Poul M. F. Nielsen

A unique micromechanocalorimeter for simultaneous measurement of heat rate and force production of cardiac trabeculae carneae

To study cardiac muscle energetics quantitatively, it is of paramount importance to measure, simultaneously, mechanical and thermal performance. Ideally, this should be achieved under conditions that minimize the risk of tissue anoxia, especially under high rates of energy expenditure. In vitro, this consideration necessitates the use of preparations of small radial dimensions. To that end, we have constructed a unique micromechanocalorimeter, consisting of an open-ended flow-through microcalorimeter, a force transducer, and a pair of muscle-length actuators. The device enables the metabolic and mechanical performance of cardiac trabeculae carneae to be investigated for prolonged periods in a continuously replenished oxygen- and nutrient-rich environment.

A compound ampoule for large-volume controllable jet injection

We present a new design for a needle-free injector ampoule, using two concentric pistons to pressurize the fluid during the injection. The smaller, inner piston is used to provide an initial high-velocity piercing jet; it then engages the outer piston to deliver the remaining drug via a low-velocity jet. The goal of this design is to enable needle-free delivery of relatively large volumes to controlled depths in tissue, a task impractical with conventional ampoules and actuators. We demonstrate this concept by constructing a 1.2mL ampoule, measuring the jet velocity it produces in free air, and performing a set of injections into post-mortem porcine tissue. The ampoule smoothly produces the two desired phases of an injection, with a smooth transition of jet velocity as the two pistons engage. The injection is able to penetrate porcine skin to a controlled depth and deliver fluid to the subcutaneous and/or intramuscular layers, though further investigation is required to ensure that all of the fluid delivered can be retained at the desired depth.

A device for controlled jet injection of large volumes of liquid

We present a needle-free jet injection device controllably actuated by a voice coil and capable of injecting up to 1.3 mL. This device is used to perform jet injections of ~900 μL into porcine tissue. This is the first time that delivery of such a large volume has been reported using an electronically controllable device. The controllability of this device is demonstrated with a series of ejections where the desired volume is ejected to within 1 % during an injection at a predetermined jet velocity.We present a needle-free jet injection device controllably actuated by a voice coil and capable of injecting up to 1.3 mL. This device is used to perform jet injections of ~900 μL into porcine tissue. This is the first time that delivery of such a large volume has been reported using an electronically controllable device. The controllability of this device is demonstrated with a series of ejections where the desired volume is ejected to within 1 % during an injection at a predetermined jet velocity.

Trapeziometacarpal joint contact varies between men and women during three isometric functional tasks

Trapeziometacarpal (TMC) joint osteoarthritis (OA) affects women two to six times more than men, and is influenced by stresses and strains in the cartilage. The purpose of this study was to characterise sex and age differences in contact area and peak stress location of the healthy TMC joint during three isometric tasks including pinch, grasp and jar twist. CT images of the hand from 50 healthy adult men and women were used to create a statistical shape model that was used to create finite element models for each subject and task. Force-driven simulations were performed to evaluate cartilage contact area and peak stress location. We tested for sex and age differences using Principal Component Analysis, linear regression, and Linear Discriminant Analysis. We observed sex differences in peak stress location during pinch (pxa0=xa0.0206), grasp (pxa0=xa0.0264), and jar twist (pxa0=xa0.0484). The greatest sex differences were observed during jar twist, where 94% of peak stresses in men were located in the centre compared with 50% in the central-volar region in women. These findings show that peak stress locations are more variable in women during grasp and jar twist than men, and suggest that women may employ different strategies to perform these tasks.

