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Accepted Manuscripts

BASIC VIEW  |  EXPANDED VIEW
research-article
J. Med. Devices   doi: 10.1115/1.4035983
Anticoagulants are the treatment of choice for pulmonary embolism. When these fail or are contraindicated, vena cava filters are effective devices for preventing clots from the legs from migrating to the lung. Many uncertainties exist when a filter is inserted, especially during physiological activity such as normal breathing and the Valsalva manoeuvre. These activities are often connected with filter migration and vena cava damage due to the various related vein geometrical configurations. In this work we analysed the response of the vena cava during normal breathing and Valsalva manoeuvre, for a healthy vena cava and after insertion of a commercial Günther-Tulip filter. Computational fluid dynamics (CFD) and patient specific data are used for analysing blood flow inside the vena cava during these manoeuvres. While during normal breathing the vena cava flow can be considered almost stationary with a very low pressure gradient, during Valsalva the extravascular pressure compresses the vena cava resulting in a drastic reduction of the vein section, a global flow decrease through the cava but increasing the velocity magnitude. This change in section is altered by the presence of the filter which forces the section of the vena cava before the renal veins to keep open. The effect of the presence of the filter is investigated during these manoeuvres showing changes in wall shear stress and velocity patterns.
TOPICS: Filters, Blood flow, Flow (Dynamics), Computational fluid dynamics, Pressure, Uncertainty, Damage, Shear stress, Kidney, Lung, Pressure gradient, Physiology
research-article
J. Med. Devices   doi: 10.1115/1.4035984
This paper introduces a new design for individually controlled magnetic artificial cilia for use in fluid devices, and specifically intended to improve the mixing in DNA microarray experiments. The design has been implemented using a low-cost prototype that can be fabricated using polydimethylsiloxane (PDMS) and off-the-shelf parts, and achieves large cilium deflections (59% of the cilium length). The device's performance is measured via a series of mixing experiments using different actuation patterns inspired by the blinking vortex theory. The experimental results, quantified using the relative standard deviation of the color when mixing two colored inks, show that exploiting the individual control leads to faster mixing (38% reduction in mixing time) than when operating the device in a simultaneous-actuation mode with the same average cilium beat frequency. Furthermore, the experimental results show an optimal beating pattern that minimizes the mixing time. The existence and character of this optimum is predicted by simulations using a blinking-vortex approach for 2D ideal flow, suggesting that the blinking-vortex model can be used to predict the effect of parameter variation on the experimental system.
TOPICS: Flow (Dynamics), Fluids, Simulation, Inks, Plasma desorption mass spectrometry, Engineering prototypes, Design, Engineering simulation, Vortices, Deflection, DNA
Technical Brief
J. Med. Devices   doi: 10.1115/1.4035982
In this article, the design and development of a real-time heart rate (HR) and respiratory rate (RR) monitoring device is reported. The proposed device is designed to impose minimum data acquisition hazards on the subject. In standard bedside monitors, HR and RR are derived from ECG and respiration signals, respectively, and different electrodes are required for capturing the 12-lead ECG and respiration via a chest belt, which is cumbersome for patients and healthcare providers. Respiration signal has an impact on ECG due to anatomical proximity of the heart and lung, and ECG is modulated by respiration,a phenomenon known as Respiratory Sinus Arrhythmia (RSA). In the proposed method, the ECG signal is acquired using clip electrodes at the wrists and the respiration signal is extracted from the ECG using an Arduino Uno microcontroller-based real-time processing of ECG. RR is then derived from ECG-derived Respiration (EDR). The prototype is tested on healthy subjects and compared to measurements taken using a standard MP45 data acquisition device associated with a Biopac Student Lab (BSL). A mean percentage error of 5.54±8.48% was observed under normal breathing conditions and an error of -3.41 ±3.27% was observed for a single subject tested under a variety of breathing conditions, such as resting, stair-climbing, and paced breathing. The proposed algorithm can also be used in combination with standard ECG monitoring systems to measure HR and RR, without any data acquisition hazard to the subject.
