Needle insertion into soft tissue: a survey

Effect of Polymer Volume Fraction on Fracture Initiation in Soft Gels at Small Length Scales

The influence of polymer volume fraction, ϕ_v on fracture initiation via puncture is studied in self-assembled triblock copolymer gels. Spherically tipped indenters of radii varying over a wide range were used to characterize puncture at length scales on the same order of magnitude as the elasto-capillary length (∼μm) and significantly below the elasto-fracture length (∼mm) for ϕ_v = 0.12-0.53. Critical energy release rate, G_c for ϕ_v = 0.12-0.30 was found to be in agreement with the predicted scaling from the classical Lake-Thomas model modified for gel fracture via the failure mechanism of chain pull-out and plastic yielding of micelles (G_c ∼ ϕ_v^2.2). Interestingly, we demonstrate that fracture initiation energy, Γ_o, from puncture scales as Γ_o ∼ ϕ_v, thus, indicating the role played by different fundamental mechanisms governing fracture initiation in soft gels. Additionally, gels with ϕ_v = 0.53 show deviation from experimental scalings for G_c and Γ_o, likely due to a change in micellar morphology leading to anomalous fracture behavior.

Evaluating the Impact of Human Factors and Pen Needle Design on Insulin Pen Injection

BACKGROUND

Limited published data exists quantifying the influence of human factors (HF) and pen needle (PN) design on delivery outcomes of pen injection systems. This preclinical in vivo study examines the impact of PN hub design and applied force against the skin during injection on needle penetration depth (NPD).

METHOD

To precisely locate injection depth, PN injections (20 µl; 2 IU, U-100 volume equivalent) of iodinated contrast agent were administered to the flank of Yorkshire swine across a range of clinically relevant application forces against the skin (0.25, 0.75, 1.25, and 2.0 lbf). The NPD, representing in vivo needle tip depth in SC tissue, from four 32 G × 4 mm PN devices (BD Nano^™ 2nd Gen and three commercial posted-hub PN devices; n = 75/device/force, 1200 total) was measured by fluoroscopic imaging of the resulting depot.

RESULTS

The reengineered hub design more closely achieved the 4 mm target NPD with significantly less variability ( P = .006) than commercial posted-hub PN devices across the range of applied injection forces. Calculations of IM (intramuscular) injection risk completed through in silico probability model, using NPD and average human tissue thickness measurements, displayed a commensurate reduction (~2-8x) compared to conventional PN hub designs.

CONCLUSIONS

Quantifiable differences in injection depth were observed between identical labeled length PN devices indicating that hub design features, coupled with aspects of variable injection technique, may influence injection depth accuracy and consistency. The reengineered hub design may reduce the impact of unintended individual technique differences by improving target injection depth consistency and reducing IM injection potential.

Three-dimensional therapy needle applicator segmentation for ultrasound-guided focal liver ablation

PURPOSE

Minimally invasive procedures, such as microwave ablation, are becoming first-line treatment options for early-stage liver cancer due to lower complication rates and shorter recovery times than conventional surgical techniques. Although these procedures are promising, one reason preventing widespread adoption is inadequate local tumor ablation leading to observations of higher local cancer recurrence compared to conventional procedures. Poor ablation coverage has been associated with two-dimensional (2D) ultrasound (US) guidance of the therapy needle applicators and has stimulated investigation into the use of three-dimensional (3D) US imaging for these procedures. We have developed a supervised 3D US needle applicator segmentation algorithm using a single user input to augment the addition of 3D US to the current focal liver tumor ablation workflow with the goals of identifying and improving needle applicator localization efficiency.

METHODS

The algorithm is initialized by creating a spherical search space of line segments around a manually chosen seed point that is selected by a user on the needle applicator visualized in a 3D US image. The most probable trajectory is chosen by maximizing the count and intensity of threshold voxels along a line segment and is filtered using the Otsu method to determine the tip location. Homogeneous tissue mimicking phantom images containing needle applicators were used to optimize the parameters of the algorithm prior to a four-user investigation on retrospective 3D US images of patients who underwent microwave ablation for liver cancer. Trajectory, axis localization, and tip errors were computed based on comparisons to manual segmentations in 3D US images.

RESULTS

Segmentation of needle applicators in ten phantom 3D US images was optimized to median (Q1, Q3) trajectory, axis, and tip errors of 2.1 (1.1, 3.6)°, 1.3 (0.8, 2.1) mm, and 1.3 (0.7, 2.5) mm, respectively, with a mean ± SD segmentation computation time of 0.246 ± 0.007 s. Use of the segmentation method with a 16 in vivo 3D US patient dataset resulted in median (Q1, Q3) trajectory, axis, and tip errors of 4.5 (2.4, 5.2)°, 1.9 (1.7, 2.1) mm, and 5.1 (2.2, 5.9) mm based on all users.

