Pre-rigor filleting and brining of farmed cod: Influence on quality and storage stability

Pre-rigor filleting as well as brining with a mixture of phosphates and salt could influence several quality parameters of cod fillets. The aim of this work was to evaluate which of these processes that affected selected quality parameters of farmed cod the most. The analyses were performed at several points during storage, enabling that the effects of time of filleting, brining and storage could be evaluated simultaneously.Pre- and post-rigor non-brined fillets had similar and significant weight loss during storage. The weight increase of pre- and post-rigor fillets due to brining were 2% and almost 10%, respectively, and brining significantly reduced the weight loss during storage. Liquid loss and total viable count (TVC) were significantly influenced by rigor state at time of filleting, brining and storage time, while water content was influenced significantly by time of filleting and brining. Brining and storage time significantly influenced the whiteness, while time of filleting and storage time had significant influence upon the fillet index. The growth of Photobacterium phosphoreum was affected by storage time only, and the pH of the fillets was not influenced significantly by any of the parameters tested.     

Autocorrelation techniques in color flow imaging: signal model andstatistical properties of the autocorrelation estimates

A review of the scattering theory for moving blood, and a model for the signal in a multigated pulsed wave Doppler system is presented. The model describes the relation between a general time-variable velocity field and the signal correlation in space and time, including the effect of movement of the ultrasonic beam for color flow imaging systems with mechanical scanning. In the case of a constant and rectilinear velocity field, a parametric model for the autocorrelation function is deduced. General formulas for a full second order characterization of the set of autocorrelation estimates, with arbitrary lags in the spatial and temporal directions, are developed. The formulas are applied to the parametric model, and numerical results for the estimator variance are presented. A qualitative evaluation of the theoretical results has been performed by offline-processing of 2-D Doppler signals from a color flow imaging scanner. The benefit of spatial and temporal averaging is demonstrated by using different averaging filters to the same set of recorded data     

Interaction of alkali, alkaline-earth and sulphate ions with clay minerals and sedimentary rocks

Ion-exchange isotherms of kaolinite and montmorillonite for calcium, barium and sulphate ions in a solution at constant pH near neutral have been examined. The ionic strength of the solutions ranged from seawater to formation waters from oil reservoirs in the North Sea. ⁴⁵Ca-, ¹³³Ba- or ³⁵SO₄-tagged solutions with added NaCl as supported electrolyte were used for adsorption measurements. From distribution coefficients found for CaCl₂/NaCl or BaCl₂/NaCl in the clay suspensions, the adsorbed quantities of divalent cations can be predicted for sedimentary rocks with a given mineralogical composition. These results show that the equivalent ionic fractions of alkaline-earth ions adsorbed on clay pretreated with seawater, or formation water, fit the normalized isotherms obtained for the calcium-sodium exchange on the clay within uncertainties of ± 10%. The same correlation was not found for sulphate adsorption from seawater because the clay minerals pretreated with seawater were less reactive for sulphate adsorption. These results suggest that in addition to adsorption due to electrostatic forces, some ions were chemisorbed to the clay minerals during the pretreatment with seawater. The lower sulphate adsorption may be due to ion pair formation.     

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.     

Mathematical virology: a novel approach to the structure and assembly of viruses

Understanding the structure and life cycle of viruses is a fascinating challenge with a crucial impact on the public health sector. In the early 1960s, Caspar & Klug (Caspar & Klug 1962 Cold Spring Harbor Symp. Quant. Biol. 27, 1-24) established a theory for the prediction of the surface structures of the protein shells, called viral capsids, which encapsulate and hence provide protection for the viral genome. It is of fundamental importance in virology, with a broad spectrum of applications ranging from the image analysis and classification of experimental data to the construction of assembly models. However, experimental results have provided evidence for the fact that it is incomplete and, in particular, cannot account for the structures of Papovaviridae, which are of particular interest because they contain cancer-causing viruses. This gap has recently been closed by the viral tiling theory, which describes the locations of the protein subunits and inter-subunit bonds in viral capsids based on mathematical tools from the area of quasicrystals. The predictions and various recent applications of the new theory are presented, and it is discussed how further research along these lines may lead to new insights in virology and the design of anti-viral therapeutics.     

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%.