Changes in needle maneuver space and optimal insertion site for midline neuraxial puncture with progressive age: an analysis in computed tomography scans.

INTRODUCTION: We systematically describe the morphology and accessibility of interspinous spaces across age groups of patients. Our primary goal was to objectively estimate if the maneuver space for a virtual spinal needle changes with age. Our secondary goal was to estimate if the optimal site and angle for midline neuraxial puncture change with age. METHODS: Measurements were performed in mid-sagittal CT images. The CT images were retrospectively collected from the database of the Department of Radiology of our hospital. Three age groups were studied: 21-30 years (n=36, abbreviated Y(oung)), 51-60 years (n=43, abbreviated M(iddle-aged)) and older than 80 years (n=46, abbreviated Old).A needle trajectory is defined by the chosen puncture point and by the angle at which the needle is directed to its target. We define a Spinal Accessibility Index (SAI) by numerically integrating for an interspace all possible combinations of puncture points and angles that lead to a successful virtual puncture. Successful in this context means that the needle tip reaches the spinal or epidural space without bone contact. Reproducible calculation of the SAI was performed with the help of custom-made software. The larger the value of the SAI, the more possible successful needle trajectories exist that the practitioner may choose from.The optimal puncture point and optimal angle in an age group at a certain level of the spine are defined by the combination of these two, which generates the highest success rate of the entire sample of this age group. RESULTS: At all levels of the spine, the median SAI differed significantly between age groups (independent-samples Kruskal-Wallis test, p<0.001-0.047). The SAI consistently decreased with increasing age. Post-hoc analyses using pairwise comparisons showed a significantly higher SAI in group Y versus Old at all levels (p<0.001-0.006) except at level thoracic (Th)1-Th2 (p=0.138). The SAI was significantly higher in group M versus Old at all levels (p<0.001-0.028) except at level Th1-Th2 (p=0.061), Th4-Th5 (p=0.083), Th9-Th10 (p=1.00) and Th10-Th11 (p=1.00). CONCLUSIONS: Needle maneuver space in midline neuraxial puncture significantly decreases with progressive age at all levels of the spine. Optimal puncture points and angles are similar between age groups.

Operating Room Performance Optimization Metrics: a Systematic Review.

Literature proposes numerous initiatives for optimization of the Operating Room (OR). Despite multiple suggested strategies for the optimization of workflow on the OR, its patients and (medical) staff, no uniform description of 'optimization' has been adopted. This makes it difficult to evaluate the proposed optimization strategies. In particular, the metrics used to quantify OR performance are diverse so that assessing the impact of suggested approaches is complex or even impossible. To secure a higher implementation success rate of optimisation strategies in practice we believe OR optimisation and its quantification should be further investigated. We aim to provide an inventory of the metrics and methods used to optimise the OR by the means of a structured literature study. We observe that several aspects of OR performance are unaddressed in literature, and no studies account for possible interactions between metrics of quality and efficiency. We conclude that a systems approach is needed to align metrics across different elements of OR performance, and that the wellbeing of healthcare professionals is underrepresented in current optimisation approaches.

Overcoming pubic arch interference in prostate brachytherapy using steerable needles.

Purpose: A proportion of patients are not directly eligible for prostate brachytherapy (BT) due to pubic arch interference (PAI). Constraints in positioning sources behind the pubic arch due to linear, horizontal needle paths, may hamper effective irradiation of the target volume. This work evaluated the effect of prostate volume (Vp) and patient posture change on the amount of PAI, and demonstrated that steerable needles may broaden the inclusion criteria for patients with enlarged prostates and observed PAI. Material and methods: Twenty-seven patients (Vp > 60 cc) were included in this study. Access obstruction to the prostate was evaluated using diagnostic magnetic resonance imaging (MRI) scans, after six upward rotations of the pelvis and the prostate in 5 degree steps, to indicate the effect of patient posture change from supine to lithotomy position. For patients with PAI, we evaluated if the steerable needle could access the obstructed volume of the prostate. Results: The data showed no clear relation between Vp and PAI. In 23 of the 27 patients, in which PAI was observed, 14 showed obstruction of the prostate of ≥ 10 mm in the supine position (mean PAI ± standard deviation: 15.2 ±3.8 mm). Anatomical rotation reduced PAI by 4.8 mm after every 10 degrees of upward rotation, still resulting in obstructions of 8.1 ±2.4 mm in 10 of the 14 cases after 15 degree rotation. The steerable needle enabled access to all the required coordinates of the prostate. Conclusions: The ability to steer along curved paths enables prostate BT in patients with enlarged prostates and PAI, and reduces the change of needing to abandon treatment.

