Volume 22, Issue 6

In this paper, we extend a previously reported intensity-based nonrigid registration algorithm by using a novel regularization term to constrain the deformation. Global motion is modeled by a rigid transformation while local motion is described by a free-form deformation based on B-splines. An information theoretic measure, normalized mutual information, is used as an intensity-based image similarity measure. Registration is performed by searching for the deformation that minimizes a cost function consisting of a weighted combination of the image similarity measure and a regularization term. The novel regularization term is a local volume-preservation (incompressibility) constraint, which is motivated by the assumption that soft tissue is incompressible for small deformations and short time periods. The incompressibility constraint is implemented by penalizing deviations of the Jacobian determinant of the deformation from unity. We apply the nonrigid registration algorithm with and without the incompressibility constraint to precontrast and postcontrast magnetic resonance (MR) breast images from 17 patients. Without using a constraint, the volume of contrast-enhancing lesions decreases by 1%-78% (mean 26%). Image improvement (motion artifact reduction) obtained using the new constraint is compared with that obtained using a smoothness constraint based on the bending energy of the coordinate grid by blinded visual assessment of maximum intensity projections of subtraction images. For both constraints, volume preservation improves, and motion artifact correction worsens, as the weight of the constraint penalty term increases. For a given volume change of the contrast-enhancing lesions (2% of the original volume), the incompressibility constraint reduces motion artifacts better than or equal to the smoothness constraint in 13 out of 17 cases (better in 9, equal in 4, worse in 4). The preliminary results suggest that incorporation of the incompressibility regularization term improves intensity-based free-form nonrigid registration of contrast-enhanced MR breast images by greatly reducing the problem of shrinkage of contrast-enhancing structures while simultaneously allowing motion artifacts to be substantially reduced.

在本文中，我们通过使用一种新的正则化项来约束变形，对先前报道的基于强度的非刚性配准算法进行了扩展。全局运动通过刚性变换建模，而局部运动则通过基于B样条的自由形变来描述。使用基于信息论的度量——归一化互信息，作为基于强度的图像相似性度量。配准通过搜索使代价函数最小化的变形来实现，该代价函数由图像相似性度量和正则化项的加权组合构成。新的正则化项是局部体积保持（不可压缩性）约束，其动机是假设软组织在小变形和短时间内是不可压缩的。不可压缩性约束通过惩罚变形雅可比行列式与1的偏差来实现。我们将带有和不带有不可压缩性约束的非刚性配准算法应用于17名患者的增强前和增强后磁共振（MR）乳腺图像。在没有约束的情况下，对比增强病变的体积减少了1%至78%（平均26%）。通过盲法视觉评估减影图像的最大强度投影，将使用新约束获得的图像改善（运动伪影减少）与使用基于坐标网格弯曲能量的平滑约束获得的改善进行比较。对于两种约束，随着约束惩罚项权重的增加，体积保持效果改善，而运动伪影校正效果变差。对于给定的对比增强病变体积变化（原始体积的2%），在17例中有13例中，不可压缩性约束减少运动伪影的效果优于或等于平滑约束（其中9例更优，4例相等，4例更差）。初步结果表明，加入不可压缩性正则化项可以极大地减少对比增强结构的收缩问题，同时允许运动伪影显著减少，从而改善对比增强MR乳腺图像的基于强度的自由形变非刚性配准。

Knowledge-based segmentation has been explored significantly in medical imaging. Prior anatomical knowledge can be used to define constraints that can improve performance of segmentation algorithms to physically corrupted and incomplete data. In this paper, the objective is to introduce such knowledge-based constraints while preserving the ability of dealing with local deformations. Toward this en...

基于知识的分割在医学影像中已得到广泛探索。先验解剖知识可用于定义约束，从而提高分割算法在处理物理损坏和不完整数据时的性能。本文旨在引入此类基于知识的约束，同时保留处理局部变形的能力。为此...

In this paper, we show how a dense surface point distribution model of the human face can be computed and demonstrate the usefulness of the high-dimensional shape-space for expressing the shape changes associated with growth and aging. We show how average growth trajectories for the human face can be computed in the absence of longitudinal data by using kernel smoothing across a population. A trai...

在本文中，我们展示了如何计算人脸密集表面点分布模型，并证明了高维形状空间在表达与生长和衰老相关的形状变化方面的有用性。我们展示了如何通过使用核平滑跨越人群，在缺乏纵向数据的情况下计算人脸的平均生长轨迹。一个训练...

