Virtual Noncontrast Abdominal Imaging with Photon-counting Detector CT

Background: Accurate CT attenuation and diagnostic quality of virtual noncontrast (VNC) images acquired with photon-counting detector (PCD) CT are needed to replace true noncontrast (TNC) scans. Purpose: To assess the attenuation errors and image quality of VNC images from abdominal PCD CT compared with TNC images. Materials and Methods: In this retrospective study, consecutive adult patients who underwent a triphasic examination with PCD CT from July 2021 to October 2021 were included. VNC images were reconstructed from arterial and portal venous phase CT. The absolute attenuation error of VNC compared with TNC images was measured in multiple structures by two readers. Then, two readers blinded to image reconstruction assessed the overall image quality, image noise, noise texture, and delineation of small structures using five-point discrete visual scales (5 = excellent, 1 = nondiagnostic). Overall image quality greater than or equal to 3 was deemed diagnostic. In a phantom, noise texture, spatial resolution, and detectability index were assessed. A detectability index greater than or equal to 5 indicated high diagnostic accuracy. Interreader agreement was evaluated using the Krippendorff alpha coefficient. The paired t test and Friedman test were applied to compare objective and subjective results. Results: Overall, 100 patients (mean age, 72 years +/- 10 [SD]; 81 men) were included. In patients, VNC image attenuation values were consistent between readers (alpha = .60), with errors less than 5 HU in 76% and less than 10 HU in 95% of measurements. There was no evidence of a difference in error of VNC images from arterial or portal venous phase CT (3.3 HU vs 3.5 HU, P = .16). Subjective image quality was rated lower in VNC images for all categories (all, P < .001). Diagnostic quality of VNC images was reached in 99% and 100% of patients for readers 1 and 2, respectively. In the phantom, VNC images exhibited 33% higher noise, blotchier noise texture, similar spatial resolution, and inferior but overall good image quality (detectability index >20) compared with TNC images. Conclusion: Abdominal virtual noncontrast images from the arterial and portal venous phase of photon-counting detector CT yielded accurate CT attenuation and good image quality compared with true noncontrast images. (C) RSNA, 2022

Automated summary

This study assessed the attenuation errors and image quality of abdominal virtual noncontrast (VNC) images acquired with photon-counting detector (PCD) CT compared to true noncontrast (TNC) images. The results showed consistent attenuation values in VNC images with small errors. Subjective image quality ratings were lower in VNC images, but the diagnostic quality still reached a good level.