CONCLUSIONS

Segmentation of needle applicators in 3D US images during minimally invasive liver cancer therapeutic procedures could provide a utility that enables enhanced needle applicator guidance, placement verification, and improved clinical workflow. A semi-automated 3D US needle applicator segmentation algorithm used in vivo demonstrated localization of the visualized trajectory and tip with less than 5° and 5.2 mm errors, respectively, in less than 0.31 s. This offers the ability to assess and adjust needle applicator placements intraoperatively to potentially decrease the observed liver cancer recurrence rates associated with current ablation procedures. Although optimized for deep and oblique angle needle applicator insertions, this proposed workflow has the potential to be altered for a variety of image-guided minimally invasive procedures to improve localization and verification of therapy needle applicators intraoperatively.

A simple insertion technique to reduce the bending of thinbevel-point needles

Objective: Needle insertion is a common component of most diagnostic and therapeutic interventions. Needles with asymmetrically sharpened points such as the bevel point are ubiquitous. Their insertion path is typically curved due to the rudder effect at the point. However, the common planned path is straight, leading to targeting errors. We present a simple technique that may substantially reduce these errors. The method was inspired by practical experience, conceived mathematically, and refined experimentally. Methods: Targeting errors are reduced by flipping the bevel on the opposite side (rotating the needle 180° about its axis), at a certain depth during insertion. The ratio of the flip depth to the full depth of insertion is defined as the flip depth ratio (FDR). Based on a model, FDR is constant 0.3. Results: Experimentally, the ratio depends on the needle diameter, 0.35 for 20Ga and 0.45 for 18Ga needles. Thinner needles should be flipped a little shallower, but never less than 0.3. Conclusion: Practically, a physician may expect to reduce ∼80% of needle deflection errors by simply flipping the needle. The technique may be used by hand or with guidance devices.

Using Simulation to Help Specify Design Parameters for Vacuum-Assisted Needle Biopsy Systems

Needle biopsy is a routine medical procedure for examining tissue or biofluids for the presence of disease using standard methods of pathology. The finite element analysis (FEA) methodology can provide guidance for optimizing the geometric parameters. The needle biopsy is simulated and analyzed while varying the needle angle, the aperture size and the slice-push ratio k. The results indicate that tissue reaction force in the axial direction of needle gradually decreases, and the stress and strain are more concentrated at the tip of needle with the increases of tip angle; the tissue reaction force decreases, and the torque increases while the slice-push ratio increases; and higher slice–push ratio can increase the peak stress concentration on the cutting edge and deformation of tissue; in the process of core needle cutting, increasing slice–push ratio can reduce the tissue reaction force significantly. While the aperture on distal wall of outer cannula becomes wider, the tissue reaction force increases significantly, and the cutting process will be more unstable. The results have the potential to provide important insight for improving the needle biopsy design process.

Characterization of an artificial skull cap for cranio-maxillofacial surgery training

Cranial grafts are favored to reconstruct skeletal defects because of their reduced resorption and their histocompatibility. Training possibilities for novice surgeons include the "learning by doing" on the patient, specimens or simulators. Although the acceptance of simulators is growing, the major drawback is the lack of validated bone models. The aim of this study was to create and validate a realistic skull cap model and to show superiority compared to a commercially available skull model. Characteristic forces during machinery procedures were recorded and thickness parameters from the bony layers were obtained. The thickness values of the bone layers of the developed parietal bone were comparable to the human ones. Differences between drilling and sawing forces of human and artificial bones were not detected using statistical analysis. In contrast the parameters of the commercially available skull model were significantly different. However, as a result, a model-based simulator for tabula externa graft lift training, consisting of a brain, skull bone cap and covering soft tissues was created. This simulator enables the training of all procedural steps of a "split thickness graft lift". In conclusion, an artificial skull cap suitable for parietal graft lift training was manufactured and validated against human parietal bones.

Novel clinical device tracking and tissue event characterization using proximally placed audio signal acquisition and processing

We propose a new and complementary approach to image guidance for monitoring medical interventional devices (MID) with human tissue interaction and surgery augmentation by acquiring acoustic emission data from the proximal end of the MID outside the patient to extract dynamical characteristics of the interaction between the distal tip and the tissue touched or penetrated by the MID. We conducted phantom based experiments (n = 955) to show dynamic tool/tissue interaction during tissue needle passage (a) and vessel perforation caused by guide wire artery perforation (b). We use time-varying auto-regressive (TV-AR) modelling to characterize the dynamic changes and time-varying maximal energy pole (TV-MEP) to compute subsequent analysis of MID/tissue interaction characterization patterns. Qualitative and quantitative analysis showed that the TV-AR spectrum and the TV-MEP indicated the time instants of the needle path through different phantom objects (a) and clearly showed a perforation versus other generated artefacts (b). We demonstrated that audio signals acquired from the proximal part of an MID could provide valuable additional information to surgeons during minimally invasive procedures.

Real-Time Curvature Detection of a Flexible Needle with a Bevel Tip

As one of the major methods for the diagnosis and treatment of cancers in their early stages, the percutaneous puncture technique has bright prospect in biopsy, ablation, proximity radiotherapy, and drug delivery. Recent years, researchers found the flexible needle cannot realize feedback control during the puncture surgeries only by path planning. To solve this problem, the flexible needle is tried to achieve real-time detection in this paper. Compared with previous methods, the strain gauges glued on the needle surface rather than the medical imaging techniques is used to collect the information to reconstruct the needle curve, which is benefit to integrate the whole system and obtain a more simple and accurate closed-loop control. This paper presented the math model of curve fitting and analyzed the causes of curve fitting errors. To verify the feasibility of this method, an experiment setup was built. Results from the experiments validated the solution in this paper to be effective.

