The Study Of Biomechanical Characteristics Of Abdominal Aortic Aneurysm And Intraluminal Thrombus By Multiple Ultrasonic Technology

Background and purposeThe occurrence and development of Abdominal aortic aneurysm (Abdominal aortic aneurysm, AAA) result in many etiological factors related to genetics, environmental studies, biochemistry factors and so on. The exact pathogenesis is still being studied in. The incidence of AAA was becoming an increasing trend and the latest data shows that in the United States every year about 30,000 people dead of AAA rupture whose mortality rate was, as high as 90%, far more than the general cancer. The more effective early diagnosis and prediction of the rupture risks of AAA is become an urgent task. Two-dimensional color Doppler ultrasound (2D-CDUS) is a simple, non-invasive, low cost and high accuracy inspection technology. It can observe AAA's location, size, morphology, hemodynamics and hemorheology parameters in real-time. Two-dimensional speckle tracking imaging (2DSTI) is a new quantitative technology of ultrasound observing myocardium and blood vessel wall's velocity, strain, strain rate and other biomechanical parameters. The technology can more realistically and accurately reflect the movement of the organization because of its high time resolution, without being affected by the surrounding organization and non-angle dependent. In this study, we detected the AAA's physical structure, hemodynamic status, blood vessels bio-mechanical properties and thrombosis characteristics by using 2D-CDUS, M-mode ultrasound and 2DSTI technology. Compared the datas with that of the normal abdominal aorta in order to provide valuable ultrasound imaging information for the mechanical characteristics of AAA motion and local tissue characteristics of thrombus.Materials and Methods1. AAA Group: 19 cases were males and 7 females, aged 36 to 83 years, with an average 58±13.5 years of age. All patients underwent spiral CTA or magnetic resonance angiography (MRA) to confirm the diagnosis of the AAA.The tumor diameter were greater than 4.0cm and the largest diameter was up to 6.67cm.19 patients around the tumor cavity associated with thrombosis, four patients with multiple thrombus within the AAA, a total of 24 exploration and thrombosis. AAA tumor with cystic and spindle morphology mainly a small number of irregular shape. Normal group:come to my hospital examination of the healthy volunteers,30 cases,18 cases were males and 12 females, aged 29 to 73 years old, with an average 51±13.4 years of age. After physical examination, laboratory tests and imaging examination were excluded heart, brain, kidney and large blood vessels.2. Use Philips iE33 ultrasonic diagnostic apparatus for this study. Select the C5-2 probe (frequency 2.0～5.0 MHz) for the normal abdominal aorta and AAA to be performed 2D-CDUS, M-mode ultrasound examination and select S5-1 probe (frequency 1.0～5.0 MHz) for both groups' two-dimensional dynamic image acquisition. The analysis software was TMQA, ROI plug-in of off-line Qlab.3. M-mode ultrasound examination parameters:the diameter difference between peak systolic diameter and the smallest diastolic diameter(ΔD), wall displacement of middle and lower segment of abdominal aorta and the entrance, the largest tumor diameter and the export of AAA. Color Doppler and spectral Doppler detection method and parameters: Color Doppler showed intraluminal blood flow color, direction, filling degree of normal abdominal aorta and AAA to determine the nature of blood flow. Doppler spectral displayed and detected the peak systolic flow velocity (Vmax) of middle and lower segment of abdominal aorta and the entrance, the largest tumor diameter and the export of AAA.2DSTI detection method and parameters:Import three cardiac cycles' short-axis dynamic images of the lower normal abdominal aorta and the AAA's maximum tumor diameter into Qlab off-line workstation for analysis by using TMQA plug-in. The main measure indicators for each segment of the two parts were the maximum systolic radial displacement, peak time of radial displacement, maximum diastolic radial velocity, peak time of radial velocity, rate of the radial area change (FAC), peak radial strain (RSmax), peak radial strain rate (RSRmax), peak circumferential strain (CSmax) and peak circumferential strain rate (CSRmax). Analyze the FAC, RSmax, CSmax, and local torsion angle (RA) of the of the segment with thrombosis.Measure the the changes in echo intensity in a cardiac cycle at the part of thrombus adjacent to the tumor cavity, the middle of thrombus and adjacent to the AAA wall by using ROI plug-in.Results1. M-mode ultrasound results:Normal abdominal aorta anterior wall displacement was farther than posterior wall displacement. Every segment displacement value andΔD of middle abdominal aorta was larger than that of lower segment of abdominal aorta. The anterior and posterior wall displacement and AD were all negatively correlated to the age of the people in normal group. The AAA's posterior wall motion values were all smaller than the anterior wall's. The displacement at the entrance and the export were farther than that of at the largest tumor diameter. Compared the normal group with the AAA group, the latter's anterior and posterior wall displacement values were both smaller than the former's.2. Color Doppler and spectral Doppler results: Color Doppler showed a single red laminar flow within the normal abdominal aorta which was bright red, full of the lumen and showed regular red "flash" blood flow signal in a cardiac cycle. When the color blood flow velocity gauge was low, the lower segment of abdominal aorta in each cardiac cycle could present as "red-blue-red" rapidly flashes of blood flow signal. The blood flow signals in AAA were combined red and blue color blood flow signals and the direction of blood flow was disorders. The color blood flow signals was faint in some larger aneurysms which were poor filling. Swirling vortex signs appeared in the AAA and color blood flow signal was defects at the thrombosis. Spectral Doppler showed the middle abdominal aorta blood flow spectrum band was slightly wider than lower segment of abdominal aorta and the middle segment had a certain degree of forward flow signals in diastole. Abdominal aortic lower segment's systolic flow spectrum was steep and there was a reverse wave in early diastole. The blood flow Vmax values of middle abdominal aorta were greater than the lower segment. AAA group's spectral Doppler blood flow velocity decreased significantly and appeared positive or negative bi-directional flow spectrum throughout the whole cardiac cycle. There was noticeable negative blood flow spectrum in some tumor cavity during the diastole. Compared to the entrance's Vmax, the other position's Vmax was lower and the export's Vmax was higher than that of middle of AAA's cavity. Except the export, the Vmax of AAA's each part was lower than that of normal abdominal aorta lower segment.3. 