The radiologist locates the change, plans the access route and spares adjacent structures. The needle position is continuously monitored using the US. Very thin needles are used for some punctures (fine needle puncture/FNP). If a somewhat thicker needle is required (punch biopsy), a local anesthetic is administered beforehand.
When a drain is inserted, the pathological process (e.g. local accumulation of pus) is punctured and drained and cleaned via a catheter.