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Commentary

J. Med. Devices. 2013;7(3):030401-030401-1. doi:10.1115/1.4025423.

The following technical briefs were submitted, peer reviewed, and accepted for presentation at the 2013 University of Minnesota's Design of Medical Devices (DMD) Conference (www.dmd.umn.edu) held April 9–11, 2013 at The Commons Hotel in Minneapolis, MN. We especially wish to acknowledge Dr. Just Herder who tirelessly chaired the review process, recruited appropriate paper reviewers, and kept us on schedule.

Commentary by Dr. Valentin Fuster

Technical Briefs

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2013;7(3):030921-030921-2. doi:10.1115/1.4024522.

We design an auto-tracking flexible tip for an endoscope to implement the shared control in assistive laparoscopic surgery. The flexible tip can bend in all direction dynamically to keep the target within the visible filed during surgical tools operating on the anatomy. The kinematic model to describe the view filed of the steerable endoscope has been derived for control purpose. Experimental verification on auto-tracking of the target object using visual servo control has also been performed.

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2013;7(3):030925-030925-2. doi:10.1115/1.4024492.
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2013;7(3):030929-030929-2. doi:10.1115/1.4024518.
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2013;7(3):030936-030936-2. doi:10.1115/1.4024498.
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2013;7(3):030946-030946-2. doi:10.1115/1.4024517.
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2013;7(3):034501-034501-4. doi:10.1115/1.4024643.

Single-use radio-attenuating gloves are devices protecting the operator's hand by reducing the exposition to scattered radiations during radiological-guided intervention. Expensive, these devices are important, as they contribute to lessen the annual dose to which personals are exposed to. However, inconsistencies in their protection value have been reported between theoretical and clinical practice. In this study, we aim to highlight the normative bias existing in standard norms for radioprotective assessments. Using thermoluminescent captors positioned inside and outside the glove, we designed an EN1331-1 norm-inspired bench test with five brands of radio-attenuating gloves. At 100 keV and 56 cm away from the source, we measured indirect beam and attenuated doses in a clinical setting. From the attenuation index measured, we deduced attenuation rates. We then compared our results to their commercial technical data sheets. The assessed attenuating rates of the tested references were 20%, 30%, 32%, 15%, and 25%. Theoretical rates are, respectively, 38%, 43%, 30%, 26%, and 35%. Only one reference showed no difference between commercial and technical attenuating values (p = 0.12). The inconsistencies between observed and theoretical attenuation value show the importance of the conditions in which protection is assessed. Without complete information, the choice of a protective device as simple as a glove is biased, and this may lead to inappropriate protection of the operator, which should raise concern, as interventional radiology is now widespread in routine practice.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2013;7(3):034502-034502-7. doi:10.1115/1.4024645.

Robotic testing offers potential advantages over conventional methods including coordinated control of multiple degrees of freedom (DOF) and enhanced fidelity that to date have not been fully utilized. Previous robotic efforts in spine biomechanics have largely been limited to pure displacement control methods and slow quasi-static hybrid control approaches incorporating only one motion segment unit (MSU). The ability to program and selectively direct single or multibody spinal end loads in real-time would represent a significant step forward in the application of robotic testing methods. The current paper describes the development of a custom programmable robotic testing system and application of a novel force control algorithm. A custom robotic testing system with a single 4 DOF serial manipulator was fabricated and assembled. Feedback via position encoders and a six-axis load sensor were established to develop, program, and evaluate control capabilities. A calibration correction scheme was employed to account for changes in load sensor orientation and determination of spinal loads. A real-time force control algorithm was implemented that employed a real-time trajectory path modification feature of the controller. Pilot tests applied 3 Nm pure bending moments to a human cadaveric C2–T1 specimen in flexion and extension to assess the ability to control spinal end loads, and to compare the resulting motion response to previously published data. Stable accurate position control was achieved to within ±2 times the encoder resolution for each axis. Stable control of spinal end body forces was maintained to within a maximum error of 6.3 N in flexion. Sagittal flexibility data recorded from rostral and caudally placed six-axis load sensors were in good agreement, indicating a pure moment loading condition. Individual MSU rotations were consistent with previously reported data from nonrobotic protocols. The force control algorithm required 5–10 path iterations before converging to programmed end body forces within a targeted tolerance. Commercially available components were integrated to create a fully programmable custom 4 DOF gantry robot. Individual actuator performance was assessed. A real-time force control algorithm based on trajectory path modification was developed and implemented. Within a reasonable number of programmed path iterations, good control of spinal end body forces and moments, as well as a motion response consistent with previous reported data, were obtained throughout a full physiologic flexion-extension range of motion in the human subaxial cervical spine.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2013;7(3):034503-034503-3. doi:10.1115/1.4024156.

