Research Papers

J. Med. Devices. 2017;11(3):031001-031001-6. doi:10.1115/1.4036024.

This study sought to determine the feasibility of using noninvasive cardiac hemodynamics (NICHE), a new noninvasive Doppler-based device, to monitor real-time, simultaneous tissue and blood-flow Doppler measurements in a clinical setting, and to obtain preliminary performance data compared to a commercially available system. Doppler-based measurements have been shown to correlate well with invasive hemodynamic data and diastolic function, but their use in clinical applications has been limited by various technical issues. The NICHE device was developed to obtain simultaneous tissue and blood-flow Doppler measurements automatically, in real-time and in a hands-free manner. Thirty participants (ten normal volunteers and 20 patients in a cardiac rehab program) underwent standard echocardiographic/Doppler studies followed immediately by NICHE monitoring. Early diastolic transmitral blood-flow velocity (E) and tissue Doppler myocardial wall velocity during early relaxation (E′) were acquired using a standard echo device; and E/E′ was derived post hoc. NICHE measurements included E, E′, and directly measured instantaneous E/E′. NICHE was successfully used in 28 participants. Measurements of ENICHE ranged from 40 cm/s to over 120 cm/s and correlated well with Eecho (R = 0.93). ENICHE ranged from 2 to 23 cm/s and correlated well with the averaged Eecho (R = 0.91). Directly measured E/ENICHE ratios ranged from 3 to 23 and correlated well with derived E/Eecho (R = 0.91). The NICHE device can monitor patients in a hands-free manner and can supply real-time Doppler derived measurements of hemodynamic parameters and diastolic function that correlate well with measurements from standard echo devices.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(3):031002-031002-11. 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 maneuver. These activities are often connected with filter migration and vena cava damage due to the various related vein geometrical configurations. In this work, we analyzed the response of the vena cava during normal breathing and Valsalva maneuver, for a healthy vena cava and after insertion of a commercial Günther-Tulip® filter. Validated computational fluid dynamics (CFD) and patient specific data are used for analyzing blood flow inside the vena cava during these maneuvers. 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 the 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 maneuvers showing changes in wall shear stress and velocity patterns.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(3):031003-031003-10. 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.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(3):031004-031004-7. doi:10.1115/1.4036025.

To facilitate the design of the serialized implants and to satisfy the requirements of the population, a novel method is put forward for constructing an average bone model (ABM) with semantic parameters as a template. First, the ABM is created from the existing bone models, among which each bone has an equal contribution to the ABM. Second, combined with medical semantics, some characteristic points and semantic parameters are defined on the ABM, and then, parameter values for each bone can be automatically obtained through its registration and deformation to the ABM. Finally, an average bone template (ABT) is constructed by configuring the semantic parameters and by building the constraints between parameters. Taking 100 femur models as samples, we construct the ABT, and the template can be easily extended to generate a new average template through the given average equation.

Topics: Bone , Deformation
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(3):031005-031005-10. doi:10.1115/1.4036335.

To develop and evaluate the clinical application of a multimodal colposcopy combining multispectral reflectance, autofluorescence, and red, green, blue (RGB) imaging for noninvasive characterization of cervical intraepithelial neoplasia (CIN). We developed a multimodal colposcopy system that combined multispectral reflectance, autofluorescence, and RGB imaging for noninvasive characterization of CIN. We studied the optical properties of cervical tissue first; then the imaging system was designed and tested in a clinical trial where comprehensive datasets were acquired and analyzed to differentiate between squamous normal and high grade types of cervical tissue. The custom-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 performance characteristics of this system were comparable to the gold standard histopathologic measurements with statistical significance. Our pilot study demonstrated the clinical potential of this multimodal colposcopic system for noninvasive characterization of CIN. The proposed system was simple, noninvasive, cost-effective, and portable, making it a suitable device for deployment in developing countries or rural regions of limited resources.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(3):031006-031006-7. doi:10.1115/1.4036580.

