Laboratory for Molecular and Functional Imaging: From Physiology to Therapy, FRE 3313 CNRS/University of Bordeaux 2, 33076 Bordeaux, France.
IEEE Trans Med Imaging. 2011 Oct;30(10):1737-45. doi: 10.1109/TMI.2011.2144615. Epub 2011 May 5.
Real time magnetic resonance imaging (MRI) is rapidly gaining importance in interventional therapies. An accurate motion estimation is required for mobile targets and can be conveniently addressed using an image registration algorithm. Since the adaptation of the control parameters of the algorithm depends on the application (targeted organ, location of the tumor, slice orientation, etc.), typically an individual calibration is required. However, the assessment of the estimated motion accuracy is difficult since the real target motion is unknown. In this paper, existing criteria based only on anatomical image similarity are demonstrated to be inadequate. A new criterion is introduced, which is based on the local magnetic field distribution. The proposed criterion was used to assess, during a preparative calibration step, the optimal configuration of an image registration algorithm derived from the Horn and Schunck method. The accuracy of the proposed method was evaluated in a moving phantom experiment, which allows the comparison with the known motion pattern and to an established criterion based on anatomical images. The usefulness of the method for the calibration of optical-flow based algorithms was also demonstrated in vivo under conditions similar to thermo-ablation for the abdomen of twelve volunteers. In average over all volunteers, a resulting displacement error of 1.5 mm was obtained (largest observed error equal to 4-5 mm) using a criterion based on anatomical image similarity. A better average accuracy of 1 mm was achieved using the proposed criterion (largest observed error equal to 2 mm). In both kidney and liver, the proposed criterion was shown to provide motion field accuracy in the range of the best achievable.
实时磁共振成像（MRI）在介入治疗中迅速得到重视。对于移动目标，需要进行准确的运动估计，这可以方便地使用图像配准算法来解决。由于算法的控制参数的调整取决于应用（靶向器官、肿瘤位置、切片方向等），通常需要进行单独的校准。然而，由于实际目标运动是未知的，因此评估估计运动的准确性是困难的。在本文中，证明了仅基于解剖图像相似性的现有标准是不充分的。引入了一种新的标准，它基于局部磁场分布。在预备校准步骤中，使用所提出的标准评估了源自 Horn 和 Schunck 方法的图像配准算法的最佳配置。在所提出的方法的准确性在移动体模实验中进行了评估，该实验允许与已知的运动模式和基于解剖图像的既定标准进行比较。该方法在类似于腹部热消融的条件下在十二位志愿者体内用于校准光流算法，这也证明了其有用性。在所有志愿者中，基于解剖图像相似性的标准获得了 1.5 毫米的位移误差（最大观察误差等于 4-5 毫米）。使用所提出的标准获得了更好的平均精度 1 毫米（最大观察误差等于 2 毫米）。在肾和肝中，所提出的标准被证明可以提供最佳可实现的运动场精度。