Diastolic dysfunction likely contributes to all cases of congestive heart failure and is solely responsible for many. Existing cardiac support devices largely ignore diastolic dysfunction and may exacerbate it. Current diastolic devices in development rely on either extensive extraventricular fixation or intraventricular implantation with complications associated with blood contact. A diastolic recoil device is proposed that pneumatically locks to the outside of the heart wall. The end-diastolic total biventricular pressure-volume relationship (EDTBPVR) was used to evaluate, in vitro, the ability of a recoil device to modulate filling mechanics through pneumatic locking as the method of fixation. The pressure in a model heart was incremented and the corresponding volume changes were measured. The heart model and device were pneumatically locked together using a vacuum sac to model the pericardium. The diastolic recoil component shifted the EDTBPVR towards lower pressures at low volumes, providing up to 0.9 kPa (9 cm H2O) of suction, demonstrating enhanced diastolic recoil at beginning diastole. We conclude that pneumatic locking appears to be a viable method for a recoil device to engage the heart.

Topics: Pressure , Vacuum , Suction , Blood , Failure
Commentary by Dr. Valentin Fuster

Research Paper

J. Med. Devices. 2013;7(3):031001-031001-6. doi:10.1115/1.4024659.

If a custom hip stem could be designed according to X-ray films, the cost of the hip stem would be reduced, and a simpler designing method could be provided than using computer tomography images. In addition, the problem, which is that hip stems cannot be designed for some revision operations because of metal artifacts in computer tomography images, could be solved. A software system for designing custom hip stems based on X-ray films was developed. In order to verify whether the software system could be used, eleven femurs were used for this study. Hip stems for these eleven femurs were designed by using the software system. Ten of these femurs were taken computer tomography scans directly. According to the data collected from the computer tomography images, models of these ten femurs were rebuilt. Ten hip stem models, designed for these ten femurs, were simulated to be inserted into corresponding femur models. Results show each of the ten hip stems matches its corresponding femur. The hip stem designed for the remaining femur was manufactured and inserted in the remaining femur. Cancellous bone, retained in the matching area, was about 1–1.5 mm thick. From the above verifications, it could be concluded that the software system for designing custom hip stems based on X-ray films could be used to design custom hip stems.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2013;7(3):031002-031002-7. doi:10.1115/1.4024647.

This paper presents the research and results for an automated jerk-type nystagmus identification system that makes use of an efficient, low cost video-oculography (VOG) device, designed for telemedicine applications. The pupil position is estimated by a hybrid tracking algorithm from the captured VOG images. It is also shown that wavelet analysis with an appropriate mother wavelet, coupled with well-defined geometric constraints can provide a reliable and robust nystagmus identification algorithm. Some original research regarding robust analysis for signals with mixed content is also presented.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2013;7(3):031003-031003-9. doi:10.1115/1.4024160.