Block-matching-based registration to evaluate ultrasound visibility of percutaneous needles in liver-mimicking phantoms.

PURPOSE: To present a novel methodical approach to compare visibility of percutaneous needles in ultrasound images. METHODS: A motor-driven rotation platform was used to gradually change the needle angle while capturing image data. Data analysis was automated using block-matching-based registration, with a tracking and refinement step. Every 25 frames, a Hough transform was used to improve needle alignments after large rotations. The method was demonstrated by comparing three commercial needles (14G radiofrequency ablation, RFA; 18G Trocar; 22G Chiba) and six prototype needles with different sizes, materials, and surface conditions (polished, sand-blasted, and kerfed), within polyvinyl alcohol phantom tissue and ex vivo bovine liver models. For each needle and angle, a contrast-to-noise ratio (CNR) was determined to quantify visibility. CNR values are presented as a function of needle type and insertion angle. In addition, the normalized area under the (CNR-angle) curve was used as a summary metric to compare needles. RESULTS: In phantom tissue, the first kerfed needle design had the largest normalized area of visibility and the polished 1 mm diameter stainless steel needle the smallest (0.704 ± 0.199 vs. 0.154 ± 0.027, p < 0.01). In the ex vivo model, the second kerfed needle design had the largest normalized area of visibility, and the sand-blasted stainless steel needle the smallest (0.470 ± 0.190 vs. 0.127 ± 0.047, p < 0.001). As expected, the analysis showed needle visibility peaks at orthogonal insertion angles. For acute or obtuse angles, needle visibility was similar or reduced. Overall, the variability in needle visibility was considerably higher in livers. CONCLUSION: The best overall visibility was found with kerfed needles and the commercial RFA needle. The presented methodical approach to quantify ultrasound visibility allows comparisons of (echogenic) needles, as well as other technological innovations aiming to improve ultrasound visibility of percutaneous needles, such as coatings, material treatments, and beam steering approaches.

Steerable needles for radio-frequency ablation in cirrhotic livers.

Accurate needle placement in deep-seated liver tumours can be difficult. In this work, we disclose two new manually controlled steerable needles for 17G radio-frequency ablation probe placement. The needles contain stylets with embedded compliant joints for active tip articulations, and concentric tubes for (curved-path) guidance. Needle steering was evaluated sequentially by intended users and in intended-use tissue types. Six interventional radiologists evaluated the needle in repeated ultrasound-guided steering tasks in liver-mimicking phantoms. Targets were located at a 100 mm depth and 20 mm lateral offset from the initial insertion line. The resulting mean absolute tip placement error was 1.0 ± 1.0 mm. Subsequently, steering-induced tissue damage was evaluated in fresh cirrhotic human liver explants. The surface area of puncture holes was estimated in scanned histology slides, using a connected-components analysis. The mean surface area was 0.26 ± 0.16 mm2 after steering with a median radius of curvature of 0.7 × 103 mm, versus 0.35 ± 0.15 mm2 after straight-path insertions with the steerable needle and 0.15 ± 0.09 mm2 after straight-path RFA probe insertions. The steering mechanisms proposed enable clinically relevant path corrections for 17G needles. Radiologists were quickly adept in curved-path RFA probe placement and the evaluation of histological tissue damage demonstrated a potentially safe use during liver interventions.

