Single spectrum three-material decomposition with grating-based x-ray phase-contrast CT

Abstract

Grating-based x-ray phase-contrast imaging provides three simultaneous image channels originating from a single image acquisition. While the phase signal provides direct access to the electron density in tomography, there is additional information on sub-resolutional structural information which is called dark-field signal in analogy to optical microscopy. The additional availability of the conventional attenuation image qualifies the method for implementation into existing diagnostic routines. The simultaneous access to the attenuation coefficient and the electron density allows for quantitative two-material discrimination as demonstrated lately for measurements at a quasi-monochromatic compact synchrotron source. Here, we investigate the transfer of the method to conventional polychromatic x-ray sources and the additional inclusion of the dark-field signal for three-material decomposition. We evaluate the future potential of grating-based x-ray phase-contrast CT for quantitative three-material discrimination for the specific case of early stroke diagnosis at conventional polychromatic x-ray sources. Compared to conventional CT, the method has the potential to discriminate coagulated blood directly from contrast agent extravasation within a single CT acquisition. Additionally, the dark-field information allows for the clear identification of hydroxyapatite clusters due to their micro-structure despite a similar attenuation as the applied contrast agent. This information on materials with sub-resolutional microstructures is considered to comprise advantages relevant for various pathologies.

Quantitative X-ray phase contrast computed tomography with grating interferometry

“…The study presented there lead to precise calculation iodine contrast agent concentration [81]. A further step is the combination of spectral detector information with GBPC-CT, which enables noise reduction and consequent increase in quantitative electron density resolution [143].…”

“…With the electron density and attenuation coefficient at hand, as it is the case with GBPC-CT, one can determine also the effective atomic number Z eff as shown in refs. [57,76,78,81]. The effective atomic number is like the electron density an absolute physical quantity that can be used for material characterization and decomposition, although theoretical calculation of the effective atomic number varies [120][121][122].…”

“…In Braig et al, three-material decomposition was performed using electron density, effective atomic number, and the dark-field signal provided by laboratory GBPC-CT. The study presented there lead to precise calculation iodine contrast agent concentration [ 81 ]. A further step is the combination of spectral detector information with GBPC-CT, which enables noise reduction and consequent increase in quantitative electron density resolution [ 143 ].…”

“…In addition, Hounsfield units for the phase (HUp) [57,75] or the effective atomic number Z eff can be calculated [76][77][78]. The complementarity of the attenuation and phase signal of GBPC-CT can be used to perform material decomposition [79] or a decomposition similar to spectral CT into electron density and effective atomic number [80][81][82].…”

One-step Method for Material Quantitation using In-line Tomography with Single Scanning

“…According to some conversion formulas for material decomposition in phase-contrast imaging [4], [5], [10], the β and δ of the sample can be expressed as a linear combination of β and δ of the two basic materials, respectively . The decomposition of the sample can be carried out:…”