TOPICS: Stairs, Engineering prototypes, Algorithms, Design, Electrodes, Errors, Health care, Lung, Monitoring systems, Signals, Students, Arrhythmias, Data acquisition, Belts, Hazards
research-article
J. Med. Devices   doi: 10.1115/1.4035981
Recent clinical studies showed that the hemodynamic energy loss of the surgical conduit used in 3rd-stage repair of single-ventricle heart defects (Fontan surgery) determines the post-operative exercise capacity. Still, our understanding of the Fontan pathway energy loss is based on fully-functional conduits that are acquired from patients with optimal post-operative health, while a significant portion of the patients struggle with severe complications due to their gradually failing physiology. In this study, the hemodynamics of severely deformed surgical pathways due to torsional deformation and anastomosis offset, are investigated. We designed a mock-up circuit to replicate the mechanically failed inferior vena cava (IVC) anastomosis morphologies under physiological venous pressure (9, 12, 15 mmHg), in vitro, employing the commonly used conduit materials; PTFE, Dacron and porcine pericardium. For three twist angles (0°, 30°, 60°) and caval offsets (0Diameter, 0.5D and 1D) conduit shapes are digitized in 3D and employed in computational fluid dynamic simulations to determine the corresponding hydrodynamic efficiency levels. A total of 81 deformed configurations are analyzed in which the pressure drop values increased 80 to 1070 % with respect to the uniform diameter IVC conduit. Surgical materials resulted significant variations in terms of flow separation and energy loss. The porcine pericardium and PTFE conduit resulted 8 and 3 times more pressure drop than the Dacron conduit, respectively. If anastomosis twist and/or offset cannot be avoided due to the patients anatomy, alternative materials with high structural stiffness can be considered.
TOPICS: Energy dissipation, Buckling, Surgery, Physiology, Hemodynamics, Pressure drop, Shapes, Stiffness, Anatomy, Circuits, Flow separation, Computational fluid dynamics, Engineering simulation, Pressure, Deformation, Maintenance, Simulation
Guest Editorial
Marc Horner
J. Med. Devices   doi: 10.1115/1.4036591
TOPICS: Safety, Computer simulation, Cardiovascular devices, Experimental methods
research-article
J. Med. Devices   doi: 10.1115/1.4036580
To reform diabetes management painless and reliable noninvasive blood glucose (NIBG) measurement technique has been explored since last three decades. In the present work photoplethysmogram (PPG) signal is used to measure the variations in blood glucose concentration. However, the literature reveals that physiological perturbations such as temperature, skin moisture and sweat cause poor accuracy of NIBG measurement. The task of minimizing the effect of these perturbations and to improve accuracy is an important research area. Therefore, along with PPG sensor, Galvanic Skin Response (GSR) and temperature sensors are also used to achieve more accurate NIBG measurement. The accuracy of the proposed Multi-sensor system is evaluated by pairing and comparing non-invasively measured data with invasively measured readings. The study is made on 50 non-diabetic subjects with BMI 27.3±3 kg/m2. Two machine learning techniques, i.e. Multiple Linear Regression (MLR) and Artificial Neural Network (ANN) are used to estimate the glucose concentration from extracted data. The results reveal that the MAPE and correlation coefficient are significantly improved in comparison to the techniques reported in the literature.
TOPICS: Sensors, Blood glucose measurement, Skin, Artificial neural networks, Diabetes, Blood glucose, Signals, Temperature, Machinery, Temperature sensors, Physiology, Glucose
Technical Brief
J. Med. Devices   doi: 10.1115/1.4036581
Interventional catheter ablation treatment is a non-invasive approach for normalizing heart rhythm in patients with arrhythmia. Catheter ablation can be assisted with magnetic resonance imaging (MRI) to provide high-contrast images of the heart vasculature for diagnostic and intra-procedural purposes. Typical MRI images are captured using surface imaging coils which are external to the tissue being imaged. The image quality and the scanning time required for producing an image are directly correlated to the distance between the tissue being imaged and the imaging coil. The objective of this work is to minimize the spatial distance between the target tissue and the imaging coil by placing the imaging coil directly inside the heart through the use of an expandable origami catheter structure. In this study, geometrical analysis is utilized to optimize the size and shape of the origami structure and MRI scans are taken to confirm the MRI compatibility of the structure. The origami expandable mechanism could also be applied to other medical device designs that require expandable structures.
