The DECT expands the functionality of traditional CT by providing images in the range of 40 to 140 keV VMIs and material separation technology[22, 23]. VMIs with low keV reconstruction (40-70 keV VMIs) can improve the contrast of iodine and the improve detection of BUC lesions[24]. VMIs with high keV reconstruction (80-140 keV VMI) reduce the sclerotic artifacts at the hip joint[25]. Iodine-water and water-iodine maps, based on material separation technology, can objectively reflect the iodine uptake and blood supplying changes in the lesions[26].
In this study, we investigated the impact of 13 different reconstruction parameters on the discrimination of BUC grading, including 40-140 keV VMIs, iodine-water maps, and water-iodine maps. For the models constructed using different parameters, the AUC of the training set and validation set ranged from 0.91 to 0.96 (greater than 0.9) and 0.84 to 0.90 (greater than 0.8), indicating a high diagnostic value for predicting BUC grading. Moreover, there was no significant difference in the AUC of the discrimination ability among the different parameters, indicating that changes in spectral parameters do not affect the discriminatory ability. For further validation the performance of these radiomic models, the DCA was also conducted, and the results support that within a certain threshold range, the net benefit of both high and low-energy VMIs and iodine-based image models was helpful in clinical decision-making. The imaging-genomic models constructed based on 13 different parameter images could successfully differentiate high and low-grade BUC, and spectral CT parameter variations did not affect the accuracy of the imaging-genomic discrimination models for BUC.
Due to reasons such as small tumor volume and low X-ray attenuation, conventional CT scans sometimes have difficulty diagnosing some BCa[24]. Previous study has shown[27] that VMIs can improve the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). In addition, the reconstruction of images at 40 keV enhances the contrast of BCa and the bladder wall, representing the optimal single energy for diagnosing BCa. The venous phase provides higher temporal images for detecting bladder cancer, making it easier to segment the tumor with minimal manual delineation. Therefore, in this study, the VOI of BCa was delineated on 40 keV VMI during the venous phase.
Researchers used 40-140 keV VMIs for the study of differentiating parotid tumors and adenolymphomas, the results indicate that for the classification of benign parotid tumors, the texture analysis of a multi-energy dataset is superior to the texture analysis of a single-energy dataset at 65 keV VMI[28]. In a study by Forghani et al.[29], which evaluated the lymph node metastasis of head and neck squamous cell carcinoma, texture features and iodine-based images were extracted from 40 to 140 keV VMI (at 5 keV intervals). The results showed that multi-energy texture analysis outperforms the analysis of datasets at single energies, but the texture analysis of the iodine map does not affect the model's performance. Simplifying the model (increasing the interval from 5 keV to 10 keV) has minimal impact on the overall performance. Thirteen radiomic models constructed based on different parameters can successfully distinguish between high- and low-grade bladder cancer. In this study, there was no further statistical analysis of the discriminative performance of the multi-energy model, as the AUC values of using different energy images in the ROC study were all greater than 0.91, indicating a high diagnostic efficiency.
Through the analysis of the 13 selected optimal subsets, GLCM features were selected as non-zero coefficients in 10 of the 13 radiomics models, excluding 80 keV VMI, 130 keV VMI, and iodine map. This is crucial for maintaining the high efficiency of the multiple radiomics models, as GLCM features can quantify the structural changes of cells and their organelles under various conditions, serving as essential factors in distinguishing between low-grade and high-grade tumors[30]. Furthermore, non-zero coefficients for GLDM features were observed in the lower-level 40-70 keV VMIs (except for 60 keV), while non-zero coefficients for GLRLM features were present in the higher-level 80-140 keV VMIs (except for 100 keV). Additionally, non-zero coefficients for GLSZM features were identified in the base substance map. These results suggest that different types of images can capture features that correlate with high and low tumor grades. Moreover, the study findings revealed that the inverse difference normalized (IDN) features derived from GLCM were exclusively present in the 40 keV VMI for distinguishing tissue components, potentially linked to the heightened tissue contrast in the 40 keV VMI.
Our study has several limitations. First, the study was retrospective and may result in inherent biases. Second, some discrepancies caused by manually outlined VOIs are unavoidable, even though we had made efforts to minimize the bias by using two trained radiologists. Third, our data were only from a single center. In the future, we will try to collect multicenter data to reinforce the conclusions of our study.
In conclusion, the variation of spectral CT parameters does not affect the radiomics-based prediction of the pathological grading of BUC. Even if different relevant features are selected from images with different parameters, the accuracy of the model is not impacted.