The applications of interventional ultrasound are countless but can be divided into two major groups: Diagnostic interventions include biopsy of solid tissue, aspiration of fluid and instillation of diagnostic material such as contrast agents through a catheter. Therapeutic interventions comprise drainage of fluid collections like ascites, pleural and pericardial effusions, lymphoceles and abscesses, tubulation of hollow organs as in nephrostomies, gastrostomies and cholecystostomies and tissue ablation.
Regardless of the purpose of the intervention the principles of ultrasound guidance remains the same and can be described as either the "needle guide" or the "free hand" technique. A needle guide is a dedicated device, purpose-made to fit a specific transducer or set of transducers in a way that makes an electronically displayed punctureline on the monitor correspond with the needle canal on the guide, when attached to that particular transducer. Using a needle guide provides safer control of the needle during insertion, but it is on the cost of lesser flexibility of needle manipulation and limited degree of freedom regarding puncture direction. With the "free hand" technique there is no physical connection between needle and transducer and thus no limitations exist regarding point of needle insertion or angel of puncture. There is no punctureline on the monitor and the needle may be inserted from any direction parallel or perpendicular to the scanning plane, which ever solution is most suitable according to the situation at hand.
Two factors have changed interventional ultrasound in recent years: Contrast ultrasound can distinguish malignant lesions from benign lesions (as haemangiomas) in the liver, thus reducing the amount of biopsies significantly. Fusion imaging (CT and US) can guide the interventionalist for a safer and more accurate puncture procedure in cases of poor US visibility.