Research on Cross-Sectional Imaging of Elasticity around Atherosclerotic Plaque with Transcutaneous Ultrasound

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The phased tracking method is unique in its extremely higher spatial and temporal resolution. This report shows the cross sectional image of the elasticity around the atherosclerotic plaque with this phase tracking method using transcutaneous ultrasound.The minimum value of the measurable velocity is 0.5 mm/s and the time interval, ΔT, of integration is 222 μs. In this condition, the lowest value of the change in thickness is found to be about 0.1μm in the measurements using a water tank. Such a minute change in thickness cannot be measured by CT, MRI, or standard ultrasonic diagnostic equipment.By presetting multiple points with equal intervals of 375 μm in the arterial wall at the R-wave of the ECG, and applying the above method to each point, the change in thickness in each layer between the succeeding points is determined. The change in thickness of each layer from that at the R-wave is then converted into color maps and displayed. By the proposed procedure described above, the elastic modulus E of the human carotid artery is noninvasively evaluated for the five layers along the ultrasonic beam.By modifying the method and system described above so that the elastic modulus of each local point in the arterial wall and the atherosclerotic plaque is determined by controlling the position of the ultrasonic beam. The results are then converted into another color map representing local elasticity in the cross sectional image. The regional elasticity is measured at each point along the ultrasonic beams at 30 positions along the axial direction of the artery. The resolution in the depth direction and axial direction is 375 μm and 0.98 mm, respectively. The atherosclerotic plaque has been characterized as the compliant material interior surrounded by much elastic material. With extrapolation of the results in an in vitro study, we interpreted the surrounding thin layer as the fibrous cap of the plaque.