Stress distribution analysis in healthy and stenosed carotid artery models reconstructed from in vivo ultrasonography

Purpose@#This study investigated the accuracy of models reconstructed from ultrasound image processing by comparing the radial displacement waveforms of a subject-specific artery model and evaluated stress changes in the proximal shoulder, throat, and distal shoulder of the plaques depending on the degree of carotid artery stenosis. @*Methods@#Three groups of subjects (healthy and with less than 50% or more carotid stenosis) were evaluated with ultrasonography. Two-dimensional transverse imaging of the common carotid artery was performed to reconstruct the geometry. A longitudinal view of the same region was recorded to extract the Kelvin viscoelastic model parameters. The pulse pressure waveform and the effective pressure of perivascular tissue were loaded onto the internal and external walls of the model. Effective, circumferential, and principal stresses applied to the plaque throat, proximal shoulder, and distal shoulder in the transverse planes were extracted. @*Results@#The radial displacement waveforms of the model were closely correlated with those of image processing in all three groups. The mean of the effective, circumferential, and principal stresses of the healthy arteries were 15.01±4.93, 12.97±5.07, and 12.39±2.86 kPa, respectively. As stenosis increased from mild to significant, the mean values of the effective, circumferential, and first principal stresses increased significantly (97%, 74%, and 103% at the plaque throat, respectively) (P<0.05). The minimum effective stress was at the lipid pool. The effective stress in calcified areas was higher than in other parts of the artery wall. @*Conclusion@#This model can discriminate differences in stresses applied to mildly and severely stenotic plaques.

Assessing the blood pressure waveform of the carotid artery using an ultrasound image processing method

PURPOSE: The aim of this study was to introduce and implement a noninvasive method to derive the carotid artery pressure waveform directly by processing diagnostic sonograms of the carotid artery. METHODS: Ultrasound image sequences of 20 healthy male subjects (age, 36±9 years) were recorded during three cardiac cycles. The internal diameter and blood velocity waveforms were extracted from consecutive sonograms over the cardiac cycles by using custom analysis programs written in MATLAB. Finally, the application of a mathematical equation resulted in time changes of the arterial pressure. The resulting pressures were calibrated using the mean and the diastolic pressure of the radial artery. RESULTS: A good correlation was found between the mean carotid blood pressure obtained from the ultrasound image processing and the mean radial blood pressure obtained using a standard digital sphygmomanometer (R=0.91). The mean absolute difference between the carotid calibrated pulse pressures and those measured clinically was −1.333±6.548 mm Hg. CONCLUSION: The results of this study suggest that consecutive sonograms of the carotid artery can be used for estimating a blood pressure waveform. We believe that our results promote a noninvasive technique for clinical applications that overcomes the reproducibility problems of common carotid artery tonometry with technical and anatomical causes.

[Radial motion of the carotid artery wall: a block matching algorithm approach]

During recent years, evaluating the relation between mechanical properties of the arterial wall and cardiovascular diseases has been of great importance. On the other hand, motion estimation of the arterial wall using a sequence of noninvasive ultrasonic images and convenient processing methods might provide useful information related to biomechanical indexes and elastic properties of the arteries and assist doctors to discriminate between healthy and diseased arteries. In the present study, a block matching based algorithm was introduced to extract radial motion of the carotid artery wall during cardiac cycles. The program was implemented to the consecutive ultrasonic images of the common carotid artery of 10 healthy men and maximum and mean radial movement of the posterior wall of the artery was extracted. Manual measurements were carried out to validate the automatic method and results of two methods were compared. Paired t-test analysis showed no significant differences between the automatic and manual methods [P>0.05]. There was significant correlation between the changes in the instantaneous radial movement of the common carotid artery measured with the manual and automatic methods [with correlation coefficient 0.935 and P<0.05]. Results of the present study showed that by using a semi automated computer analysis method, with minimizing the user interfere and no attention to the user experience or skill, arterial wall motion in the radial direction can be extracted from consecutive ultrasonic frames.

Carotid artery wall motion estimation from consecutive ultrasonic images: comparison between block-matching and maximum-gradient algorithms

Radial movement of the arterial wall is a well-known indicator of the mechanical properties of arteries in arterial disease examinations. In the present study, two different motion estimation methods, based on the block-matching and maximum-gradient algorithms, were examined to extract the radial displacement of the carotid artery wall. Each program was separately implemented to the same axial consecutive ultrasound images of the carotid artery of 10 healthy men, and the radial displacement waveform of this artery was extracted during two cardiac cycles. The results of the two methods were compared using the linear regression and Bland-Altman statistical analyses. The maximum and mean displacements traced by the block-matching algorithm were compared with the same parameters traced by the maximum-gradient algorithm. The frame numbers in which the maximum displacement of the wall occurred were compared too. There were no significant differences between the maximum and the mean displacements traced by the block-matching algorithm and the same parameters traced by the maximum-gradient algorithm according to the pair t-test analysis [p value > 0.05]. There was a significant correlation between the radial movement of the common carotid artery measured with the block-matching and maximum-gradient methods [with a correlation coefficient of 0.89 and p value < 0.05]. The Bland-Altman analysis results confirmed a good agreement between the two methods in measuring the radial movement, with a mean difference and limits of agreement of 0.044 +/- 0.038. The results showed that both methods found the maximum displacement occurring in the same frame. Both block-matching and maximum-gradient algorithms can be used to extract the radial displacement of the carotid artery wall and in addition, with respect to the pixel size as error, the same results can be obtained