Spectral ρZ-Projection Method for Characterization of Body Fluids in Computed Tomography: Ex Vivo Experiments1.

Rationale and Objectives: The identification of body fluids in computed tomography poses a major diagnostic challenge. The chemical composition of body fluids deviates only slightly from water with very similar computed tomographic (CT) values, which typically range from 0 to 100 HU. The aim of this study was to assess physical and chemical properties of different body fluids in an ex vivo setting. Materials and Methods: A total of 44 samples of blood, blood mixed with pus, pus, bile, and urine obtained during diagnostic and therapeutic punctures were scanned at 80 and 140 kV. Data was quantitatively assessed using the spectral ρZ-projection algorithm, which converts dual-energy CT scans into mass density (ρ) and effective atomic number (Z_eff. ) information. Results: Attenuation values measured at 80 and 140 kV were largely overlapping. CT values allowed, to some degree, for the differentiation of bile or pus from blood or the blood/pus mixture. By applying the ρZ-projection, most substances, except for urine, were distinguishable with only small standard deviations ranging between 0.003 and 0.007 g/cm³ for mass density and between 0.020 and 0.043 for Z_eff. . Conclusion: The ρZ-projection method is suited to quantitatively assess mass density and effective atomic number of ex vivo body fluid samples. In clinical routine, this technique might be useful for identifying unclear fluid collections even in unenhanced computed tomography. [Copyright &y& Elsevier]