Biomedical subjects

M G de Kroon

Publications and source records attributed to M G de Kroon.

4 recordsLinked to original sources

PubMed1995

Ultrasound backscatter at 30 MHz from human blood: influence of rouleau size affected by blood modification and shear rate.

High frequency intravascular ultrasound may show a high intensity backscatter from blood which hampers the discrimination between lumen and arterial wall. In this study, the acoustic behaviour of blood at 30 MHz in relation to rouleau size was analyzed. In a Couette viscometer, high frequency (20-40 MHz) backscatter data from normal and modified blood samples from eight volunteers were obtained at shear rates from 0 to 1000 s-1. The acoustic behaviour of blood was quantified by the integrated backscatter power and the spectral slope of the backscatter coefficient. Backscatter from blood depended on rouleau size. At a shear rate of zero, both whole blood and rouleau-enhanced blood showed a 11-dB-higher integrated backscatter power than rouleau-suppressed blood, which itself was 10 dB higher than that of hemolysed blood, the latter showing a 6-dB-higher backscatter than saline. Platelets did not contribute to the backscatter power. Plasma and saline produced no detectable integrated backscatter power other than noise. The spectral slope of whole and rouleau-enhanced blood was small (1 and 0.5, respectively), whereas rouleau-suppressed blood and hemolysed blood (both with a slope of 3.3) behaved almost like a Rayleigh scattering medium (slope = 4). The backscatter from rouleau-suppressed blood showed no shear rate dependence. At low shear rates ( < 0.8 s-1 for integrated backscatter power and < 0.2 s-1 for the spectral slope), whole blood and rouleau-enhanced blood tended to the results from the static situation (no shear). At high shear rates ( > 80 s-1 for integrated backscatter power and >11 s-1 for spectral slope), these samples tended to the results of rouleau-suppressed blood. Ultrasound backscatter at 30 MHz from human blood is only caused by red blood cells. With increasing aggregate (rouleau) size, the integrated backscatter power increased by 11 dB, and the spectral slope decreased from 3.3 to 1.

Blood↗

PubMed1991

Backscatter directivity and integrated backscatter power of arterial tissue.

A 27 MHz transducer, mounted on an ultrasonic microscope, was used to quantify the dependence of backscatter power on the angle of incidence of arterial vessels. Due to variations in the angle of incidence significant variations in backscatter power were found in the intima, the muscular and elastic media, the adventitia and the external elastic lamina. The muscular and the elastic media show anisotropic behaviour in their angle dependence, i.e. the extent of the angle dependence depends on the direction of angle variation. This anisotropic nature is probably caused by the dominant orientation of smooth muscle cells or elastin fibers in these tissue layers. Measurements on 13 specimens of the iliac artery showed that each tissue type of the vessel has its own specific angle dependent behaviour. In the future this property might be used for quantitative tissue characterization.

Humans↗

PubMed1991

Cyclic changes of blood echogenicity in high-frequency ultrasound.

Ultrasound images from human arteries obtained in vivo with an intravascular 30 MHz ultrasound imaging device show that blood echogenicity changes during the cardiac cycle. Quantitative measurements of blood echogenicity during the cardiac cycle suggest that these variations may be related to changes in the state of erythrocyte aggregation, which are induced by varying shear rate.

Blood Flow Velocity↗

PubMed1991

Angle-dependent backscatter from the arterial wall.

The anisotropic nature of intra-arterial echographic images is reported, and the source of this anisotropy is investigated using postmortem human iliac arteries. A 27 MHz transducer, mounted on an ultrasonic microscope, is used to quantify the angular dependence of the backscatter power versus the angle of incidence, and these results are correlated with histological findings. Besides the observed differences in the acoustic response of morphologically different tissues, significant variations in backscatter power are found in both media and internal elastic lamina due to variations in the angle of incidence. This angle dependence is caused by the dominant orientation of fibers in tissue layers and by the shape and size various scattering particles. The results indicate that long microscopic structures with one main orientation are responsible for the backscattered signal and that the angular-dependent response is related to the histologically determined orientation of these fibers. These results may have an impact on the assessment of intra-arterial echographic images.

Blood Vessels↗