Suitability of recent hardware accelerators (DSPs, FPGAs, and GPUs) for computer vision and image processing algorithms

Abstract Computer vision and image processing algorithms form essential components of many industrial, medical, commercial, and research-related applications. Modern imaging systems provide high resolution images at high frame rates, and are often required to perform complex computations to process image data. However, in many applications rapid processing is required, or it is important to minimise delays for analysis results. In these applications, central processing units (CPUs) are inadequate, as they cannot perform the calculations with sufficient speed. To reduce the computation time, algorithms can be implemented in hardware accelerators such as digital signal processors (DSPs), field-programmable gate arrays (FPGAs), and graphics processing units (GPUs). However, the selection of a suitable hardware accelerator for a specific application is challenging. Numerous families of DSPs, FPGAs, and GPUs are available, and the technical differences between various hardware accelerators make comparisons difficult. It is also important to know what speed can be achieved using a specific hardware accelerator for a particular algorithm, as the choice of hardware accelerator may depend on both the algorithm and the application. The technical details of hardware accelerators and their performance have been discussed in previous publications. However, there are limitations in many of these presentations, including: inadequate technical details to enable selection of a suitable hardware accelerator; comparisons of hardware accelerators at two different technological levels; and discussion of old technologies. To address these issues, we introduce and discuss important considerations when selecting suitable hardware accelerators for computer vision and image processing tasks, and present a comprehensive review of hardware accelerators. We discuss the practical details of chip architectures, available tools and utilities, development time, and the relative advantages and disadvantages of using DSPs, FPGAs, and GPUs. We provide practical information about state-of-the-art DSPs, FPGAs, and GPUs as well as examples from the literature. Our goal is to enable developers to make a comprehensive comparison between various hardware accelerators, and to select a hardware accelerator that is most suitable for their specific application.

The effect of jet speed on large volume jet injection

Abstract Jet injection presents a promising alternative to needle and syringe injection for transdermal drug delivery. The controllability of recently‐developed jet injection devices now allows jet speed to be modulated during delivery, and has enabled efficient and accurate delivery of volumes up to 0.3 mL. However, recent attempts to inject larger volumes of up to 1 mL using the same methods have highlighted the different requirements for successful delivery at these larger volumes. This study aims to establish the jet speed requirements for delivery of 1 mL of liquid using a controllable, voice coil driven injection device. Additionally, the effectiveness of a two‐phase jet speed profile is explored (where jet speed is deliberately decreased toward the end of the injection) and compared to the constant jet speed case. A controllable jet injection device was developed to deliver volumes of 1 mL of liquid at jet speeds >140 m/s. This device was used to deliver a series of injections into post‐mortem porcine tissue in single and two‐phase jet speed profiles. Single‐phase injections were performed over the range 80 m/s to 140 m/s. Consistent delivery success (>80% of the liquid delivered) was observed at a jet speed of 130 m/s or greater. Consistent penetration into the muscle layer coincided with delivery success. Two‐phase injections of 1 mL were performed with a first phase volume of 0.15 mL, delivered at 140 m/s, while the injection of the remainder of fluid was delivered at a second phase speed that was varied over the range 60 m/s to 120 m/s. Ten two‐phase injections were performed with a second phase speed of 100 m/s producing a mean delivery volume of 0.8 mL ± 0.2 mL, while the single‐phase injections at 100 m/s achieved a mean delivery volume of 0.4 mL ± 0.3 mL. These results demonstrate that a reduced jet speed can be used in the later stages of a 1 mL injection to achieve delivery success at a reduced energy cost. We found that a jet speed approaching 100 m/s was required following initial penetration to successfully deliver 1 mL, whereas speeds as low as 50 m/s have been used for volumes of <0.3 mL. These findings provide valuable insight into the effect of injection volume and speed on delivery success; this information is particularly useful for devices that have the ability to vary jet speed during drug delivery. Graphical abstract Figure. No caption available. HighlightsThe jet injection of 1 mL required a greater jet speed later in the injection than that reported for volumes ≤0.3 mL.A two‐phase jet speed profile successfully delivered 1 mL at a reduced energy cost relative to single‐speed injections.Subcutaneous injections demonstrated a correlation between the volume delivered and the penetration depth.

