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10:40   Medical Instruments 10:40 15 mins THREE-DIMENSIONAL FLEXIBLE NEEDLE STEERING USING AN AUTOMATED BREAST VOLUME ULTRASOUND SCANNER Momen Abayazid, Anastasios Zompas, Sarthak Misra Abstract: Needle insertion into soft tissue is a minimally invasive procedure used for diagnostic and therapeutic purposes such as biopsy and brachytherapy, respectively. In the current study, we integrate 3D tracking, path planning and control algorithms to steer a bevel-tipped flexible needle to reach a target in 3D space while avoiding an obstacle. We introduce a system that uses a clinical ultrasound transducer (Automated Breast Volume Scanner (ABVS)) for 3D online needle tracking. The algorithms used in the system are validated by conducting insertion experiments into a soft-tissue phantom while avoiding virtual obstacles. The contributions of this work include the following: (a) to the best of our knowledge this is the first study to use ABVS technique for target localization and needle tip tracking in a 3D ultrasound-guided steering system; (b) experimental evaluation of needle steering towards a target while avoiding an obstacle. The experimental setup is divided into two parts. First, the insertion device allows the needle to be inserted and rotated about its axis. The details of the needle insertion device are presented in previous work. Second, the ABVS transducer that permits the ultrasound transducer to scan the phantom with a constant velocity. The 15 MHz transducer is connected to a Siemens Acuson S2000 ultrasound machine (Siemens AG, Erlangen, Germany). The needle is inserted into a soft-tissue phantom made of a gelatin mixture. The flexible needle is made of a super-elastic Nitinol alloy (nickel and titanium). The Nitinol needle has a diameter of 0.5 mm with a bevel angle (at the tip) of 30º. Different experimental scenarios are conducted to evaluate the performance of the proposed needle tracking, path planning and control algorithms. The needle curvature in the phantom is determined empirically. A safety margin is added to the needle curvature value to compensate for variations or disturbances that may take place during insertion. The ultrasound scan velocity is 1.5-1.7 mm/s. Each experimental case is performed five times. The phantom is scanned pre-operatively to localize the physical target in the soft-tissue phantom. The obtained target and obstacle locations are exported to the path planning algorithm. The control algorithm steers the needle along the generated path to avoid the obstacle and reach the target using milestones. The path is updated every second to avoid the obstacle and to correct for needle tip deviation during insertion. The targeting error is the absolute distance between the target position that is pre-defined and needle tip position obtained from the needle tracking algorithm. The results show that the needle did not collide with the obstacles in any experimental trials. The mean targeting error ranges between 0.64±0.24 mm and 0.94±0.37 mm. The achieved submillimeter accuracy suggests that our approach is sufficient to target the smallest lesions (2mm diameter) that can be detected using state-of-the-art ultrasound imaging systems. 10:55 15 mins STATISTICAL MODEL OF CATHETER ABLATION TARGETS FOR TREATMENT OF ATRIAL FIBRILLATION Ahmed AlAgamy, Rashed Karim, Aruna Arujuna, James Harrison, Steven Williams, Kawal Rhode, Hans van Assen Abstract: Introduction: Atrial Fibrillation (AFib) is the most common cardiac arrhythmia causing chaotic contraction of the atria. Catheter ablation is considered an established therapeutic alternative to anti-arrhythmic medications for paroxysmal and persistent AFib. Paroxysmal AFib is commonly treated by pulmonary vein isolation (PVI), the creation of circumferential lesions around the PV ostia [1]. We developed an ablation target probability model for the left atrium. It is based on intra-procedural ablation target data from fifteen patients with AFib. Motivation: The goals of the proposed model are the following: 1) determine the region of interest selection in pencil beam wall thickness imaging with MRI [2], 2) distinguish necrotic tissue due to ablation from fibrotic tissue due to AFib, 3) to enable patient-specific ablation strategy planning and annotation, and 4) to study variations in ablation patterns between different centers which would help drive automated robot-assisted ablation procedures [3]. Method: The proposed model is based on patients with paroxysmal (AFib) only. A left atrium mean model mesh was used as a common reference for mapping and projecting ablation targets from all patient specific electro-anatomical meshes. This was achieved using landmark registration (LM) and the iterative closest point (ICP) registration algorithm [4]. The projected ablation targets were used to calculate ablation target density. This allowed an ablation target probability density function for PVI lesion sets to be deduced. The probability distribution resulting from the previous steps is smoothed by convolution with a 3D Gaussian kernel. This compensates for the inherited uncertainty in localization of the catheter position, as well as the errors introduced from ablation target mapping steps. The smoothed probability density function is visualized on the left atrial mean mesh as a color encoded lesion map. Results: The resulting probability distribution shows PVI contours in areas that are recommended for