A robust local pulse wave imaging method based on digital image processing techniques

The original diameter velocity loop method (ln(D)U-loop) cannot accurately extract the blood vessel diameter waveform when the quality of ultrasound image data is not high (such as obesity, age, and the operation of the ultrasound doctor), so it is unable to measure the pulse wave velocity (PWV) of the ascending aorta. This study proposes a diameter waveform extraction method combining threshold, gradient filtering, and the center of gravity method. At the same time, the linear regression method of searching for the rising point of the systolic period is replaced by the optimal average of two linear regression methods. This method can also extract the diameter waveform with poor-quality images and obtain a more accurate PWV. In vivo experimental data from 17 (age 60.5 ± 9.2) elderly patients with cerebral infarction and 12 (age 32.5 ± 5.6) healthy young adults were used for processing, and the results showed that the mean PWV using the ln(D)U-loop method was 12.56 (SD = 3.47) ms-1 for patients with cerebral infarction and 6.81 (SD = 1.73) ms-1 for healthy young adults. The PWV results based on the Wilcoxon rank-sum test and calculated based on the improved ln(D)U-loop method were both statistically significant (p < 0.01). The agreement analysis (Bland-Altman analysis) between the QA-loop and ln(D)U-loop methods showed that the mean deviation of the measured PWV was 0.07 m/s and the standard deviation of the deviation was 1.18 m/s. The experimental results demonstrated the effectiveness of the improved ln(D)U-loop method proposed in this paper on poor-quality images. This study can improve the possibility of the ln(D)U-loop method being widely used in the clinical measurement of ascending aortic PWV.