Deep learning for surgical phase recognition using endoscopic videos.

BACKGROUND: Operating room planning is a complex task as pre-operative estimations of procedure duration have a limited accuracy. This is due to large variations in the course of procedures. Therefore, information about the progress of procedures is essential to adapt the daily operating room schedule accordingly. This information should ideally be objective, automatically retrievable and in real-time. Recordings made during endoscopic surgeries are a potential source of progress information. A trained observer is able to recognize the ongoing surgical phase from watching these videos. The introduction of deep learning techniques brought up opportunities to automatically retrieve information from surgical videos. The aim of this study was to apply state-of-the art deep learning techniques on a new set of endoscopic videos to automatically recognize the progress of a procedure, and to assess the feasibility of the approach in terms of performance, scalability and practical considerations. METHODS: A dataset of 33 laparoscopic cholecystectomies (LC) and 35 total laparoscopic hysterectomies (TLH) was used. The surgical tools that were used and the ongoing surgical phases were annotated in the recordings. Neural networks were trained on a subset of annotated videos. The automatic recognition of surgical tools and phases was then assessed on another subset. The scalability of the networks was tested and practical considerations were kept up. RESULTS: The performance of the surgical tools and phase recognition reached an average precision and recall between 0.77 and 0.89. The scalability tests showed diverging results. Legal considerations had to be taken into account and a considerable amount of time was needed to annotate the datasets. CONCLUSION: This study shows the potential of deep learning to automatically recognize information contained in surgical videos. This study also provides insights in the applicability of such a technique to support operating room planning.

Reprocessing filtering facepiece respirators in primary care using medical autoclave: prospective, bench-to-bedside, single-centre study.

OBJECTIVE: There are widespread shortages of personal protective equipment as a result of the COVID-19 pandemic. Reprocessing filtering facepiece particle (FFP)-type respirators may provide an alternative solution in keeping healthcare professionals safe. DESIGN: Prospective, bench-to-bedside. SETTING: A primary care-based study using FFP-2 respirators without exhalation valve (3M Aura 1862+ (20 samples), Maco Pharma ZZM002 (14 samples)), FFP-2 respirators with valve (3M Aura 9322+ (six samples) and San Huei 2920V (16 samples)) and valved FFP type 3 respirators (Safe Worker 1016 (10 samples)). INTERVENTIONS: All masks were reprocessed using a medical autoclave (17 min at 121°C with 34 min total cycle time) and subsequently tested up to three times whether these respirators retained their integrity (seal check and pressure drop) and ability to filter small particles (0.3-5.0 µm) in the laboratory using a particle penetration test. RESULTS: We tested 33 respirators and 66 samples for filter capacity. All FFP-2 respirators retained their shape, whereas half of the decontaminated FFP-3 respirators showed deformities and failed the seal check. The filtering capacity of the 3M Aura 1862 was best retained after one, two and three decontamination cycles (0.3 µm: 99.3%±0.3% (new) vs 97.0±1.3, 94.2±1.3% or 94.4±1.6; p<0.001). Of the other FFP-2 respirators, the San Huei 2920 V had 95.5%±0.7% at baseline vs 92.3%±1.7% vs 90.0±0.7 after one-time and two-time decontaminations, respectively (p<0.001). The tested FFP-3 respirator (Safe Worker 1016) had a filter capacity of 96.5%±0.7% at baseline and 60.3%±5.7% after one-time decontamination (p<0.001). Breathing and pressure resistance tests indicated no relevant pressure changes between respirators that were used once, twice or thrice. CONCLUSION: This small single-centre study shows that selected FFP-2 respirators may be reprocessed for use in primary care, as the tested masks retain their shape, ability to retain particles and breathing comfort after decontamination using a medical autoclave.

Designing and validating a PVA liver phantom with respiratory motion for needle-based interventions.

