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

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. 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. 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; CNR VT−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. 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.