Biomedical subjects

D Y Fei

Publications and source records attributed to D Y Fei.

At least 19 recordsLinked to original sources

PubMed2001

Rapid measurement of aortic wave velocity: in vivo evaluation.

A 1D MR sequence has been developed for determining aortic flow wave velocity (WV), a metric of arterial compliance, within a single cardiac cycle. Studies were carried out on the thoracic aortas of 10 normal volunteers. Correlative WV data were also acquired from each subject using a conventional phase-velocity 2D mapping technique. Aortic WV in this cohort was found to range from 411 to 714 cm/s and was highly correlated (R = 0.95) between the two methods. Peak blood velocity was also measured using both methods and found to agree closely. The reproducibility of WV measurements using the rapid 1D method averaged 7.6%, which is comparable or better than that achieved using existing noninvasive techniques. Magn Reson Med 46:95-102, 2001.

Adult↗

PubMed2001

Rapid aortic wave velocity measurement with MR imaging.

The utility of a one-dimensional magnetic resonance (MR) sequence to rapidly and accurately measure wave velocity in vivo was evaluated. Studies were conducted in the thoracic aortas of 20 healthy subjects of varying age, and the MR method was validated in a compliant tube model. Aortic wave velocity ranged from 3.8 to 9.7 m/sec and demonstrated a positive correlation with subjects' age. Peak blood velocity ranged from 47 to 125 cm/sec and exhibited a strong negative correlation with subjects' age.

Adult↗

PubMed2001

Novel method to correct displacement profile images and calculate flow vector fields using saturation-tagging MR imaging.

Saturation-tagging Magnetic Resonance (MR) imaging provides a simple and robust means to directly visualize displacement profiles within fluid flow fields. Although useful for velocity quantitation as well as for qualitative depiction of flow patterns in certain well-defined flow fields, the technique is prone to distortions due to oblique flow (misregistration artifact) and ambiguity of fluid vector trajectories in complex flow situations. A novel method is proposed whereby two images are acquired, differing in the temporal position of the phase encoding gradient. Theoretical analysis shows that from the paired images, distortion of the two-dimensional displacement profile can be corrected and fluid velocity vectors extracted, even if the flow directions are unknown. In the simpler case of flow oblique to the gradient principal axes, but with a known trajectory, only one image is necessary to correct the displacement profile distortion and extract the velocity information. MRI experiments in a straight tube model have been carried out to evaluate the feasibility of this method. Good agreement is achieved between the results from MR imaging and those predicted via computer simulation.

Algorithms↗

PubMed2000

Psychophysiological and psychophysical responses to experimental pain induced by two types of cutaneous thermal stimuli.

Evoked potentials (EPs) to noxious thermal stimulation of skin may provide information about integrity of the nociceptive afferent system and thus small afferent fiber integrity. Here we describe subjective report, EPs and response times to noxious contact thermal and laser stimuli in the same subjects. Pain quality to both forms of stimulation was consistently reported as a brief pricking or stinging sensation (first pain), occasionally followed, after a silent period, by a diffuse burning sensation (second pain). EPs to laser generated heat pulses consisted of bi- or triphasic waveforms with a large positive wave at approximately 300 ms following arm stimulation and 360 ms following stimulation of the leg. EPs to contact heat pulses consisted of a single, scalp positive wave occurring approximately 830 ms following arm stimulation and 890 ms following leg stimulation. Both forms of noxious stimulation activated afferents with a conduction velocity consistent with that of A-delta fibers ( approximately 10 m/s) and with the psychophysical attributes of first pain.

Electroencephalography↗

PubMed1997

Feasibility of angle independent Doppler color imaging for in vivo application: preliminary study on carotid arteries.

An experimental system has been used to acquire Doppler color images using a linear transducer from an ultrasound scanner to reconstruct angle independent Doppler color (AIDC) images in normal carotid arteries in 21 volunteers. Images were first taken from relatively straight segments in the common carotid artery, and comparisons were made in a small area at the center stream. At peak systole, the correlation coefficient of the velocity amplitudes between AIDC imaging (AIDCI) and duplex scanning was 0.94; the correlation coefficient between the flow angles measured from AIDCI and the angles of the vessel wall was 0.99. Periodic variations of the flow angle over the cardiac cycle were always observed by AIDCI, whereas the changes in the geometric angle of the vessel itself were insignificant. This observation suggests that the AIDCI technique is sensitive to alterations of flow direction. On the other hand, the deviation of the flow angle from a fixed correction angle in duplex scanning may cause a certain degree of error in velocity determination. AIDC images were also obtained at the carotid bifurcation. The results show that the AIDCI technique is able to depict major flow features, such as velocity skewing, flow separation, flow reversal and vortical flow, in a complex flow field.

