Stiffness Assessment and Lump Detection in Minimally Invasive Surgery Using In-House Developed Smart Laparoscopic Forceps

Abstract

Minimally invasive surgery (MIS) incorporates surgical instruments through small incisions to perform procedures. Despite the potential advantages of MIS, the lack of tactile sensation and haptic feedback due to the indirect contact between the surgeon's hands and the tissues restricts sensing the strength of applied forces or obtaining information about the biomechanical properties of tissues under operation. Accordingly, there is a crucial need for intelligent systems to provide an artificial tactile sensation to MIS surgeons and trainees. This study evaluates the potential of our proposed real-time grasping forces and deformation angles feedback to assist surgeons in detecting tissues' stiffness. A prototype was developed using a standard laparoscopic grasper integrated with a force-sensitive resistor on one grasping jaw and a tunneling magneto-resistor on the handle's joint to measure the grasping force and the jaws' opening angle, respectively. The sensors' data are analyzed using a microcontroller, and the output is displayed on a small screen and saved to a log file. This integrated system was evaluated by running multiple grasp-release tests using both elastomeric and biological tissue samples, in which the average force-to-angle-change ratio precisely resembled the stiffness of grasped samples. Another feature is the detection of hidden lumps by palpation, looking for sudden variations in the measured stiffness. In experiments, the real-time grasping feedback helped enhance the surgeons' sorting accuracy of testing models based on their stiffness. The developed tool demonstrated a great potential for low-cost tactile sensing in MIS procedures, with room for future improvements. Significance: The proposed method can contribute to MIS by assessing stiffness, detecting hidden lumps, preventing excessive forces during operation, and reducing the learning curve for trainees.

Keywords: Minimally invasive surgery; angle sensor; force sensor; laparoscopy; lump detection; robotic surgery; stiffness assessment; tactile sensing.

FIGURE 1.

(a) COMSOL Multiphysics^® simulation showing the cross-sectional deformation of two ellipsoid 3-D objects with different stiffness induced by the same amount of vertically applied force (softer object on the left, MPa, and stiffer one on the right, MPa). (b) Schematic of the grasping tip of surgical forceps acting on two objects with different stiffness. The initial angle when the grasper is fully open is zero. When the jaw closes, the value of the angle increases. In case 1, the same amount of applied force induces higher deformation in the soft material. In case 2, reaching the same deformation level requires a higher amount of applied force on the hard object.

FIGURE 2.

Image of the developed ‘smart laparoscopic grasping forceps’ and zoomed-in insets on the different integrated components: the A201 FlexiForce FSR installed on the grasping tip, the ASR002 Smart TMR and rotating magnet integrated on the rotation point of the handle, and the electrical connections between the Arduino microcontroller and sensors inside the electronics box with an LCD.

FIGURE 3.

Calibration curve for the FlexiForce A201 sensor showing the measured outputs from the voltage divider circuit applied forces.

FIGURE 4.

PDMS samples palpation: (a) Image of the first four PDMS samples. (b) Plot of force and angle output signals from repetitive grasp-release events performed using our smart laparoscopic grasping forceps on the four PDMS samples. (c) Grasping force exerted on the four PDMS samples while securing the grasps at a constant angle. (d) Bar chart showing the average force-to-angle-change ratio of the four PDMS samples out of 10 repetitive grasps for each, reflecting the stiffness index, , with standard deviation error bars.

FIGURE 5.

Chicken meat slices palpation: (a) Image of the raw and pan-fried chicken meat slices. (b) Plot of force and angle output signals from repetitive grasp-release testing performed using the smart laparoscopic grasping forceps on the two chicken meat samples. (c) Grasping force exerted on the two chicken meat slices while securing the grasps at a constant angle (the viscoelastic properties of the chicken meat show a decrease in the grasping force over time).

FIGURE 6.

Lump detection: plot of force and angle output signals from grasping the highlighted positions on the raw chicken slice embedded with a small cooked chicken piece located at position X.