PURPOSE: The purpose is to design and validate an anthropomorphic polyvinyl alcohol (PVA) liver phantom with respiratory motion to simulate needle-based interventions. Such a system can, for example, be used as a validation tool for novel needles. METHODS: Image segmentations of CT scans of four patients during inspiration and expiration were used to measure liver and rib displacement. An anthropomorphic liver mold based on a CT scan was 3D printed and filled with 5% w/w PVA-to-water, undergoing two freeze-thaw cycles, in addition to a 3D-printed compliant rib cage. They were both held in place by a PVA abdominal phantom. A sinusoidal motion vector, based on the measured liver displacement, was applied to the liver phantom by means of a motion stage. Liver, rib cage and needle deflection were tracked by placing electromagnetic sensors on the phantom. Liver and rib cage phantom motion was validated by comparison with the CT images of the patients, whereas needle deflection was compared with the literature. RESULTS: CT analysis showed that from the state of expiration to inspiration, the livers moved predominantly toward the right (mean: 2 mm, range: - 11 to 11 mm), anterior (mean: 15 mm, range: 9-21 mm) and caudal (mean: 16 mm, range: 6-24 mm) direction. The mechatronic design of the liver phantom gives the freedom to set direction and amplitude of the motion and was able to mimic the direction of liver motion of one patient. Needle deflection inside the phantom increased from 1.6 to 3.8 mm from the initial expiration state to inspiration. CONCLUSIONS: The developed liver phantom allows for applying different motion patterns and shapes/sizes and thus allows for patient-specific simulation of needle-based interventions. Moreover, it is able to mimic appropriate respiratory motion and needle deflection as observed in patients.

A Methodical Quantification of Needle Visibility and Echogenicity in Ultrasound Images.

During ultrasound-guided percutaneous interventions, needle localization can be a challenge. To increase needle visibility, enhancements of both the imaging methods and the needle surface properties have been investigated. However, a methodical approach to compare potential solutions is currently unavailable. The work described here involves automated image acquisition, analysis and reporting techniques to collect large amounts of data efficiently, delineate relevant factors and communicate effects. Data processing included filtering, line fitting and image intensity analysis steps. Foreground and background image samples were used to compute a contrast-to-noise ratio or a signal ratio. The approach was evaluated in a comparative study of commercially available and custom-made needles. Varied parameters included needle material, diameter and surface roughness. The shafts with kerfed patterns and the trocar and chiba tips performed best. The approach enabled an intuitive polar depiction of needle visibility in ultrasound images for a large range of insertion angles.

Face and construct validity of TU-Delft epidural simulator and the value of real-time visualization.

BACKGROUND AND OBJECTIVES: Learning epidural anesthesia traditionally involves bedside teaching. Visualization aids or a simulator can help in acquiring motor skills, increasing patient safety and steepening the learning curve. We evaluated the face and construct validity of the TU-Delft Epidural Simulator and the effect of needle visualization. METHODS: Sixty-eight anesthesiologists, anesthesia residents, and final-year medical students tested the epidural simulator. Participants performed six epidural simulations with and six without needle visualization. We tested face validity on a Likert scale questionnaire. We collected data with the simulator software (spinal taps, dura contacts, bone contacts, attempts, and time) and tested for correlation with the performer's experience (construct validity). A visualization aid was tested in a randomized crossover design. RESULTS: Face validity as rated by the participants was above average, with a mean of 3.7 (2.0-4.8) on a 5-point scale. Construct validity was indicated by significantly more spinal taps (0.4 [0-4) vs 0.07 [0-2], p=0.04) and more dura contacts (0.58 [0-6] vs 0.37 [0-3], p=0.002) by the inexperienced group compared with the expert group. The visualization aid improved performance by reducing the number of bone contacts and the number of attempts, and by decreasing the procedure time. Prior visualization training reduced the total procedure time from 279 s (69-574) to 180 s (53-605) (p=0.01) for the "blind" procedure. CONCLUSIONS: The TU-Delft Epidural Simulator is a useful tool for teaching motor skills during epidural needle placement. Prior use of a visualization tool improves performance even without visual support during consequent simulations.