TOPICS: Cardiovascular system, Catheters, Magnetic resonance imaging, Imaging, Biological tissues, Ablation (Vaporization technology), Medical devices, Arrhythmias, Shapes
research-article
J. Med. Devices   doi: 10.1115/1.4036490
Background: Drilling through bone is a common task during otologic procedures. Currently, the drilling tool is manually held by the surgeon. This project was to demonstrate the feasibility of using the da Vinci Research Kit (dVRK) to hold the drill and provide force feedback for temporal bone drilling. Methods: A modified da Vinci surgical instrument with force sensing was developed to enable robotically assisted drilling for otologic surgery. To provide intuitive motion and force feedback, the master–slave kinematics were analyzed and a suitable mapping was implemented. Results: Several experiments were completed including trajectory tracking of master–slave motion, drill instrument calibration, and force feedback using a temporal bone model. The results showed that good trajectory tracking performance, and minor calibration errors were achieved. In addition, force feedback from the drill instrument could be felt at the master arm. Conclusions: A robotically assisted surgical drill for otologic surgery was developed and demonstrated using the dVRK. In the future, it may be feasible to use master–slave surgical robot systems for temporal bone drilling.
TOPICS: Drills (Tools), Instrumentation, Surgery, Force feedback, Drilling, Bone, Trajectories (Physics), Calibration, Errors, Kinematics, Robots, Surgical tools
research-article
J. Med. Devices   doi: 10.1115/1.4036391
Overlapping stents are widely used in vascular stent surgeries. However, the rate of stent fractures (SF) and in-stent restenosis (ISR) after using overlapping stents is higher than those after using a single stent. The current studies to investigate the nature of overlapping stents were mainly based on medical images, which can only reveal the effect of surgery without providing insights on how stent overlapping influences the implantation process. In this paper, a finite element analysis of overlapping stent implantation process was performed to study the interaction between overlapping stents. Four different cases based on three typical stent overlapping modes and two classical balloons were carried out. The results showed that overlapping contact patterns among struts were edge to edge, edge to surface and non-contact. These were mainly induced by the non-uniform deformation of stent in the radial direction and stent tubular structures. Meanwhile the results showed the most of contact pressure concentrated occurred in the edge of overlapping struts. In the stent overlapping evolution, the pattern of most contacts was edge to edge contact at beginning; and edge to surface contact pattern occurred as the contact pressure increase. The interactions between overlapping stents suggest that the failure of overlapping stent frequently occurs in the edge of stent, it matches favorably to an experiment about the safety of overlapping stent. This paper provides a fundamental understanding of overlapping stent’s mechanical properties.
TOPICS: Finite element analysis, stents, Surgery, Pressure, Deformation, Safety, Fracture (Materials), Mechanical properties, Biomedical imaging, Failure, Fracture (Process)
research-article
J. Med. Devices   doi: 10.1115/1.4036334
In order to evaluate the performance of stents used in transcatheter aortic valve implantation (TAVI), finite element simulations are set up to reconstruct patient specific contact forces between implant and its surrounding tissue. Previous work used structural beam elements to set-up a numerical model of the CoreValve stent used in TAVI and developed a procedure for implementing kinematic boundary conditions from noisy CT scanning data. This study evaluates element size selection and quantitatively investigates the choice of a linear elastic constitutive model for the Nitinol stent under physiological loading conditions. It is shown that this simplification leads to reliable results and enables a huge reduction in computation time. Further, the procedure used to compensate for noisy postoperative CT data is tested by adding artificial noise. It is concluded, that for physiologically relevant loading ranges, the procedure yields convergent results and successfully eliminates the influence of the noise.
