PURPOSE: In an effort to evaluate intrinsic physical properties using dual energy CT rather than kVp dependent Hounsfield Units, our purpose was to determine average effective atomic number (Zeff) and Electron Density (ED) values, relative to water, of tissues of the brain and head, using spectral CT data.
MATERIALS AND METHODS: Scans of 33 patients who underwent non contrast enhanced head CT (IQon, Philips Healthcare, Eindhoven, Nederland) between February and September 2017, with no radiological findings were retrospectively reviewed. Non contrast enhanced series were performed at 120 kVp on a detection based dual energy system. Zeff and ED images were retrospectively reconstructed directly from the scanner spectral acquisition. Pixel values were received from ROIs of 3 gray-white matter pairs, CSF, vitreous, optic lens and retro-buccal fat. Paired t-test was used to assess the significance of the difference of measurements between gray and white matter and between CSF and vitreous.
RESULTS: 330 ROIs were marked, resulting in 21328 pixels of gray and white matter, 3579 pixels of CSF, vitreous and fat, and 2583 pixels of the lens. Average ROI area was 8.5±1.5mm2 for the lens and 24.9±0.4mm2 for all other structures. Zeff for gray matter, white matter, CSF, vitreous, lens and fat were 7.32±0.06, 7.19±0.05, 7.28±0.05, 7.28±0.03, 7.27±0.06, and 5.92±0.24, respectively. ED for these structures was 103.01±0.23, 102.79±0.21, 100.34±0.28, 100.43±0.16, 107.42±1.6, and 92.88±0.6 %EDW, respectively (Figure). P-value for comparison of gray and white matter Zeff and ED were
CONCLUSIONS: Some tissues of the brain and head evaluated in this study have unique Zeff and ED values, allowing for definition based on physical properties rather than Hounsfield Units that are kVp dependent.
