Abstract Content:

Objective: Discuss the image quality and diagnostic performance of dual-layer spectral detector CT virtual non-contrast (VNC) compared to true non-contrast (TNC) in renal cysts,to reduce the radiation dose received by patients.

Methods: This study prospectively enrolled 43 patients (28 males, 15 females, mean age 56.81±11.95 years) who underwent adrenal enhancement examinations using a dual-layer spectral detector CT (Spectral CT 7500; Philips Healthcare) at West China Hospital of Sichuan University between August 2023 and December 2024. All patients underwent enhanced scanning, including TNC , arterial and portal venous phase. Obtain virtual non-contrast (VNCa) images in the arterial phase and virtual non-contrast (VNCp) images in the portal venous phase at the post-processing workstation. The study conducted quantitative and qualitative analyses between TNC and VNC. (1) Quantitative analyses: By manually placing the area of interest ROI, the CT values and noise (standard deviation, SD) of different tissues were compared among the TNC, VNCa, and VNCp image groups. The signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and the differences in CT values between VNC and TNC images were calculated for each ROI. Measurement Method: Choose the largest cross-sectional plane of the cyst for measurement, with the ROI encompassing two-thirds of the lesion; The ROIs for subcutaneous fat, muscles, liver, spleen, pancreas, and abdominal aorta are fixed at 100 mm²; At the center of the renal hilum, the ROI covers two-thirds of the renal cortex, medulla, and the short-axis renal vein. At the level of the renal artery origin, the ROI covers two-thirds of the short-axis renal artery; To ensure measurement accuracy, all measurement were obtained at the central slice and two adjacent slices above and below, totaling three planes, and take the average value as the final result. (2) Qualitative analyses: The subjective image quality of the three image sets was independently assessed by two observers on a 5-point Likert scale, the higher scores denoted superior image quality.（3）Record the radiation doses for the non-contrast scan and both phases of contrast-enhanced scan separately. Statistical analyses was performed using paired t-tests or Wilcoxon signed-rank tests.

Results: The study included a total of 43 patients, with 85 renal cysts were detected. (1) Statistical analyses showed that the CT attenuation values of cysts were consistently lower VNC than TNC (P<0.001), However, the differences in CT values between VNC and TNC all fell within the acceptable threshold of 10 HU, Moreover, the difference between VNCa and TNC was significantly lower than that between VNCp and TNC (8.25 ± 0.68 vs. 10.37 ± 0.78 HU; P<0.05); Noise in VNCa images did not significantly differ from TNC (P>0.05), but VNCa demonstrated a higher signal-to-noise ratio than VNCp (0.57±0.07 vs. 0.39±0.07). For most of the surrounding noncystic tissues, VNC and TNC images demonstrated good agreement, with the attenuation differences consistently within ≤10 HU. (2)In subjective image quality assessment, TNC images generally outperformed VNC images, but VNC images still received higher scores from two observers. No statistically significant difference was found between VNC and TNC. (3) For the radiation dose, the total effective radiation dose for 43 patients in the TNC, VNCa, and VNCp phases was 16.03 ± 5.73 mSv, excluding TNC, the effective radiation dose decreased to 10.67 ± 3.68 mSv, resulting in a reduction of approximately 33.44%.

Conclusions: In summary, for the evaluation of renal cysts, VNC images demonstrate good consistency with TNC images. In particular, VNCa images can provide CT attenuation values and signal-to-noise ratios comparable to TNC. Therefore, Vnca can be replace TNC and effectively reduce radiation dose.