In this paper, we propose a new representation of the cortical surface that may be used to study the cortex folding process and to recover some putative stable anatomical landmarks called sulcal roots usually buried in the depth of adult brains. This representation is a primal sketch derived from a scale space computed for the mean curvature of the cortical surface. This scale-space stems from a d...

在本文中，我们提出了一种新的皮层表面表示方法，可用于研究皮层折叠过程，并恢复一些被称为沟根的可能稳定的解剖学标志，这些标志通常埋藏在成人脑的深处。这种表示方法是从皮层表面平均曲率尺度空间推导出的原始草图。该尺度空间源于一个d...

Patient motion can cause image artifacts in single photon emission computed tomography despite restraining measures. Data-driven detection and correction of motion can be achieved by comparison of acquired data with the forward projections. This enables the brain locations to be estimated and data to be correctly incorporated in a three-dimensional (3-D) reconstruction algorithm. Digital and physi...

尽管采取了约束措施，患者运动仍可能导致单光子发射计算机断层扫描中的图像伪影。通过将采集的数据与前向投影进行比较，可以实现数据驱动的运动检测和校正。这使得能够估计脑部位置，并将数据正确纳入三维重建算法。数字和生理...

In the cardiovascular arena, percutaneous catheter-based interventional (i.e., therapeutic) procedures include a variety of coronary and other vascular system interventions. These procedures use two-dimensional (2-D) X-ray-based imaging as the sole or the major imaging modality for procedure guidance and quantification of key parameters. Coronary vascular curvilinearity is one key parameter that r...

在心血管领域，经皮导管介入（即治疗性）手术包括多种冠状动脉和其他血管系统干预措施。这些手术使用基于二维（2-D）X射线的成像作为指导手术和量化关键参数的唯一或主要成像方式。冠状动脉血管曲率是一个关键参数，它...

Magnetic resonance angiography (MRA) has become an important tool for the clinical evaluation of vascular disease. Flow measurement with phase-contrast (PC) magnetic resonance (MR) imaging provides a powerful method for evaluation of blood velocity information inside vessels. However, image artifacts from complex flow patterns including slow flow, recirculation zone, and pulsatile flow can adverse...

磁共振血管造影（MRA）已成为临床评估血管疾病的重要工具。相位对比磁共振成像（PC-MRI）提供的血流测量是评估血管内血流速度信息的有力方法。然而，来自复杂流动模式的图像伪影，包括慢流、再循环区和脉动流，可能对...

A finite-element analysis (FEA) model of an intact lumbar disc-body unit was generated. The vertebral body of the FEA model consisted of a solid tetrahedral core of trabecular bone surrounded by a cortical shell. The disc consisted of an incompressible nucleus surrounded by nonlinear annulus fibers embedded in a solid ground substance. The purpose was to create a FEA model suitable for clinical pu...

生成了一个完整的腰椎间盘-椎体单元的有限元分析模型。该FEA模型的椎体由实心四面体结构的松质骨核心及其周围的皮质骨壳组成。椎间盘由不可压缩的髓核和嵌入固体基质中的非线性纤维环组成。目的是创建一个适用于临床的FEA模型...

In radiotherapy (RT), organ motion caused by breathing prevents accurate patient positioning, radiation dose, and target volume determination. Most of the motion-compensated trial techniques require collaboration of the patient and expensive equipment. Estimating the motion between two computed tomography (CT) three-dimensional scans at the extremes of the breathing cycle and including this inform...

在放射治疗（RT）中，由呼吸引起的器官运动妨碍了患者的精确定位、辐射剂量和靶区体积的确定。大多数运动补偿试验技术需要患者配合和昂贵的设备。估计呼吸周期极端之间两次计算机断层扫描（CT）三维扫描之间的运动，并将此信息纳入...

We propose a method of using a relatively low degree of freedom (DOF) warping to accurately measure the interval change of lesions having homogeneous contrast. The setting presented here presupposes the use of interval computed tomography (CT) liver exams. After a 3 /spl times/ 24 DOF warping of the later examination to match the liver's pose in the earlier exam of the interval pair is performed, ...

我们提出了一种使用相对低自由度（DOF）扭曲来准确测量具有均匀对比度的病变间隔变化的方法。这里提出的场景假定使用间隔计算机断层扫描（CT）肝脏检查。在对后续检查进行3×24自由度的扭曲以匹配间隔对中先前检查的肝脏姿态后，...