Biomedical subjects

D Y Fei

Publications and source records attributed to D Y Fei.

24 records · Page 2Linked to original sources

PubMed1984

Effect of flow disturbance on ultrasonic backscatter from blood.

Due to the better resolution and performance provided by the new generation of real-time high resolution ultrasonic scanners, blood now becomes a tissue which can also be visualized ultrasonically. There is strong experimental evidence indicating that the echogenicity of blood is increased as a result of erythrocyte aggregation. In this paper, we will show that flow disturbance may also play a significant role in influencing blood ultrasonic backscatter or echogenicity. Our results indicate that the introduction of turbulent flow can cause ultrasonic backscatter from erythrocyte suspensions to increase appreciably for hematocrits greater than 10%. We will also show that this increase may be correlated to the turbulent intensity. Moreover, the scattering peak is observed to shift to lower hematocrits when turbulence is eliminated. Experimental results obtained for uniform flow are in excellent agreement with theoretical models for small spherical scatterers which predict a scattering maximum at a hematocrit of 13%.

Animals↗

PubMedDate not supplied

Ultrasonic characterization of blood during coagulation.

Recently ultrasound has been found to be extremely useful in detecting intracardiac thrombi as well as intracranial hemorrhages in neonates. The principal criterion used for clinical diagnosis of thrombus has been an increase in the echogenicity of clotted blood. However, echogenicity is a rather nonspecific and qualitative description of tissue ultrasonic properties. A rise in echogenicity could be the result of an increase in ultrasonic backscatter, or a decrease in attenuation, or a combination of both. In order to ascertain the mechanism responsible for the clinically observed increase in echogenicity and thus put the technique on a firm foundation, we have measured serially the ultrasonic velocity, attenuation and backscatter in human blood up to 24 hours following the onset of coagulation. Preliminary results show that all three ultrasonic properties increase during this time period. At 24 hours following clotting, the mean rises in velocity, attenuation and backscatter are 3.36 +/- 0.35 X 10(3) cm/sec, 2.3 +/- 0.22 db/cm and 18.5 +/- 1.2 dB per unit volume of blood (at 7.5 MHz and a temperature of 23 degrees C), respectively. These results indicate that the increase in echogenicity of a thrombus is due to a substantial increase in ultrasonic backscatter, which is moderated to a certain extent by the accompanied increase in attenuation.

Acoustics↗

PubMedDate not supplied

MR imaging of model fluid velocity profiles.

A projection MR technique for imaging the velocity profiles of moving fluids has been applied to various steady flow models designed to simulate a variety of flow conditions. From such profiles can be readily deduced peak velocities, volume flow rates, information concerning the degree of flow development, features such as flow separation, and estimates shear stresses at the vessel wall.

Blood Flow Velocity↗

PubMedDate not supplied

New method to obtain ultrasonic angle independent Doppler color images using a sector transducer.

A new method based on the multiple beam procedure to obtain ultrasonic angle independent Doppler color (AIDC) images using Doppler color imaging with a sector transducer has been developed. The transducer was sequentially placed at three locations with different direction orientations to acquire velocity information for the same flow field. Equations have been derived and used to obtain the velocity amplitude and flow direction angle for each point in the flow field from the acquired velocity data and the known positions of the transducer. AIDC images then can be reconstructed. To evaluate the feasibility of this method, AIDC images using a sector transducer have been reconstructed for steady flow fields in a latex tube model and for blood flow in the abdominal aorta of normal human subjects. The quantitative results obtained using this method were in reasonably good agreement with those obtained from existing reference methods.

Aorta, Abdominal↗

PubMedDate not supplied

Quantitative phase-velocity MR imaging of in-plane laminar flow: effect of fluid velocity, vessel diameter, and slice thickness.

Quantitative MR phase imaging is frequently used to measure spin velocities. A potential difficulty may arise, however, when in-plane phase images are acquired of a vessel carrying laminar flow, for which the fluid velocity profile is parabolic. In that case, depending on the flow velocity (v), the vessel diameter (D), and the chosen MR slice thickness (ST), a spin velocity gradient will be present to some extent within each intraluminal voxel. The resulting intravoxel phase dispersion may be expected to affect the net pixel phase value, and hence compromise the assumed linear correlation between phase shift and velocity. In this study, the effects of alterations of v, D, and ST on the apparent image phase are investigated for the case of laminar flow directed parallel to the sequence read gradient. A theoretical model is developed and the conclusions experimentally tested using a flow phantom. The data demonstrate that when quantitating inplane phase-flow images, significant velocity underestimations may occur when the net flow-induced phase shifts are small and the MR slice thickness is an appreciable fraction of the vessel diameter.

Humans↗

PubMedDate not supplied

Somatosensory evoked potentials associated with thermal activation of type II Adelta mechanoheat nociceptive afferents.

We evaluated evoked potentials (EPs) to noxious contact heat pulses delivered to hairy skin of healthy adults. Heat pulses from an adapting temperature of 34 degrees C to a target temperature of 52 degrees C, produced two scalp positive waves. The first peaked at 44 degrees to 45 degrees C (approximately 500 ms following stimulus onset), while the second peaked approximately 300 ms following the 52 degrees C heat pulse (approximately 1 s after stimulus onset). The first positive wave was absent from an adapting temperature of 39 degrees C, suggesting loss of synchronized activation of warm and/or low threshold mechanothermal afferents. The second EP was observed following stimulation from both adapting temperatures and was associated with subjective report of first pain. Latency difference of the pain EP from arm and leg were consistent with conduction in Adelta nociceptive afferents (approximately 10/ms). EPs to painful contact thermal stimuli may be of value in the evaluation of small fiber peripheral neuropathies and assessment of altered pain states.

Adult↗