Department of Clinical Physics, Royal London Hospital, 56-76, Ashfield Street, Whitechapel, London, UK.
Ultrasonics. 2014 Feb;54(2):428-41. doi: 10.1016/j.ultras.2013.04.015. Epub 2013 Apr 27.
This study aimed to utilise a tissue mimicking material (TMM) in order to embed in vitro carotid plaque tissue so that its acoustic properties could be assessed. Here, an International Electrotechnical Commission (IEC) agar-based TMM was adapted to a clear gel by removal of the particulates. This clear TMM was measured with sound speed at 1540 ms(-1) and an attenuation coefficient of 0.15 dB cm(-1)MHz(-1). Composite sound speed was then measured through the embedded material using a scanning acoustic microscope (SAM). Both broadband reflection and transmission techniques were performed on each plaque specimen in order to ensure the consistency of the measurement of sound speed, both at 21 °C and 37 °C. The plaque was measured at two temperatures to investigate any effect on the lipid content of the plaque. The contour maps from its associated attenuation plots were used to match the speed data to the photographic mask of the plaque outline. This physical matching was then used to derive the sound speed from the percentage composition seen in the histological data by solution of simultaneous equations. Individual speed values for five plaque components were derived; TMM, elastin, fibrous/collagen, calcification and lipid. The results for derived sound speed in the TMM were consistently close to the expected value of soft tissue, 1540 ms(-1). The fibrous tissue showed a mean value of 1584 ms(-1) at 37 °C. The derived sound speeds for elastic and lipid exhibited large inter-quartile ranges. The calcification had higher sound speed than the other plaque components at 1760-2000 ms(-1). The limitations here lay in the difficulties in the matching process caused by the inhomogeneity of the plaque material and shrinkage during the histological process. Future work may concentrate on more homogeneous material in order to derive sound speed data for separate components. Nevertheless, this study increases the known data ranges of the individual components within a plaque. This information may be used help to assess the mechanical properties and structural integrity and its associated vulnerability or risk of embolization in future diagnostic ultrasound techniques.
本研究旨在利用组织模拟材料（TMM）嵌入体外颈动脉斑块组织，以评估其声学特性。为此，将国际电工委员会（IEC）基于琼脂的 TMM 进行了改良，通过去除颗粒物质制成了透明凝胶。这种透明 TMM 的声速测量值为 1540ms(-1)，衰减系数为 0.15dBcm(-1)MHz(-1)。然后，使用扫描声学显微镜（SAM）通过嵌入材料测量复合声速。为了确保声速测量的一致性，对每个斑块标本均进行了宽带反射和透射技术测试，测量温度分别为 21°C 和 37°C。测量斑块的两个温度，以研究其脂质含量的任何影响。通过关联衰减图的等高线图，将速度数据与斑块轮廓的照相掩模匹配。然后，通过求解联立方程，将组织学数据中观察到的百分比组成用于声速的物理匹配。从五个斑块成分中得出了单个速度值：TMM、弹性蛋白、纤维/胶原、钙化和脂质。TMM 的导出声速结果始终接近软组织的预期值 1540ms(-1)。37°C 时纤维组织的平均声速为 1584ms(-1)。弹性和脂质的导出声速呈现出较大的四分位间距。钙化的声速高于其他斑块成分，为 1760-2000ms(-1)。这里的限制在于斑块材料的不均匀性和组织学过程中的收缩导致匹配过程中的困难。未来的工作可能集中在更均匀的材料上，以便为单独的成分推导声速数据。尽管如此，本研究增加了斑块内各个成分的已知数据范围。该信息可用于帮助评估未来诊断超声技术中的机械性能、结构完整性及其相关脆弱性或栓塞风险。