paroxysmal AFib treatment [1]. The right inferior pulmonary vein (RIPV) shows a lower overall ablation probability than the other PVs. This is due to the difficulty in accessing the RIPV from the catheter’s entry point Conclusion: We have presented an ablation target probability density model for the left atrium built from the intra-procedural data of paroxysmal AFib patients. Such a model has the potential to guide successful ablation strategies and reveal differences in ablation patterns between treatment centers. REFERENCES [1] Calkins, H., et al., Heart Rhythm 9(4) (Apr 2012) 632-696 [2] Koken, P., et al., Proceedings 19th ISMRM Scientific Meeting, Canada. (2011) [3] Pappone, C., et al., J Am Coll Cardiol 47(7) (Apr 2006) 1390-400 [4] Zhang, Z., International Journal of Computer Vision 13(2) (1994) 119-152 11:10 15 mins THE HELIXFLEX: A DEXTEROUS INSTRUMENT FOR MINIMALLY INVASIVE SURGERY Paul Henselmans, Giada Gerboni, Paul Breedveld Abstract: The pituitary gland is the hormone gland that, amongst other functions, regulates the hormone production in the human body. It is positioned in the skull base just beneath the brain, and surrounded by important and delicate neurovascular structures as the optic chiasm and carotid artery. A tumor on or near the pituitary can therefore not only result in abnormal hormone regulation, but can also lead to vision loss and headaches. The least invasive surgical path to the intracranial areas is the endoscopic approach through the nostrils, referred to as Endonasal Skull Base Surgery (ESBS) [1]. The resulting pathway is narrow and often referred to as a corridor. As multiple instruments need to be inserted through this corridor, the space for sideway movements of these instruments is limited. Moreover, this situation can easily lead to undesired collisions between instruments, is it by the shafts inside or the surgeons hands outside of the patients body. Ideally then, one would like the ability of maneuvering the instruments’ end-effector while its shaft remains in a stable stationary position. Steerable instruments might provide a solution. These instruments include a steerable segment between the shaft and end-effector, allowing for the re-orientation of the end-effector in reference to the shaft. A well-known example of a steerable instrument is the Endowrist which is incorporated in the Da Vinci surgical system of Intuitive Surgical [2]. These type of steerable instruments are, however, not suitable for ESBS. The reason is that while one can re-orientate the end-effector, its position is still directly coupled to the shaft. This means that for sufficient motion of the end-effector, shaft motion is inevitable. For this reason a new cable actuation method, referred to as multi-actuation, has been developed at the BITE group of TU Delft. Inspired by the anatomical construction of a squid tentacle, multi-actuation uses multiple cable-routings to enhance the dexterity of a steerable instrument. It was found that by using helical as well as parallel cable-routings a cable structure could be realized that enables the re-orientation and re-positioning of the end-effector in reference to the shaft. Such dexterity would allow for sufficient motion of the end-effector while the shaft remains is a stable stationary position. The principles of multi-actuation have been successfully incorporated in a prototype called the HelixFlex. The HelixFlex is a handheld instrument with a diameter of 5 mm. It is capable of 4 DoF motion which can be controlled by a single point in the handle. Furthermore it contains a locking system that allows the user to lock the end-effector in any desired orientation and position. 11:25 15 mins CLOSED-LOOP CONTROL OF A ROBOTICALLY-ACTUATED DELIVERY SHEATH (RADS) FOR CARDIOVASCULAR APPLICATIONS Gustaaf Vrooijink, Jan Grandjean, Sarthak Misra Abstract: Recent technological advancements have significantly improved treatment of cardiovascular diseases. Valve-related diseases such as severe symptomatic aortic stenosis and insufficiency require treatment by open heart aortic valve surgery with cardiopulmonary bypass. This procedure is often considered a high risk for the patients with comorbidities. As an alternative, treatment can be provided by minimally invasive surgery such as transfemoral (TF) and transapical (TA) transcatheter aortic valve implantation (TAVI) [1]. Complications in TAVI-related procedures are often caused by prosthetic valve malpositioning. Complications can result in severe peri-prosthetic aortic regurgitation, valve embolization and occlusion of arteries. Therefore, outcome of the procedure is closely related to valve placement. The clinician often has limited and non-intuitive control over the tip of the instrument by manipulating its base, which is outside the body. Integration of robotically-controlled instruments has the potential to assist the clinician in accurate valve positioning. Further, compensation for beating heart and respiration motions could be provided by model predictive control and motion profiles based on patient data. In this study, we describe and demonstrate that a robotically-actuated delivery sheath (RADS) can potentially be used to assist the clinician in valve positioning. The RADS consists of a rigid shaft combined with a flexible articulating tip segment. The tip can be controlled in two degrees-of-freedom by using an antagonistically-configured and pulley driven cable mechanism [2]. The RADS is inserted in a water container and its tip motion tracked by two-dimensional ultrasound. The ultrasound image plane is orientated perpendicular to the shaft of the instrument and positioned at the tip. Direct and inverse kinematic models are used to describe the non-linear relation between cable displacements at the base and the corresponding tip position. Both modeling and ultrasound tracking are used in closed-loop control of the instrument tip. We use Kalman filtering to reduce noise in the system. The effect of mechanical hysteresis in the instrument is reduced by a compensation strategy. We experimentally evaluated the integrated system along various paths. Results show a mean tip positioning errors of 0.75 mm and 1.13 mm along the x- and y-axis, respectively. 