TOPICS: Finite element analysis, Modeling, Valves, stents, Noise (Sound), Biological tissues, Constitutive equations, Engineering simulation, Kinematics, Computer simulation, Simulation, Beams (Structural), Physiology, Boundary-value problems, Computation, Computerized tomography, Nickel titanium alloys
research-article
J. Med. Devices   doi: 10.1115/1.4036335
Objective: To develop and evaluate the clinical application of a multimodal colposcopy combining multispectral reflectance, autofluorescence and RGB imaging for early screening of cervical intraepithelial neoplasia (CIN). Methods: We developed a multimodal colposcopy system that combined multispectral reflectance, autofluorescence, and RGB imaging for early screening of CIN. We studied the optical properties of cervical tissue first, then the imaging system was designed and tested in clinical trial where comprehensive datasets were acquired and analyzed to differentiate between squamous normal and high grade types of cervical tissue. Results: The specially designed multimodal colposcopy is capable of acquiring multispectral reflectance images, autofluorescence images, and RGB images of cervical tissue consecutively. The classification algorithm was employed on both normal and abnormal cases for image segmentation. The sensitivity and specificity performance of this system related to gold standard of histopathology show statistical significance. Conclusions: Our pilot study demonstrated the clinical potential of this multimodal colposcopic system for early screening of CIN. The low-cost portable characteristics, the simple operating process, and the simple image segmentation algorithm of this system make it possibility to address the needs for CIN early screening in a rapid, cost-effective, and non-invasive fashion in the developing countries.
TOPICS: Tumors, Imaging, Reflectance, Biological tissues, Image segmentation, Algorithms, Developing nations
Technical Brief
J. Med. Devices   doi: 10.1115/1.4036336
This work exploits the advantages of compliant mechanisms (devices that achieve their motion through the deflection of flexible members) to enable the creation of small instruments for minimally invasive surgery. Using flexures to achieve motion presents challenges, three of which are considered in this work. First, compliant mechanisms generally perform inadequately in compression. Second, for a $\pm90^{\circ}$ range of motion desired for each jaw, the bending stresses in the flexures are prohibitive considering materials used in current instruments. Third, for cables attached at fixed points on the mechanism the mechanical advantage will vary considerably during actuation. Research results are presented that address these challenges using compliant mechanism principles as demonstrated in a 2-degree-of-freedom L-Arm gripper.
TOPICS: Grippers, Compliant mechanisms, Instrumentation, Surgery, Compression, Deflection, Cables, Bending (Stress)
research-article
J. Med. Devices   doi: 10.1115/1.4036337
The purpose of this study was to evaluate the suitability of a novel radio-frequency identification (RFID)-based tracking system for intraoperative magnetic resonance imaging (MRI). A RFID tracking system was modified to fulfill MRI-compatibility and tested according to ASTM and NEMA. The influence of the RFID tracking system on MRI was analyzed in a phantom study using a HASTE and TrueFISP sequence. The RFID antenna was gradually moved closer to the isocenter of the MR scanner from 90 to 210 cm to investigate the influence of the distance. Furthermore the RF was gradually changed between 865-869 MHz for a distance of 90 cm, 150 cm and 210 cm to the isocenter of the magnet to investigate the influence of the frequency. The specific spatial resolution was measured with and without a permanent line of sight (LOS). After the modification of the reader no significant change of the SNR could be observed with increasing distance of the RFID tracking system to the isocenter of the MR scanner. Also different radio frequencies of the RFID tracking system did not influence the SNR of the MR images significantly. The specific spatial resolution deviated on average by 8.97 ± 7.33 mm with LOS and 11.23 ± 12.03 mm without LOS from the reference system. The RFID tracking system had no relevant influence on the MR image quality. RFID tracking solved the LOS problem. However the spatial accuracy of the RFID tracking system has to be improved for medical usage.
