Piecewise Pulse Wave Imaging (pPWI) for Detection and Monitoring of Focal Vascular Disease in Murine Aortas and Carotids In Vivo

Abstract

Atherosclerosis and Abdominal Aortic Aneurysms (AAAs) are two of the most common vascular diseases. Current clinical criteria in monitoring and risk assessment of these diseases exhibit profound weaknesses. Since both diseases are associated with mechanical changes in the arterial wall, Pulse Wave Imaging (PWI), a technique developed by our group to assess and quantify the mechanical properties of the aortic wall in vivo, may provide valuable diagnostic information. However, using PWI to acquire a single regional Pulse Wave Velocity (PWV) value of the entire imaged section of the diseased artery would not provide sufficiently localized information on the pathology. Hence, the implementation of piecewise Pulse Wave Imaging (pPWI) aims at addressing the issue of focal vascular disease. The feasibility of this novel technique is tested on murine normal, aneurysmal and atherosclerotic arteries in order to assess its effectiveness in monitoring each disease. Sub-regional PWVs were then estimated within 2-4 mm segments along the length of the arterial wall and estimates of the local stiffness of each segment referred to as local PWI Modulus (EPWI) values were calculated using the Moens-Korteweg equation. Stiffness maps were constructed for each case and provided localized spatial information on sub-regional PWV and EPWI measurements. Overall stiffness was found to increase in the atherosclerotic cases. The mean sub-regional PWV was found to be 2.57±0.18 m/s for the normal aortas (n = 7) with a corresponding mean EPWI of 43.82±5.86 kPa. A significant increase (p ≤ 0.001) in the group means of the sub-regional PWVs was found between the normal aortas and the aortas of mice on high-fat diet for 20 (3.30±0.36 m/s) and 30 weeks (3.56±0.29 m/s). The mean of the sub-regional PWVs (1.57±0.78 m/s) and EPWI values (19.23±15.47 kPa) decreased significantly in the aneurysmal aortas (p ≤ 0.05). Furthermore, the mean coefficient of determination (r2) of the normal aortas was significantly higher (p ≤ 0.05) than those of the aneurysmal and atherosclerotic cases. These results demonstrated that pPWI may be able to provide useful biomarkers for monitoring focal vascular diseases.

Pulse wave imaging using coherent compounding in a phantom andin vivo

“…In order to address this issue, our group has developed Pulse Wave Imaging (PWI), an ultrasound-based noninvasive technique that provides estimates of the regional PWV with the accompanying r 2 measurement quality indicator [14], [15]. This technique has recently been extended into piecewise PWI (pPWI) to achieve better resolution, on the scale of a few millimeters of arterial vessel length [16]. One of the main advantages of PWI compared to other MRI- and ultrasound-based techniques that have been developed to provide regional PWV estimates [17], [18], [19], [20], is that it visualizes the propagation of the pulse wave at extremely high temporal and spatial resolutions.…”

“…Consequently, various features of the propagation can be characterized and used to diagnose vascular disease [21]. Additionally, estimating the PWVs within small sections of the imaged artery allows spatial maps of PWV and PWI modulus maps, which represent a relative metric of stiffness and can be used to detect and monitor atherosclerosis and AAAs [16]. …”

In vivo repeatability of the pulse wave inverse problem in human carotid arteries

“…RF signals were reconstructed from channel data acquired from a longitudinal view of the common carotid artery, approximately 20mm below the carotid bifurcation. Plane wave compounding with 5 beam steering angles (−3°,−1.5°,0°,1.5°,3°) was implemented to improve image quality while maintaining a very high frame rate of approximately 2000 frames/s (Apostolakis et al 2016b). The carotid bifurcation was marked on the neck before imaging, and the distance between the end of the probe and the bifurcation was measured for each subject, as illustrated in figure 1.…”

Detecting Regional Stiffness Changes in Aortic Aneurysmal Geometries Using Pressure-Normalized Strain

“…To avoid the need for blood pressure measurement, some authors have advocated the use of pulse wave imaging (PWI) to directly measure tissue modulus from the Moens–Korteweg equation (Cloonan et al 2014; Luo et al 2009; Vappou et al 2010). PWI has been validated in a series of FE modeling, vessel phantom and animal and human clinical feasibility studies (Apostolakis et al 2016; Cloonan et al 2014; Li et al 2013; Luo et al 2009; Shahmirzadi and Konofagou 2012). Although PWI can provide accurate measures of in vivo tissue stiffness, one of the greatest limitations of PWI is the degradation of the measurement second to pulse wave reflections at inclusion bodies and branch points, as well as variations in wall thickness, luminal radius and assumptions of tissue density (Apostolakis et al 2016; McGarry et al 2016; Shahmirzadi and Konofagou 2012).…”

“…PWI has been validated in a series of FE modeling, vessel phantom and animal and human clinical feasibility studies (Apostolakis et al 2016; Cloonan et al 2014; Li et al 2013; Luo et al 2009; Shahmirzadi and Konofagou 2012). Although PWI can provide accurate measures of in vivo tissue stiffness, one of the greatest limitations of PWI is the degradation of the measurement second to pulse wave reflections at inclusion bodies and branch points, as well as variations in wall thickness, luminal radius and assumptions of tissue density (Apostolakis et al 2016; McGarry et al 2016; Shahmirzadi and Konofagou 2012). As with previous techniques, PWI is also limited in its assumption of simplistic axisymmetric homogenous geometries, which negatively bias results in complicated aneurysm geometries and locations of wave reflections.…”