Rationale and Objectives
The Lung Image Database Consortium (LIDC) is developing a publicly available database of thoracic computed tomography (CT) scans as a medical imaging research resource to promote the development of computer-aided detection or characterization of pulmonary nodules. To obtain the best estimate of the location and spatial extent of lung nodules, expert thoracic radiologists reviewed and annotated each scan. Because a consensus panel approach was neither feasible nor desirable, a unique two-phase, multicenter data collection process was developed to allow multiple radiologists at different centers to asynchronously review and annotate each CT scan. This data collection process was also intended to capture the variability among readers.
Materials and Methods
Four radiologists reviewed each scan using the following process. In the first or “blinded” phase, each radiologist reviewed the CT scan independently. In the second or “unblinded” review phase, results from all four blinded reviews were compiled and presented to each radiologist for a second review, allowing the radiologists to review their own annotations together with the annotations of the other radiologists. The results of each radiologist’s unblinded review were compiled to form the final unblinded review. An XML-based message system was developed to communicate the results of each reading.
Results
This two-phase data collection process was designed, tested, and implemented across the LIDC. More than 500 CT scans have been read and annotated using this method by four expert readers; these scans either are currently publicly available at http://ncia.nci.nih.gov or will be in the near future.
Conclusions
A unique data collection process was developed, tested, and implemented that allowed multiple readers at distributed sites to asynchronously review CT scans multiple times. This process captured the opinions of each reader regarding the location and spatial extent of lung nodules.
Computed tomography (CT) is being investigated for a variety of radiologic tasks involving lung nodules and lung malignancies. These activities include using low-dose CT as a screening tool for the early detection of lung cancer in high-risk populations ( ), evaluating the response of primary and metastatic lung lesions to various therapies ( ), and characterizing indeterminate nodules as benign or malignant ( ). Radiologists are faced with the task of both identifying and characterizing lung nodules on large, multidetector row CT scans for these applications. This has motivated interest and research into computer-aided diagnosis (CAD) methods, with several commercial systems having either already received Food and Drug Administration approval or having been submitted for approval of CAD or CAD-like systems.
To further stimulate research and development activities in this area, the National Cancer Institute (NCI) formed the Lung Image Database Consortium: the LIDC ( ). The mission of the LIDC is to 1) to develop an image database as a web-accessible international research resource for the development, training, and evaluation of CAD methods for lung cancer detection and diagnosis using CT and 2) to create this database to enable the correlation of performance of CAD methods for detection and classification of lung nodules with spatial, temporal, and pathologic ground truth. The intent of this database is to hasten advancement of lung nodule CAD research by 1) providing clinical images to investigators who might not have access to patient images and 2) creating a reference database that will support the relative comparison of different CAD systems performance, thus eliminating database composition as a source of variability in system performance ( ). This database requires the collection of an appropriate set of scans, and the creation of “truth” for each scan.
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Materials and methods
Definitions of Objects to be Marked and Annotation Requirements
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Nodules that are <3 mm but are clearly benign (ie, solidly calcified) were specifically excluded from being marked, as were nonnodules <3 mm. Each of the included categories is described below along with the annotation requirements for each. This is summarized in Table 1 .
Table 1
Summary of Categories of Objects to be Marked and the Annotation Requirements
Category Annotation Subjective Assessment Nodule ≥3 mm ( Fig 1 ) Draw complete contour Yes ( Fig 7 ) Nodule <3 mm ( Fig 2 ) Mark approximate centroid None Non-nodule ≥3 mm ( Fig 3 ) Mark approximate centroid None Non-nodule <3 mm No marking None
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Nodules ≥3 mm, Regardless of Presumed Histology
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Nodules <3 mm
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Nonnodules ≥3 mm
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Design of the Multiple Reader, Multiple Session Process
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Blinded Reading Phase
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Unblinded Reading Phase
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An example interface is shown in Fig 7 . This figure illustrates that each of these characteristics are rated on a five-point scale, except for internal structure and calcification. For some of the categories, descriptive terms were used for all five possible responses; for others, no descriptive terms were associated with the five possible responses. For example, a numeric value is available if the reader wants to score a lesion’s sphericity somewhere between “ovoid” and “round,” though no satisfactory descriptive term could be found.
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Implementation and infrastructure
Prequisites
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Anonymization of CT Image Data
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XML-Based Specification of Annotations
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The complete specification for the XML file is described by its schema and documentation, which can be found on the NCIA website http://ncia.nci.nih.gov/collections/ .
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Messaging System
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Software Tools for Annotation
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Results
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Conclusion
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