Increasing frame rate in ultrasound imaging by temporal morphing using tissue Doppler

The diagnostic value of echocardiographic images seems to diminish when the frame rate is low. In this work, morphing based on velocity information was used to improve the perceived smoothness of B-mode cine-loops with low frame rate. Based on an estimate of the velocity field calculated from B-mode speckle tracking and tissue Doppler measurements, morphed cine-loops with arbitrarily high frame rate were created. Morphing was applied to cardiac ultrasound cine-loops with apical insonation. The quality of the morphed data was evaluated by removing frames from duplex B-mode and tissue Doppler recordings, then replacing the removed B-mode frames with morphed ones. The decimated and morphed sequences were compared to the original ones. Wall motion scoring, a subjective evaluation technique for regional viability of the myocardium, was applied to data from 20 patients with varying pathology. Sixty cine-loops were scored twice, first with original data and later with morphed data. The results were compared for each recording, and the scorings were identical in the two cases for 94% of the segments. We conclude that much of the diagnostic value is retained in recordings with 15 frames per second when temporal morphing is applied.     

Spectral Doppler estimation utilizing 2-D spatial information and adaptive signal processing

The trade-off between temporal and spectral resolution in conventional pulsed wave (PW) Doppler may limit duplex/triplex quality and the depiction of rapid flow events. It is therefore desirable to reduce the required observation window (OW) of the Doppler signal while preserving the frequency resolution. This work investigates how the required observation time can be reduced by adaptive spectral estimation utilizing 2-D spatial information obtained by parallel receive beamforming. Four adaptive estimation techniques were investigated, the power spectral Capon (PSC) method, the amplitude and phase estimation (APES) technique, multiple signal classification (MUSIC), and a projection-based version of the Capon technique. By averaging radially and laterally, the required covariance matrix could successfully be estimated without temporal averaging. Useful PW spectra of high resolution and contrast could be generated from ensembles corresponding to those used in color flow imaging (CFI; OW = 10). For a given OW, the frequency resolution could be increased compared with the Welch approach, in cases in which the transit time was higher or comparable to the observation time. In such cases, using short or long pulses with unfocused or focused transmit, an increase in temporal resolution of up to 4 to 6 times could be obtained in in vivo examples. It was further shown that by using adaptive signal processing, velocity spectra may be generated without high-pass filtering the Doppler signal. With the proposed approach, spectra retrospectively calculated from CFI may become useful for unfocused as well as focused imaging. This application may provide new clinical information by inspection of velocity spectra simultaneously from several spatial locations.     

Real-time scan assistant for echocardiography

A real-time scan assistant (SA) for use with echocardiography is presented. The motivation is to aid nonexpert users in capturing apical 4-chamber views (A4CH) during echocardiography. The algorithm is based on a parametric multi-chamber model of the A4CH view, updated in an extended Kalman filter framework. The regional model goodness-of-fit is used to calculate a score, which is provided to the user during acquisition, together with an icon (emoticon) indicating whether the current view is acceptable or not. The SA was implemented on a commercially available scanner. A feasibility test was performed using two healthy volunteers as models and 10 medical students acting as nonexpert users. The students examined the models on two occasions, separated more than four days in time. Half of the students used the SA during the first exam and no SA at the second exam. The other half used the opposite order. The recordings were later rated by a cardiologist. A Wilcoxon signed pair rank test revealed a statistically significant improvement when using SA. Nine cases were rated as poor without using the SA. In eight (89%) of these cases, view quality improved to acceptable when the SA was used.     

Synthetic transmit beam technique in an aberrating environment

Parallel beamforming is a commonly used method for increasing the frame rate in ultrasound imaging systems. By receiving in several directions for each transmission, the frame rate is increased. However, this method also introduces blocklike artifacts in the B-mode image, due to the reception offsets when compared with the transmission direction. The synthetic transmit beam technique (STB) has been previously proposed as a compensation technique when addressing these artifacts. Previous work by Hergum et al. investigated the performance of this method in regard to the case of 2 parallel beams in tissue mimicking phantoms without aberrations. This study is a continuation of that work in which this method is tested in an aberrating environment using 4 parallel beams. Several quantitative and qualitative performance aspects of this method have been investigated such as lateral shift invariance, beam-to-beam correlation fluctuations, speckle- tracking performance, improvements from higher order STB interpolation and beam profile shape preservation, as well as perceived image quality improvements. The results were obtained from simulations, in vivo measurements, and in vitro measurements. The results showed that aberration amplified the image artifacts for regular parallel beamforming, which resulted in more shift variance, lower beam-to-beam correlation, higher speckle- tracking error, and more variation in beam profile shape. Compared with regular parallel beamforming, STB resulted in a significantly better image quality and a higher score in all measuring methods. The improvements from using STB were largest in cases involving aberration. Using STB, the variation in beam-to-beam correlation was reduced from 30% to 1%, and the standard deviation of the speckle-tracking error was reduced from 8% to 1.5%.     

