Position-force control in the identification of tissue structures using the spectrophotometric method

Abstract

BACKGROUND: Time-resolved spectrophotometry enables the contact probing of biological tissues at a depth of two millimeters to several centimeters, with a spatial resolution of one to five millimeters. This technique provides a quantitative assessment of optical parameters, concentrations of main chromophores, identification of tissue type and inclusions in the volume, which is relevant for intraoperative diagnostics [1–3]. The variability of optical properties during probe squeezing necessitates the implementation of force control of squeezing, which, like positioning, is used in robotic surgery and diagnostics [4–11]. A combined mechanical and spectrophotometric approach holds promise in this regard. However, further research is required concerning spectrophotometer setup, the development of test objects, and the determination of the possibilities of positioning-force-controlled spectrophotometry for the identification of tissues and inclusions. Development of approaches to active positional force control to study the functionality of spectrophotometry in identifying tissue structures. MATERIALS AND METHODS: An experimental bench was constructed based on a two-wavelength spectrophotometer with OxiplexTS frequency approach (ISS Inc., USA). This bench allows for the position control of the optical probe using a robotic mini-manipulator (U-Arm, China). Additionally, a software program was developed to record the pressing force of the fabricated probe in a customized nozzle for the manipulator. Finally, an algorithm was proposed for processing experimental data to estimate biomechanical, optical, and physiological parameters of the tissue. A single healthy subject participated in the experimental study. Measurements were conducted on the dorsal and ventral surfaces of the forearm and on the palmar surface of the hypotenar. RESULTS: The quantitative assessment of elastic properties of biological tissue can be achieved through the use of force-displacement data. The simultaneous registration of optical parameters, concentrations of hemoglobin fractions in a unit of the investigated volume, and tissue saturation in the dynamics of probe pressing allows for the estimation of microcirculatory blood flow, the revelation of the presence and type of large vessels. The standard silicone test objects used for spectrophotometer calibration do not align with the mechanical properties of biological tissues. Given the diminutive dimensions of the optical probe, this discrepancy introduces an additional degree of uncertainty in the quantitative assessment of tissue properties. CONCLUSIONS: The addition of active force control and automated positioning of the optical probe during spectrophotometry enhances its functional capabilities for identifying tissue structures and expands its applications in robotic pre-, intra- and post-operative diagnostics. For further studies on a larger number of tissues, tissue structures and mimicking tissue test objects, an improvement of the experimental bench is required: increase of the sensitivity of the force sensor, smoothness and discreteness of the motion during positioning, e.g. by replacing the mini manipulator by a collaborative robot. The improvement of the software part implies the implementation of synchronization with OxiplexTS through its input interface module, writing a program for automatic surface scanning.

Keywords

• force control
• optical properties
• mechanical properties
• biotissue