Department of Radiotherapy, University Medical Center Utrecht, Heidelberglaan 100, 3584 CX, Utrecht, The Netherlands. Author to whom correspondence may be addressed.
Phys Med Biol. 2019 Apr 26;64(9):095006. doi: 10.1088/1361-6560/ab15ed.
For the purpose of magnetic resonance imaging (MRI) guidance of prostate high-dose-rate (HDR) brachytherapy, this paper presents a study on the potential of clinically relevant MRI sequences to facilitate tracking or localization of brachytherapy devices (HDR source/titanium needle), and which could simultaneously be used to visualize the anatomy. The tracking or localization involves simulation of the MRI artifact in combination with a template matching algorithm. Simulations of the MRI artifacts induced by an HDR brachytherapy source and a titanium needle were implemented for four types of sequences: spoiled gradient echo, spin echo, balanced steady-state free precession (bSSFP) and bSSFP with spectral attenuated inversion recovery (SPAIR) fat suppression. A phantom study was conducted in which mentioned sequences (in 2D) as well as the volumetric MRI sequences of the current clinical scan protocol were applied to obtain the induced MRI artifacts for an HDR source and a titanium needle. Localization of the objects was performed by a phase correlation based template matching algorithm. The simulated images demonstrated high correspondences with the acquired MR images, and allowed localization of the objects. A comparison between the object positions obtained for all applied MRI sequences showed deviations (from the average position) of 0.2-0.3 mm, proving that all MRI sequences were suitable for localization of the objects, irrespective of their 2D or volumetric nature. This study demonstrated that the MRI artifact induced by an HDR source or a titanium needle could be simulated for the four investigated types of MRI sequences (spoiled gradient echo, spin echo, bSSFP and bSSFP-SPAIR), valuable for real-time object localization in clinical practice. This leads to more flexibility in the choice of MRI sequences for guidance of HDR brachytherapy, as they are suitable for both object localization and anatomy visualization.
为了在磁共振成像（MRI）引导下进行前列腺高剂量率（HDR）近距离放射治疗，本文研究了临床相关 MRI 序列在追踪或定位近距离放射治疗设备（HDR 源/钛针）方面的潜力，这些序列同时可用于可视化解剖结构。这种追踪或定位涉及 MRI 伪影的模拟与模板匹配算法的结合。对 HDR 近距离放射治疗源和钛针引起的 MRI 伪影进行了模拟，涉及四种类型的序列：扰相梯度回波、自旋回波、平衡稳态自由进动（bSSFP）和带频谱衰减反转恢复（SPAIR）脂肪抑制的 bSSFP。进行了一项体模研究，在该研究中，应用了上述序列（二维）以及当前临床扫描方案的容积 MRI 序列，以获得 HDR 源和钛针的诱导 MRI 伪影。通过基于相位相关的模板匹配算法进行物体定位。模拟图像与采集的 MRI 图像具有高度的一致性，并且可以实现物体的定位。对所有应用的 MRI 序列获得的物体位置进行比较，结果显示位置偏差（与平均位置相比）为 0.2-0.3 毫米，证明所有 MRI 序列都适合于物体的定位，而与它们的二维或容积性质无关。这项研究表明，HDR 源或钛针引起的 MRI 伪影可以针对四种研究的 MRI 序列（扰相梯度回波、自旋回波、bSSFP 和 bSSFP-SPAIR）进行模拟，这对于临床实践中的实时物体定位非常有价值。这使得在 HDR 近距离放射治疗的引导中选择 MRI 序列更加灵活，因为它们既适合于物体定位，也适合于解剖结构可视化。
