1. A method of positioning an interventional instrument within a portion of human or animal tissue, comprising: positioning a portion of human or animal tissue in a biopsy device, wherein the tissue has some normal tissue and some lesion tissue, wherein the tissue is maintained in a substantially fixed position with respect to the biopsy device, wherein the biopsy device comprises at least one fiducial marker which can be identified under an imaging modality; imaging the tissue via the imaging modality to produce a calibration image of the tissue, wherein the calibration image shows the position of the at least one fiducial marker; imaging the tissue via the imaging modality to produce a diagnostic image of the tissue, wherein the diagnostic image shows the position of the lesion tissue; calibrating the biopsy device with respect to the at least one fiducial marker; calculating the location of the lesion tissue with respect to the biopsy device; positioning an interventional instrument in the tissue such that the interventional instrument is in a desired position with respect to the lesion tissue based on the calculated location of the lesion tissue; imaging the tissue via the imaging modality to produce an interventional image of the tissue with the interventional instrument positioned in the tissue, wherein the lesion tissue can be differentiated from the normal tissue, wherein the interventional image shows the position of the interventional instrument and the lesion tissue; adjusting the position of the interventional instrument, if needed, based on the relative position of the interventional instrument and the lesion tissue.