Noninvasive blood glucose (NIBG) measurement technique has been explored for the last three decades to facilitate diabetes management. Photoplethysmogram (PPG) signal may be used to measure the variations in blood glucose concentration. However, the literature reveals that physiological perturbations such as temperature, skin moisture, and sweat lead to less accurate NIBG measurements. The task of minimizing the effect of these perturbations for accurate measurements is an important research area. Therefore, in the present work, galvanic skin response (GSR) and temperature measurements along with PPG were used to measure blood glucose noninvasively. The data extracted from the sensors were used to estimate blood glucose concentration with the help of two machine learning (ML) techniques, i.e., multiple linear regression (MLR) and artificial neural network (ANN). The accuracy of proposed multisensor system was evaluated by pairing and comparing noninvasive measurements with invasively measured readings. The study was performed on 50 nondiabetic subjects with body mass index (BMI) 27.3 ± 3 kg/m2. The results revealed that multisensor NIBG measurement system significantly improves mean absolute prediction error and correlation coefficient in comparison to the techniques reported in the literature.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(3):031007-031007-5. 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 half-Fourier acquisition single-shot turbospin echo (HASTE) and true fast imaging with steady-state precession sequence (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 and 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 signal-to-noise ratio (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.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(3):031008-031008-7. doi:10.1115/1.4036650.

The aim of this study is to develop an intramedullary telescopic nail that—in contrast to the current standard—is rotationally stable and firmly anchored in the bone proximally and distally, without containing any extraosseous components that may alter the surrounding soft tissue. Three prototypes for a positive-locking adapted telescopic intramedullary nail (PLATIN) were developed. In a series of biomechanical tests, the prototypes were compared with two Fassier–Duval telescopic nails, which represent the clinical standard. Axial pressure, torsion, and four-point bending measurements were carried out in a materials testing machine, with the telescopic nails implanted into composite bone. Tests were conducted without failure and up to failure. Specifically, the force required for telescoping, as well as torsional stiffness and bending stiffness, was investigated. Taking into account differences that were inherent in the materials, the prototypes showed similar results in the four-point bending tests. In the pressure tests, the prototypes required greater forces than the Fassier–Duval nails. The torsional stiffness was between 0.020 N·m/deg and 0.135 N·m/deg, depending on the diameter of the nail. Positive-locking effect was achieved by a hexagonal shape of an inner rod part and a hexagonal form-fitting outer tube part. Proximal and distal locking of the telescopic nail in the bone was performed by usage of K-Wires in specific arranged drill holes at the end of both parts. Based on these satisfactory results, the future clinical application of positive-locking irrotational telescopic nails can be expected. Furthermore, redesign or development of new designs for existing telescopic nails is recommended.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(3):031009-031009-10. doi:10.1115/1.4036490.

Drilling through bone is a common task during otologic procedures. Currently, the drilling tool is manually held by the surgeon. A robotically assisted surgical drill with force sensing for otologic surgery was developed, and the feasibility of using the da Vinci research kit to hold the drill and provide force feedback for temporal bone drilling was demonstrated in this paper. To accomplish intuitive motion and force feedback, the kinematics and coupling matrices of the slave manipulator were analyzed and a suitable mapping was implemented. Several experiments were completed including trajectory tracking, drill instrument calibration, and temporal bone drilling with force feedback. The results showed that good trajectory tracking performance and minor calibration errors were achieved. In addition, temporal bone drilling could be successfully performed and force feedback from the drill instrument could be felt at the master manipulator. In the future, it may be feasible to use master–slave surgical robotic systems for temporal bone drilling.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(3):031010-031010-11. doi:10.1115/1.4036652.

