A noticeable solution to sample significant cancer with few biopsies is cancer-image-guided targeting. Targeting biopsy lesions of MRI abnormality presents substantial clinical potential for the management of prostate cancer.

We developed an MR Safe robotic-assistant device for endorectal prostate biopsy. This is built entirely of nonmagnetic and electrically nonconductive materials, is electricity free, and uses pneumatic actuation and optical sensors.


MR Safe Robot for Endorectal Prostate Biopsy

The robot has a compact and simple 3 degree-of-freedom (DoF) structure, two for orienting a needle-guide and one to preset the depth of needle insertion. This assists the physician by automatically orienting the needle-guide on target and setting the depth of needle insertion under MRI guidance. The target is selected in the MRI. Needle insertion and biopsy are performed manually through the guide.

The robot attaches with a base plate to the MRI table and the patient is placed on the table in the prone position. The robot is placed manually and the support arm is locked in place to maintain this position throughout the procedure.

The MR Safe robot is controlled with an MR Conditional electro-pneumatic and electro-optical Interface and MR Unsafe Robot Controller.


MR Safe robot

Robotic motion is generated by two PneuStep motors located within the body of the robot and one in the Needle-Depth Driver. The motors are controlled with air and light through a bundle of hoses that connects the Robot to an Interface. A first motor adjusts the angle of the endorectal extension (R1) supported by a revolute joint (R) through a harmonic transmission. The second motor engages a screw transmission supported by a prismatic joint (P) and slides the bottom of the needle-guide through a revolute joint (R). A needle-spacer is mounted on the needle and a nut is threaded to it. The position of the nut over the spacer is adjusted automatically by the third motor located within the Needle-Depth Driver.


MR Safe robot

Numerous preclinical experiments were conducted to determine the functionality and targeting performance of the robot. Imaging experiments show unperceivable differences between MRI acquired without the robot, with the robot in place, and with the robot in motion. Changes of SNR between these case are <1%.
The results of targeting precision and accuracy experiments are:




Bench tests



CT-guided, in vitro



MRI-guided, in vitro



MRI-guided, animal




These demonstrate that the MR Safe device is sufficiently accurate to guide needle placement for prostate biopsy. For more details, please see the references below.


Stoianovici D, Kim C, Srimathveeravalli G, Sebrecht P, Petrisor D, Coleman J, Solomon SB, Hricak H: MRI-Safe Robot for Endorectal Prostate Biopsy, IEEE/ASME Transactions on Mechatronics. Aug 2014; Vol.19(4) pp.1289-1299. PMCID:4219418
MRI-safe robot for targeted transrectal prostate biopsy: animal experiments