Carotid Arteries↗

PubMed1995

Computer implementation in the reconstruction of 2-D flow velocity fields in ultrasound Doppler color imaging.

Doppler color imaging can easily render flow information within the vessels and simultaneously provide anatomic information for diagnostic purposes. However, the angle dependence problem of the Doppler velocity measurement is a significant barrier for continuing progress toward quantitative clinical applications of this technology. This paper presents a method and the computer implementation for reconstruction of the 2-D flow velocity field (angle independent) in ultrasound Doppler color imaging. Formulae for deriving angle independent velocity amplitude and angle direction from the color images acquired with a linear array transducer are given. The hardware configuration of the data acquiring and processing system is described. Major considerations in the development of algorithms, especially the strategies for reducing the computation time are presented.

Algorithms↗

PubMed1995

A theory to correct the systematic error caused by the imperfectly matched beam width to vessel diameter ratio on volumetric flow measurements using ultrasound techniques.

When a multigate procedure is used to measure volumetric flow in vessels, in addition to the flow rate result obtained from the conventional velocity profile method, a second result from an "average velocity profile method" can be obtained simultaneously. The latter method obtains the flow rate from the product of the average velocity across the profile and the cross-sectional area of the vessel. A theoretical model has been used to study the effect of the beam width to vessel diameter ratio (BWR) on these two results, as well as a third flow rate result obtained from the uniform insonation method. A theory has been established to correct the systematic error caused by the imperfectly matched BWR associated with each method. It uses a correction factor and the difference between the results from the average velocity profile method and the velocity profile method to compensate for the systematic error. The relationship between an optimal correction factor and the BWR under different flow conditions has been studied. The results using the correction theory in this model show that if the estimated BWR is within +/- 0.1 from the actual BWR value, the theoretical error in volumetric flow estimation can be limited to within 6.5% for the entire range of BWR.

Algorithms↗

PubMed1994

Angle independent Doppler color imaging: determination of accuracy and a method of display.

A multiple beam technique was utilized to obtain angle independent Doppler color images (AIDCI) using an ultrasonic scanner with a linear transducer. A quantitative study using steady flow models has been performed to evaluate the accuracy of this method in velocity measurements. The results show that the velocity amplitudes measured with this method correlated with those calculated from the measured flow rates (r = 0.95-0.98). The flow angles obtained with this method also correlated with those calculated from the coordinates of the tube image (r = 0.93-0.96). To improve the interpretation of the angle independent results, a method for visualizing two-dimensional flow fields is presented and compared with two existing methods.

Blood Flow Velocity↗

PubMed1994

The effect of angle and flow rate upon hemodynamics in distal vascular graft anastomoses: a numerical model study.

Flow in distal end-to-side anastomoses of iliofemoral artery bypass grafts was simulated using a steady flow, three-dimensional numerical model. With the proximal artery occluded, anastomotic angles were varied over 20, 30, 40, 45, 50, 60 and 70 deg while the inlet Reynolds numbers were 100 and 205. Fully developed flow in the graft became somewhat skewed toward the inner wall with increasing angle for both Reynolds numbers. Separated flow regions were seen along the inner arterial wall (toe region) for angles > or = 60 deg at Re = 100 and for angles > or = 45 deg at Re = 205 while a stagnation point existed along the outer arterial wall (floor region) for all cases which moved downstream relative to the toe of the anastomosis with decreasing angles. Normalized shear rates (NSR) along the arterial wall varied widely throughout the anastomotic region with negative values seen in the separation zones and upstream of the stagnation points which increased in magnitude with angle. The NSR increased with distance downstream of the stagnation point and with magnitudes which increased with the angle. Compared with observations from chronic in vivo studies, these results appear to support the hypothesis of greater intimal hyperplasia occurring in regions of low fluid shear.

Anastomosis, Surgical↗

PubMed1990

Model studies of nonsteady flow using magnetic resonance imaging.

A bolus-tracking magnetic resonance imaging (MRI) method has been employed to measure velocity profiles for oscillatory flow with and without a steady flow component as well as pulsatile flow in an axisymmetric tube model. A range of flow conditions within normal physiological limits was tested. The imaged velocity profiles were observed to be generally in accord with theoretical predictions. Instantaneous flow rates calculated from the MR images agreed well with those assessed using an ultrasonic flowmeter. Because MRI is noninvasive and poses few risks to subjects, this technique is potentially useful for studying vascular hemodynamics in vivo.

