Dual-layer spectral detector computed tomography for adrenal adenoma characterization: radiation dose reduction and quantitative agreement of multiphase virtual noncontrast with true noncontrast imaging.

Background: Computed tomography (CT) is the preferred imaging modality for evaluating adrenal lesions; however, the associated radiation exposure remains a significant concern. Dual-layer spectral detector CT (SDCT)-derived virtual noncontrast (VNC) images may reduce radiation exposure by eliminating dedicated noncontrast scans, yet their agreement with true noncontrast (TNC) imaging remains debated. This study aimed to quantitatively evaluate the agreement and image quality of VNC images [reconstructed from the arterial phase (VNCa) and portal venous phase (VNCp)] compared to TNC images in adrenal adenomas stratified by lipid content, and to assess the radiation dose reduction.

Methods: A total of 103 patients with adrenal adenomas treated at the Adrenal Disease Center of West China Hospital of Sichuan University between March 2023 and September 2024 were enrolled in this prospective study. All patients underwent dual-layer SDCT examination, including TNC and arterial and venous phase scans. VNC images were reconstructed from contrast-enhanced phases. Objective metrics, including CT attenuation value [Hounsfield units (HU)], noise (standard deviation), signal-to-noise ratio (SNR), contrast-to-noise ratio, and absolute attenuation error, and subjective image quality were compared. Interobserver agreement was assessed through the calculation of interclass correlation coefficients. For objective and subjective comparisons between TNC and VNC images, statistical analyses were performed with paired t-tests and Wilcoxon signed-rank tests. The radiation dose with and without TNC was calculated.

Results: This study included 103 patients (48 males and 55 females) with a mean age of 51.33±12.55 years. A total of 123 adrenal adenomas were identified, including 28 lipid-rich adenomas and 95 lipid-poor adenomas. For lipid-poor adenomas, VNC and TNC images showed excellent agreement in CT attenuation values (P>0.05), and compared to VNCp images, VNCa images exhibited significantly lower noise (17.44±3.39 vs. 18.64±2.91 HU; P<0.001) and higher SNR (1.68±0.76 vs. 1.55±0.67; P<0.001). In lipid-rich adenomas, VNC images overestimated CT attenuation, showing high absolute attenuation errors (VNCaerror: 9.92±6.49 HU; VNCperror: 8.50±5.17 HU), although these remained within the acceptable threshold of ≤10 HU. In the subjective scores of image quality, TNC images outperformed VNC images [TNC: median 5, interquartile range (IQR) 5-5; VNC: median 5 (IQR 4-5); P<0.001], although VNC scores remained high. No significant statistical difference was observed between the VNCa and VNCp scores (P>0.05). For most of the surrounding nonadenoma tissues, VNC and TNC images demonstrated good agreement, with attenuation differences consistently within ≤10 HU. Replacing TNC images with VNCa images could reduce the effective dose by approximately 32.63% for lipid-poor adenomas.

Conclusions: Our findings suggest that for lipid-poor adenomas, VNCa demonstrates high agreement with TNC and provides superior image quality, supporting its use as a TNC substitute for reduced radiation dose. For lipid-rich adenomas, VNC should be applied with caution due to the potential risk of attenuation overestimation. Subtype classification remains essential in such studies.