Progress in Developing a Standard Reference Material for Lung CT
H Chen-Mayer1*, Z Levine1, P Judy2, (1) National Institute of Standards and Technology, Gaithersburg, MD, (2) Brigham & Women's Hospital, Boston, MATH-E-217BCD-5 Thursday 1:00:00 PM - 2:50:00 PM Room: 217BCD
Purpose: Report of progress in developing a 'standard reference material' for tissue density variations obtained in CT scans. This effort is driven both by the mission of NIST as a standard institute, and by the activities of the RSNA COPDGene phantom design work.
Methods: We continue the development effort of one set of such standards by characterizing them in a NIST traceable standard beam quality, starting by the calibration of a small ionization chamber (0.6 cc) in the NIST standard beam qualities. The chamber then becomes the transfer detector for measurements performed on a commercial CT machine. We have selected foam blocks (cut to 5 cm x 4 cm x 1.9 cm) with 5 densities ranging from 0.06 to 0.30 g/cm³, with an HU value nominally between -950 and -695. We and performed transmission measurements on four batches foams, each containing 5 densities, and each density contains 10 blocks. We extracted the linear attenuation coefficient of the foams for each the available CT energies (90, 120, and 140 kV). A small water phantom of the same transverse dimension was scanned together with the foams to obtain the attenuation coefficient of water for the HU calculation. A full CT was then performed to obtain the HU value from the machine.
Results: The HU values obtained from the three energies using the transmission measurement of the foam and water vs those obtained from the full CT agreed to within 0.3% (stdm) averaged over all samples.
Conclusion: We have made progress toward developing a standard reference material for lung CT applications. Physical density measurements traceable to NIST standards are underway. The transmission measurements will also be performed on the NIST M-beams to create a correlation between the CT spectrum and the standard spectrum for these foams.