Randomization and blinding
Patients were randomly divided into five groups by computer random method based on the duration of the VFP application. SPSS26.0 software was used to generate a random sequence, and the random assignment scheme was saved in light-tight envelopes. Envelopes were opened sequentially in the order of enrollment, and patients were assigned to the assigned group according to the assignment scheme in the envelope. Four centers enrolled participants at the same time. Enrollment was terminated when the total number of participants reached the final required sample size. Because patients and study operators were aware of device use, the study was blinded only to study personnel who performed the ultrasonography.