Clutter rejection filters in color flow imaging: a theoretical approach

A general class of linear clutter rejection filters is described, covering the commonly used filter types including FIR/IIR filters with linear initialization, as well as regression filters, where the clutter component is estimated by least square curve fitting. The filter can be described by a complex valued matrix, and a frequency response is defined. However, in contrast to a time invariant filter, the general linear filter may create frequency components which are not present in the input signal. This produces bias in the velocity and velocity spread estimates. It is shown that the clutter filter effect on the autocorrelation estimates can be described by a frequency domain transfer function, but unlike time invariant filters, the transfer function is different for each temporal lag of the autocorrelation function. Using a two dimensional (axial and temporal dimension) model of the received signal, the bias in velocity and velocity spread is quantified, both for the autocorrelation algorithm and the time shift cross-correlation estimator. Theoretical expressions, as well as numerical examples are given.     

Yield,nitrogen recovery efficiency and quality of vegetables grown with organic waste-derived fertilisers

More sustainable production of high-quality, nutritious food is of worldwide interest. Increasing nutrient recycling into food systems is a step in this direction. The objective of the present study was to determine nitrogen (N) fertiliser effects of four waste-derived and organic materials in a cropping sequence of broccoli, potato and lettuce grown at two latitudes (58° and 67°N) in Norway during 3 years. Effects of anaerobically digested food waste (AD), shrimp shell (SS), algae meal (AM) and sheep manure (SM) at different N application rates (80 and 170 kg N ha^?1 for broccoli, and 80 and 60 kg N ha^?1 for potato and lettuce, respectively) and residual effects were tested on crop yield, N uptake, N recovery efficiency (NRE), N balance, N content in produce, mineral N in soil, product quality parameters and content of nitrate in lettuce. Mineral fertiliser (MF) served as control. Effects on yield, N uptake, NRE, N balance and product quality parameters could to a great extent be explained by estimated potentially plant-available N, which ranked in the order of AD > SS > SM > AM. Results for crops fertilised with AD and SS were not significantly different from MF at the same N application rate, while AM, in agreement with its negative effect on N mineralisation, gave negative or near-neutral effects compared to the control. No residual effect was detected after the year of application. The results showed that knowledge about N dynamics of relevant organic waste-derived fertilisers is necessary to decide on the timing and rate of application.     

Biofunctional Silk/Neuron Interfaces

Silk fibroin (SF) is a biocompatible and slowly biodegradable material with excellent mechanical properties and huge potential for use as biofunctional interface in electronic devices that aim to stimulate and control neural network activity and peripheral nerve repair. It is shown that SF films act as material interfaces that support the adherence and neurite outgrowth of dorsal root ganglion (DRG) neurons and preserve neuronal functions. Silk films preserve the capability of neuronal cells to fire and DRG neurons on silk films retain the intracellular free Ca²⁺ concentration ([Ca²⁺]_i) response to capsaicin, a typical noxious stimulus for this neuronal culture model. It is also demonstrated that nerve growth factor (NGF)‐functionalized silk films promote neurite outgrowth and modulate functional properties of DRG neurons. The results show that silk preserves DRG neuronal physiology and is a promising biomaterial platform for the future development of devices with goals including functional recovery of injured neurons, neurite functional outgrowth in vitro, or functional electrostimulation in vivo.     

The influence of individual and contextual work factors on workers' compliance with health and safety routines

This study investigated the relationships between workers’ compliance with health and safety (H&S) routines and instructions adopted in the company (dependent variable) and psychological demands, decision authority, social support, management support, unionization and H&S management system (independent variables). A cross-sectional questionnaire study was performed among 1051 workers and the managers of 102 small- and medium-sized motor vehicle repair garages. Multilevel modeling was performed to account for the hierarchical structure of the data. At the worker level, high compliance with H&S routines correlated significantly with both social support and H&S-related management support. At the garage level, mean management support and a well-developed H&S management system correlated significantly with high workers’ compliance. Changing both the individual and contextual factors in the work environment may thus increase workers’ participation in H&S activities.