Blood Flow Velocity↗

PubMed1990

Velocity profiles in stenosed models using magnetic resonance imaging.

A time-of-flight MRI velocity measurement technique is evaluated against corresponding LDV measurements in a constriction tube model over a range of physiologic flow conditions. Results from this study show that MR displacement images can: (1) be obtained within both laminar and turbulent jets (maximum stenotic Re approximately equal to 4,200); (2) measure mean jet velocities up to 172 cm/s, and (3) detect low forward and reverse velocity regions near the tube wall just downstream of the stenosis (0 less than or equal to L/D less than or equal to 2). Regions between the jet termination point and reestablishment of laminar flow (Re greater than 1,500, greater than 1,000 and greater than 110 downstream of 40, 60 and 80% stenosis, respectively) cannot presently be detected by this technique.

Blood Flow Velocity↗

PubMed1988

Flow dynamics in a stenosed carotid bifurcation model--Part I: Basic velocity measurements.

A model of the human carotid artery bifurcation has been constructed and tested under mean physiologic flow conditions (fluid viscosity = 0.035 poise; mean Re inlet = 400; unconstricted flow split = 70:30, internal carotid artery:external carotid artery). Smooth, axisymmetric constrictor plugs with 0, 20, 40, 60, and 80% diameter reduction are placed in the simulated proximal internal carotid artery to provide a range of flow conditions similar to those found clinically. Axial velocity measurements are made at sites +/- 0.625 radius within the lumen of the tube at distances of 0, 1, 3, 5 and 10 diameters downstream of the constrictor throat using H2 bubble markers and a 7.5 MHz ultrasound pulse Doppler. Measurement of mean, mode -3 dB down high and low and -9 dB down high and low velocities are made from selected fast-Fourier transform (FFT) spectra. The flow field downstream of the 0% diameter reduction is entirely laminar, exhibiting a peak skewed toward the flow divider along the entire 10 diameters downstream and having a consistently narrow bandwidth. Obstruction of the flow channel produces increased axial velocity at the constrictor (20%), an oscillatory jet extending approximately 5 diameters downstream (40%), a transitional jet extending approximately 5 diameters downstream (60%) and a turbulent jet extending approximately 3 diameters downstream (80%). Velocity bandwidth (both -3 dB and -9 dB) increases with degree of constriction and low velocity flow patterns exist between the center line and both tube walls. Presence of constriction produces characteristic downstream flow patterns which are distinctive for each degree of diameter reduction.

Blood Flow Velocity↗

PubMed1988

Flow dynamics in a stenosed carotid bifurcation model--Part II: Derived indices.

Basic velocity measurements from the previous study in this issue of modelled carotid artery bifurcation disease are post-processed to derive indices potentially useful for clinical diagnosis. Selected parameters are based upon ultrasound pulse Doppler velocity measurements made at sites +/- 0.625 radius at axial distances of 0, 1, 3, 5, and 10 diameters downstream of smooth, axially symmetric constrictions of 0, 20, 40, 60, and 80% diameter reduction. Indices based on single point velocity measurements include: (a) the center-line velocity index (CVI) at the throat of the constrictor which is sensitive to all degrees of constriction (p less than 0.05), and (b) various measures of velocity disturbance (VDI1-VD14) which show greatest sensitivity when measured at one-fourth diameter from the tube wall. Cross-sectional indices include: (a) the maximum slope index (MSI) which separates constrictions of less than 60% diameter reduction from those having greater than or equal to 60% diameter reduction (p less than 0.05), and (b) the cross-sectional profile index (CPI) which separates constrictions of less than or equal to 20% diameter reduction from those having greater than 20% diameter reduction (p less than 0.05). A field profile index (FPI) utilizes data from all available sites up to 5 diameters downstream and is able to separate all constrictor groups (p less than 0.05). Presence of constrictions produces characteristic flow patterns which can be quantified using indices based on the downstream velocity spectra. Specifically, locally increased velocity is very sensitive to degree of constriction and is best detected along the center line. Disturbance effects, while less pronounced, are complementary to changes in velocity magnitude and are first seen off-axis. Multiple point profile measures (cross sectional and full field) are also sensitive to degree of constriction and are best evaluated at 1 diameter and over 5 diameters, respectively, downstream of the constriction. All of the nondimensional indices offer the advantages of reduced probe and angle dependence and particular approaches may be implemented according to the data collection capability of the instrument used.

Blood Flow Velocity↗

PubMed1988

Velocity profiles in stenosed tube models using magnetic resonance imaging.