Needle placement errors: do we need steerable needles in interventional radiology?

PURPOSE: Accurate and precise needle placement is of utmost importance in interventional radiology. However, targeting can be challenging due to, eg, tissue motion and deformation. Steerable needles are a possible solution to overcome these challenges. The present work studied the clinical need for steerable needles. We aimed to answer three subquestions: 1) What are the current challenges in needle placement? 2) What are allowable needle placement errors? and 3) Do current needles need improvement and would steerable needles add clinical value? METHODS: A questionnaire was administered at the Annual Meeting of Cardiovascular and Interventional Radiology Society of Europe in 2016. In total, 153 respondents volunteered to fill out the survey, among them 125 (interventional) radiologists with experience in needle placement. RESULTS: 1) Current challenges in needle placement include patient-specific and technical factors. Movement of the target due to breathing makes it most difficult to place a needle (90%). 2) The mean maximal allowable needle placement error in targeted lesions is 2.7 mm. A majority of the respondents (85%) encounter unwanted needle bending upon insertion. The mean maximal encountered unwanted needle bending is 5.3 mm. 3) Needles in interventional radiology need improvement, eg, improved needle visibility and manipulability, according to 95% of the respondents. Added value for steerable needles in current interventions is seen by 93% of the respondents. CONCLUSION: Steerable needles have the potential to add clinical value to radiologic interventions. The current data can be used as input for defining clinical design requirements for technical tools, such as steerable needles and navigation models, with the aim to improve needle placement in interventional radiology.

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.

Navigation of guidewires and catheters in the body during intervention procedures: a review of computer-based models.

Guidewires and catheters are used during minimally invasive interventional procedures to traverse in vascular system and access the desired position. Computer models are increasingly being used to predict the behavior of these instruments. This information can be used to choose the right instrument for each case and increase the success rate of the procedure. Moreover, a designer can test the performance of instruments before the manufacturing phase. A precise model of the instrument is also useful for a training simulator. Therefore, to identify the strengths and weaknesses of different approaches used to model guidewires and catheters, a literature review of the existing techniques has been performed. The literature search was carried out in Google Scholar and Web of Science and limited to English for the period 1960 to 2017. For a computer model to be used in practice, it should be sufficiently realistic and, for some applications, real time. Therefore, we compared different modeling techniques with regard to these requirements, and the purposes of these models are reviewed. Important factors that influence the interaction between the instruments and the vascular wall are discussed. Finally, different ways used to evaluate and validate the models are described. We classified the developed models based on their formulation into finite-element method (FEM), mass-spring model (MSM), and rigid multibody links. Despite its numerical stability, FEM requires a very high computational effort. On the other hand, MSM is faster but there is a risk of numerical instability. The rigid multibody links method has a simple structure and is easy to implement. However, as the length of the instrument is increased, the model becomes slower. For the level of realism of the simulation, friction and collision were incorporated as the most influential forces applied to the instrument during the propagation within a vascular system. To evaluate the accuracy, most of the studies compared the simulation results with the outcome of physical experiments on a variety of phantom models, and only a limited number of studies have done face validity. Although a subset of the validated models is considered to be sufficiently accurate for the specific task for which they were developed and, therefore, are already being used in practice, these models are still under an ongoing development for improvement. Realism and computation time are two important requirements in catheter and guidewire modeling; however, the reviewed studies made a trade-off depending on the purpose of their model. Moreover, due to the complexity of the interaction with the vascular system, some assumptions have been made regarding the properties of both instruments and vascular system. Some validation studies have been reported but without a consistent experimental methodology.

Measuring surgical safety during minimally invasive surgical procedures: a validation study.

