In breast cancer patients, some nodules are only visible on MRI, thus, requiring MRI-guidance to perform the biopsy. MRI interventions are cumbersome due to the magnetic field and the constrained working space. An MR safe robotic system actuated by pneumatic stepper motors may enable these procedures, improving both accuracy and image-guided navigation. A compact multipurpose pneumatic stepper motor has been designed with outer dimensions$(45 \times 40\times 15)\mathbf{mm}^{\mathbf{3}}$. This is configurable as a linear, rotational or curved stepper motor with a customizable step size and radius of curvature. Five copies of these motors actuate the Sunram 7 biopsy robot, of which the moving part (without protruding racks and tubes) measures$(130 \times 65\times 55)\mathbf{mm}^{\mathbf{3}}$. After manually choosing the target location and angle of approach, the needle is robotically inserted into the breast and the integrated pneumatic biopsy gun is fired to sample tissue from the lesion. The maximum torque of the presented motor is 0.61 N m at 6 bar which can be achieved using 13-teeth polycarbonate gears. Using 17-teeth gears for higher accuracy and a more convenient working pressure of 2 bar the maximum torque is 0.28 N m. The accuracy in free air of the Sunram 7 robot is 1.69mm and 1.72mm in X and Z-direction respectively, with a resulting 2-D error of 2.54 mm. The workspace volume is 4.1 L. When targeting 10 mm-sized lesions in phantoms under MRI guidance, Sunram 7 achieved a success rate of 68%. The minimum interval between two successive biopsies was 5:47 minutes. The presented multipurpose stepper motor has distinct advantages over previous designs in terms of robustness, customizability, printability and ease of integration in MR safe robotics. The Sunram 7 is able to perform accurate MRI-guided biopsies in a large workspace volume while reducing the intervention time when compared to the gold standard (i.e., MRI-guided free-hand biopsy).

Breast cancer is the most frequently life-threatening diagnosed type of cancer among women. Early and accurate diagnosis by acquiring a tissue sample using biopsy techniques is essential. However, small lesions only visible by MRI are often missed in standard methods, indicating the need for a robotic-assisted biopsy system that is MRI-compatible. Existing proof-of-concepts are difficult to employ due to large sizes and/or actuation complexities. Therefore, a compact pneumatically-actuated 5 DOF MRI-compatible robot was further developed and controlled by a computerized valve manifold. Accuracy and efficiency measurements have been performed using two different PVC breast phantoms with embedded fish oil capsules (mimicking lesions) inside a 0.25T MRI scanner. Preliminary results show that the end-effector was able to hit the targeted capsules, and that the position accuracy is in the range of 4.7-7.3 mm. The developed robotic system has potential to perform MRI-guided breast biopsies accurately and improve the clinical workflow.

Targeting of small lesions with high precision is essential in an early phase of breast cancer for diagnosis and accurate follow up, and subsequently determines prognosis. Current techniques to diagnose breast cancer are suboptimal, and there is a need for a small, MRI-compatible robotic system able to target lesions with high precision and direct feedback of MRI. Therefore, the design and working mechanism of the new Stormram 4, an MRI-compatible needle manipulator with four degrees of freedom, will be presented to take biopsies of small lesions in the MRI scanner. Its dimensions (excluding racks and needle) are 72×51×40 mm, and the system is driven by two linear and two curved pneumatic stepper motors. The T-26 linear motor measures 26×21×16 mm, has a nominal step size of 0.25 mm and the measured maximum force is 63N at 0.65 MPa. The workspace has a total volume of 2.2 L. Accuracy measurements have shown that the mean positioning error is 0.7 mm, with a reproducibility of 0.1 mm. Velocity measurements with 5 m long tubes show a maximum stepping frequency of 8 Hz (maximum force) to 30 Hz (unloaded). These results show that the robot might be able to target lesions with sub-millimeter accuracy within reasonable time for the MRI-guided breast biopsy procedure.