A new type of therapeutic equipment is designed herein, using concepts of convective heat transfer and spray cooling, to treat patients suffering from brain-hyperthermia. The equipment is aimed to provide emergency treatment in order to prevent disability or possible mortality because thermoregulatory system of the patients fails to maintain a homeostasis. The equipment uses noncontact method of forced convection, applied uniformly at body exteriors. The heat exchanger is designed to contain four independent pipe-sections with orifice openings around the body. The cool-air, maintained within ASHRAE’s thermal comfort bounds, is sprayed through the orifices. Design improvements have been made on the basis of image analysis of the flow. The boundary layer (BL) analysis has also been performed over a specially designed mannequin with induced hyperthermia characteristics. The testing indicates a decay of ∼6 °C in 280 min with a time constant of 2 h. Comparative to existing techniques, in addition to being a noncontact approach, the equipment shows better thermoregulatory performance along with a flexibility to accommodate different body contours.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(3):031011-031011-9. doi:10.1115/1.4037052.

Polyurethane shape memory polymer (SMP) foams have been developed for various embolic medical devices due to their unique properties in minimally invasive biomedical applications. These polyurethane materials can be stored in a secondary shape, from which they can recover their primary shape after exposure to an external stimulus, such as heat and water exposure. Tailored actuation temperatures of SMPs provide benefits for minimally invasive biomedical applications, but incur significant challenges for SMP-based medical device sterilization. Most sterilization methods require high temperatures or high humidity to effectively reduce the bioburden of the device, but the environment must be tightly controlled after device fabrication. Here, two probable sterilization methods (nontraditional ethylene oxide (ntEtO) gas sterilization and electron beam irradiation) are investigated for SMP medical devices. Thermal characterization of the sterilized foams indicated that ntEtO gas sterilization significantly decreased the glass transition temperature. Further material characterization was undertaken on the electron beam (ebeam) sterilized samples, which indicated minimal changes to the thermomechanical integrity of the bulk foam and to the device functionality.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(3):031012-031012-11. doi:10.1115/1.4036654.

Instrument-assisted soft tissue manipulation (IASTM) is a form of mechanotherapy, e.g., massage, that uses rigid devices which may be machined or cast. The delivered force, which is a critical parameter during IASTM, is not measured and not standardized in current clinical IASTM practice. In addition to the force, the angle of treatment and stroke frequency play an important role during IASTM. For accurate IASTM treatment, there is a strong need to scientifically characterize the IASTM delivered force, angle of treatment, and stroke frequency. This paper presents a novel, mechatronic design of an IASTM device that can measure the localized pressure on the soft tissue in a clinical treatment. The proposed design uses a three-dimensional (3D) load cell, which can measure all three-dimensional force components simultaneously. The device design was implemented using an IMUduino microcontroller board which provides tool orientation angles. These orientation angles were used for coordinate transformation of the measured forces to the tool–skin interface. Additionally, the measured force value was used to compute the stroke frequency. This mechatronic IASTM tool was validated for force measurements in the direction of tool longitudinal axis using an electronic plate scale that provided the baseline force values to compare with the applied force values measured by the tool. The load cell measurements and the scale readings were found to agree within the expected degree of accuracy.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(3):031013-031013-8. doi:10.1115/1.4037187.

Esophageal varices are a significant complication of portal hypertension. Endoscopic variceal ligation (EVL) is one of the clinical standards for treating these varices and preventing their hemorrhage. Limitations of EVL include the risk of stricture formation and postband ulcer bleeding due to the damage caused to the esophageal mucosa, as well as the need for multiple endoscopic treatment sessions to eradicate the varices. The goal of this study is to develop a device and evaluate the technical feasibility of microwave ablation to seal esophageal varices, while preventing thermal damage to the surface mucosal tissue. A microwave applicator with a directional radiation pattern was developed for endoscopic ablation of esophageal varices. Electromagnetic and bioheat transfer computational models were employed to optimize the design of the microwave applicator and evaluate energy delivery strategies for this application. Experiments in ex vivo and in vivo tissue were employed to verify simulation results. Simulations predicted enhanced heating performance of the antenna using an angled monopole radiating element. Further, simulations indicate that while the endoscopic cap attenuated electric fields in tissue, it also enhanced surface cooling of tissue, increasing the likelihood of preserving mucosal tissue. Experiments in ex vivo tissue indicated the feasibility of sealing veins with 77 W microwave power delivered for 30 s. In vivo experiments demonstrated the ability to seal veins, while preserving surface tissue. This study demonstrated the technical feasibility of microwave thermal ablation for treating esophageal varices using a 2.45 GHz water-cooled directional microwave applicator.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Med. Devices. 2017;11(3):034501-034501-6. 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 2.8 mm, 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 (1.13 N ± 0.53 N versus 1.10 N ± 0.51 N, p-value: 0.416), but has much greater range of motion (maximum deflection of 72 deg compared to 0 deg). 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.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(3):034502-034502-6. 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 (MIS). 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 ±90deg 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 two-degree-of-freedom (2DoF) L-Arm gripper.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(3):034503-034503-2. doi:10.1115/1.4036026.

