A Magnetic Resonance Imaging (MRI) tornpatible core biopsy instrument includes a detachable probe assembly to enhance the accuracy of placement at a biopsy site and avoid repeated insertions, even when used in a closed MRI magnet bore. In particular, the detachable probe assembly is configured for attachment to a localization fixture for accurate stereotopic placement to the desired biopsy site. While disengaged, dual lumens (vacuum and cutter) of the probe assembly allow applying vacuum to, draining fluid from, and insertion of fluids to the biopsy site. The biopsy instrument handle readily engages to the probe assembly for taking samples. Features are included for visual indications of the position of the cutter, prevention of disengagement when the cutter is advanced into the probe assembly, and a tolerance take-out feature that minimizes the deadzone gap at a distal end of the probe assembly, allowing samples to be taken close to sensitive tissues.