A variable stiffness mechanism for steerable percutaneous instruments: integration in a needle

Needles are advanced tools commonly used in minimally invasive medical procedures. The accurate manoeuvrability of flexible needles through soft tissues is strongly determined by variations in tissue stiffness, which affects the needle-tissue interaction and thus causes needle deflection. This work presents a variable stiffness mechanism for percutaneous needles capable of compensating for variations in tissue stiffness and undesirable trajectory changes. It is composed of compliant segments and rigid plates alternately connected in series and longitudinally crossed by four cables. The tensioning of the cables allows the omnidirectional steering of the tip and the stiffness tuning of the needle. The mechanism was tested separately under different working conditions, demonstrating a capability to exert up to 3.6 N. Afterwards, the mechanism was integrated into a needle, and the overall device was tested in gelatine phantoms simulating the stiffness of biological tissues. The needle demonstrated the capability to vary deflection (from 11.6 to 4.4 mm) and adapt to the inhomogeneity of the phantoms (from 21 to 80 kPa) depending on the activation of the variable stiffness mechanism. Graphical abstract ᅟ.

Validation of a simulator for cranial graft lift training: Face, content, and construct validity

PURPOSE

Surgical skills can be improved through practical exercise. The use of specimens, human as well as animal, or live animals for surgical training is limited due to ethical concerns. Drawbacks of simulators are costs, fidelity and creditibility. Thus, simulators must be evaluated objectively to determine their validity before they can be used as teaching modalities. The aim of this study was to verify the face content and construct validity of a novel model-based simulator for lifting tabula externa transplants from the parietal skull.

MATERIALS AND METHODS

Participants were invited to perform a tabula externa graft lift during a training session on the simulator. Task performance was analyzed with a standardized assessment tool evaluating realism and appropriateness. Specialist ratings were used to evaluate the performance of the participants. This was an exploratory study using a questionnaire, at Kepler University Hospital, Linz, Austria, a university hospital. According to their expertise in craniomaxillofacial surgery, 17 participants were subdivided into 3 groups: 8 novices, 7 experts and 2 raters.

RESULTS

The face validity (realism) obtained an average score of 4.2 of a maximum of 5 points. Likewise, the content validity (appropriateness as a teaching modality) obtained an average score of 4.8 of maximum 5 points. No differences were found between experts and novices concerning the recorded surgery completion times (p = 0.418) or the sizes of the lifted grafts (p = 0.110). During the evaluation of task performance, the expert surgeons (46.9 ± 3.7) were graded significantly better than the novices (36.4 ± 8.5), which proved the construct validity of the simulator (p = 0.001).

CONCLUSION

All investigated validities were confirmed and approved the simulator as a valid training tool for parietal graft lift.

Sliding mode control of a shape memory alloy actuated active flexible needle

In medical interventional procedures such as brachytherapy, biopsy and radio-frequency ablation, precise tracking through the preplanned desired trajectory is very essential. This important requirement is critical due to two major reasons: anatomical obstacle avoidance and accurate targeting for avoiding undesired radioactive dose exposure or damage to neighboring tissue and critical organs. Therefore, a precise control of the needling device in the unstructured environment in the presence of external disturbance is required to achieve accurate target reaching in clinical applications. In this paper, a shape memory alloy actuated active flexible needle controlled by an adaptive sliding mode controller is presented. The trajectory tracking performance of the needle is tested while having its actual movement in an artificial tissue phantom by giving various input reference trajectories such as multi-step and sinusoidal. Performance of the adaptive sliding mode controller is compared with that of the proportional, integral and derivative controller and is proved to be the effective method in the presence of the external disturbances.

Controlling the error on target motion through real-time mesh adaptation: Applications to deep brain stimulation

An error-controlled mesh refinement procedure for needle insertion simulations is presented. As an example, the procedure is applied for simulations of electrode implantation for deep brain stimulation. We take into account the brain shift phenomena occurring when a craniotomy is performed. We observe that the error in the computation of the displacement and stress fields is localised around the needle tip and the needle shaft during needle insertion simulation. By suitably and adaptively refining the mesh in this region, our approach enables to control, and thus to reduce, the error whilst maintaining a coarser mesh in other parts of the domain. Through academic and practical examples we demonstrate that our adaptive approach, as compared with a uniform coarse mesh, increases the accuracy of the displacement and stress fields around the needle shaft and, while for a given accuracy, saves computational time with respect to a uniform finer mesh. This facilitates real-time simulations. The proposed methodology has direct implications in increasing the accuracy, and controlling the computational expense of the simulation of percutaneous procedures such as biopsy, brachytherapy, regional anaesthesia, or cryotherapy. Moreover, the proposed approach can be helpful in the development of robotic surgeries because the simulation taking place in the control loop of a robot needs to be accurate, and to occur in real time.