BACKGROUND: During the implementation of new interventions (i.e., surgical devices and technologies) in the operating room, surgical safety might be compromised. Current safety measures are insufficient in detecting safety hazards during this process. The aim of the study was to observe whether surgical teams are capable of measuring surgical safety, especially with regard to the introduction of new interventions. METHODS: A Surgical Safety Questionnaire was developed that had to be filled out directly postoperative by three surgical team members. A potential safety concern was defined as at least one answer between (strongly) disagree and indifferent. The validity of the questionnaire was assessed by comparison with the results from video analysis. Two different observers annotated the presence and effect of surgical flow disturbances during 40 laparoscopic hysterectomies performed between November 2010 and April 2012. RESULTS: The surgeon reported a potential safety concern in 16% (85/520 questions). With respect to the scrub nurse and anesthesiologist, this was both 9% (46/520). With respect to the preparation, functioning, and ease of use of the devices in 37.5-47.5% (15-19/40 procedures) a potential safety concern was reported by one or more team members. During procedures after which a potential safety concern was reported, surgical flow disturbances lasted a higher percentage of the procedure duration [9.3 ± 6.2 vs. 2.9 ± 3.7% (mean ± SD), p < .001]. After procedures during which a new instrument or device was used, more potential safety concerns were reported (51.2 vs. 23.1%, p < .001). CONCLUSIONS: Potential safety concerns were especially reported during procedures in which a relatively high percentage of the duration consisted of surgical flow disturbances and during procedures in which a new instrument or device was used. The Surgical Safety Questionnaire can act as a validated tool to evaluate and maintain surgical safety during minimally invasive procedures, especially during the introduction of a new intervention.

Optimal Point of Insertion and Needle Angle in Neuraxial Blockade Using a Midline Approach: A Study in Computed Tomography Scans of Adult Patients.

BACKGROUND AND OBJECTIVES: Neuraxial blockade using a midline approach can be challenging. Part of this challenge lies in finding the optimal approach of the needle to its target. The present study aimed at finding (1) the optimal point of insertion of the needle between the tips of 2 adjacent spinous processes and (2) the optimal angle relative to the skin at which the needle should approach the epidural or subarachnoid space. METHODS: A computer algorithm systematically analyzed computed tomography scans of vertebral columns of a cohort of 52 patients. On midsagittal sections, the possible points of insertion of a virtual needle and the corresponding angles through which the epidural or subarachnoid space can be reached were calculated. RESULTS: The point chosen to introduce the needle between 2 adjacent spinous processes determines the range of angles through which the epidural or subarachnoid space can be reached. At the thoracic interspaces 1-2 through 3-4, thoracic interspaces 5-6 through 9-10, and at the lumbar vertebral interspaces 2-3 through 4-5, the optimal point of insertion is slightly inferior to the point halfway between the tips of the spinous processes. For thoracic interspace 4-5, the optimal point of insertion is slightly superior to the point halfway between the tips of the spinous processes. For the other interspaces, the optimal point of insertion is approximately halfway between the tips of the spinous processes. The optimal angle to direct the needle varies from 9 degrees at the thoracolumbar junction and at the lumbar interspaces 3-4 and 4-5, to 53 degrees at the thoracic interspace 7-8. CONCLUSIONS: Our study has resulted in practical suggestions-based on accurate, reproducible measurements in patients-as to where to insert the needle and how to angulate the needle when performing neuraxial anesthesia using a midline approach.

Dataset on force measurements of needle insertions into two ex-vivo human livers.

A needle-tissue interaction experiment has been carried out, by inserting the inner needle of a trocar needle into two ex-vivo human livers. The dataset contains the forces that act on the needle during insertion and retraction into the livers. In addition, a MATLAB code file is included that provides base-level analysis of the data and generates force-position diagrams of the needle insertions. The dataset is available on Mendeley Data (do1i:10.17632/94s7xd9mzt.2), and is made publicly available to enable other researchers to use it for their own research purposes. For further interpretation and discussion of the data, one is referred to the associated research article entitled "PVA matches human liver in needle-tissue interaction" de Jong et al., 2017.

