Present study deals with improvement in conventional technique of spraying liquid nitrogen on cancerous lesions to improve its efficacy. It is an attempt to demarcate the variation in outcome when cryogen is sprayed through customised multi-hole nozzle (MHN). Influence of mass flow rate on cryoablation while varying the number of holes in MHNs is analysed experimentally. Another section of the study focuses on impact of the rate of evaporation of cryogen when margin among the holes is changed. Total 6 MHNs are fabricated while changing their geometrical parameters. Single freeze-thaw cycle is carried out to spray liquid nitrogen on tissue mimicking gel with a spraying distance of 18 mm. Temperature profile captured through infrared images advocates that lethal area formed through the application of MHNs with 5 holes is larger than MHNs with 4 holes on the surface of gel. It reflects the influence of central hole on necrosis. In order to necrotize lesion through freezing, the most desired cooling rate (CR) varies from 50∘C/min to 200∘C/min. It is achieved up to a depth of 2 mm below the gel surface and in a radius of 10 mm from the centre of spray (CS) for all MHNs, except 4C. Most optimised margin in terms of cryoablation is also estimated in the study. MHN with 1.5 mm margin provides the most optimised results in terms of cryoablation when MHNs with the central hole are considered while MHN with 1 mm margin provides most optimised result when MHNs without central hole are considered. On the basis of observations made through thermal images it can be said that multiple freezing fronts are not observed on the gel surface which aids in the formation of lone giant ice ball. This provides an extra edge to the treatment methodology because alteration in the dimensions of necrotic zone can be made by changing the duration of spray. Larger lateral spread of necrotic zone will also reduce the number of sittings required for the treatment of larger lesions.

中文翻译：

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冷冻喷雾中多孔喷嘴的性能表征

目前的研究涉及改进将液氮喷洒在癌性病变上的传统技术，以提高其疗效。当冷冻剂通过定制的多孔喷嘴 (MHN) 喷射时，试图区分结果的变化。实验分析了质量流速对冷冻消融的影响，同时改变了 MHN 中的孔数。研究的另一部分侧重于改变孔之间的边缘时冷冻剂蒸发速率的影响。在改变几何参数的同时制造了总共 6 个 MHN。进行单次冻融循环，将液氮喷洒在组织模拟凝胶上，喷洒距离为 18 mm。通过红外图像捕获的温度分布主张通过应用5孔MHNs形成的致死面积大于凝胶表面4孔MHNs。它反映了中心孔对坏死的影响。为了通过冷冻使病变坏死，最需要的冷却速率 (CR) 从 50∘C/min 到 200∘C/min 不等。对于所有 MHN，除 4C 外，它在凝胶表面下方 2 毫米的深度和距离喷雾中心 (CS) 10 毫米的半径内实现。研究中还估计了冷冻消融方面最优化的余量。当考虑具有中心孔的 MHN 时，具有 1.5 mm 余量的 MHN 在冷冻消融方面提供了最优化的结果，而在考虑没有中心孔的 MHN 时，具有 1 mm 余量的 MHN 提供了最优化的结果。根据通过热图像进行的观察，可以说在凝胶表面没有观察到多个冻结前沿，这有助于形成孤立的巨大冰球。这为治疗方法提供了额外的优势，因为可以通过改变喷雾持续时间来改变坏死区的尺寸。坏死区较大的横向扩散也将减少治疗较大病变所需的坐位次数。