It may be necessary to take a sample (biopsy) from an organ or tissue that is not easily accessible (eg. liver, breast lump). In order to avoid major surgery, the biopsy may be taken using a specially designed needle with a solid thin rod (trocar) down the centre of the needle (cannula). The biopsy needle is inserted through the skin and into the target organ or tissue. Ultrasound guidance may be used to accurately locate the required tissue. Once near the target tissue the trocar is withdrawn from the biopsy needle and the needle is advanced and rotated to cut out a tiny segment of the tissue. This can then be sucked back into the needle by an attached syringe. The needle is withdrawn, and the sample expelled and examined under a microscope after staining.