A new thermal perfusion probe operates by imposing a thermal event on the tissue surface and directly measuring the temperature and heat flux response of the tissue with a small sensor. The thermal event is created by convectively cooling the surface with a small group of impinging jets using room temperature air. The hypothesis of this research is that this sensor can be used to provide practical burn characterization of depth and severity by determining the thickness of nonperfused tissue. To demonstrate this capability the measurement system was tested with a phantom tissue that simulates the blood perfusion of tissue. Different thicknesses of plastic were used at the surface to mimic layers of dead tissue. A mathematical model developed by Alkhwaji et al. (2012, “New Mathematical Model to Estimate Tissue Blood Perfusion, Thermal Contact Resistance and Core Temperature,” ASME J. Biomech. Eng., 134, p. 081004) is used to determine the effective values of blood perfusion, core temperature, and thermal resistance from the thermal measurements. The analytical solutions of the Pennes bioheat equation using the Green's function method is coupled with an efficient parameter estimation procedure to minimize the error between measured and analytical heat flux. Seven different thicknesses of plastic were used along with three different flow rates of perfusate to simulate burned skin of the phantom perfusion system. The resulting values of thermal resistance are a combination of the plastic resistance and thermal contact resistance between the sensor and plastic surface. Even with the uncertainty of sensor placement on the surface, the complete set of thermal resistance measurements correlate well with the layer thickness. The values are also nearly independent of the flow rate of the perfusate, which shows that the parameter estimation can successfully separate these two parameters. These results with simulated burns show the value of this minimally invasive technique to measure the thickness of nonperfused layers. This will encourage further work with this method on actual tissue burns.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2013;7(3):031004-031004-12. doi:10.1115/1.4024660.

The success of flexible instruments in surgery requires high motion and force fidelity and controllability of the tip. However, the friction and the limited stiffness of such instruments limit the motion and force transmission of the instrument. In a previous study, we developed a flexible multibody model of a surgical instrument inside an endoscope in order to study the effect of the friction, bending and rotational stiffness of the instrument and clearance on the motion hysteresis and the force transmission. In this paper, we present the design and evaluation of an experimental setup for the validation of the flexible multibody model and the characterization of the instruments. A modular design was conceived based on three key functionalities: the actuation from the proximal end, the displacement measurement of the distal end, and the measurement of the interaction force. The exactly constrained actuation module achieves independent translation and rotation of the proximal end. The axial displacement and the rotation of the distal end are measured contactless via a specifically designed air bearing guided cam through laser displacement sensors. The errors in the static measurement are 15 μm in translation and 0.15 deg in rotation. Six 1-DOF load cell modules using flexures measure the interaction forces and moments with an error of 0.8% and 2.5%, respectively. The achieved specifications allow for the measurement of the characteristic behavior of the instrument inside a curved rigid tube and the validation of the flexible multibody model.

Commentary by Dr. Valentin Fuster

Design Innovation Paper

J. Med. Devices. 2013;7(3):035001-035001-5. doi:10.1115/1.4024646.

The human ankle-foot system conforms to a circular effective rocker shape for walking, but to a much flatter effective shape for standing and swaying. Many persons with lower limb amputations have impaired balance and reduced balance confidence, and may benefit from prostheses designed to provide flatter effective rocker shapes during standing and swaying tasks. This paper describes the development and testing of an ankle-foot prosthesis prototype that provides distinctly different mechanical properties for walking and standing/swaying. The prototype developed was a single-axis prosthetic foot with a lockable ankle for added stability during standing and swaying. The bimodal ankle-foot prosthesis prototype was tested on pseudoprostheses (walking boots with prosthetic feet beneath) for walking and standing/swaying loads, and was compared to an Otto Bock single-axis prosthetic foot and to able-bodied data collected in a previous study. The height-normalized radius of the effective rocker shape for walking with the bimodal ankle-foot prototype was equal to that found earlier for able-bodied persons (0.17); the standing and swaying effective shape had a lower height-normalized radius (0.70) compared with that previously found for able-bodied persons (1.11). The bimodal ankle-foot prosthesis prototype had a similar radius as the Otto Bock single-axis prosthetic foot for the effective rocker shape for walking (0.17 for both), but had a much larger radius for standing and swaying (0.70 for bimodal, 0.34 for single-axis). The results suggest that the bimodal ankle-foot prosthesis prototype provides two distinct modes, including a biomimetic effective rocker shape for walking and an inherently stable base for standing and swaying. The radius of the prototype's effective rocker shape for standing/swaying suggests that it may provide inherent mechanical stability to a prosthesis user, since the radius is larger than the typical body center of mass’s distance from the floor (between 50–60% of height). Future testing is warranted to determine if the bimodal ankle-foot prosthesis will increase balance and balance confidence in prosthesis users.

Commentary by Dr. Valentin Fuster

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