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

Abstract

Background: The low clinically approved doses of gadolinium-based contrast agents (GBCA) 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 GBCA given their associated high gadolinium concentrations within hepatocytes. Objective: To investigate the potential of gadoxetate disodium in combination with PCD CT and low-keV 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, respectively). These solutions, along with deionized water, were evaluated in an anthropomorphic abdominal phantom using a clinical PCD-CT scanner; virtual monoenergetic images (VMI) at 40, 50, 60, and 70 keV, along with virtual noncontrast (VMC) images, 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 lowest attenuation. The maximum attenuation reached 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 GBCA, albeit approximately 8-times greater than clinical doses and 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.