Content-based image-retrieval system in chest computed tomography for a solitary pulmonary nodule: method and preliminary experiments.

PURPOSE: The aim of this study was to develop a new diagnostic support system using content-based image-retrieval technology. In this article, we describe the mechanism and preliminary evaluation of this system for use with CT images of solitary pulmonary nodules.
MATERIALS AND METHODS: With the approval of the institutional review board of Shizuoka Cancer Center, we built a database that included CT images of 461 solitary pulmonary nodules. With this database, we developed a system that automatically extracts the pulmonary nodule when the nodule area is clicked, retrieves previous cases based on an image analysis of the extracted lesion, and generates reports of the pulmonary nodule semi-automatically. We compared the percentage of correct diagnoses with and without the system using 30 solitary pulmonary nodules, which were not included in the database, with one radiologist and two residents. As a per-user evaluation, the number of clicks required to extract the nodule region and the extracted regions was compared, and presented candidate cases were evaluated. As an evaluation of the retrieval results, the presented candidate cases were evaluated by comparing the number of diagnostic matches (benign/malignant) between the queries and four presented cases. Additionally, to evaluate the validity of the retrieval technology, the radiologist selected the most similar cases presented by the system and evaluated the visual similarity on a five-point scale.
RESULTS: With this system, the percentage of correct diagnoses for the radiologist improved from 80 to 93%. For the two residents, the diagnostic accuracy improved from 66.7 to 80% and from 76.7 to 90%, respectively. The evaluation of the number of clicks required indicated that for 19 cases with the radiologist and 12 and 11 cases with the two residents, respectively, only one click was required to extract the region. When the extracted regions were compared between the radiologist and the residents, 22 and 19 cases had a Dice's Coefficient of 0.85 or higher, respectively. For the radiologist, the number of cases that matched the diagnosis (benign/malignant) averaged 3.7 ± 0.5 among 23 malignant cases and 1.7 ± 1.4 among 7 benign cases, while for the residents, these values were 3.6 ± 0.5 and 1.1 ± 0.9, and 3.4 ± 0.8 and 1.1 ± 1.3, respectively. With regard to visual evaluations by the radiologist, there were 15 similar cases and 11 somewhat similar cases.
CONCLUSION: These results suggest that, despite some differences in the search results among the users, this system has been confirmed that it can improve the accuracy of diagnosis as it displays similar cases at high probability. In addition, with the use of this system, past cases and their reports can be effectively referred to. Therefore, this diagnostic-assistant system has the potential to improve the efficiency of the CT image-reading workflow.