Sunnybrook Research Institute, Sunnybrook Health Sciences Centre, 2075 Bayview Avenue, Toronto, ON, M4N 3M5, Canada. Department of Medical Biophysics, Faculty of Medicine, University of Toronto, 101 College Street Suite 15-701, Toronto, ON M5G 1L7, Canada. Author to whom any correspondence should be addressed.
Phys Med Biol. 2018 Jul 17;63(14):145017. doi: 10.1088/1361-6560/aacf75.
The simulation accuracy of transvertebral ultrasound propagation using a multi-layered ray acoustics model based on CT-derived vertebral geometry was investigated through comparison with experimental measurements of pressure fields in ex vivo human vertebral foramen. A spherically focused transducer (5 cm diameter, f-number 1.2, 514 kHz) was geometrically focused to the centre of individual thoracic vertebral foramen, through the posterior bony elements. Transducer propagation paths through the laminae and the spinous processes were tested. Simulation transducer-vertebra configurations were registered to experiment transducer-vertebra configurations, and simulation accuracy of the simulation model was evaluated for predicting maximum transmitted pressure to the canal, voxel pressure in the canal, and focal distortion. Accuracy in predicting maximum transmitted pressure was calculated by vertebra, and it is shown that simulation predicts maximum pressure with a greater degree of accuracy than a vertebra-specific insertion loss. Simulation error in voxel pressure was evaluated using root-mean-square error and cross-correlation, and found to be similar to the water-only case. Simulation accuracy in predicting focal distortion was evaluated by comparing experiment and simulation maximum pressure location and weighted >50% focal volume location. Average simulation error across all measurements and simulations in maximum pressure location and weighted >50% focal volume location were 2.3 mm and 1.5 mm, respectively. These errors are small relative to the dimensions of the transducer focus (4.9 mm full width half maximum), the spinal cord (10 mm diameter), and vertebral canal diameter (15-20 mm diameter). These results suggest that ray acoustics can be applied to simulating transvertebral ultrasound propagation.
基于 CT -derived 椎体几何形状的多层射线声学模型对经椎间孔超声传播的模拟精度进行了研究，通过与离体人椎间孔内压力场的实验测量结果进行了比较。一个球形聚焦换能器（直径 5cm，f-number 为 1.2，514kHz）通过后部骨性结构，在几何上聚焦到各个胸椎间孔的中心。测试了换能器在椎板和棘突中的传播路径。模拟换能器-椎体的配置与实验换能器-椎体的配置进行了配准，评估了模拟模型的模拟准确性，以预测对管腔的最大传输压力、管腔内的体素压力和焦点失真。通过椎体计算了预测最大传输压力的准确性，结果表明模拟比特定插入损耗更准确地预测最大压力。使用均方根误差和互相关评估了体素压力的模拟误差，发现与仅水的情况相似。通过比较实验和模拟的最大压力位置和加权 >50%焦点体积位置来评估模拟在预测焦点失真方面的准确性。在最大压力位置和加权 >50%焦点体积位置的所有测量和模拟的平均模拟误差分别为 2.3mm 和 1.5mm。这些误差相对于换能器焦点的尺寸（4.9mm 全宽半最大值）、脊髓（10mm 直径）和椎管直径（15-20mm 直径）较小。这些结果表明，射线声学可用于模拟经椎间孔超声传播。