Novel design of honeybee-inspired needles for percutaneous procedure

The focus of this paper is to present new designs of innovative bioinspired needles to be used during percutaneous procedures. Insect stingers have been known to easily penetrate soft tissues. Bioinspired needles mimicking the barbs in a honeybee stinger were developed for a smaller insertion force, which can provide a less invasive procedure. Decreasing the insertion force will decrease the tissue deformation, which is essential for more accurate targeting. In this study, some design parameters, in particular, barb shape and geometry (i.e. front angle, back angle, and height) were defined, and their effects on the insertion force were investigated. Three-dimensional printing technology was used to manufacture bioinspired needles. A specially-designed insertion test setup using tissue mimicking polyvinyl chloride (PVC) gels was developed to measure the insertion and extraction forces. The barb design parameters were then experimentally modified through detailed experimental procedures to further reduce the insertion force. Different scales of the barbed needles were designed and used to explore the size-scale effect on the insertion force. To further investigate the efficacy of the proposed needle design in real surgeries, preliminary ex vivo insertion tests into bovine liver tissue were performed. Our results show that the insertion force of the needles in different scales decreased by 21-35% in PVC gel insertion tests, and by 46% in bovine liver tissue insertion tests.

Kalman filter-based EM-optical sensor fusion for needle deflection estimation

PURPOSE

In many clinical procedures such as cryoablation that involves needle insertion, accurate placement of the needle's tip at the desired target is the major issue for optimizing the treatment and minimizing damage to the neighboring anatomy. However, due to the interaction force between the needle and tissue, considerable error in intraoperative tracking of the needle tip can be observed as needle deflects.

METHODS

In this paper, measurements data from an optical sensor at the needle base and a magnetic resonance (MR) gradient field-driven electromagnetic (EM) sensor placed 10 cm from the needle tip are used within a model-integrated Kalman filter-based sensor fusion scheme. Bending model-based estimations and EM-based direct estimation are used as the measurement vectors in the Kalman filter, thus establishing an online estimation approach.

RESULTS

Static tip bending experiments show that the fusion method can reduce the mean error of the tip position estimation from 29.23 mm of the optical sensor-based approach to 3.15 mm of the fusion-based approach and from 39.96 to 6.90 mm, at the MRI isocenter and the MRI entrance, respectively.

CONCLUSION

This work established a novel sensor fusion scheme that incorporates model information, which enables real-time tracking of needle deflection with MRI compatibility, in a free-hand operating setup.

Laser Doppler sensing for blood vessel detection with a biologically inspired steerable needle

Puncturing blood vessels during percutaneous intervention in minimally invasive brain surgery can be a life threatening complication. Embedding a forward looking sensor in a rigid needle has been proposed to tackle this problem but, when using a rigid needle, the procedure needs to be interrupted and the needle extracted if a vessel is detected. As an alternative, we propose a novel optical method to detect a vessel in front of a steerable needle. The needle itself is based on a biomimetic, multi-segment design featuring four hollow working channels. Initially, a laser Doppler flowmetry probe is characterized in a tissue phantom with optical properties mimicking those of human gray matter. Experiments are performed to show that the probe has a 2.1 mm penetration depth and a 1 mm off-axis detection range for a blood vessel phantom with 5 mm s^-1 flow velocity. This outcome demonstrates that the probe fulfills the minimum requirements for it to be used in conjunction with our needle. A pair of Doppler probes is then embedded in two of the four working channels of the needle and vessel reconstruction is performed using successive measurements to determine the depth and the off-axis position of the vessel from each laser Doppler probe. The off-axis position from each Doppler probe is then used to generate a 'detection circle' per probe, and vessel orientation is predicted using tangent lines between the two. The vessel reconstruction has a depth root mean square error (RMSE) of 0.3 mm and an RMSE of 15° in the angular prediction, showing real promise for a future clinical application of this detection system.

Force Modeling, Identification, and Feedback Control of Robot-Assisted Needle Insertion: A Survey of the Literature

Robot-assisted surgery is of growing interest in the surgical and engineering communities. The use of robots allows surgery to be performed with precision using smaller instruments and incisions, resulting in shorter healing times. However, using current technology, an operator cannot directly feel the operation because the surgeon-instrument and instrument-tissue interaction force feedbacks are lost during needle insertion. Advancements in force feedback and control not only help reduce tissue deformation and needle deflection but also provide the surgeon with better control over the surgical instruments. The goal of this review is to summarize the key components surrounding the force feedback and control during robot-assisted needle insertion. The literature search was conducted during the middle months of 2017 using mainstream academic search engines with a combination of keywords relevant to the field. In total, 166 articles with valuable contents were analyzed and grouped into five related topics. This survey systemically summarizes the state-of-the-art force control technologies for robot-assisted needle insertion, such as force modeling, measurement, the factors that influence the interaction force, parameter identification, and force control algorithms. All studies show force control is still at its initial stage. The influence factors, needle deflection or planning remain open for investigation in future.

Using needle orientation sensing as surrogate signal for respiratory motion estimation in percutaneous interventions

PURPOSE

To develop and evaluate an approach to estimate the respiratory-induced motion of lesions in the chest and abdomen.