Prior studies have linked microbial contamination of intravenous (IV) ports and stopcocks with postoperative infections. Existing technologies to address contamination are not consistently utilized because of the time and effort they require. Herein, novel barrier devices were created that form a protective shell to passively prevent contact between injection sites and practitioner hands or environmental surfaces while still allowing rapid connection of a syringe for injection of medications via an opening in the shell. Prototypes were tested using a grossly contaminated environment and adenosine triphosphate (ATP)-bioluminescence assay. For eight pairs of unshielded versus shielded IV ports/stopcocks, average contamination was 4102 versus 35 RLU (p < 0.02), respectively, indicating that the devices could significantly reduce IV port/stopcock contamination.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(3):034504-034504-7. doi:10.1115/1.4036338.

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.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(3):034505-034505-6. doi:10.1115/1.4036581.

Interventional catheter ablation treatment is a noninvasive 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 intraprocedural purposes. Typical MRI images are captured using surface imaging coils that 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 using 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.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(3):034506-034506-10. doi:10.1115/1.4037054.

The induction of a mild reduction in body core temperature has been demonstrated to provide neuroprotection for patients who have suffered a medical event resulting in ischemia to the brain or vital organs. Temperatures in the range of 32–34 °C provide the required level of protection and can be produced and maintained by diverse means for periods of days. Rewarming from hypothermia must be conducted slowly to avoid serious adverse consequences and usually is performed under control of the thermal therapeutic device based on a closed-loop feedback strategy based on the patient's core temperature. Given the sensitivity and criticality of this process, it is important that the device control system be able to interact with the human thermoregulation system, which itself is highly nonlinear. The therapeutic hypothermia device must be calibrated periodically to ensure that its performance is accurate and safe for the patient. In general, calibration processes are conducted with the hypothermia device operating on a passive thermal mass that behaves much differently than a living human. This project has developed and demonstrated an active human thermoregulation simulator (HTRS) that embodies major governing thermal functions such as central metabolism, tissue conduction, and convective transport between the core and the skin surface via the flow of blood and that replicates primary dimensions of the torso. When operated at physiological values for metabolism and cardiac output, the temperature gradients created across the body layers and the heat exchange with both an air environment and a clinical water-circulating cooling pad system match that which would occur in a living body. Approximately two-thirds of the heat flow between the core and surface is via convection rather than conduction, highlighting the importance of including the contribution of blood circulation to human thermoregulation in a device designed to calibrate the functioning of a therapeutic hypothermia system. The thermoregulation simulator functions as anticipated for a typical living patient during both body cooling and warming processes. This human thermoregulatory surrogate can be used to calibrate the thermal function of water-perfused cooling pads for a hypothermic temperature management system during both static and transient operation.

Commentary by Dr. Valentin Fuster

Expert View

J. Med. Devices. 2017;11(3):034701-034701-8. 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. In an effort to increase the utilization and success of this pathway, the FDA has analyzed data from HDE approvals from 2007 to 2015 to identify factors that have contributed to a successful HDE marketing application. There were 28 HDE approvals during the analysis period and were based on a broad range of data constituting valid scientific evidence. Most had at least one prospectively conducted clinical trial to support safety and probable benefit. An analysis of these HDE approvals demonstrates that the FDA exercises a high degree of flexibility when reviewing HDE applications.

Commentary by Dr. Valentin Fuster

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