Hrovat Mirko, Kolandaivelu Aravindan, Wang Yifan, Gunderman Anthony, Halperin Henry R, Chen Yue, Schmidt Ehud J
Mirtech, Boston, MA, United States.
Medicine (Cardiology), Johns Hopkins University, Baltimore, MD, United States.
Front Med (Lausanne). 2024 Feb 13;11:1225848. doi: 10.3389/fmed.2024.1225848. eCollection 2024.
In the US, 1.4 million people have implanted ICDs for reducing the risk of sudden death due to ventricular arrhythmias. Cardiac MRI (cMR) is of particular interest in the ICD patient population as cMR is the optimal imaging modality for distinguishing cardiac conditions that predispose to sudden death, and it is the best method to plan and guide therapy. However, all ICDs contain a ferromagnetic transformer which imposes a large inhomogeneous magnetic field in sections of the heart, creating large image voids that can mask important pathology. A shim system was devised to resolve these ICD issues. A shim coil system (CSS) that corrects ICD artifacts over a user-selected Region-of-Interest (ROI), was constructed and validated.
A shim coil was constructed that can project a large magnetic field for distances of ~15 cm. The shim-coil can be positioned safely anywhere within the scanner bore. The CSS includes a cantilevered beam to hold the shim coil. Remotely controlled MR-conditional motors allow 2 mm-accuracy three-dimensional shim-coil position. The shim coil is located above the subjects and the imaging surface-coils. Interaction of the shim coil with the scanner's gradients was eliminated with an amplifier that is in a constant current mode. Coupling with the scanners' radio-frequency (rf) coils, was reduced with shielding, low-pass filters, and cable shield traps. Software, which utilizes magnetic field (B) mapping of the ICD inhomogeneity, computes the optimal location for the shim coil and its corrective current. ECG gated single- and multiple-cardiac-phase 2D GRE and SSFP sequences, as well as 3D ECG-gated respiratory-navigated IR-GRE (LGE) sequences were tested in phantoms and = 3 swine with overlaid ICDs.
With all cMR sequences, the system reduced artifacts from >100 ppm to <25 ppm inhomogeneity, which permitted imaging of the entire left ventricle in swine with ICD-related voids. Continuously acquired Gradient recalled echo or Steady State Free Precession images were used to interactively adjust the shim current and coil location.
The shim system reduced large field inhomogeneities due to implanted ICDs and corrected most ICD-related image distortions. Externally-controlled motorized translation of the shim coil simplified its utilization, supporting an efficient cardiac MRI workflow.
在美国，有140万人植入了植入式心律转复除颤器（ICD）以降低室性心律失常导致的猝死风险。心脏磁共振成像（cMR）在ICD患者群体中备受关注，因为cMR是区分易导致猝死的心脏疾病的最佳成像方式，也是规划和指导治疗的最佳方法。然而，所有ICD都包含一个铁磁变压器，它会在心脏部分区域施加一个大的不均匀磁场，产生大的图像空洞，可能掩盖重要病变。为此设计了一种匀场系统来解决这些ICD问题。构建并验证了一种能在用户选择的感兴趣区域（ROI）上校正ICD伪影的匀场线圈系统（CSS）。
构建了一个能在约15厘米距离内投射大磁场的匀场线圈。该匀场线圈可安全地放置在扫描 bore 内的任何位置。CSS包括一个用于固定匀场线圈的悬臂梁。远程控制的磁共振兼容电机可实现2毫米精度的三维匀场线圈定位。匀场线圈位于受试者和成像表面线圈上方。通过处于恒流模式的放大器消除了匀场线圈与扫描仪梯度的相互作用。通过屏蔽、低通滤波器和电缆屏蔽陷阱减少了与扫描仪射频（rf）线圈的耦合。利用ICD不均匀性的磁场（B）映射的软件计算匀场线圈的最佳位置及其校正电流。在体模和3头植入了ICD的猪身上测试了心电图门控的单心动周期和多心动周期二维梯度回波（GRE）和稳态自由进动（SSFP）序列，以及三维心电图门控呼吸导航反转恢复梯度回波（LGE）序列。
使用所有cMR序列时，该系统将伪影的不均匀性从>100 ppm降低到<25 ppm，这使得在有ICD相关空洞的猪身上能够对整个左心室进行成像。连续采集的梯度回波或稳态自由进动图像用于交互式调整匀场电流和线圈位置。
该匀场系统减少了因植入ICD导致的大场不均匀性，并校正了大多数与ICD相关的图像失真。匀场线圈的外部控制电动平移简化了其使用，支持高效的心脏MRI工作流程。