Extended depth measurement for a Stokes sample imaging polarimeter

A non-destructive imaging technique is required for quantifying the anisotropic and heterogeneous structural arrangement of collagen in soft tissue membranes, such as bovine pericardium, which are used in the construction of bioprosthetic heart valves. Previously, our group developed a Stokes imaging polarimeter that measures the linear birefringence of samples in a transmission arrangement. With this device, linear retardance and optic axis orientation; can be estimated over a sample using simple vector algebra on Stokes vectors in the Poincaré sphere. However, this method is limited to a single path retardation of a half-wave, limiting the thickness of samples that can be imaged. The polarimeter has been extended to allow illumination of narrow bandwidth light of controllable wavelength through achromatic lenses and polarization optics. We can now take advantage of the wavelength dependence of relative retardation to remove ambiguities that arise when samples have a single path retardation of a half-wave to full-wave. This effectively doubles the imaging depth of this method. The method has been validated using films of cellulose of varied thickness, and applied to samples of bovine pericardium.

High speed, spatially-resolved diffuse imaging for jet injection depth estimation

Needle-free jet injection is a transdermal drug delivery technique wherein a liquid drug is pressurized, and ejected through a ~200 μm orifice at high speed (~200 m/s). The resulting fluid jet can rapidly penetrate through the skin, and disperse in the underlying tissue at a speed-related depth. Our electronically controllable injection systems uniquely offer the possibility of depth-control during injection. To this end, we have developed a spatially-resolved diffuse imaging technique to provide an estimate of the injection depth. An injection system was constructed to couple a collimated laser beam into the fluid jet as it was ejected through the orifice. During an injection, the penetration of the jet into a tissue-mimicking phantom eroded an unobstructed optical path for the laser beam before it impinged on the scattering medium at the bottom of the hole. This resulted in a pattern of backscattered light around the injection site that varied as a function of injection depth. We performed laser-coupled injections into a light-scattering polyacrylamide gel, while recording high-speed videos of the diffuse light exiting from the side and surface of the phantom. The centroid of the light distribution exiting from the side of the phantom was used as the estimate for the injection depth. A strong correlation was found between the depth of the centroid and the surface light profile, showing that it is possible to infer the injection depth from the spatial distribution of light around the injection site alone.

Probabilistic description of infant head kinematics in abusive head trauma

Abstract Abusive head trauma (AHT) is a potentially fatal result of child abuse, but the mechanisms by which injury occur are often unclear. To investigate the contention that shaking alone can elicit the injuries observed, effective computational models are necessary. The aim of this study was to develop a probabilistic model describing infant head kinematics in AHT. A deterministic model incorporating an infant’s mechanical properties, subjected to different shaking motions, was developed in OpenSim. A Monte Carlo analysis was used to simulate the range of infant kinematics produced as a result of varying both the mechanical properties and the type of shaking motions. By excluding physically unrealistic shaking motions, worst-case shaking scenarios were simulated and compared to existing injury criteria for a newborn, a 4.5 month-old, and a 12 month-old infant. In none of the three cases were head kinematics observed to exceed previously-estimated subdural haemorrhage injury thresholds. The results of this study provide no biomechanical evidence to demonstrate how shaking by a human alone can cause the injuries observed in AHT, suggesting either that additional factors, such as impact, are required, or that the current estimates of injury thresholds are incorrect.

Sensorless position control of voice-coil motors for needle-free jet injection

This paper demonstrates a simple method for sensorless position estimation and control of a linear voice-coil actuator. Such actuators are currently used in needle-free jet injector prototypes. The sensorless method makes use of the position dependent impedance of the voice-coil at high frequencies to produce an estimate of coil position. This is achieved through the addition of a high frequency signal to the motors driving signal. The position and frequency dependence of the voice-coil impedance is presented. Also the ability of this sensorless position estimation method to control position to a square set point is demonstrated using PID control. A jet injection is performed in order to observe the ability of this position sensing method to track position in such a high speed application.