The Art of Electrosurgery: Trainees and Experts.

The benefits of electrosurgery have been acknowledged since the early 1920s, and nowadays more than 80% of surgical procedures involve devices that apply energy to tissues. Despite its widespread use, it is currently unknown how the operator's choices with regard to instrument selection and application technique are related to complications. As such, the manner in which electrosurgery is applied can have a serious influence on the outcome of the procedure and the well-being of patients. The aim of this study is to investigate the variety of differences in usage of electrosurgical devices. Our approach is to measure these parameters to provide insight into application techniques. A sensor was developed that records the magnitude of electric current delivered to an electrosurgical device at a frequency of 10 Hz. The sensor is able to detect device activation times and a reliable estimate of the power-level settings. Data were recorded for 91 laparoscopic cholecystectomies performed by different surgeons and residents. Results of the current measurement data show differences in the way electrosurgery is applied by surgeons and residents during a laparoscopic cholecystectomy. Variations are seen in the number of activations, the activation time, and the approach for removal of the gallbladder. Analysis showed that experienced surgeons have a longer activation time than residents (3.01 vs 1.41 seconds, P < .001) and a lower number of activations (102 vs 123). This method offers the opportunity to relate application techniques to clinical outcome and to provide input for the development of a best practice model.

PVA matches human liver in needle-tissue interaction.

Medical phantoms can be used to study needle-tissue interaction and to train medical residents. The purpose of this research is to study the suitability of polyvinyl alcohol (PVA) as a liver tissue mimicking material in terms of needle-tissue interaction. Insertions into ex-vivo human livers were used for reference. Six PVA samples were created by varying the mass percentage of PVA to water (4m% and 7m%) and the number of freeze-thaw cycles (1, 2 and 3 cycles, 16hours of freezing at -19°C, 8hours of thawing). The inner needle of an 18 Gauge trocar needle with triangular tip was inserted 13 times into each of the samples, using an insertion velocity of 5 mm/s. In addition, 39 insertions were performed in two ex-vivo human livers. Axial forces on the needle were captured during insertion and retraction and characterized by friction along the needle shaft, peak forces, and number of peak forces per unit length. The concentration of PVA and the number of freeze-thaw cycles both influenced the mechanical interaction between needle and specimen. Insertions into 4m% PVA phantoms with 2 freeze-thaw cycles were comparable to human liver in terms of estimated friction along the needle shaft and the number of peak forces. Therefore, these phantoms are considered to be suitable liver mimicking materials for image-guided needle interventions. The mechanical properties of PVA hydrogels can be influenced in a controlled manner by varying the concentration of PVA and the number of freeze-thaw cycles, to mimic liver tissue characteristics.

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.

Manually controlled steerable needle for MRI-guided percutaneous interventions.

This study aims to develop and evaluate a manually controlled steerable needle that is compatible with and visible on MRI to facilitate full intra-procedural control and accurate navigation in percutaneous interventions. The steerable needle has a working channel that provides a lumen to a cutting stylet or a therapeutic instrument. A steering mechanism based on cable-operated compliant elements is integrated in the working channel. The needle can be steered by adjusting the orientation of the needle tip through manipulation of the handle. The steering mechanism is evaluated by recording needle deflection at constant steering angles. A steering angle of 20.3° results in a deflection of 9.1-13.3 mm in gelatin and 4.6-18.9 mm in porcine liver tissue at an insertion depth of 60 mm. Additionally, the possibility to control the needle path under MRI guidance is evaluated in a gelatin phantom. The needle can be steered to targets at different locations while starting from the same initial position and orientation under MRI guidance with generally available sequences. The steerable needle offers flexibility to the physician in control and choice of the needle path when navigating the needle toward the target position, which allows for optimization of individual treatment and may increase target accuracy.