TOPICS: Magnetic resonance imaging, Navigation, Resolution (Optics), Magnets, Phantoms, Biomedicine, ASTM International
Technical Brief
J. Med. Devices   doi: 10.1115/1.4036338
Objectives: Accurate needle guidance is essential for a number of 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. Methods: We fabricated an MR-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. Results: 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 shown nearly similar accuracy to electromagnetic tracking (i.e. 0.89 ± 0.09 mm). Conclusion: We demonstrated feasibility of the FBG-based tracking system for MR guided interventions with differences under 1 mm between tracking systems. Significance: This study establishes the needle tracking accuracy of FBG needle tracking for image-guided procedures.
TOPICS: needles, Shapes, Fiber Bragg gratings, Sensors, Radiofrequency ablation, Tumors, Magnetic fields, Magnetic resonance imaging, Optical fiber, Phantoms, Deflection, Errors, Liver, Navigation
Expert View
J. Med. Devices   doi: 10.1115/1.4036333
The Food and Drug Administration’s (FDA) Humanitarian Device Exemption (HDE) is a unique marketing approval pathway for medical devices targeting diseases affecting small (rare) patient populations. Analyses of HDE approvals from 2007-2015 revealed that approvals were based on a broad range of data constituting valid scientific evidence to support a finding of safety and probable benefit and demonstrated that the FDA exercises a high degree of flexibility when reviewing HDE applications.
TOPICS: Diseases, Frequency-domain analysis, Food and Drug Administration, Drugs, Food products, Safety, Medical devices
research-article
J. Med. Devices   doi: 10.1115/1.4036299
This research was directed toward quantitatively characterizing the effects of arterial mechanical treatment procedures on the stress and strain energy states of the artery wall. Finite element simulations of percutaneous transluminal angioplasty and orbital atherectomy were performed on arterial lesion models with various extents and types of plaque. Stress fields in the artery were calculated and strain energy density was used as an explicit description of potential damage to the artery. The research also included numerical simulations of changes in arterial compliance due to orbital atherectomy. The angioplasty simulations show that the damage energy fields in the media and adventitia are predominant in regions of the lesion that are not protected by a layer of calcification. It was observed that softening the plaque components leads to a lower peak stress and therefore lesser damage energy in the media and adventitia under the action of a semi-compliant balloon. Orbital atherectomy simulations revealed that the major strain energy density dissipated is concentrated in the plaque components in contact with the spinning tool. The damage and peak stress fields in the media and adventitia components of the vessel were significantly less. This observation suggests less mechanically induced trauma during a localized procedure like orbital atherectomy. Artery compliance was calculated pre- and-post treatment and an increase was observed after the orbital atherectomy procedure. The localized plaque disruption produced in atherectomy suggests that the undesirable stress states in angioplasty can be mitigated by a combination of procedures such as atherectomy followed by angioplasty.
TOPICS: Computer simulation, Biological tissues, Damage, Stress, Engineering simulation, Simulation, Density, Spinning (Textile), Finite element analysis, Vessels, Energy levels (Quantum mechanics), Spin (Aerodynamics)
research-article
J. Med. Devices   doi: 10.1115/1.4036286
A numerical analysis of a semi-enclosed tubular Mechanical Embolus Retrieval Device (MERD) for the treatment of Acute Ischemic Stroke (AIS) is presented. In this research, the FEA (Finite Element Analysis) methodology is used to evaluate mechanical performance and provide suggestions for optimizing the geometric design. A MERD fabricated from nickel-titanium alloy (Nitinol) tubing is simulated and analyzed under complex in-vivo loading conditions involving shape-setting, crimping, deployment, and embolus retrieval. As a result, the peak strain of the shape-setting procedure is proved to be safe for the device pattern. However, the MERD shows poor mechanical behavior after crimping into a catheter, because the peak crimping strain obtains a value of 12.1%. The delivery and deployment step demonstrates that the artery wall has little risk of serious injuries or ruptures. In addition, the process of simulation of embolus retrieval and device system migration inside the cerebral artery lumen provides useful information during the design process.
