Image: Fig. 1a and Fig. 1b depict the guided signals in the intact and fractured long bones, respectively. These images shows an (a) intact and (b) 1-mm width 100% depth fracture (Photo courtesy of Science China Press).
Research has revealed that mode conversion of ultrasonic-guided waves can quantitatively indicate the fracture degree of long cortical bone, which may provide a new way of evaluating long bone fracture and monitor healing.
This study was published July 24, 2014, in the journal SCIENCE CHINA Physica, Mechanica & Astronomica
. Prof. T.A. De-an, from School of Information Science and Technology at Fudan University (Shanghai, China) led the study, which quantitatively analyzed the impact of fracture width and depth on the amplitude of guided waves.
Bone fracture is a medical disorder in which bone discontinuity is created by stresses higher than the bone can bear. Statistical studies show that 5%–10% of the fractured patients are suffering healing complications. Fracture healing is a proliferative process, and full recovery can take up to three to five years. The pathology in the healing process is easily overlooked, leading to severe bone loss and secondary damage, impacting the physical condition of the patients. Therefore, early diagnosis of the healing problem is key to ensure the healing process. The accurate diagnosis and dynamic monitoring are essential for prompt treatment.
With the advantages of quantitative ultrasound (QUS), such as portability, inexpensive, and nonionizing radiation, ultrasonic guided waves can also detect the geometry of long cortical bone, (e.g., profile, thickness, and section) and measure the material parameters (e.g., BMD, porosity and Young’s modulus), which has attracted increasing attention. However, due to the little understood nature of ultrasound propagation in long cortical bones, ultrasonic-guided wave technology has not been widely applied to the clinical practice of the long bone fracture evaluation.
Numeric simulations are performed to analyze the guided waves propagation in the fractured long bone. The novelty of this study is the use of narrowband low-frequency ultrasound to avoid the multimode overlap. Only two fundamental guided modes, symmetric S0 and asymmetric A0, are excited, which simplifies the mode separation and quantitative determination. The impact of fracture width and depth on the amplitudes of each guided modes were quantitatively discussed in the article. The amplitude of the A0 mode is very sensitive to the width and depth variation. The ratio between the amplitudes of S0 and A0 is further proposed to be used in the evaluation of the fracture degree.
The mode conversion of the ultrasonic-guided waves can, therefore, characterize the changes in the fracture depth and fracture width and provide quantitative parameters fracture evaluation. The study may also be helpful to the ultrasound monitoring of long bone healing, according to the researchers.