Estimating 2-D vector velocities using multidimensional spectrum analysis

Wilson (1991) presented an ultrasonic wideband estimator for axial blood flow velocity estimation through the use of the 2-D Fourier transform. It was shown how a single velocity component was concentrated along a line in the 2-D Fourier space, where the slope was given by the axial velocity. Later, it was shown that this approach could also be used for finding the lateral velocity component by also including a lateral sampling. A single velocity component would then be concentrated along a plane in the 3-D Fourier space, tilted according to the 2 velocity components. This paper presents 2 new velocity estimators for finding both the axial and lateral velocity components. The estimators essentially search for the plane in the 3- D Fourier space, where the integrated power spectrum is largest. The first uses the 3-D Fourier transform to find the power spectrum, while the second uses a minimum variance approach. Based on this plane, the axial and lateral velocity components are estimated. Several phantom measurements, for flow-to-depth angles of 60, 75, and 90 degrees, were performed. Multiple parallel lines were beamformed simultaneously, and 2 different receive apodization schemes were tried. The 2 estimators were then applied to the data. The axial velocity component was estimated with an average standard deviation below 2.8% of the peak velocity, while the average standard deviation of the lateral velocity estimates was between 2.0% and 16.4%. The 2 estimators were also tested on in vivo data from a transverse scan of the common carotid artery, showing the potential of the vector velocity estimation method under in vivo conditions.     

The impact of aberration on high frame rate cardiac B-mode imaging

In echocardiography, especially in 3D echocardiography, achieving high frame rates is a major challenge. A suggested solution is parallel receive beamforming. Without any compensation, this approach is known to produce block-like artifacts, where each block corresponds to one parallel receive group. In this work, in vitro imaging, in vivo imaging, and simulations were used to investigate the artifacts. In vitro, imaging a tissue phantom, the artifacts were successfully compensated for. However, in vivo, imaging the heart, the compensation techniques no longer sufficed and the artifacts persisted. With in vivo imaging, aberrating tissue layers are present between the heart and the probe. To investigate the effects of aberration on a parallel receive system, an in vitro experiment was performed with and without a silicon phase aberrator in front of the probe. The aberrator caused the artifacts to appear even when compensation techniques were applied. Simulations confirmed the measured results and indicated that distorted beam profiles and decorrelation between parallel receive groups caused the artifacts. To quantify the magnitude of the artifacts, a correlation-based indicator was developed. The indicator separated images with and without artifacts and confirmed that the artifacts appeared from the combination of parallel receive beams and aberration.     

Moniliformin in Norwegian grain.

Norwegian grain samples (73 oats, 75 barley, 83 wheat) from the 2000-02 growing seasons were examined for contamination with moniliformin, and the association between the fungal metabolite and the number of kernels infected with common Fusaria was investigated. Before quantification of moniliformin using ion pairing reversed-phase high-performance liquid chromatography with diode array ultraviolet light detection, all samples were extracted using acetonitrile/water (84/16) and disposable strong anion exchange columns used for clean up. The limit of detection was 40 microg kg(-1). Moniliformin was found in 25, 32 and 76% of the barley, oats and wheat samples, respectively. The maximum concentrations of moniliformin in barley, oats and wheat were 380, 210 and 950 microg kg(-1), respectively. At the same time, the prevalence and infection level of the moniliformin-producing F. avenaceum/arthrosporioides was as high as 100 and >53% on average, respectively. Moniliformin concentrations were significantly correlated to the variables grain species, growing season and infection with F. avenaceum/arthrosporioides and F. culmorum. The survey indicates that the prevalence of moniliformin in Norwegian grain is high, especially in wheat. On the other hand, field conditions in Norway do not seem to favour contamination of grain with high levels of moniliformin.     

Efficient differential timeslice computation

Transaction-time databases support access to not only the current database state, but also previous database states. Supporting access to previous database states requires large quantities of data and necessitates efficient temporal query processing techniques. Previously, we presented a log based storage structure and algorithms for the differential computation of previous database states. Timeslices-i.e., previous database states-are computed by traversing a log of database changes, using previously computed and cached timeslices as outsets. When computing a new timeslice, the cache will contain two candidate outsets: an earlier outset and a later outset. The new timeslice can be computed by either incrementally updating the earlier outset or decrementally “downdating” the later outset using the log. The cost of this computation is determined by the size of the log between the outset and the new timeslice. The paper proposes an efficient algorithm that identifies the cheaper outset for the differential computation. The basic idea is to compute the sizes of the two pieces of the log by maintaining and using a tree structure on the timestamps of the database changes in the log. The lack of a homogeneous node structure, a controllable and high fill factor for nodes, and of appropriate node allocation in existing tree structures (e.g., B⁺ trees, Monotonic B⁺ trees, and Append only trees) render existing tree structures unsuited for our use. Consequently, a specialized tree structure, the pointer-less insertion tree, is developed to support the algorithm. As a proof of concept, we have implemented a main memory version of the algorithm and its tree structure     