TOPICS: Design, Simulation, Nickel titanium alloys, Finite element analysis, Shapes, Wounds, Cerebral arteries, Risk, Mechanical behavior, Numerical analysis, Catheters, Rupture, Tubing, Equipment performance
research-article
J. Med. Devices   doi: 10.1115/1.4036287
This paper describes the use of analytical methods to determine machinable centrifugal impeller geometries and the use of computational fluid dynamics for predicting impeller performance. An analytical scheme is described to determine machinable geometries for a shrouded centrifugal impeller with blades composed of equiangular spirals. The scheme is used to determine the maximum machinable blade angles for impellers with 3 to 9 blades in a case study. Computational fluid dynamics is then used to analyse all machinable geometries and determine the optimal blade number and angle based on measures of efficiency, rotor speed, blade shear stress and eddy viscosity. The effect of tip width on rotor speed and efficiency is also examined. It is found that, for our case study, a six or seven bladed impeller with a low blade angle provides maximum efficiency and minimum hemolysis.
TOPICS: Impellers, Blood, Optimization, Pumps, Machinability, Blades, Rotors, Computational fluid dynamics, Analytical methods, Eddies (Fluid dynamics), Viscosity, Shear stress
Technical Brief
J. Med. Devices   doi: 10.1115/1.4036136
Surgical endoscopy has gained traction over the past several decades as a viable option for therapeutic interventions in the gastrointestinal tract. It utilizes natural orifice access which shortens hospital stay, minimizes patient discomfort, and decreases overall healthcare costs. However, the inability to effectively retract and position target tissue is a significant limitation for these procedures. Current instruments are unable to triangulate and can only be manually withdrawn or advanced through the channels. There is a need to provide better access and control of soft tissue to be able to perform more complex and complete endoscopic resections. We have developed a novel device to provide optimal tissue retraction for endoscopic procedures. Our device consists of an articulating tissue retractor and a specialized handle. Two articulating curves were created that can manipulate the position and direction of the retractor tip. Each curve is independently adjusted by locking thumb sliders, allowing for increased range of motion and retraction independent of endoscope position. With a diameter of 2.8mm, the proposed device can be used in current endoscopic equipment. Preliminary testing showed that our retractor has comparable slip strength to a commercially available device (1.13N +/- 0.53N vs. 1.10N +/- 0.51N, p-value: 0.416), but has much greater range of motion (maximum deflection of 72 compared to 0). This increased range of motion allows the articulating grasper to better triangulate and preserve visualization of the dissection plane, allowing it to overcome the most significant barrier restricting endoscopic surgery.
TOPICS: Surgery, Endoscopic devices, Biological tissues, Instrumentation, Testing, Visualization, Deflection, Endoscopes, Health care, Traction, Soft tissues
research-article
J. Med. Devices   doi: 10.1115/1.4036095
This paper presents design optimization of an MRI-actuated steerable catheter for atrial fibrillation ablation in the left atrium. The catheter prototype, built over polymer tubing, is embedded with current-carrying electromagnetic coils. The prototype can be deflected to a desired location by controlling the currents passing through the coils. The design objective is to develop a prototype that can successfully accomplish the ablation task. To complete the tasks, the catheter needs to be capable of reaching a set of desired targets selected by a physician on the chamber and keeping a stable contact with the chamber surface. The design process is based on the maximization of the steering performance of the catheter by evaluating its workspace in free space. The selected design is validated by performing a simulation of an ablation intervention on a virtual model of the left atrium with a real atrium geometry. This validation shows that the prototype can reach every target required by the ablation intervention and provide an appropriate contact force against the chamber.
TOPICS: Magnetic resonance imaging, Catheters, Design, Ablation (Vaporization technology), Engineering prototypes, Vacuum, Simulation, Tubing, Currents, Geometry, Optimization, Polymers