MATERIALS AND METHODS

The proposed approach uses the motion of an initial reference needle inserted into a moving organ to estimate the lesion (target) displacement that is caused by respiration. The needles position is measured using an inertial measurement unit (IMU) sensor externally attached to the hub of an initially placed reference needle. Data obtained from the IMU sensor and the target motion are used to train a learning-based approach to estimate the position of the moving target. An experimental platform was designed to mimic respiratory motion of the liver. Liver motion profiles of human subjects provided inputs to the experimental platform. Variables including the insertion angle, target depth, target motion velocity and target proximity to the reference needle were evaluated by measuring the error of the estimated target position and processing time.

RESULTS

The mean error of estimation of the target position ranged between 0.86 and 1.29 mm. The processing maximum training and testing time was 5 ms which is suitable for real-time target motion estimation using the needle position sensor.

CONCLUSION

The external motion of an initially placed reference needle inserted into a moving organ can be used as a surrogate, measurable and accessible signal to estimate in real-time the position of a moving target caused by respiration; this technique could then be used to guide the placement of subsequently inserted needles directly into the target.

Performance of Robotic Assistance for Skull Base Biopsy: A Phantom Study

Objectives  This study aims to evaluate the feasibility of a custom robot system guided by optical cone beam computed tomography (CBCT)-based navigation for skull base biopsy. Design  An accuracy study was conducted. Setting  Platform for navigation and robot-aided surgery technology. Participants  Phantom skull. Main Outcome Measures  The primary outcome measure was to investigate the accuracy of robot-assisted needle biopsy for skull base tumors. A 14-gauge needle was automatically inserted by the five degrees of freedom robot into the intended target, guided by optical navigation. The result was displayed on the graphical user interface after matrix transformation. Postoperative image scanning was performed, and the result was verified with image fusion. Results  All 20 interventions were successfully performed. The mean deviation of the needle tip was 0.56 ± 0.22 mm (measured by the navigation system) versus 1.73 ± 0.60 mm (measured by image fusion) ( p  < 0.05). The mean insertion depth was 52.3 mm (range: 49.7-55.2 mm). The mean angular deviations off the x-axis, y-axis, and z-axis were 1.51 ± 0.67, 2.33 ± 1.65, and 1.47 ± 1.16 degrees, respectively. Conclusions  The experimental results show the robot system is efficient, reliable, and safe. The navigation accuracy is a significant factor in robotic procedures.

Mechanisms of ovipositor insertion and steering of a parasitic wasp

Drilling into solid substrates with slender beam-like structures is a mechanical challenge, but is regularly done by female parasitic wasps. The wasp inserts her ovipositor into solid substrates to deposit eggs in hosts, and even seems capable of steering the ovipositor while drilling. The ovipositor generally consists of three longitudinally connected valves that can slide along each other. Alternative valve movements have been hypothesized to be involved in ovipositor damage avoidance and steering during drilling. However, none of the hypotheses have been tested in vivo. We used 3D and 2D motion analysis to quantify the probing behavior of the fruit-fly parasitoid Diachasmimorpha longicaudata (Braconidae) at the levels of the ovipositor and its individual valves. We show that the wasps can steer and curve their ovipositors in any direction relative to their body axis. In a soft substrate, the ovipositors can be inserted without reciprocal motion of the valves. In a stiff substrate, such motions were always observed. This is in agreement with the damage avoidance hypothesis of insertion, as they presumably limit the overall net pushing force. Steering can be achieved by varying the asymmetry of the distal part of the ovipositor by protracting one valve set with respect to the other. Tip asymmetry is enhanced by curving of ventral elements in the absence of an opposing force, possibly due to pretension. Our findings deepen the knowledge of the functioning and evolution of the ovipositor in hymenopterans and may help to improve man-made steerable probes.

A novel approach to an automated needle insertion in brachytherapy procedures

One of the most challenging phases in interstitial brachytherapy is the placement of the needles. In these medical procedures, the needles are inserted inside the tissue to guide the positioning of the radioactive sources. The low-dose-rate radioactive sources are placed inside the tissue permanently, whereas a radioactive source in the high-dose-rate brachytherapy is temporarily placed in the desired positions so that the delivery of the prescription dose to the clinical targets can be achieved. Consequently, the precise needle placement directly influences the radiation dose delivery and the treatment outcomes of patients. Any deviation from the desired position of the radioactive sources can cause a suboptimal dose distribution and inadequate tumor coverage. Therefore, it is of significant importance to develop a robust and sophisticated tool that can perform the automatic needle placement with a high level of accuracy for different medical procedures and conditions. In this study, we propose a novel concept for the automatic needle insertion using a new miniature automated robotic system. The mathematical model of this system was presented in detail, allowing the implementation of the model predictive control that can be used to govern the mechanism. The purpose of this approach was to minimize the lateral components of the generalized reactive force which is responsible for the tissue displacement and, consequently, for the needle deflection. The proposed approach was designed to predict and to compensate for the unmeasured disturbances, such as needle deflection or tissue resistance and reactive force, and it was capable of correcting them without waiting until the effect appears at the output of the system causing the needle deviation from the desired positions. The extensive simulation of the system was presented to evaluate the feasibility of the method and the parameters of interest including displacements, system errors and system responses to the change in the environmental conditions.

