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Eight different layouts of nodules were specified by placing them in premarked positions within the phantom vasculature, where they were either attached to vessels or suspended in foam (non-attached configuration). Care was taken to maintain constant positioning of the nodules when a particular layout was scanned multiple times or with different protocols. For that purpose, vessels on which nodules were attached were color coded. Table 1 tabulates the nodule configuration for the nodule layouts that are currently available at https://imaging.nci.nih.gov/ncia/login.jsf in terms of nodule positioning, size, shape, and density. Figure 3 shows a schematic diagram of the currently available layouts. All tables and figures in this document will be updated as more data is posted.
Insert Table 1 HERE
Figure 3. Schematic diagram of Nodule Layout#1 in terms of nodule placement. Vessel branches within the anthropomorphic phantom were color coded for the purpose of mapping nodules to specific positions within the phantom's vasculature structure in a reproducible manner.
The phantom was scanned using a Philips 16-row scanner (Mx8000 IDT, Philips Healthcare, Andover, MA) and a Siemens 64-row scanner (Somatom Definition 64, Siemens Medical Solutions USA, Inc., Malvern, PA). Scans were acquired with varying combinations of effective dose, pitch, and slice collimation, and were reconstructed with varying combinations of slice thicknesses and reconstruction kernels. Ten exposures were acquired for each imaging protocol. The phantom position was not changed during the 10 repeat exposures; however it was repositioned between different imaging protocols or different nodule layouts. Table 2 summarizes the imaging protocols for the nodule layout.
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Series description: Contains information on reconstructed slice thickness (in mm), reconstructed slice increment (in mm), and reconstruction filter or kernel (currently either C for detail, or B for medium). Insert Table 2 HERE
For example: there are 16 studies for Nodule Layout #1 (4 exposures x 2 slice collimations x 2 pitch settings). Each study contains 30 series (10 repeat scans x 3 reconstructed slice thickness x 1 reconstruction kernel).
A key component of the CT lung phantom project is the ability to compare the estimated nodule size with the known true size or reference gold standard. As part of our project, volume was used as a surrogate measure of size. The true volume estimate of each synthetic nodule was derived from weight and density measures. Both the CIRS-and Kyotokagaku nodules were accompanied by density measures. Nodule weights were measured in our lab using a precision scale of 0.1 mg tolerance (Adventurer Pro AV 2646, Ohaus Corp, Pine Brook, NJ). Three repeat weight measurements were made and these weights were averaged to produce a final estimated weight for each nodule. Our estimates of the true volume of the synthetic nodules in each layout are summarized in Table 3 along with approximated xyz location of nodule center in the CT scans. Insert Table 3 HERE