Blood noise reduction in intravascular ultrasound imaging

Scattering from red blood cells (blood noise) increases significantly as the ultrasound frequency is increased above 10 MHz. This reduces the contrast between the vessel wall and the lumen in intravascular ultrasound imaging which makes it difficult to localize the vessel wall and plaque. A blood noise filter based on beam tilting and digital lateral low pass filtering is described. Beam tilting introduces a Doppler shift from blood which results in a frequency separation of the vessel wall signal and the blood noise. The performance of the filter is investigated by simulations and by in vitro experiments. The filter is found to be effective for blood velocities exceeding approximately 50 cm s^-1 at a 20 MHz ultrasound frequency with a beam tilt angle of 10 degrees and a frame rate of 15 f.p.s. By increasing the system frequency to 40 MHz, increase the beam tilt angle to 15 degrees and reduce the frame rate to 10 f.p.s., the filter is effective for blood velocities below 10 cm s^-1     

Metabolic Profiles of Brain Metastases

Metastasis to the brain is a feared complication of systemic cancer, associated with significant morbidity and poor prognosis. A better understanding of the tumor metabolism might help us meet the challenges in controlling brain metastases. The study aims to characterize the metabolic profile of brain metastases of different origin using high resolution magic angle spinning (HR-MAS) magnetic resonance spectroscopy (MRS) to correlate the metabolic profiles to clinical and pathological information. Biopsy samples of human brain metastases (n = 49) were investigated. A significant correlation between lipid signals and necrosis in brain metastases was observed (p < 0.01), irrespective of their primary origin. The principal component analysis (PCA) showed that brain metastases from malignant melanomas cluster together, while lung carcinomas were metabolically heterogeneous and overlap with other subtypes. Metastatic melanomas have higher amounts of glycerophosphocholine than other brain metastases. A significant correlation between microscopically visible lipid droplets estimated by Nile Red staining and MR visible lipid signals was observed in metastatic lung carcinomas (p = 0.01), indicating that the proton MR visible lipid signals arise from cytoplasmic lipid droplets. MRS-based metabolomic profiling is a useful tool for exploring the metabolic profiles of metastatic brain tumors.     

The effects of occupational health and safety management on work environment and health: a prospective study

According to Norway's Internal Control Regulation, all companies are required to have an occupational health and safety (H&S) management system. This study investigated the effects of implementing or improving occupational H&S management on the work environment, H&S-related behaviour and musculoskeletal health of workers in small and medium-sized companies. A one-year prospective cohort study, using self-administered questionnaires, was performed among the managers and blue-collar workers in 226 motor vehicle repair garages. Out of 1559 workers that responded at baseline 721 workers could be identified at follow-up. These 721 workers were included in the study. The workers in companies with improved H&S management from baseline to follow-up reported increased satisfaction with the H&S activities at the garage; improved support from management and colleagues; improved health-related support and control; and increased participation in H&S activities.     

Modification semantics in now-relative databases

Most real-world databases record time-varying information. In such databases, the notion of “the current time,” or NOW, occurs naturally and prominently. For example, when capturing the past states of a relation using begin and end time columns, tuples that are part of the current state have some past time as their begin time and NOW as their end time. While the semantics of such variable databases has been described in detail and is well understood, the modification of variable databases remains unexplored. This paper defines the semantics of modifications involving the variable NOW. More specifically, the problems with modifications in the presence of NOW are explored, illustrating that the main problems are with modifications of tuples that reach into the future. The paper defines the semantics of modifications—including insertions, deletions, and updates—of databases without NOW, with NOW, and with values of the type NOW+Δ, where Δ is a non-variable time duration. To accommodate these semantics, three new timestamp values are introduced. Finally, implementation is explored. We show how to represent the variable NOW with columns of standard SQL data types and give a mapping from SQL on NOW-relative data to standard SQL on these columns. The paper thereby completes the semantics, the querying, and the modification of now-relative databases.     

The effect of including myocardial anisotropy in simulated ultrasound images of the heart

We have examined the effect of incorporating tissue anisotropy in simulated ultrasound images of the heart. In simulation studies, the cardiac muscle (myocardium) is usually modeled as a cloud of uncorrelated point scatterers. Although this approach successfully generates a realistic speckle pattern, it fails to reproduce any effects of image anisotropy seen in real ultrasound images. We hypothesize that some of this effect is caused by the varying orientation of anisotropic myocardial structures relative to the ultrasonic beam and that this can be taken into account in simulations by imposing an angle dependent correlation of the scatterer points. Ultrasound images of a porcine heart were obtained in vitro, and the dominating fiber directions were estimated from the insonification angles that gave rise to the highest backscatter intensities. A cylindrical sample of the myocardium was then modeled as a grid of point scatterers correlated in the principal directions of the muscle fibers, as determined experimentally. Ultrasound images of the model were simulated by using a fast k-space based convolution approach, and the results were compared with the in vitro recordings. The simulated images successfully reproduced the insonification dependent through-wall distribution of backscatter intensities in the myocardial sample, as well as a realistic speckle pattern.