Thompson R S, Wilson L S
School of Mathematics and Statistics, University of Sydney, NSW, Australia.
Ultrasound Med Biol. 1996;22(6):719-34. doi: 10.1016/0301-5629(96)00047-6.
The intravascular insonation of a blood vessel in the presence of an impedance interface between blood and the inner vessel wall is studied theoretically. The model, which uses a ray approximation, is three dimensional and allows consideration of arbitrary noncircular lumen shapes. Model results are presented for the image geometry, and the insonating intensity over the vessel wall. It is shown that the inner lumen can be imaged accurately with the transducer at any position within the lumen, and at any forward viewing angle, provided the point of origin of the beam is stationary. If it is not stationary but rotating with the same angular velocity as the beam itself, the inner vessel wall is not mapped accurately. A particular geometric distortion which has been observed in practice is predicted if the transducer is near vessel wall. Acoustic impedance interfaces will be encountered in vascular disease because the speed of sound in fatty plaque is less than in blood, whereas the speed of sound in fibrous and calcified plaque is greater than in blood. A simplified model representation of an atherosclerotic lumen in developed using a cardioid-like curve and a single impedance interface. Model results show that refraction at this interface leads to an intensity distribution which is not uniform around the lumen, and which depends on lumen shape and transducer position. The exception is the special case of a circular lumen with a centrally positioned transducer. Noncircular impedance interfaces encountered in vivo in vascular disease may cause considerable intensity distortion, particularly if the transducer is close to the wall in an irregularly shaped lumen.
本文从理论上研究了在血液与血管内壁之间存在阻抗界面的情况下，对血管进行血管内超声检查的情况。该模型采用射线近似法，为三维模型，可考虑任意非圆形管腔形状。给出了图像几何形状以及血管壁上超声强度的模型结果。结果表明，只要波束的原点固定，换能器在管腔内的任何位置以及任何前视角度下，都能准确成像管腔内情况。如果波束原点不固定，而是以与波束本身相同的角速度旋转，则无法准确绘制血管内壁图像。如果换能器靠近血管壁，预计会出现一种在实际中观察到的特定几何畸变。在血管疾病中会遇到声阻抗界面，因为脂肪斑块中的声速小于血液中的声速，而纤维和钙化斑块中的声速大于血液中的声速。使用类似心形曲线和单个阻抗界面建立了动脉粥样硬化管腔的简化模型表示。模型结果表明，该界面处的折射会导致强度分布在管腔周围不均匀，且取决于管腔形状和换能器位置。圆形管腔且换能器位于中心位置的特殊情况除外。在血管疾病体内遇到的非圆形阻抗界面可能会导致相当大的强度畸变，特别是当换能器在形状不规则的管腔中靠近管壁时。
