Photon-counting detector CT for follow-up after TACE in hepatocellular carcinoma: effects of reconstruction kernel and sharpness

Purpose To compare the performance of different reconstruction kernels and sharpness levels in photon-counting detector CT (PCD-CT) for post-transarterial chemoembolization (TACE) imaging of hepatocellular carcinoma (HCC), with particular emphasis on residual viable tumor conspicuity, and to identify reconstruction settings that may improve clinical follow-up assessment.Methods In this retrospective study, 72 patients with HCC undergoing TACE were included. Triple-phase contrast-enhanced CT images were reconstructed using body regular (Br) and quantitative regular (Qr) kernels at four different sharpness levels (36, 40, 44, and 48). Quantitative analysis included image noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and edge sharpness. Subjective image quality was assessed by two readers using a 5-point Likert scale.Results Increasing kernel sharpness significantly increased image noise and decreased SNR and CNR across all contrast-enhanced phases (e.g., arterial phase, Br kernel, noise 16.8 ± 2.1 to 36.1 ± 4.2; CNRVT-L, median 2.4 [IQR: 1.3-4.2] to 1.2 [IQR: 0.6-1.9]). At matched sharpness levels, Qr kernels exhibited slightly lower image noise and higher viable tumor SNR than Br kernels, particularly at low-to-moderate sharpness. Edge sharpness improved with increasing kernel sharpness for both Br and Qr, with Br demonstrating higher edge clarity for viable tumor-lipiodol deposition. Subjective assessment showed very good inter-reader agreement (κ = 0.81-0.95). Overall image quality decreased with higher kernel sharpness, whereas task-specific evaluations revealed kernel-dependent differences: Br44 provided superior vessel and viable tumor-lipiodol visualization, while Qr40 achieved better residual viable tumor clarity.Conclusion Reconstruction kernel type and sharpness level significantly influence quantitative and subjective image quality in post-TACE PCD-CT of HCC. Optimized reconstruction kernel and sharpness settings may improve residual viable tumor conspicuity and facilitate lesion assessment.