Coaxial needle insertion assistant for epidural puncture effect of lateral force on needle.

We validated the effectiveness of a coaxial needle insertion assistant under the condition that the needles were laterally deformed. The coaxial needle insertion assistant separates the cutting force at the needle tip from shear friction on the needle shaft, and haptically display it to a user in order to assists her/his perception during epidural puncture. An outer needle covers the side of an inner needle, preventing the shear friction from acting on the inner needle. However when the needles are laterally deformed and make contact to each other, it is concerned that the effect of the separation is degraded. In this paper, the users punctured an artificial tissue with variable insertion angles, so that the needle is intentionally laterally deformed. The overshoot and user confidence in detecting puncture was examined.

Coaxial needle insertion assistant with enhanced force feedback.

Many medical procedures involving needle insertion into soft tissues, such as anesthesia, biopsy, brachytherapy, and placement of electrodes, are performed without image guidance. In such procedures, haptic detection of changing tissue properties at different depths during needle insertion is important for needle localization and detection of subsurface structures. However, changes in tissue mechanical properties deep inside the tissue are difficult for human operators to sense, because the relatively large friction force between the needle shaft and the surrounding tissue masks the smaller tip forces. A novel robotic coaxial needle insertion assistant, which enhances operator force perception, is presented. This one-degree-of-freedom cable-driven robot provides to the operator a scaled version of the force applied by the needle tip to the tissue, using a novel design and sensors that separate the needle tip force from the shaft friction force. The ability of human operators to use the robot to detect membranes embedded in artificial soft tissue was tested under the conditions of 1) tip force and shaft force feedback, and 2) tip force only feedback. The ratio of successful to unsuccessful membrane detections was significantly higher (up to 50%) when only the needle tip force was provided to the user.

Intraoperative forces and moments analysis on patient head clamp during awake brain surgery.

In brain surgery procedures, such as deep brain stimulation, drug-resistant epilepsy and tumour surgery, the patient is intentionally awakened to map functional neural bases via electrophysiological assessment. This assessment can involve patient's body movements; thus, increasing the mechanical load on the head-restraint systems used for keeping the skull still during the surgery. The loads exchanged between the head and the restraining device can potentially result into skin and bone damage. The aim of this work is to assess such loads for laying down the requirements of a surgical robotics system for dynamic head movements compensation by fast moving arms and by an active restraint able to damp such actions. A Mayfield(®) head clamp was tracked and instrumented with strain gages (SGs). SG locations were chosen according to finite element analyses. During an actual brain surgery, displacements and strains were measured and clustered according to events that generated them. Loads were inferred from strain data. The greatest force components were exerted vertically (median 5.5 N, maximum 151.87 N) with frequencies up to 1.5 Hz. Maximum measured displacement and velocity were 9 mm and 60 mm/s, with frequencies up to 2.8 Hz. The analysis of loads and displacements allowed to identify the surgery steps causing maximal loads on the head-restraint device.

Accurate calibration method for 3D freehand ultrasound probe using virtual plane.

PURPOSE: In this paper a new, easy-to-manufacture and easy-to-use ultrasound (US) probe calibration phantom for 3D freehand scanning is presented and evaluated, together with a new method for achieving an accurate and user-robust calibration using virtual plane. METHODS: The phantom allows the optically tracked US probe to perform two rotations and two translations while keeping the image of a tensioned wire in the image plane. This approach allows obtaining a sharp image of the wire independently from the probe pose. The virtual plane allows the calibration algorithm to converge minimizing the required number of US probe tracked poses. The US image and position data are synchronized via a CORBA interface, created within the Image Guided Surgery Toolkit (IGSTK) framework. The calibration algorithm and the calibration protocol were evaluated in a set of experiments carried out by different test-users. RESULTS: The calibration method proved to be accurate and precise: 3D point reconstruction accuracy resulted 0.2 mm as mean value, while the precision was 0.4 mm as standard deviation. CONCLUSIONS: The technique showed to be suitable for medical applications from morphological diagnosis to intraoperative surgical planning adaption.

Force feedback in a piezoelectric linear actuator for neurosurgery.

BACKGROUND: Force feedback in robotic minimally invasive surgery allows the human operator to manipulate tissues as if his/her hands were in contact with the patient organs. A force sensor mounted on the probe raises problems with sterilization of the overall surgical tool. Also, the use of off-axis gauges introduces a moment that increases the friction force on the bearing, which can easily mask off the signal, given the small force to be measured. METHODS: This work aims at designing and testing two methods for estimating the resistance to the advancement (force) experienced by a standard probe for brain biopsies within a brain-like material. The further goal is to provide a neurosurgeon using a master-slave tele-operated driver with direct feedback on the tissue mechanical characteristics. Two possible sensing methods, in-axis strain gauge force sensor and position-position error (control-based method), were implemented and tested, both aimed at device miniaturization. The analysis carried out was aimed at fulfilment of the psychophysics requirements for force detection and delay tolerance, also taking into account safety, which is directly related to the last two issues. Controller parameters definition is addressed and consideration is given to development of the device with integration of a haptic interface. RESULTS: Results show better performance of the control-based method (RMSE < 0.1 N), which is also best for reliability, sterilizability, and material dimensions for the application addressed. CONCLUSIONS: The control-based method developed for force estimation is compatible with the neurosurgical application and is also capable of measuring tissue resistance without any additional sensors. Force feedback in minimally invasive surgery allows the human operator to manipulate tissues as if his/her hands were in contact with the patient organs.

Experimental evaluation of a coaxial needle insertion assistant with enhanced force feedback.

During needle insertion in soft tissue, detection of change in tissue properties is important both for diagnosis to detect pathological tissue and for prevention to avoid puncture of important structures. The presence of a membrane located deep inside the tissue results in a relatively small force variation at the needle tip that can be masked by relatively large friction force between the needle shaft and the surrounding tissue. Also, user perception of force can be limited due to the overall small force amplitude in some applications (e.g. brain surgery). A novel robotic coaxial needle insertion assistant was developed to enhance operator force perception. The coaxial needle separates the cutting force at the needle tip from shear friction on the needle shaft. The assistant is force controlled (admittance control), providing the operator with force feedback that is a scaled version of the force applied by the needle tip to the tissue. The effectiveness of the assistant in enhancing the detection of different tissue types was tested experimentally. Users were asked to blindly insert a needle into artificial tissues with membranes at various depths under two force feedback conditions: (1) shaft and tip force together, and (2) only tip force. The ratio of successful to unsuccessful membrane detection was significantly higher when only the needle tip force is displayed to the user. The system proved to be compliant with the clinical applications requirements.