Normalization of magnetic resonance images and its application to the diagnosis of the scoliotic spine
Normalization of magnetic resonance images and its application to the diagnosis of the scoliotic spine
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磁共振图像标准化及其在脊柱侧凸诊断中的应用
DOI：
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发表时间：
2011
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通讯作者：
F. Jäger
中科院分区：
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作者：
F. Jäger
由于其出色的软组织对比度和新颖的创新采集序列，磁共振成像已成为医疗保健中最受欢迎的成像方式之一。然而，相关的采集伪影会显著降低图像质量。因此，这种缺陷会干扰对所获取图像的评估。在最坏的情况下，它们甚至可能导致医生做出错误的决定。此外，它们可能负面地影响数据的自动处理，例如，图像分割或配准。最常观察到的伪影是强度不均匀性和缺失的序列依赖性一般强度尺度。本文介绍了几种新的光强变化校正技术。在此基础上，我们展示了它们在临床应用中的优势。许多用于校正不均匀性的最先进的方法缺乏普遍性、效率或准确性。我们提出了新的方法，克服这些缺点，通过引入先验知识的目标函数和映射到一个分而治之的策略的优化过程。实验表明，我们可以提高约18.2%，而国家的最先进的方法只能达到11.6%的临床相关的三维血管造影组织类的平均分离度。新获取的图像的强度到一般强度尺度的映射必须保留图像的直方图的结构特征。此外，它必须是可逆的。因此，许多标准化方法估计相当粗略的强度变换。我们提出了几种与图像配准技术密切相关的标准化方法。这些方法计算等强度映射。此外，所提出的方法是唯一已知的进行联合标准化并且可以处理具有非常大视野的图像的方法。实验表明，我们的方法实现了约86.2%的T1w图像的主要组织类的平均强度重叠。最常用的最先进的方法导致只有70.1%的重叠。为了说明所提出的标准化技术的适用性和重要性，我们介绍了一个系统的计算机辅助评估脊柱侧凸的异常。它是基于使用马尔可夫随机场理论的脊髓分割。从预处理到结果的可视化，所有需要的步骤都被提出。为了评估该系统，我们使用自动计算的平面之间的角度通过椎骨和平面估计的医学专家。这导致小于六度的平均角度差足够精确以适用于临床环境。
Due to its excellent soft tissue contrast and novel innovative acquisition sequences, Magnetic Resonance Imaging has become one of the most popular imaging modalities in health care. However, associated acquisition artifacts can significantly reduce image quality. Consequently, this imperfections can disturb the assessment of the acquired images. In the worst case, they may even lead to false decisions by the physician. Moreover, they can negatively influence an automatic processing of the data, e.g., image segmentation or registration. The most commonly observed artifacts are intensity inhomogeneities and a missing sequence-dependent general intensity scale. In this thesis, several novel techniques for the correction of the intensity variations are introduced. Further on, we demonstrate their advantages in a clinical application. Many state–of–the–art approaches for correction of inhomogeneities lack either generalizability, efficiency, or accuracy. We present novel methods that overcome these drawbacks by introducing prior knowledge in the objective function and by mapping the optimization process onto a divide–and–conquer like strategy. The experiments show that we can increase the average separability of tissue classes in clinical relevant 3-d angiographies by approximately 18.2% whereas state–of–the–art methods could only achieve 11.6%. The mapping of the intensities of a newly acquired image to a general intensity scale has to preserve the structural characteristics of the image’s histogram. Further, it has to be invertible. Hence, many standardization approaches estimate a rather coarse intensity transformation. We propose several methods for standardization that are closely related to image registration techniques. These methods compute a perintensity mapping. In addition, the methods presented are the only ones known that do a joint standardization and that can handle images with a very large field–of– view. The experiments show that our method achieves an average intensity overlap of the major tissue classes of T1w images of about 86.2%. The most commonly used state–of–the–art method resulted in only 70.1% overlap. In order to illustrate the applicability and importance of the proposed normalization techniques, we introduce a system for the computer-aided assessment of anomalies in the scoliotic spine. It is based on the segmentation of the spinal cord using Markov random field theory. All required steps are presented, from the pre-processing to the visualization of the results. In order to evaluate the system, we use the angle between automatically computed planes through the vertebrae and planes estimated by medical experts. This results in a mean angle difference of less than six degrees being accurate enough to be applicable in a clinical environment.