Assessment of the Accuracy of Optical Shape Sensing for Needle Tracking Interventions

Accurate needle guidance is essential for a number of magnetic resonance imaging (MRI)-guided percutaneous procedures, such as radiofrequency ablation (RFA) of metastatic liver tumors. A promising technology to obtain real-time tracking of the shape and tip of a needle is by using high-frequency (up to 20 kHz) fiber Bragg grating (FBG) sensors embedded in optical fibers, which are insensitive to external magnetic fields. We fabricated an MRI-compatible needle designed for percutaneous procedures with a series of FBG sensors which would be tracked in an image-guidance system, allowing to display the needle shape within a navigation image. A series of phantom experiments demonstrated needle tip tracking errors of 1.05 ± 0.08 mm for a needle deflection up to 16.82 mm on a ground-truth model and showed nearly similar accuracy to electromagnetic (EM) tracking (i.e., 0.89 ± 0.09 mm). We demonstrated feasibility of the FBG-based tracking system for MRI-guided interventions with differences under 1 mm between tracking systems. This study establishes the needle tracking accuracy of FBG needle tracking for image-guided procedures.

Active Localization and Tracking of Needle and Target in Robotic Image-Guided Intervention Systems

This paper describes a framework of algorithms for the active localization and tracking of flexible needles and targets during image-guided percutaneous interventions. The needle and target configurations are tracked by Bayesian filters employing models of the needle and target motions and measurements of the current system state obtained from an intra-operative imaging system which is controlled by an entropy-minimizing active localization algorithm. Versions of the system were built using particle and unscented Kalman filters and their performance was measured using both simulations and hardware experiments with real magnetic resonance imaging data of needle insertions into gel phantoms. Performance of the localization algorithms is given in terms of accuracy of the predictions and computational efficiency is discussed.

Real-Time Error Control for Surgical Simulation

OBJECTIVE

To present the first a posteriori error-driven adaptive finite element approach for real-time simulation, and to demonstrate the method on a needle insertion problem.

METHODS

We use corotational elasticity and a frictional needle/tissue interaction model. The problem is solved using finite elements within SOFA.¹ For simulating soft tissue deformation, the refinement strategy relies upon a hexahedron-based finite element method, combined with a posteriori error estimation driven local -refinement.

RESULTS

We control the local and global error level in the mechanical fields (e.g., displacement or stresses) during the simulation. We show the convergence of the algorithm on academic examples, and demonstrate its practical usability on a percutaneous procedure involving needle insertion in a liver. For the latter case, we compare the force-displacement curves obtained from the proposed adaptive algorithm with that obtained from a uniform refinement approach.

CONCLUSIONS

Error control guarantees that a tolerable error level is not exceeded during the simulations. Local mesh refinement accelerates simulations.

SIGNIFICANCE

Our work provides a first step to discriminate between discretization error and modeling error by providing a robust quantification of discretization error during simulations.

Haptic Feedback in Needle Insertion Modeling and Simulation

Needle insertion is the most basic skill in medical care, and training has to be imparted not only for physicians but also for nurses and paramedics. In most needle insertion procedures, haptic feedback from the needle is the main stimulus in which novices need training. For better patient safety, the classical methods of training the haptic skills have to be replaced with simulators based on new robotic and graphics technologies. This paper reviews the current advances in needle insertion modeling, classified into three sections: needle insertion models, tissue deformation models, and needle-tissue interaction models. Although understated in the literature, the classical and dynamic friction models, which are critical for needle insertion modeling, are also discussed. The experimental setup or the needle simulators that have been developed to validate the models are described. The need of psychophysics for needle simulators and psychophysical parameter analysis of human perception in needle insertion are discussed, which are completely ignored in the literature.

Evaluation of Direct Haptic 4D Volume Rendering of Partially Segmented Data for Liver Puncture Simulation

This work presents an evaluation study using a force feedback evaluation framework for a novel direct needle force volume rendering concept in the context of liver puncture simulation. PTC/PTCD puncture interventions targeting the bile ducts have been selected to illustrate this concept. The haptic algorithms of the simulator system are based on (1) partially segmented patient image data and (2) a non-linear spring model effective at organ borders. The primary aim is to quantitatively evaluate force errors caused by our patient modeling approach, in comparison to haptic force output obtained from using gold-standard, completely manually-segmented data. The evaluation of the force algorithms compared to a force output from fully manually segmented gold-standard patient models, yields a low mean of 0.12 N root mean squared force error and up to 1.6 N for systematic maximum absolute errors. Force errors were evaluated on 31,222 preplanned test paths from 10 patients. Only twelve percent of the emitted forces along these paths were affected by errors. This is the first study evaluating haptic algorithms with deformable virtual patients in silico. We prove haptic rendering plausibility on a very high number of test paths. Important errors are below just noticeable differences for the hand-arm system.

