The influence of fine-needle aspiration on dual-layer detector spectral CT parameters of papillary thyroid carcinoma: a propensity-match analysis.

Abstract

Background: Dual-layer detector spectral computed tomography (DLCT) and fine-needle aspiration (FNA) are commonly used in papillary thyroid carcinoma (PTC). However, whether FNA affects DLCT quantitative parameters remains uncertain. This study aimed to investigate the effect of FNA on DLCT parameters in PTC and to determine the optimal timing for DLCT examination.

Methods: This retrospective study included 689 patients with PTC, who were categorized into pre-FNA (n = 222) and post-FNA (n = 467) groups according to the sequence of FNA and DLCT. Propensity score matching (PSM) was applied to balance confounding variables. Sensitivity analyses were performed using inverse probability of treatment weighting and multivariate regression. DLCT parameters, including virtual monoenergetic images (VMIs) at 40, 70, and 100 keV; spectral attenuation curve slope (λ_HU); iodine concentration (IC); normalized IC (NIC); effective atomic number (Z_eff); and normalized Zeff (NZ_eff), were compared between groups in arterial (AP) and venous phases (VP). Post-FNA time intervals were ranked and divided into deciles. For each DLCT parameter, standardized differences from the pre-FNA baseline were plotted across deciles to propose temporal cutoffs, which were validated by comparing post-FNA subgroups with the pre-FNA group.

Results: Covariates were well balanced after PSM, with all standardized mean differences below 0.25. Sensitivity analyses confirmed consistent direction of effect estimates across methods. Two clinically relevant exploratory temporal landmarks were observed around 6 and 18 days. Within 6 days after FNA, significant differences were observed in AP VMIs (40, 70, 100 keV), λHU, IC, NIC, and VP VMI at 100 keV. Between 7 and 18 days, only VP-IC remained significantly altered. Beyond 18 days, no parameters differed from pre-FNA baselines.

Conclusions: DLCT parameters showed a dynamic post-FNA temporal pattern, with early and later candidate recovery windows centered around approximately 6 and 18 days. From a clinical perspective, DLCT may be considered before FNA or after about 6 days, whereas a later interval around 18 days may be preferable when minimizing biopsy-related perturbation is particularly important.