Kardoulaki Evdokia M, Syms Richard R A, Young Ian R, Choonee Kaushal, Rea Marc, Gedroyc Wladyslaw M W
Department of Electrical and Electronic Engineering, Imperial College London, London SW7 2AZ, United Kingdom.
Department of Radiology, Imperial College Healthcare NHS Trust, Paddington, London W2 1NY, United Kingdom.
Med Phys. 2015 Mar;42(3):1389-97. doi: 10.1118/1.4908225.
Flexible microcoils integrated with ablation catheters can improve the temperature accuracy during local MR-thermometry in Nd:YAG laser interstitial thermal therapies. Here, the authors are concerned with obtaining a preliminary confirmation of the clinical utility of the modified catheter. They investigate whether the thin-film substrate and copper tracks of the printed coil inductor affect the symmetry of the thermal profile, and hence of the lesion produced.
Transmission spectroscopy in the near infrared was performed to test for the attenuation at 1064 nm through the 25 μm thick Kapton substrate of the microcoil. The radial transmission profile of an infrared high-power, light emitting diode with >80% normalized power at 1064 nm was measured through a cross section of the modified applicator to assess the impact of the copper inductor on the optical profile. The measurements were performed in air, as well as with the applicator surrounded by two types of scattering media; crystals of NaCl and a layer of liver-mimicking gel phantom. A numerical model based on Huygens-Fresnel principle and finite element simulations, using a commercially available package (COMSOL Multiphysics), were employed to compare with the optical measurements. The impact of the modified optical profile on the thermal symmetry was assessed by examining the high resolution microcoil derived thermal maps from a Nd:YAG laser ablation performed on a liver-mimicking gel phantom.
Less than 30% attenuation through the Kapton film was verified. Shadowing behind the copper tracks was observed in air and the measured radial irradiation correlated well with the diffraction pattern calculated numerically using the Huygens-Fresnel principle. Both optical experiments and simulations, demonstrate that shadowing is mitigated by the scattering properties of a turbid medium. The microcoil derived thermal maps at the end of a Nd:YAG laser ablation performed on a gel phantom in a 3 T scanner confirm that the modified irradiation pattern does not disrupt the thermal symmetry, even though, unlike tissue, the gel is minimally scattering.
The results from this initial assessment indicate that microcoils can be safely integrated with ablation catheters and ensure that the complete necrosis of the liver tumor can still be achieved.
与消融导管集成的柔性微线圈可提高钕：钇铝石榴石激光间质热疗中局部磁共振测温期间的温度准确性。在此，作者关注获得改良导管临床效用的初步确认。他们研究印刷线圈电感器的薄膜基板和铜迹线是否会影响热分布的对称性，进而影响所产生病变的对称性。
进行近红外透射光谱分析，以测试通过微线圈25μm厚的聚酰亚胺基板在1064nm处的衰减。通过改良施源器的横截面测量在1064nm处归一化功率>80%的红外高功率发光二极管的径向透射分布，以评估铜电感器对光学分布的影响。测量在空气中进行，以及施源器被两种散射介质包围时进行；氯化钠晶体和一层仿肝凝胶体模。使用商业软件包（COMSOL Multiphysics）基于惠更斯 - 菲涅耳原理和有限元模拟的数值模型，用于与光学测量结果进行比较。通过检查在仿肝凝胶体模上进行的钕：钇铝石榴石激光消融得到的高分辨率微线圈热图，评估改良光学分布对热对称性的影响。
验证了通过聚酰亚胺薄膜的衰减小于３０％。在空气中观察到铜迹线后方的阴影，并且测量的径向辐照度与使用惠更斯 - 菲涅耳原理数值计算的衍射图案良好相关。光学实验和模拟均表明，浑浊介质散射特性可减轻阴影。在3T扫描仪中对凝胶体模进行钕：钇铝石榴石激光消融结束时，微线圈热图证实，即使与组织不同，凝胶的散射极小，改良的辐照模式也不会破坏热对称性。
该初步评估结果表明，微线圈可安全地与消融导管集成，并确保仍可实现肝肿瘤的完全坏死。