Toward Transoral Peripheral Lung Access: Combining Continuum Robots and Steerable Needles

Lung cancer is the most deadly form of cancer in part because of the challenges associated with accessing nodules for diagnosis and therapy. Transoral access is preferred to percutaneous access since it has a lower risk of lung collapse, yet many sites are currently unreachable transorally due to limitations with current bronchoscopic instruments. Toward this end, we present a new robotic system for image-guided trans-bronchoscopic lung access. The system uses a bronchoscope to navigate in the airway and bronchial tubes to a site near the desired target, a concentric tube robot to move through the bronchial wall and aim at the target, and a bevel-tip steerable needle with magnetic tracking to maneuver through lung tissue to the target under closed-loop control. In this work, we illustrate the workflow of our system and show accurate targeting in phantom experiments. Ex vivo porcine lung experiments show that our steerable needle can be tuned to achieve appreciable curvature in lung tissue. Lastly, we present targeting results with our system using two scenarios based on patient cases. In these experiments, phantoms were created from patient-specific computed tomography information and our system was used to target the locations of suspicious nodules, illustrating the ability of our system to reach sites that are traditionally inaccessible transorally.

Development of Aspiration-Assisted End-Cut Coaxial Biopsy Needles

Needle biopsy procedures, such as fine-needle aspiration and core needle biopsy, are used to extract tissue samples for diagnosis, and collection of larger samples allows for more accurate diagnosis of cancers. The combination of lower needle insertion force, less needle deflection, and reduced friction between the tissue and needle surface also leads to a more efficient biopsy procedure. In this research, a new end-cut-type coaxial needle with a modified aspiration mechanism has been developed to extract large tissue with minimal damage. The study shows that the clearance between the inner stylette and external needle and the insertion speed are the key factors affecting the biopsy performance including syringe friction force and amount of tissue extracted. Larger tissue samples (gelatin and chicken breast are used as samples here) can be obtained when inserting at lower speeds and using coaxial needles with smaller clearances between the external needles and inner stylettes. For solid samples (gelatin), the space inside the external needle is nearly filled with the solid sample. For samples consisting of both solid (chicken meat) and liquid components, a slower needle insertion results in extraction of more liquid than solid. To extract larger solid samples, high-speed needle insertion is required. This paper presents the design and manufacture of the system, protocol to evaluate the needle biopsy, and evaluation of the needle biopsy performance using gelatin and chicken breast as tissue samples.

Intraoperative factors associated with stranded source placement accuracy in low-dose-rate prostate brachytherapy

PURPOSE

The quality of a low-dose rate prostate brachytherapy implant depends on the accurate placement of sources in their planned locations. This study investigates intraoperative factors that potentially contribute to stranded source placement inaccuracy in prostate brachytherapy.

METHODS AND MATERIALS

Intraoperative video images of the brachytherapist's hand motions and needle insertions during the implant procedure were acquired for analysis. Using video analysis software, maximum and average needle insertion velocities were determined. The number of needle insertion attempts and the use of the brachytherapist's other hand to manipulate the needle direction were also recorded. Sources misplacements were analyzed using an ultrasound-based method described elsewhere.

RESULTS

Fifteen patients agreed to undergo this study; 1619 ¹²⁵I seeds were inserted using 357 needles; 1197 seeds were confidently identified using ultrasound images and included in the analysis. The mean overall misplacement was 0.49 cm (0-2 cm, 95% CI = 0.47-0.51); 614 seeds were delivered with a single pass and 583 seeds with >1 passes (range 2-6). The mean maximum needle velocity was 12.34 cm s^-1 (range 4-28 cm s^-1) and mean average velocity was 4.76 cm s^-1 (range 0.4-17.4 cm s^-1); 747 seeds were delivered with manipulation of the needle. The generalized linear model test was used to analyze factors contributing to seed misplacement, and it was found that a maximum speed <12 cm s^-1 was associated with a decrease in seed misplacement by 0.049 cm vs. a maximum speed >12 cm s^-1, p = 0.0121). Other evaluated factors were found to have no statistically significant correlation with seed misplacement: average speed (p = 0.4947), manual manipulation of needle (p = 0.9264), and number of needle passes (p = 0.8907).

CONCLUSIONS

This study identified that needles inserted with lower maximum velocity were associated with less seed misplacement. Manual manipulation of the needle, number of passes, and average speed did not show statistically significant correlation with seed misplacement.

The influence of tip shape on bending force during needle insertion

Steering of needles involves the planning and timely modifying of instrument-tissue force interactions to allow for controlled deflections during the insertion in tissue. In this work, the effect of tip shape on these forces was studied using 10 mm diameter needle tips. Six different tips were selected, including beveled and conical versions, with or without pre-bend or pre-curve. A six-degree-of-freedom force/torque sensor measured the loads during indentations in tissue simulants. The increased insertion (axial) and bending (radial) forces with insertion depth - the force-displacement slopes - were analyzed. Results showed that the ratio between radial and axial forces was not always proportional. This means that the tip load does not have a constant orientation, as is often assumed in mechanics-based steering models. For all tip types, the tip-load assumed a more radial orientation with increased axial load. This effect was larger for straight tips than for pre-bent or pre-curved tips. In addition, the force-displacement slopes were consistently higher for (1) increased tip angles, and for (2) beveled tips compared to conical tips. Needles with a bent or curved tip allow for an increased bending force and a decreased variability of the tip load vector orientation.

