instruments for performing percutaneous biopsy procedures are disclosed , which have advantageous features for improving functionality and performance over prior art devices . these instruments comprise two types , single - use devices , and multiple - use devices having active tissue capture capability . improved features include the ability to retrieve and evaluate multiple tissue samples during a single insertion procedure , without physical handling of the samples , as well as constructional features , such as a molded tissue cassette housing , variant vacuum port embodiments suited for different tissue environments , and a method for backflushing the instrument to remove biological debris , among others .