Temporal Resolution Velocity Research Articles

Calculating the velocity of a fast‐moving snow avalanche using an infrasound array

AbstractOn 19 January 2012, a large D3 avalanche (approximately 103 t) was recorded with an infrasound array ideally situated for observing the avalanche velocity. The avalanche crossed Highway 21 in Central Idaho during the largest avalanche cycle in the 15 years of recorded history and deposited approximately 8 m of snow on the roadway. Possible source locations along the avalanche path were estimated at 0.5 s intervals and were used to calculate the avalanche velocity during the 64 s event. Approximately 10 s prior to the main avalanche signal, a small infrasound signal originated from the direction of the start zone. We infer this to be the initial snow pack failure, a precursory signal to the impending avalanche. The avalanche accelerated to a maximum velocity of 35.9 ± 7.6m s−1 within 30 s before impacting the highway. We present a new technique to obtain high spatial and temporal resolution velocity estimates not previously demonstrated with infrasound for avalanches and other mass wasting events.

MR Image-Based Geometric and Hemodynamic Investigation of the Right Coronary Artery with Dynamic Vessel Motion

The aim of this study was to develop a fully subject-specific model of the right coronary artery (RCA), including dynamic vessel motion, for computational analysis to assess the effects of cardiac-induced motion on hemodynamics and resulting wall shear stress (WSS). Vascular geometries were acquired in the right coronary artery (RCA) of a healthy volunteer using a navigator-gated interleaved spiral sequence at 14 time points during the cardiac cycle. A high temporal resolution velocity waveform was also acquired in the proximal region. Cardiac-induced dynamic vessel motion was calculated by interpolating the geometries with an active contour model and a computational fluid dynamic (CFD) simulation with fully subject-specific information was carried out using this model. The results showed the expected variation of vessel radius and curvature throughout the cardiac cycle, and also revealed that dynamic motion of the right coronary artery consequent to cardiac motion had significant effects on instantaneous WSS and oscillatory shear index. Subject-specific MRI-based CFD is feasible and, if scan duration could be shortened, this method may have potential as a non-invasive tool to investigate the physiological and pathological role of hemodynamics in human coronary arteries.

MRI myocardial motion and fiber tracking: a confirmation of knowledge from different imaging modalities

A helical configuration underlies the anatomy of cardiac structure, and a structure/function relationship is needed to determine if the ventricular myocardial band model defines this spatial relationship. This report explores how studies of velocity-encoded phase contrast magnetic resonance imaging (MRI) for myocardial motion and fiber tracking algorithms that imply fiber orientations can (a) quantify regional myocardial wall motion of the entire heart, (b) determine if these motion of implied fiber orientation link with the helical heart model, and (c) reveal if this new knowledge correlates with imaging information from other different imaging modalities. Accumulated left ventricular motion patterns that accurately differentiate radial (i.e. contraction and expansion), rotational (i.e. twisting and untwisting), and longitudinal (i.e. lengthening and shortening) motion components are correlated with structure/function data achieved by sonomicrometer crystals, echocardiography, corrosion casts, and MUGA recordings. Acceleration fiber tracking to determine fiber orientation and cardiac motion during the ejection and rapid filling phases of the cardiac cycle corresponded to maximal force displayed by ultrasonic crystals placed into the angulation of the presumed functional units of the descending and ascending segments of the apical loop of the helical ventricular myocardial band, and motion by echocardiographic recordings. These integrated findings imply a favourable interaction of MRI with the myocyte orientation of the helical ventricular myocardial band. These composite findings indicate that phase contrast MRI techniques for high temporal resolution velocity mapping during cardiac motion and myocardial fiber tracking confirm other technologies, and centralize the capacity of MRI to link other imaging methods together relative to a single helical structural model. The close agreement amongst a spectrum of imaging studies provide a very powerful integration that transcends a single look; the same thing is observed by each component of global technology, thereby implying that the helical ventricular band is the structural basis for these functional changes.

Investigating myocardial motion by MRI using tissue phase mapping

Velocity-encoded phase contrast magnetic resonance imaging (MRI) provides a tool to quantify regional myocardial wall motion of the entire heart. It allows the acquisition of three-directional velocity vector fields with high spatial resolution that reflect the temporal evolution of myocardial velocities over the cardiac cycle. In contrast to other imaging modalities such as echocardiography left ventricular performance can be assessed without limited anatomical or functional coverage. Compared to other techniques that quantify local myocardial contractility (e.g. implanted ultrasonic crystals) by means of regional displacement, phase contrast MRI provides information about local and global left ventricular velocities (i.e. motion) by utilizing the intrinsic motion sensitivity of MRI. The resultant motion components of contraction, expansion, rotation, lengthening, and shortening of the left ventricle are described in high spatial and temporal detail. Phase contrast measurements were performed in 12 healthy volunteers with a respiratory-gated technique in order to achieve a high temporal resolution of 13.8ms to demonstrate the detailed assessment of global and regional myocardial motion. Data revealed details in left ventricular motion patterns that were previously not seen in phase contrast measurements and are only known from echocardiography. For all volunteers, characteristic myocardial motion patterns and locally different radial (i.e. contraction and expansion), rotational (i.e. twisting and untwisting) and longitudinal (i.e. lengthening and shortening) motion components could be detected with high accuracy. The phase contrast MRI technique for high temporal resolution velocity mapping is therefore very promising for the investigation and better understanding of the myocardial motion in normal subjects and patients with disturbed left ventricular performance and may validate further testing of different models of cardiac structure.

Navigator gated high temporal resolution tissue phase mapping of myocardial motion

Data acquisition for phase contrast velocity mapping of myocardial motion is typically based on multiple breath-held 2D measurements with limited acquisition duration and consequently relatively poor temporal resolution. In order to overcome the limitations of breath-hold acquisitions, an improved navigator-guided technique was implemented based on 2 navigator signals within each cardiac cycle in combination with paired acceptance and rejection criteria of successive navigator signals. Respiratory gated phase contrast measurements with 3-directional velocity encoding were performed in 12 healthy volunteers in basal, midventricular, and apical locations of the left ventricle during free breathing with a temporal resolution of 13.8 ms. Results were compared to standard breath-hold measurements with a temporal resolution of 69 ms. Data from the high temporal resolution study revealed details in left ventricular motion patterns that were previously not seen in phase contrast measurements and are only known from echocardiography. The proposed navigator gated technique for high temporal resolution velocity mapping is, therefore, highly promising for the detection of local and global motion abnormalities in patients with disturbed left ventricular performance, such as diastolic dysfunction.

High temporal resolution velocity estimates from a wind profiler

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Oceanic turbulence measurements using a coherent bistatic acoustic Doppler profiler

A 300‐kHz acoustic Doppler profiler has been developed to measure turbulent processes in the upper ocean. Acoustic energy from scatterers ensonified by a single, narrow‐beam, pulsed transmitter is received by four fan beam response hydrophones placed radially around the transmitted transducer. The present system allows three‐component velocity profiles to be estimated every 10 cm over a 5‐ to 20‐m range with high temporal resolution and adequate velocity range by using a dual interpulse period coherent sampling method. Examples of the high spatial and temporal resolution velocity fields are shown from recent measurements immediately below open ocean waves and a sub‐ice boundary layer. Both the advantages and limitations of this current measurement technique will be discussed. [Work supported by ONR Physical Oceanography.]