Needle-like instruments for steering through solid organs: A review of the scientific and patent literature

High accuracy and precision in reaching target locations inside the human body is necessary for the success of percutaneous procedures, such as tissue sample removal (biopsy), brachytherapy, and localized drug delivery. Flexible steerable needles may allow the surgeon to reach targets deep inside solid organs while avoiding sensitive structures (e.g. blood vessels). This article provides a systematic classification of possible mechanical solutions for three-dimensional steering through solid organs. A scientific and patent literature search of steerable instrument designs was conducted using Scopus and Web of Science Derwent Innovations Index patent database, respectively. First, we distinguished between mechanisms in which deflection is induced by the pre-defined shape of the instrument versus mechanisms in which an actuator changes the deflection angle of the instrument on demand. Second, we distinguished between mechanisms deflecting in one versus two planes. The combination of deflection method and number of deflection planes led to eight logically derived mechanical solutions for three-dimensional steering, of which one was dismissed because it was considered meaningless. Next, we classified the instrument designs retrieved from the scientific and patent literature into the identified solutions. We found papers and patents describing instrument designs for six of the seven solutions. We did not find papers or patents describing instruments that steer in one-plane on-demand via an actuator and in a perpendicular plane with a pre-defined deflection angle via a bevel tip or a pre-curved configuration.

Fiber-Optic Fabry-Pérot Interferometers for Axial Force Sensing on the Tip of a Needle

A range of complex percutaneous procedures, such as biopsy or regional anesthesia, rely heavily on accurate needle insertion. Small variations in the mechanical properties of the pierced tissue can however cause deviations from the projected needle path and can thus result in inaccurate placement of the needle. Navigation of a rigid needle towards the target tissue is traditionally based on the surgeons capacity to interpret small variations in the needle insertion force. A more accurate measurement of these small force variations enables improvement in needle targeting, can potentially aid in enhancing force feedback in robotic needle placement and can provide valuable information on tissue-tool interaction. In this study we investigated several concepts for the design of a force sensor based on a fiber-optic Fabry-Pérot interferometer to measure needle-tissue interaction forces on the tip of a 18 G needle, where special attention was given to concepts for a sensor with (1), an intrinsic low cross-sensitivity to temperature and (2), elementary design and fabrication. Three concepts, using either a quartz capillary, an Invar capillary or a thin polyimide film as the force sensitive element were prototyped and subjected to both static and dynamic testing. The force transducer based on a quartz capillary presented the lowest cross-sensitivity to temperature ( 12 m N / ∘ C) and good accuracy (maximum measurement error of 65 m N /10 N ) in a measurement of static forces. However, limited strength of the sensor is expected to prevent usage of the quartz capillary in small diameter needles. The concepts for a sensor based on an Invar capillary or a thin polyimide film proved a higher cross-sensitivity to temperature ( 50 m N / ∘ C and 220 m N / ∘ C, respectively) and higher maximum measurement error (350 m N /10 N , 800 m N /10 N ), comparable to those of FBG-based sensors reported in literature, but are likely to be more suitable for integration in very small biopsy needles.

A data-driven soft sensor for needle deflection in heterogeneous tissue using just-in-time modelling

Global modelling has traditionally been the approach taken to estimate needle deflection in soft tissue. In this paper, we propose a new method based on local data-driven modelling of needle deflection. External measurement of needle-tissue interactions is collected from several insertions in ex vivo tissue to form a cloud of data. Inputs to the system are the needle insertion depth, axial rotations, and the forces and torques measured at the needle base by a force sensor. When a new insertion is performed, the just-in-time learning method estimates the model outputs given the current inputs to the needle-tissue system and the historical database. The query is compared to every observation in the database and is given weights according to some similarity criteria. Only a subset of historical data that is most relevant to the query is selected and a local linear model is fit to the selected points to estimate the query output. The model outputs the 3D deflection of the needle tip and the needle insertion force. The proposed approach is validated in ex vivo multilayered biological tissue in different needle insertion scenarios. Experimental results in five different case studies indicate an accuracy in predicting needle deflection of 0.81 and 1.24 mm in the horizontal and vertical lanes, respectively, and an accuracy of 0.5 N in predicting the needle insertion force over 216 needle insertions.

Modeling and Simulation of Flexible Needle Insertion Into Soft Tissue Using Modified Local Constraints

Needle insertion is a widely used medical procedure in various minimally invasive surgeries. The estimation of the coupled needle deflection and tissue deformation during the needle insertion procedure is crucial to the success of the surgery. In this work, a novel needle deflection–tissue deformation coupling model is proposed for flexible needle insertion into soft tissue. Based on the assumption that the needle deflection is small comparing to the length of the insertion, the needle–tissue interaction model is developed based on the modified local constraint method, where the interactive forces between the needle and the tissue are balanced through integration of needle–force and tissue–force relationships. A testbed is constructed and the experiments are designed to validate the proposed method using artificial phantom with markers. Based on the experimental analysis, the cutting and friction forces are separated from the force–time curves and used as the inputs into the proposed model. The trajectories of the markers inside the soft tissue are recorded by a CCD camera to compare with the simulation trajectories. The errors between the experimental and simulation trajectories are less than 0.8 mm. The results demonstrate that the proposed method is effective to model the needle insertion procedure.