Fine needle aspiration is one of the most commonly used initial diagnostic tools for suspicious lesions. The doctor will typically use a 22 or 27 gauge needle to aspirate out free fluid and cells. It can be done in an outpatient setting and is associated with minimal pain. However, in up to 30% of cases, pathological slides from fine needle aspiration of breast lesions may be inconclusive, necessitating the need for further testing. FNA can be done to aspirate the contents of a cyst, which may relieve any pain that the cyst caused, or can be used to aspirate a suspicious lesion in conjunction with cytology (cellular analysis). If aspirating the contents of a cyst, the aspirate is usually not sent for cytology unless it is bloody. If the cyst is not detectable by touch, it may be located using ultrasound, MRI, or stereotactic mammography. Recovery time from an outpatient FNA is minimal. Core needle biopsy (CNB) is another percutaneous ("through the skin") method of breast biopsy that became more popular than FNA in the 1990s due to the larger sample of tissue CNB provides. This method is usually done under ultrasound guidance and involves using two needles, one inner "puncture" needle that is inserted into the mass, and a wider gauge needle with an open "gap" or "trough" on one side that allows for tissue to enter. A spring-loaded sheath then is triggered by the technician that covers the trough in the needle to allow sample tissue to be separated and removed for analysis. Typically 4 tissue samples are removed to minimize sample error. To prevent the need to pierce the breast repeatedly a coaxial needle left in place on top of the mass as a guide. CNB has a higher sensitivity for cancer than FNA, has lower false negatives, and has proven more successful in finding rare breast diseases like lobular carcinoma. However, this method still has relatively high rates of false negatives compared to surgical or vacuum assisted methods due to the overall low volume of tissue removed. Also, because breast tissue can be difficult to target on ultrasound, as much as 5-10% of suspicious lesions are missed by the needle and may result in a high rate of false negatives, or the need for additional biopsies. Vacuum assisted breast biopsy (VABB) is a more recent version of core needle biopsy using a vacuum technique to assist the collection of the tissue sample. Similarly to core needle biopsy the needle has a lateral ("from the side") opening and can be rotated allowing multiple samples to be collected through a single skin incision.