Biomedical subjects

Giacomo Bambi

Publications and source records attributed to Giacomo Bambi.

5 recordsLinked to original sources

PubMed2006

Noninvasive simultaneous assessment of wall shear rate and wall distension in carotid arteries.

A novel technique has been developed for the noninvasive real-time simultaneous assessment of both blood velocity profile and wall displacements in human arteries. The novel technique is based on the use of two ultrasound beams, one set at optimal angle for wall motion measurements and the other for blood velocity profile measurements. The technique was implemented on a linear array probe divided into two subapertures. A modified commercial ultrasound machine and a custom PC board based on a high-speed digital signal processor was used to process the quadrature demodulated echo signals and display results in realtime. Flow phantom experiments demonstrated the validity of the technique, providing wall shear rate (WSR) estimates within 10% of the theoretical values. The system was also tested in the common carotid arteries of 16 healthy volunteers (age 30 to 53 y). Results of simultaneous diameter distension and WSR measurements were in agreement with published data.

Adult↗

PubMed2006

Accurate Doppler angle estimation for vector flow measurements.

Traditional Doppler methods measure only the axial component of the velocity vector. The lack of information on the beam-flow angle creates an ambiguity that can lead to large errors in velocity magnitude estimates. Different triangulation techniques so far have been proposed, which basically perform multiple measurements of the Doppler frequency shift originating from the same region. In this work, an original approach is introduced, in which two ultrasound beams with known relative orientation are directed toward the same vessel, but only one of them is committed to perform a Doppler measurement; the second (reference) beam has the specific task of detecting the beam-flow angle. The latter goal is obtained by accurately identifying the achievement of the target 900 reference-beam-to-flow angle through the inspection of the backscattered Doppler signal spectrum. In transverse flow conditions, in fact, such spectrum is expected to be centered on the zero frequency, and even small deviations from the desired 900 orientation cause noticeable losses of spectral symmetry. Validation of the new method has been performed through experimental tests, which show that the beam-flow angle can be estimated with high accuracy (rms errors lower than 1 degree), and repeatable velocity magnitude measurements are possible. A procedure for automatically tracking the desired orientation by the reference beam is also introduced and shown suitable for implementation in steerable linear array transducers.

Animals↗

PubMed2004

Intraluminal ultrasound intensity distribution and backscattered Doppler power.

Ultrasound (US) incident obliquely on a cylindrical vessel is redistributed in space when the propagation path includes walls with acoustic impedance different from that of the surrounding media. We investigated this using low-density polyethylene (PE) as the vessel wall material. Both simulations and experiments were carried out. Direct hydrophone measurements of the acoustic field were made within a half section of the PE tube, and the distribution of backscattered Doppler power along a scan line was obtained using a range-Doppler instrument. Both simulation and hydrophone results demonstrate lateral shadow regions within the lumen. In every one of various Doppler flow experiments conducted, the backscattered Doppler power, compensated for on-axis transducer behaviour, increased with depth. Simulation results for an incident continuous-wave (CW) plane wave show that it tends to be focused by the curvature of the PE tube walls. The wall interactions are, however, angle-dependent and so the behaviour of a focused US beam depends on the beam as well as the walls. This study demonstrates alterations in the spatial distribution of US within a cylindrical vessel as a result of known vessel wall properties. It also provides evidence that local intensity variations within the lumen affect the relative Doppler power backscattered from small sample volumes.

Blood Vessels↗

PubMed2003

Interaction between secondary velocities, flow pulsation and vessel morphology in the common carotid artery.

The common carotid artery (CCA), one of the vessels more frequently investigated by ultrasound (US), is often modeled as a straight tube in quasi-laminar flow regimens. Experimental investigations based on a prototype multigate system show that blood velocity profiles are parabolic during diastole and early systole, and flat during the systolic peak. However, during late systole/beginning of diastole, they have an "M" shape, where the velocity near the walls is higher than in the vessel center. Moreover, the profile shape changes when the sound beam direction is moved over a given cross-section; thus, suggesting a nonaxisymmetrical velocity distribution, which contradicts the straight tube assumption. The purpose of this paper was twofold. First, the actual velocity distribution in "normal" CCAs was reconstructed. The analysis of several velocity profiles confirms that the velocity distribution is markedly asymmetrical, especially during the deceleration phase following the systolic peak. Second, a tentative explanation for such behavior is given by correlating it with the growth of secondary flows caused by the slight vessel curvature and viscous effects. This explanation is supported by the comparison between in vitro results and numerical solution of the Navier-Stokes equations in laminar pulsed-flow regimens.

Adult↗

PubMed2002

Toward a better quantitative measurement of aortic flow.

Ultrasound investigation of aortic blood flow (ABF) still represents a technically challenging task, because of the complex geometry of such a deep artery. In this paper, we present a unique experimental set-up capable of providing detailed information about blood dynamics in the aorta. The set-up is based on an esophageal probe (EP) connected to a multigate Doppler-processing system. The EP, developed for the noninvasive hemodynamic monitoring of ABF in patients under general anesthesia or in the intensive care area, must be inserted at a thoracic depth where the esophagus and the aorta are nearby and parallel. Doppler processing of pulsed wave echoes in the multigate system provides the distribution of all Doppler frequencies detected along the probe beam axis (spectral profile) in real time. The results of this investigation confirm that flow in the aorta is extremely complex, especially at the level of the aortic arch or in nonphysiologic circumstances. In general, the velocity profiles tend to be flat only during the systolic acceleration, but not during the full cardiac cycle. In most cases, they are asymmetrical, including both positive and negative components. In particular, it is shown that an appropriate positioning of the ultrasound transducer and/or the correct integration of different velocities is mandatory to make reliable ABF measurements.

Aorta↗