2DSTI results: The normal abdominal aortic anterior peak systolic radial displacement was larger than the remaining segments and the remaining segment displacement was no significant difference between them.2DSTI The anterior and posterior wall displacement of normal abdominal aorta was no significant difference detected by M-mode ultrasound and 2DSTI. Each segment of normal abdominal aorta was no significant difference between their diastolic maximum radial velocities. The time to peak radial displacement and velocity and the direction of motion of every segment were basically the same. Radial area curves showed that the radial area changed significantly in systolic period and the curve appeared steep. The radial area changed relatively slightly and regularly in diastolic period and the curve's slope was smaller. There was no significant difference at RSmax, RSRmax, CSmax and CSRmax between each segment of lower normal abdominal aorta. The three segments'values of anterior were slightly larger than that of the posterior wall'. The RSmax, RSRmax respectively were larger than the CSmax, CSRmax of each segment. Segmental RSmax, RSRmax were positively correlated to its radial peak velocity. RSmax and CSmax were negatively correlated the people's age.AAA maximum tumor diameter at each segment of systolic radial displacement curve of the relative normal displacement curve significantly slowed some segments displacement curve almost flat, and some segments have even reverse movement. The same time, diastolic maximum radial velocity curve of the relative normal velocity curve has the same slowed the trend of lower peak, the curve slope significantly smaller.The curve slope of AAA's each segment peak systolic radial displacement was significantly lower than that of the normal group's. Part of the curve was lank and some were inversion between the segments. Meanwhile, the curve of diastolic peak radial velocity was less steep than the normal group. The AAA's segmental peak systolic radial displacement was significantly smaller than the normal group's and peak diastolic radial velocity was lower than that of normal abdominal aorta. Velocity and displacement curve of each segment was apparently messy and irregular distribution and some segment's movement direction was disordered. AAA Group's segmental time to peak velocity and peak displacement was longer than the normal group. Time to peak values of posterior wall's segments was significantly shorter than the anterior wall's segments'. Compared to the normal group radial area changes, AAA group's FAC was significantly reduced. The RSmax, RSRmax, CSmax and CSRmax of AAA's every segment were smaller than the normal abdominal aorta's, especially the RSmax and RSRmax.AAA peak systolic diameter was positively related to the peak diastolic thickness of thrombosis. The values of thrombus echo intensity changes during the whole cardiac ordered from the largest to the smallest respectively were the adjacent to the tumor cavity thrombus values, the middle of thrombus values and the adjacent to the AAA wall thrombus values. The FAC was bigger with thrombosis of the border than with AAA wall boundary. With tumor thrombus surface of the boundary were larger than with AAA wall boundary at RSmax, CSmax and RA, particularly at RSmax.Conclusion1. 2DSTI technology is feasible on local segmental motion detection of abdominal aorta and AAA. It combines with 2D-CDUS and M-mode ultrasound to provide valuable imaging information for AAA research and make a good basis for mechanism study of its formation and rupture. ROI which is also known as the original data analysis technique is a new technology for AAA intraluminal thrombus detection. It can be used to quantitatively determine the thrombosis echo intensity to provide some information on their pathological conditions. This technique has an important clinical value for AAA follow-up.2. The anterior wall displacement of the normal abdominal aorta is larger than the posterior wall, which due to the special nature of abdominal aortic anatomical position. As a result of abdominal aorta lower segment's special anatomical position, blood supply distribution nature and the composition of the vascular wall, the anterior and posterior wall displacement and peak systolic blood flow velocity of lower segment of abdominal aorta are both less than the middle of the abdominal aorta. Normal abdominal aorta wall displacement, difference between peak systolic diameter and smallest diastolic diameter and peak strain all decrease with increases of the people's age, which indicates that with age increasing abdominal aortic wall elasticity and resilience both go down. In the young and the elderly, the latter is the high risk of AAA occurs.3. AAA's anterior and posterior wall displacement at its entrance, the largest tumor diameter and the export are all less than the normal abdominal aorta wall displacement, especially at the largest tumor diameter. The wall displacement, velocity, FAC, strain, strain rate of the AAA are smaller than normal abdominal aorta wall and the time to peak values prolongs. The local segments of AAA are incongruous at the time to peak values. All of these are associated with wall stiffness and decreased compliance which caused by intimae atherosclerosis, elastic fibers and collagen fibers decline in the proportion. It is also related to the changes in blood flow patterns and the different compliance of the segments which due to the various wall thickness, the different content of smooth muscle cells in the membrane and declinable blood pressure on the wall.4. The values of FAC, CSmax and RSmax measured with the boundary of thrombus are larger than with the boundary of AAA wall, which indicates that thrombosis withstand a certain degree of blood impact to AAA wall.