Introduction

Gallbladder polyps are defined as a general term for a group of diseases that originate in the wall of the gallbladder and protrude restrictively into the lumen [1], also known as polypoid lesions of gallbladder (PLGs). With the popularity of ultrasound, the detection rate of PLGs has increased. Epidemiological studies show that the prevalence of PLGs is about 0.3–12.3% in adults, where gallbladder neoplastic polyps account for only about 5% of PLGs [1, 2]. As the most common gallbladder polyps, cholesterol polyps are foamy cell clusters formed by cholesterol crystals deposited in the gallbladder wall and phagocytosed by macrophages, with the surface covering the mucosal layer of the gallbladder, and no malignant tendency has been reported in the literature [3]. According to the 2019 WHO Classification of Tumors [4], gallbladder neoplastic polyps include pyloric gland adenomas and intracholecystic papillary neoplasms. Gallbladder neoplastic polyps are prone to atypical hyperplasia and may progress to gallbladder cancer, and they are considered as precancerous lesions [5, 6]. Therefore, the accurate differentiation between cholesterol polyps and precancerous gallbladder neoplastic polyps by preoperative imaging is a pressing issue in clinical practice.

Ultrasound is the preferred imaging method for evaluating PLGs, but it is difficult to accurately distinguish cholesterol polyps from gallbladder neoplastic polyps by conventional ultrasound [7, 8]. How to improve the accuracy of ultrasonic identification of gallbladder polyp-like lesions is an urgent clinical problem. Superb microvascular imaging (SMI), as a new modality of ultrasound imaging, has unique advantages in showing the morphology of microvasculature with low flow velocity in the lesion, thereby significantly improving the resolution, sensitivity and specificity of ultrasound diagnosis [9]. The combination of the two ultrasonic modalities, namely conventional ultrasound and SMI, could contribute to more accurate diagnosis of PLG.

Recently, novel imaging technologies based on radiomics (AI) have made rapid advances, where algorithms process medical imaging data sets through hierarchical mathematical models that can learn to use biometrics to detect diagnostic patterns. Zhang et al. [10] established a neoplastic predictive model and evaluated the effectiveness of radiomics in predicting malignancy in patients with gallbladder polyps. A single-center study by ** to 8% when there is lymph node metastasis, and the rate of stage 4b gallbladder cancer is only 2% [24]. Therefore, early detection of gallbladder cancer and precancerous lesions and early intervention are important to improve the survival rate of patients.

Ultrasound has been recognized as the first choice of imaging examination for the screening and follow-up of gallbladder polyps. However, it is difficult to identify gallbladder neoplastic polyps or cholesterol polyps solely from the echogenicity, morphology, or vascularity characteristics of the lesion [25, 26]. In Table 1 of this study, although the polyp diameter, pedicle and blood flow are statistically different between the gallbladder neoplastic polyp group and cholesterol polyp group, the diagnostic accuracy is low based on these indicators. Accordingly, Domestic and international scientific guidelines over the years recommend cholecystectomy for gallbladder polyps larger than 1 cm in diameter [27]. However, the guidelines for gallbladder polyps have resulted in a large number of unnecessary cholecystectomy, which has been questioned by many scholars [28, 29]. Therefore, there is an urgent need for a new method with high accuracy and reproducibility to accurately identify gallbladder neoplastic polyps and cholesterol polyps.

The application of artificial intelligence in medical imaging is one of the hot spots in medical research. Based on the big data analysis of computer, we can obtain numerous objective image feature data with a resolution far beyond the human eye [16, 30,31,32]. In our previous study, we extracted spatial and morphological features of single-modality gray-scale ultrasound. Our study reported that adenomas polyps have a more uniform pixel distribution, with a relatively smaller proportion of hyperechoic areas inside the polyps, and adenomas polyps are larger and more irregular in morphology. These are closely related to the pathophysiological features of gallbladder neoplastic polyps and cholesterol polyps [3, 6].

In this study, we extracted dual-modality ultrasound image datasets of gray-scale ultrasound and SMI. SMI technique is a method to evaluate tissue microvascular perfusion, and it can detect low speed flow signal without contrast agent, thus giving us more diagnostic information. In the process of radiomics analysis in this paper, the SVM model using dual-modality images’ features had the best discriminative ability, and its AUC, ACC, SEN, SPE and YI all reached the best level. There were statistical differences in the AUC, YI between the dual-modality images and the B-mode images. And there were statistical differences in the AUC, ACC, SPE and YI between the dual-modality images and SMI images. It could be seen that the calibration curve (Fig. 5) of the dual-modality model was closer to the diagonal dotted line corresponding to the perfect prediction model than the single-modality models, which indicated that the dual-modality model had better prediction performance. In conclusion, the dual-modality images combined with B-mode images and SMI images have the potential to improve the accuracy of classification of PLGs. In future clinical practice, the dual-modality radiomics features will be extracted, and the classification model based on the dual-modality radiomics features will help to accurately and early identify the gallbladder neoplastic polyps from cholesterol polyps.

Our study also had some limitations. This study was our preliminary attempt to obtain dual-modality ultrasound images’ parameters as well as apply radiomics technology to identify gallbladder neoplastic polyps and cholesterol polyps of gallbladder. The sample size of this study was small, it will be expanded for deep learning in the follow-up [33]. Moreover, this study was a single-center study, and a prospective multicenter study with a large sample size need to be conducted for further validation in the future. The results in this paper are preliminary and guarantee further robust studies in the future.

Conclusions

In conclusion, with the analysis of radiomics, the dual-modality ultrasound combining B-mode ultrasound and SMI showed an excellent classification accuracy for gallbladder neoplastic polyps and cholesterol polyps of gallbladder. Our model has high sensitivity and specificity at differentiating gallbladder polyps, which means that it could be potentially used in clinical practice to avoid unnecessary cholecystectomies and missing diagnosis of gallbladder neoplastic polyps.