Hans W. Persson

Evaluation of an ultrasonic echo-tracking method for measurements of arterial wall movements in two dimensions

The longitudinal movement of blood vessel walls has so far gained little or no attention, as it has been presumed that these movements are of a negligible magnitude. However, modern high-resolution ultrasound scanners can demonstrate that the inner layers of the arterial wall exhibit considerable movements in the longitudinal direction. This paper evaluates a new, noninvasive, echo-tracking technique, which simultaneously can track both the radial and the longitudinal movements of the arterial wall with high resolution in vivo. Initially, the method is evaluated in vitro using a specially designed ultrasound phantom, which is attached to and moved by an X-Y system, the movement of which was compared with two high-resolution triangulation lasers. The results show an inaccuracy of 2.5% full scale deflection (fsd), reproducibility of 12 /spl mu/m and a resolution of 5 /spl mu/m, which should be more than sufficient for in vivo studies. The ability of the method is also demonstrated in a limited in vivo study in which a preselected part of the inner vessel wall of the right common carotid artery of a healthy volunteer is tracked in two dimensions over many cardiac cycles. The results show well reproducible x-y movement loops in which the recorded radial and longitudinal movements both are of the magnitude millimetre.

Measurement of blood perfusion in tissue using doppler ultrasound

A diagnostic tool for noninvasive evaluation of microcirculatory blood flow using continuous-wave CW Doppler ultrasound is presented. In this study, the properties of this method are investigated both theoretically and experimentally. The method utilizes a nondirectional CW Doppler flowmeter. Blood perfusion in tissue is shown to be proportional to the integral integral of fS (f)df where S(f) is the Doppler power spectrum and f is the Doppler frequency. The instrumentation needed to implement the method is described. Using an experimental flow model it is demonstrated that the above integral is proportional to the product between the number of scatterers in the sample volume of the Doppler probe and the mean speed of these scatterers. This is true even for low flow velocities (down to 1 mm/s). The results from in-vivo measurements on tissues in the finger, and the calf demonstrate that the method can monitor changes in the blood perfusion. It also shows the present limitations of the method due to movement artefacts.

A new non-invasive ultrasonic method for simultaneous measurements of longitudinal and radial arterial wall movements: first in vivo trial

During recent years, the radial movement of the arterial wall has been extensively studied, and measurements of the radial movement are now an important tool in cardiovascular research for characterizing the mechanical properties of the arterial wall. In contrast, the longitudinal movement of vessels has gained little or no attention as it has been presumed that this movement is negligible. With modern high‐resolution ultrasound, it can, however, be seen that the intima‐media complex of the arterial wall moves not only in the radial direction, but also in the longitudinal direction during pulse‐wave propagation. This paper describes a new non‐invasive ultrasonic method that is able to measure simultaneously two dimensionally arterial vessel wall movements. The method is demonstrated in a limited in vivo trial. Results from the in vivo trial show that, apart from the well‐known radial movement, there is a distinct longitudinal movement in the human common carotid artery with, in this case, the intima‐media complex moving substantially as compared with the region of the tunica adventitia. Two‐dimensional evaluation of the vessel‐wall movements, taking not only the radial movement, but also the longitudinal movement into account, may provide novel information of importance in the evaluation of vessel‐wall function.

Characterizing preferential transport during flood irrigation of a heavy clay soil using the dye Vitasyn Blau

Abstract Common irrigation procedures in many parts of the world involve flood irrigation. Observations during recent years have, however, indicated that preferential flow may be an important phenomenon that could affect the outcome of both irrigation and fertilizer application for this irrigation type. To analyze and visualize solute transport by preferential flow mechanisms, field experiments were carried out at the Cherfech Agricultural Research Station in northern Tunisia. Paths of solute transport were investigated by a 0.05-m ponded pulse of Vitasyn Blau dye allowed to infiltrate into the unsaturated heavy clay soil. Two experimental plots were prepared for the infiltration of dye by leveling the surface. Leveling was done to have similar surface conditions at the two plots. After infiltration, a trench was dug at the border of the dye-injected region to document the dye patterns vertically and horizontally. The patterns indicated strong dependence on the horizontal structure of the soil. In general, the dye was to a major extent transported along distinct cracks and ped faces in the prismatic silty clay. Only the upper 0–0.05 m depth of the tilled soil had almost a complete dye coverage. Below this depth, preferential dye patches start to develop and dye coverage is rapidly decreasing to below 50% at 0.15 m depth. Even though transport through the prismatic silty clay mainly followed cracks between the prisms, it is estimated that only 10–20% of these vertical cracks are active in conducting solutes. The results from the present study have implications for soil management in areas using flood and furrow irrigation with soils susceptible to preferential flow. Tillage depth is a factor that is likely to have a great impact on the amount of water that reaches the soil matrix. Increasing tillage depth and other management practices that break up the structure and make the soil more homogeneous will increase the efficiency of irrigation and reduce the susceptibility for preferential flow.

