Peripheral Venous Access Establishment

The goal of this clinical trial is to learn if AI-assisted site selection plus human-machine coordinated puncture improves the quality and safety of peripheral venous access for contrast-enhanced imaging in patients of all ages needing CT/MR contrast scans across three hospitals. The main questions it aims to answer are: Does the AI-assisted workflow improve the composite success rate of venous cannulation compared with routine nursing? Does this human-machine model raise first-attempt puncture success, shorten procedure time and reduce complications? Researchers will compare the AI-assisted intervention group to the routine nursing control group to see if the AI-assisted human-machine coordinated puncture brings clinical benefits. Participants will: * Receive peripheral venous cannulation for contrast-enhanced imaging. * Have arm images and clinical data collected before and after puncture. * Complete standardized venous access assessment and 24-hour post-procedure safety observation.