11:40 15 mins THE WORKING MECHANISM OF THE ‘NANOKNIFE’: HOT OR NOT ? Rudolf Verdaasdonk, John Klaessens, Hester Scheffer, Martijn Meijerink, Martijn de Bruin, Willemien van den Bos, Jantien Vogel, Marc Besselink, Jean de la Rosette Abstract: The 'NanoKnife’ was recently introduced as new technique based on irreversible electroporation (IRE) for selective treatment of tumors. Malignant tissue is exposed to a series of 90µs bursts of 20-40 A between 2-6 electrode needles at 1500V/cm interelectrode distance. The action mechanism is ascribed to high voltage damaging of ion channels in the cell membrane with minimal thermal effects. To investigate the physical mechanisms during IRE, the NanoKnife (AngioDynamics, Albany, N.Y., USA) was studied in tissue and cell-free phantoms using high speed Schlieren techniques and thermography to image instant effects and to quantify the temperature dynamics up to millisecond resolution comparing energy settings and needle configurations. The images were processed with dedicated analysis software. High speed imaging showed instant gas formation ascribed to electrolysis most pronounced at the negative electrode supported by the color change of the metal electrodes. Thermal imaging showed substantial thermal effects 5-10 mm symmetrical around the needles (thermal source) with temperature increase over 20 degrees (highest for negative electrode) remaining for several minutes. By adapting the length of the electrode, the distance and relative angle of each needle, the temperature distribution could be controlled. The presence of metal stents had minimal effect. Based on in vitro-studies, the working mechanism of the NanoKnife is partly ascribed to a substantial temperature increase while no evidence is found to support membrane damage. Future in-vivo studies are needed to observe the thermal effects in tissues with perfusion. The new insights will contribute to an effective selective treatment of tumors in e.g. liver, pancreas, kidney and prostate. 11:55 15 mins DESIGN AND EVALUATION OF A PATIENT-SPECIFIC KNEE JOINT DISTRACTION DEVICE FOR TREATMENT OF KNEE OSTEOARTHRITIS Thijmen Struik, Simon Mastbergen, Peter van Roermund, Joris Jaspers, Floris Lafeber Abstract: Osteoarthritis (OA) is characterized by cartilage loss leading to a decreased joint space width accompanied by mild synovial tissue inflammation and subchondral bone changes. Common surgical treatment in end-stage disease is joint replacement but other treatment options for knee osteoarthritis are limited in number and in clinical outcome. Especially for young patients with severe knee OA, the need for more effective options is increasing with the growing prevalence. Knee joint distraction (KJD) therapy has shown to be an effective treatment method for relatively young patients who are considered for total knee prosthesis (TKP), by postponing a first TKP.[1,2,3] During the 6-8 weeks lasting KJD procedure, the bony ends of the joint are set at a distance up to 5 millimeters with an external fixator which is attached to the patient by means of bone pins.[3,4] Although multiple studies have shown joint distraction with positive clinical outcome, acceptance of the therapy is staying behind on those results.[3,4,5] In most studies, a rigid distraction setup was used which restricts joint flexion. Joint articulation during KJD therapy is expected to increase comfort for the patient and acceptance of therapy.[5] A non-invasive method for patient-specific and joint-specific motion reproduction for application in KJD was developed. The approach comprises reproduction of relative motion between femoral and tibial bone pin sides. Motion is measured bilaterally by scratching motion paths of sharp pens (femoral side) in a deformable counterpart (tibial side). Measured motion is translated to an interconnecting element at the medial and lateral joint side. A cam following mechanism of which the interconnecting elements dictate joint motion, reproduces thirty degrees joint flexion. Feasibility of motion reproduction, including joint distraction, was evaluated on human cadaver knees (n=3) representative for passive joint motion. Motion was manually evaluated by an experienced orthopedic surgeon for irregularities. Attachment of the femoral and tibial articulating distractor parts after placement of bone pins was found to be feasible, although determination of the plane of motion could only be achieved by application of an additional alignment tool. The desired range of motion was obtained. Articulation during KJD has great potential to improve distraction therapy. The proposed method was found to be technically feasible. Clinical feasibility should be evaluated previous to clinical implementation.