Binding of mineral elements by some dietary fibre components - In vitro (II)

Abstract The binding of copper, cadmium and zinc ions to some soluble and gelforming types of dietary fibre (guar gum, low and high methoxylated pectin and sterculia gum) has been investigated potentiometrically. Considerable binding was found to low methoxylated pectin, but the binding to sterculia gum and high methoxylated pectin was less pronounced. The binding to guar gum was negligible. Thus, the formation of complexes seemed to be due to the proportion of free carboxyl groups. The amount of added metal bound to sterculia gum was proportional to the fibre concentration, whereas the pectins showed increased binding at higher fibre concentrations. This was possibly due to intermolecular interactions between the polymers and metal ions. The order of complex formation ability to the fibres investigated was different for different metals. To low methoxylated pectin the order Cu>Zn ⪢ Cd was observed.

Evaluation of doppler ultrasound for blood perfusion measurements

The need to develop clinical methods for the noninvasive monitoring of regional blood perfusion, i.e., the blood flow through the very fine capillaries in body tissue, has long been felt. Hitherto existing methods exhibit limitations, such as insufficient measurement depth and poor time- or space-resolution, which restrict the measurements that can be performed. Dymling (1982) introduced a new CW Doppler ultrasound method for noninvasive blood perfusion measurement which might be one possible solution to this problem. Preliminary experiments indicated a correlation between blood flow and measured perfusion value. Unexpectedly large variations in the recorded perfusion values lead to further investigation of the method, both in vitro using a specially designed flow phantom and in vivo. This study indicates that at least some of the large variations recorded are the result of measurement errors caused by movement artifacts or ultrasonic signal interferences. Methods to diminish the effects of these artifacts are discussed.

Non-invasive measurement of arterial longitudinal movement

In arterial vessel wall characterisation the longitudinal movements of vessels have gained little or no attention. It has been presumed that the arterial vessels move very little in the longitudinal direction. With modern high resolution ultrasound it can, however, be seen that arterial vessels move not only in the circumferential, but also in longitudinal direction. This paper describes a non-invasive, ultrasound based method which estimates the longitudinal and the circumferential movement, respectively. The method is demonstrated in a limited in vivo study of the common carotid artery. Results show that, apart from the well known circumferential movement, there is a distinct longitudinal movement.

Longitudinal displacement and intramural shear strain of the porcine carotid artery undergo profound changes in response to catecholamines

The effects of catecholamines on longitudinal displacements and intramural shear strain of the arterial wall are unexplored. Therefore, the common carotid artery of five anaesthetized pigs was investigated using an in-house developed noninvasive ultrasonic technique. The study protocol included intravenous infusion of low-dose epinephrine (β-adrenoceptor activation), as well as intravenous boluses of norepinephrine (α-adrenoceptor activation). Further, the effects of β-blockade (metoprolol) were studied. There were significant positive correlations between pulse pressure and longitudinal displacement of the intima-media complex (r = 0.72; P < 0.001), as well as between pulse pressure and intramural shear strain (r = 0.48; P < 0.001). Following administration of norepinephrine, the longitudinal displacement of the intima-media complex and intramural shear strain profoundly increased (median 190%, range 102-296%, and median 141%, range 101-182%, respectively, compared with baseline), also when given during β-blockade (median 228%, range 133-266%, and median 158%, range 152-235%, respectively). During infusion of low-dose epinephrine, the longitudinal displacement of the intima-media complex and intramural shear strain decreased (median 88%, range 69-122%, and median 69%, range 47-117%, respectively, compared with baseline). In conclusion, the present study shows, for the first time, that the longitudinal displacement and intramural shear strain of the porcine carotid artery undergo profound changes in response to catecholamines. Increase in longitudinal displacements seems to be strongly related to α-adrenoceptor activation. Thus metoprolol is insufficient to counteract a profound increase in longitudinal displacement and intramural shear strain following a surge of norepinephrine.

Electric excitation of ultrasound transducers for short pulse generation

Abstract A method for the generation of short ultrasound pulses by a piezoelectric transducer is presented. The method uses various combinations of voltage steps which are applied to the transducer as excitation pulses. Compared with conventional excitation used in echo systems this results in an appreciable shortening of the received signal. A qualitative explanation of the results obtained is given.

Optical diffraction tomography applied to airborne ultrasound

Abstract This paper describes the application of a light diffraction measurement method for airborne ultrasound. The method is based on Raman—Nath diffraction of a light beam combined with tomographic algorithms. Light intensity measurement data on acoustically diffracted light are used to characterize airborne ultrasound. The light intensity measurement data contain information on the integration of sound pressure along a specific light path. This integration allows the reconstruction of ultrasonic pressure in the cross-section of an ultrasonic beam. If the simplifying assumption of plane phase wavefronts is accepted the method gives absolute values for acoustic pressure. Reconstructions of phase surfaces are possible but are not discussed in this paper. The tomographic reconstruction of the measurement plane is done with an Algebraic Reconstruction Technique (ART) combined with nearest neighbour averaging. Three transducers were measured; results with two non-focussed air transducers with frequencies 200 kHz, 410 kHz and a focussed 1 MHz transducer are presented. Beam profiles, three-dimensional pressure maps and the optically detected acoustic ‘pulse-shape’ with tone-burst excitation are presented. The optical method offers good spatial resolution, bandwidth at least up to 1 MHz, and acoustic near-field measurements.