Ernst A, Herth FJF et al (2010) A randomized study of endobronchial valves for advanced emphysema. N Engl J Med 363:1233–1244 5. Medlar EM (1947) Variations in interlobar fissures. Am J Roentgenol Radium Ther 57:723–725 6. Mahmut M, Nishitani H (2007) Evaluation of pulmonary lobe variations using multidetector row computed tomography. J Comput Assist Tomogr 31:956–960