A time-of-flight MRI velocity measurement technique is evaluated against corresponding LDV measurements in a constriction tube model over a range of physiologic flow conditions. Results from this study show that MR displacement images can: 1) be obtained within both laminar and turbulent jets (maximum stenotic Re approximately equal to 4,200), 2) measure mean jet velocities up to 172 cm/s, and, 3) detect low forward and reverse stenosis (0 less than or equal to L/D less than or equal to 2). Regions between the jet termination point and re-establishment of laminar flow (Re greater than or equal to 1500, greater than or equal to 1000, and greater than or equal to 110 downstream of 40, 60, and 80 percent stenosis, respectively) cannot presently be detected by this technique.

Blood Flow Velocity↗

PubMed1987

Ultrasonic backscatter from bovine tissues: variation with pathology.

This is the second in a series of two papers reporting results collected on ultrasonic propagation properties, namely, velocity, attenuation, and backscatter of various mammalian tissues. In the first paper [J. Acoust. Soc. Am 78, 871 (1985)], the experimental results of five different types of normal bovine tissues were given. In this paper, results obtained for the most common bovine disease in the liver, liver abscess, and in the heart, lymphosarcoma, will be presented. These data show that the ultrasonic properties of tissues with these two types of pathologies are significantly deviated from those of normal tissues, thus providing further evidence that ultrasonic properties may be used as quantitative indicators of a certain disease for diagnostic purposes.

Animals↗

PubMed1986

Further studies on ultrasonic properties of blood clots.

Two-dimensional echocardiography has been found to be an effective clinical tool in diagnosing intracardiac thrombi. Misdiagnosis may, however, still frequently occur because of the difficulty in differentiating the thrombi from other intracavitary masses based only on the echographic appearance of these structures. Ultrasonic tissue characterization techniques have been used in attempts to minimize this diagnostic uncertainty. Previously, we have shown that all ultrasonic parameters of blood, including ultrasonic backscatter, a quantitative measure of echogenicity, at 7.5 MHz increase rapidly following clotting. In this article, we report recent results on the measurements of attenuation and backscatter of thrombi as a function of time following clotting over the frequency range of 3 MHz to 8 MHz. These results indicate that ultrasonic backscatter from thrombi 12 h old is at least 18 dB higher than that of unclotted blood over the frequency range of 3 MHz to 8 MHz, and the slope of the attenuation coefficient is increased to 0.43 dB/cm-MHz. Comparison with the backscatter of bovine myocardium shows that the myocardium is more echogenic than fresh thrombi and is less echogenic than thrombi 12 to 24 h old. Similar results were also obtained for integrated backscatter measurements over the same frequency range.

Animals↗

PubMed1985

Effects of atherosclerotic lesions on ultrasonic beam and CW Doppler signals.

Doppler ultrasound has been shown to be a useful clinical tool in the noninvasive detection of vascular stenoses, occlusion, or plaques. The presence of atherosclerotic lesions in blood vessel walls can distort the Doppler ultrasonic signal, producing inverted or biphasic tracings. This observation, in fact, has been used frequently as a criterion for the diagnosis of plaque formation and calcification of these lesions. To define the source of this distortion, we have examined the effects of various types of atherosclerotic lesions on the transmitted ultrasonic beam generated by a continuous wave (CW) Doppler ultrasonic probe. These results are compared to the Doppler flow tracings obtained by a CW ultrasonic Doppler flowmeter from blood vessels with overlaying lesions in a mock flow system. It is concluded that severe distortion in the form of beam refraction or diffraction can be produced by calcified lesions, resulting in biphasic or inverted flow signals.

Arteriosclerosis↗

PubMed1985

Ultrasonic backscatter from mammalian tissues.

Ultrasonic B-mode images are formed from echoes backscattered from tissue structures in the body. Quantitative analysis of this signal from tissues may provide additional information about the tissues which may be valuable for clinical diagnosis. Results on measurements of backscatter properties of tissues such as heart, liver, and blood have been reported by a number of investigators. Data on other tissues such as spleen, kidney, and pancreas, however, are still very scanty. In this paper, results on ultrasonic backscattering properties of bovine heart, liver, kidney, spleen, pancreas, and rat myocardium, recently obtained in our laboratory utilizing a computerized system over the frequency range of 2-7 MHz, are presented. The results show that for all the tissues investigated, backscatter from liver is the highest, while that from spleen is the lowest. Liver and pancreas exhibit frequency dependence distinctively different from other tissues. Moreover, backscatter from bovine myocardium is found to be higher than that from rat myocardium. The significance of these findings in relation to the histological composition of these tissues is discussed.

Animals↗