Doppler color-flow images from a stenosed arterial model: Interpretation of flow patterns

A novel molecular communication inspired detection method for the evolution of atherosclerosis

BACKGROUND AND OBJECTIVE

Atherosclerosis is a leading cause of potentially serious cardiovascular diseases such as heart attack, stroke, and peripheral artery disease. Due to the prolonged and non-reversible process of thickening arteries walls, atherosclerosis plaques in the blood vessels are formed that restrict the blood flow. Early detection plays a vital role in minimizing the risk as there is no reliable method to detect the early stage of the disease. This paper proposes a novel atherosclerosis detection method based on the emerging paradigm of molecular communications. The work could pave the way to implement a low-cost and straightforward early detection method of atherosclerosis in the future.

METHODS

We used COMSOL to model the physical field, coupled the fluid module and the fluid particle tracking module, and mapped the contrast agent into nanoparticles (NPs). The NPs are released at the entrance of the blood vessel and received at the exit of the blood vessel, while NPs are propagating through different arterial stenosis. The arrival probability of NPs is defined as the ratio of the number of NPs that reach the outlet to the total number of released NPs. As a result of atherosclerosis, the arrival probability of Nps is affected by the dynamic flow nature changes, thereby reflecting the arterial stenosis degree. Furthermore, we introduce the multi-release method in this study, which has a similar concept of Inter-symbol interference in traditional communication. This multi-release method leads the overlapping concentrations of NPs remaining in the vessels and enhances the differences of arrival probability in different degrees of stenosis, which increases the chance of more observable results.

RESULTS

The assessment of arterial stenosis degree can be from the early stage to the late stage of the disease. To evaluate the arterial stenosis degree, we analyzed the Poincaré maps, representing the arrival probability of NPs at different arterial stenosis. Moreover, we could directly use data to quantify the pathological process at various stages. The difference between the data results obtained through multiple release methods is more prominent than a single-released method.

CONCLUSIONS

This research proposes a new atherosclerosis detection method based on molecular communication, that is, to evaluate the arterial stenosis degree by modelling and using statistical data of NPs emission and reception in blood vessels. This method can not only use a simple method to detect the early stage of the disease. In addition, we can directly use data to quantify the pathological process of each stage, which is straightforward to assist doctors and may reduce the labour cost of traditional detection.

Variance mapping in colour flow imaging: what does it measure?

Flow disturbance is known to occur in association with high grade carotid stenosis and cause spectral broadening and fluttering in the Doppler spectral waveform distal to the stenosis. Colour flow variance mapping has been proposed as a means of documenting its presence. We prospectively evaluated this hypothesis by studying 15 patients with high grade (> 50%) stenotic lesions in the internal carotid artery. In all 15 cases, the site of increased variance on the colour Doppler map corresponded to the point of maximum velocity. In 10 cases of greater than 75% stenosis, the point of aliasing on the traditional colour Doppler map and the site of maximal variance occurred at the stenotic jet (length 7.3 +/- 2.3 mm) and not along the full length of disturbed flow (19.3 +/- 5.5 mm). In five patients with stenoses between 50-75% diameter narrowing, decreasing the colour Doppler pulse repetition frequency (PRF) created a region of abnormal variance corresponding to the site of aliasing. In all 15 stenoses, the site of maximum flow disturbance, defined as fluttering in the Doppler spectral waveform, was not apparent on the variance map. We conclude that the variance map does not reflect flow disturbance and is most likely to occur at sites of aliasing.

Simulation of three-dimensional pulsatile flow through an asymmetric stenosis

The main objective of this work was to use desktop workstations to evaluate the computer code HEMO as a tool for predicting coronary blood flows. The flows are usually characterised by complex vortical structures and transitional effects, and as such present challenging computational problems. As the results of the computations shown in the paper demonstrate, we can predict realistic pulsatile flows in constricted tubes using the Sun Sparcstation 1+ in a matter of hours. The results shown in the paper have also demonstrated that the computer simulations can be very useful as a complementary tool for experimental investigations.

Usefulness of an intravenous contrast medium in the characterization of high-grade internal carotid stenosis with color Doppler-assisted duplex imaging

BACKGROUND AND PURPOSE

The remaining limitations of ultrasonographic imaging in accurately quantifying internal carotid stenosis or diagnosing internal carotid occlusion may be overcome by enhancing the echogenicity of flowing arterial blood with contrast agents. This study assessed the usefulness of the intravenous (transpulmonary) contrast medium SH U 508 A in improving the characterization and quantification of severe internal carotid stenosis.

METHODS

We examined 32 patients (30 had vessels with a stenosis of greater than 70% luminal narrowing and 2 had vessel occlusions) using a 7.5-MHz linear-array transducer for color Doppler-assisted duplex imaging before and after injection of the contrast medium.

RESULTS

The SH U 508 A-induced increase in carotid blood echogenicity began 11 +/- 2 (mean +/- SD) seconds after the start of the bolus injection, peaked at 21 +/- 2 dB, and showed a half-life of 75 seconds. Quantitative vascular measurements (cross-sectional luminal area reduction and plaque length, respectively) obtained before and after contrast application were highly correlated (r > .90). Visualization of the entire length of the intrastenotic residual flow lumen, however, was significantly improved by contrast enhancement (52% versus 83%, P = .01).

CONCLUSIONS

This pilot study on patients with extracranial carotid artery disease suggested that ultrasonic contrast media may be most useful in improving the ultrasonography-based diagnosis of internal carotid occlusion.

Flow imaging in an end-to-side anastomosis model using two-dimensional velocity vectors

Colour flow Doppler ultrasound images from vessels of complex geometry can be difficult to interpret, thereby limiting the effectiveness of the technique to correctly assess abnormalities and to relate the images to the underlying flow field in a quantitative manner. This paper describes progress in calculating and displaying two-dimensional (2-D) velocity vectors from a 30 degrees end-to-side anastomosis model under steady flow conditions at various Reynolds numbers. Velocity vectors were computed from colour Doppler ultrasound images obtained with a linear array for several incident beam directions, and the results were displayed either as colour-encoded magnitude images or by superimposing the vectors on one of the original colour images. Results are discussed in relation to flow visualization observations and the behaviour of flow in curved vessels.

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.