Study on the Relationship between Reduced Scattering Coefficient and Young's Modulus in Microwave Ablation

Abstract

Background and objective: Due to the conspicuous curative effect, minimally invasive, small side effects and low complications, microwave ablation (MWA) is considered as another effective method for the treatment of malignant tumors besides surgical excision, chemotherapy, radiotherapy and immunotherapy. This therapy has played a huge role in clinical cancer treatment [1,2], and has been widely used in treating liver cancer [3-5], lung cancer [6,7], kidney cancer [8], thyroid cancer [9], and other common tumors. In the current clinical treatment of tumors using MWA, although temperature can be used as an important reference index for evaluating the curative effect of ablation, it cannot fully reflect the biological activity status of tumor tissue during thermal ablation. Finding multi-parameter comprehensive evaluation factors to achieve real-time evaluation of therapeutic effects has become the key for precise ablation [10-14]. More and more scholars use the reduced scattering coefficient (μ_s^') and Young's modulus (E) to evaluate the treatment outcomes of MWA. However, the intrinsic relationship between these parameters is unclear. It is necessary and valuable to investigate the specific relationship between μ_s^' and E during MWA.
Material and methods: The MWA experiment was conducted on porcine liver in vitro, the two-parameter simultaneous acquisition system was designed to obtain the reduced scattering coefficient and Young's modulus of the liver tissue during MWA (Figure 1). In the experiment, different levels of ablation power were used, namely, 50 W, 60 W, and 70 W, and different ablation duration were used, namely, 3 minutes, 5 minutes, and 8 minutes. In addition, the distance between the fiber optic probe and the microwave ablation antenna also varied from 0.2 cm, 0.5 cm, 1 cm, and to 1.5 cm, respectively. Different combinations of ablation power, ablation duration, fiber optic probe and the microwave ablation antenna distance were use in the experiment. The relationship between reduced scattering coefficient and Young's modulus was investigated.
Results: It can be found that with the increase of ablation duration at the fixed power, the Young's modulus gradually becomes larger at some regions as shown in the 2D shear wave image, which is characterized by color turning from blue to red, and the effective region is roughly elliptical(Figure 2). The effective region of the 2D shear wave image is gradually enlarging, and the average Young's modulus in the effective region is also increasing. More areas turning to red in the effective region in the shear wave image indicates that the tissue hardness is gradually expanding. It is also found that the trend of change of μ_s^' is very similar to E in the process of MWA, that is, first increasing and then reaching a steady state(Figure 3), and in some experiments, there are synchronous changes(Figure 4). Based on this, the quantitative correlation model between E-μ_s^' is established, enabling the estimation of Young's modulus of liver tissue based on reduced scattering coefficient. The maximum absolute error is 29.37 kPa and the minimum absolute error is 0.88 kPa. Conclusion: An effective E-μ_s^' correlation model is proposed. The corresponding Young's modulus’ average value can be calculated based on the reduced scattering coefficient under different states of ablation. The reduced scattering coefficient and Young's modulus of the liver tissue in the normal zone, transition zone, and coagulation zone are different, and the changes of μ_(s )^'and E are closely related to the degree of tissue thermal damage. This study contributes to the further establishment of multi-parameter MWA effectiveness evaluation model. It is also valuable for clinically evaluating the ablation outcomes of tumor in real time.
REFERENCES
[1] Dou J P, Liang P, Yu J. Microwave ablation for liver tumors. Abdom Radiol. 2016, 41(4):650-658.
[2] Wells S A, Hinshaw J L, Lubner M G, et al. Liver Ablation: Best Practice[J]. Radiol Clin North Am. 2015, 53(5):933-971.
[3] Ryu T, Takami Y, Wada Y, Wada Y, et al. Oncological outcomes after hepatic resection and/or surgical MWA for liver metastasis from gastric cancer. Asian Journal of Surgery. 2019, 42(1):100-105.
[4] De Cobelli F, Marra P, Ratti F, et al. Microwave ablation of liver malignancies: comparison of effects and early outcomes of percutaneous and intraoperative approaches with different liver conditions. Med Oncol, 2017, 34(4):49.
[5] Meloni M F, Chiang J, Laeseke P F, et al. Microwave ablation in primary and secondary liver tumours: technical and clinical approaches. Int J Hyperthermia. 2016, 33(1):15-24.
[6] Alhakim R A, Abtin F G, Genshaft S J, et al. Defining new metrics in microwave ablation of pulmonary tumors: ablation work and ablation resistance score. J Vasc Interv Radiol, 2016, 27(9):1380-1386.
[7] Vogl T J, Roman A, Nour Eldin N E A, et al. A comparison between 915 MHz and 2450 MHz microwave ablation systems for the treatment of small diameter lung metastases. Diagn Interv Radiol. 2018, 24(1):31-37.
[8] Cornelis F H, Marcelin C, Bernhard J C. Microwave ablation of renal tumors: A narrative review of technical considerations and clinical results. Diagn Interv Radiol. 2017, 98(4):287-297.
[9] Yue W, Wang S, Yu S, et al. Ultrasound-guided percutaneous microwave ablation of solitary T1N0M0 papillary thyroid microcarcinoma: Initial experience. Int J Hyperthermia. 2014, 30(2):150-157.
[10] Hu G, Qian Z, Ding S, et al. Study on the effective ablation volume of MWA of porcine livers. Photonics Lasers Med. 2013, 2(3):241-247.
[11] Zhao J, Qian Z, Liu J, et al. Real-time assessment of microwave ablation efficacy by nir spectroscopic technique. J Innov Opt Health Sci., 2014, 7(1):1350053.
[12] Zhao J, Zhao Q, Jiang Y, et al. Feasibility study of modeling liver thermal damage using minimally invasive optical method adequate for in situ measurement. J Biophotonics. 2018:e201700302.
[13] Bo X W, Li X L, Xu H X, et al. 2D shear-wave ultrasound elastography (SWE) evaluation of ablation zone following radiofrequency ablation of liver lesions: is it more accurate?. Br J Radiol. 2016, 89(1060):20150852.
[14] Sugimoto K, Oshiro H, Ogawa S, et al. Radiologic-pathologic correlation of three-dimensional shear-wave elastographic findings in assessing the liver ablation volume after radiofrequency ablation. World J Gastroenterol. 2014, 20(33):11850-11855.

Speaker

Zhiyu Qian
Department of Biomedical Engineering, Nanjing University of Aeronautics and Astronautics
China

Discussion

Ask question