Department of Radiation Oncology, University Hospital Heidelberg, Heidelberg, Germany.
National Center for Radiation Research in Oncology (NCRO), Heidelberg Institute for Radiation Oncology (HIRO), Heidelberg, Germany.
Phys Med Biol. 2024 Sep 13;69(18). doi: 10.1088/1361-6560/ad7453.
Magnetic resonance (MR) images free of artefacts are of pivotal importance for MR-guided ion radiotherapy. This study investigates MR image quality for simultaneous irradiation in an experimental setup using phantom imaging as well asimaging. Observed artefacts are described within the study and their cause is investigated with the goal to find conclusions and solutions for potential future hybrid devices.An open MR scanner with a field strength of 0.25 T has been installed in front of an ion beamline. Simultaneous magnetic resonance imaging and irradiation using raster scanning were performed to analyze image quality in dedicated phantoms. Magnetic field measurements were performed to assist the explanation of observed artifacts. In addition,images were acquired by operating the magnets for beam scanning without transporting a beam.The additional frequency component within the isocenter caused by the fringe field of the horizontal beam scanning magnet correlates with the amplitude and frequency of the scanning magnet steering and can cause ghosting artifacts in the images. These are amplified with high currents and fast operating of the scanning magnet. Applying a real-time capable pulse sequencerevealed no ghosting artifacts despite a continuously changing current pattern and a clinical treatment plan activation scheme, suggesting that the use of fast imaging is beneficial for the aim of creating high quality in-beam MR images. This result suggests, that the influence of the scanning magnets on the MR acquisition might be of negligible importance and does not need further measures like extensive magnetic shielding of the scanning magnets.Our study delimited artefacts observed in MR images acquired during simultaneous raster scanning ion beam irradiation. The application of a fast pulse sequence showed no image artefacts and holds the potential that online MR imaging in future hybrid devices might be feasible.
磁共振（MR）图像无伪影对于 MR 引导离子放射治疗至关重要。本研究通过体模成像和成像实验研究了在实验设置中同时照射时的 MR 图像质量。在研究中描述了观察到的伪影，并研究了其原因，旨在为潜在的未来混合设备找到结论和解决方案。在离子束线前安装了一台场强为 0.25 T 的开放式磁共振扫描仪。使用光栅扫描进行了同时磁共振成像和照射，以分析专用体模中的图像质量。进行了磁场测量以协助解释观察到的伪影。此外，在不传输射束的情况下操作磁铁进行束扫描时获取了图像。由水平束扫描磁铁的边缘场引起的等中心内的附加频率分量与扫描磁铁转向的幅度和频率相关，并且可以在图像中引起重像伪影。这些伪影随着电流的增加和扫描磁铁的快速操作而放大。尽管电流模式不断变化并且激活了临床治疗计划激活方案，但应用实时能力的脉冲序列显示没有重像伪影，这表明使用快速成像有利于创建高质量的射束内 MR 图像。这一结果表明，扫描磁铁对 MR 采集的影响可能可以忽略不计，并且不需要进一步的措施，例如对扫描磁铁进行广泛的磁屏蔽。我们的研究限定了在同时进行光栅扫描离子束照射期间获取的 MR 图像中观察到的伪影。快速脉冲序列的应用没有图像伪影，并且有可能在未来的混合设备中实现在线 MR 成像。
