Use of Photon-Counting Detector CT to Visualize Liver-Specific Gadolinium-Based Contrast Agents: A Phantom Study

BACKGROUND. The low clinically approved doses of gadolinium-based contrast agents (GBCAs) do not generate sufficient enhancement on CT for diagnostic purposes. Photon-counting detector (PCD) CT offers improved spectral resolution and could potentially enable visualization of hepatocyte-specific GBCAs, given their associated high gadolinium concentrations within hepatocytes. OBJECTIVE. The purpose of this study was to investigate the potential of gadoxetate disodium in combination with PCD CT and low-energy virtual monoenergetic imaging (VMI) reconstructions to achieve an increase in attenuation in a phantom. METHODS. A series of solutions was prepared of diluted gadoxetate disodium (concentrations of 0.250-2.5 μmol/mL, corresponding with doses of 25-200 μmol/kg). These solutions, along with deionized water, were evaluated in an anthropomorphic abdominal phantom using a clinical PCD CT scanner; VMI reconstructions at 40, 50, 60, and 70 keV and virtual noncontrast (VNC) imaging reconstructions were generated. Attenuation measurements were obtained; a linear regression model combined these values with previously reported in vivo data to estimate hepatic enhancement and CNR across doses. RESULTS. Attenuation increased with increasing concentration at a given energy level and with decreasing energy level for a given concentration; VNC images had the lowest attenuation. The maximum attenuation reached in the abdominal phantom was 45.2 HU for a concentration of 2.5 μmol/mL at 40 keV. A concentration of 0.25 μmol/mL had attenuation at 40 keV of 13.0 HU. The model yielded estimated in vivo hepatic enhancement at 40 keV of 4.9 HU for a dose of 25 μmol/kg, 19.9 HU for 100 μmol/kg, and 30.8 HU for 200 μmol/kg; corresponding CNRs were 0.13, 0.52, and 0.81, respectively. CONCLUSION. The combination of gadoxetate disodium and PCD CT could theoretically allow appreciable hepatic enhancement at a 200-μmol/kg dose; such effect was not observed for the clinically approved 25-μmol/kg dose. CLINICAL IMPACT. PCD CT achieved attenuation increases for gadoxetate disodium at considerably lower doses than previously documented for CT of GBCAs, albeit at approximately eight times greater than clinical doses, which were thus too high for clinical use. Additional research exploiting PCD CT technology could seek to reduce further doses required for sufficient visualization into a clinically feasible range, to potentially allow CT using a liver-specific agent.