[US-guided interventional procedures: what a radiologist needs to know]

US has important advantages in guiding interventional procedures: it is economical and widely available, it does not use ionizing radiation, and it requires less time than other techniques. US guidance can be provided using devices adapted to probes or using the freehand technique (holding the needle in one hand and the probe in the other). US-guided procedures require careful planning, adequate hemostasis or a directly compressible puncture site, the patient's informed consent, and appropriate measures to ensure asepsis and anesthesia. The technique involves introducing the needle or catheter through the plane of the US slice. The advance of the needle is controlled in real time. High resolution linear probes are ideal for interventional procedures in superficial tissues, but 3.5 MHz probes are required for procedures in deep tissues. The most common procedures include biopsies, drainages, and percutaneous injections. Biopsies can be carried out using fine needles to obtain material for cytological study (fine-needle aspiration cytology) or using large needles to obtain specimens for histologic study (core biopsy). Core biopsy is more sensitive and more specific, and it has a low rate of complications. Drainage almost always involves placing a catheter in a fluid collection; it can be done using the Seldinger techniques, trocars, or pleural catheters. US-guided percutaneous injections can be used to inject substances into infectious lesions, tumors, or nerve plexuses, and they are especially useful in musculoskeletal disease.