Griffin Gregory H, Anderson Kevan J T, Celik Haydar, Wright Graham A
Department of Medical Biophysics, Faculty of Medicine, University of Toronto, Toronto, Canada.
Imaging Research, Sunnybrook Research Institute, Toronto, Canada.
Magn Reson Med. 2015 Jan;73(1):427-41. doi: 10.1002/mrm.25103. Epub 2014 Jan 22.
Many procedures involving catheters and implanted medical devices could benefit from MRI guidance but are currently contraindicated due to risk of significant heating near linear conductive structures. A priori safety prediction is impossible in vivo and thus, safety is typically investigated in vitro by directly measuring temperature rise. Existing methods of investigating safety are inflexible and provide few data. Furthermore, they are fundamentally limited because dangerous temperatures rises can only be investigated if induced. A method of remotely predicting safety is necessary for ensuring safety in patients.
Electric current induced on the metallic object causes any dangerous heating; thus a remote method of safely characterizing the induced radiofrequency (RF) current distribution would suffice to evaluate safety assuming conservative estimates for local tissue properties. Here we propose a method of analyzing induced phase artifacts seen in low-specific absorption rate characterization images, to determine induced current on an interventional device. This induced current distribution can then be used to predict RF heating behavior under application of any other imaging sequence.
This method has been successfully used to reproduce numerical simulations in a phantom. Furthermore, the heating behavior around a conductive wire produced by a scan other than that used to characterize current was successfully predicted.
It has been shown in phantom experiments that remote current characterization can safely prevent dangerous scans as well as enable safe scans that previously would not have been attempted.
许多涉及导管和植入式医疗设备的操作可受益于磁共振成像（MRI）引导，但目前由于线性导电结构附近存在显著发热风险而被列为禁忌。体内无法进行先验安全性预测，因此，安全性通常通过直接测量温度升高在体外进行研究。现有的安全性研究方法缺乏灵活性，提供的数据很少。此外，它们存在根本局限性，因为只有在诱发危险温度升高的情况下才能对其进行研究。需要一种远程预测安全性的方法来确保患者的安全。
金属物体上感应的电流会导致任何危险的发热；因此，假设对局部组织特性进行保守估计，一种安全表征感应射频（RF）电流分布的远程方法就足以评估安全性。在此，我们提出一种分析在低比吸收率表征图像中看到的感应相位伪影的方法，以确定介入设备上的感应电流。然后，这种感应电流分布可用于预测在应用任何其他成像序列时的RF加热行为。
该方法已成功用于在体模中重现数值模拟。此外，成功预测了由用于表征电流之外的扫描产生的导线周围的加热行为。
体模实验表明，远程电流表征可以安全地防止危险扫描，并实现以前不会尝试的安全扫描。
