Shao Jiaxin, Hu Peng
Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, CA, USA.
Biomedical Physics Interdepartmental Graduate Program, University of California, Los Angeles, CA, USA.
Quant Imaging Med Surg. 2017 Apr;7(2):177-186. doi: 10.21037/qims.2017.01.01.
Assessment of lung function is vital for the diagnosis of a variety of pathological conditions. Research has been proposed to study pulmonary mechanics and kinematics using two-dimensional (2D) magnetic resonance imaging (MRI). This allows estimation of regional lung tissue mechanics but is limited to 2D information. An approach based on three-dimensional (3D) contrast-enhanced MR angiogram of pulmonary blood vessels and a non-rigid image registration technique is proposed for quantification of lung regional deformations, which can potentially be used for assessment of pulmonary parenchymal mechanics and regional ventilation for disease diagnosis without ionizing radiation.
On three volunteers, an end-expiration scan and end-inspiration scan was acquired successively for each volunteer using a 3D breath-hold contrast-enhanced MRI sequence several minutes after gadolinium injection. Subsequently, a rectangle box lung mask is manually selected for each end-expiration scan, applying non-rigid registration algorithms using cubic B-splines as transformations to align each pair of images. This incorporates the Normalized Correlation Coefficient similarity with the bending energy term as cost function with a multi-resolution multi-grid approach. Finally, the lung regional 3D deformations were obtained using the transformations obtained by registration. The alignment accuracy after non-rigid registration was estimated by using a set of branch points of pulmonary blood vessels as anatomical landmarks for each pair of images.
With contrast enhancement, the pulmonary blood vessel signal was enhanced, which greatly facilitated the non-rigid registration in the lung parenchyma. The average landmarks distances in three pairs of datasets are reduced from 17.9, 20.3 and 16.3 mm, to 1.0, 1.6 and 1.2 mm, respectively, by non-rigid registration. After registration, the average distances error of each pair of datasets was less than 0.6 mm in the right-to-left (RL) direction, less than 0.9 mm in the inferior-to-superior (IS) direction, and less than 1.2 mm in the anterior-to-posterior (AP) direction.
Results demonstrated that the proposed method can accurately register lungs with large deformations to evaluate lung regional deformation. It may be used for quantitative assessment of 3D lung regional ventilation avoiding ionizing radiation.
肺功能评估对于多种病理状况的诊断至关重要。已有研究提出使用二维（2D）磁共振成像（MRI）来研究肺力学和运动学。这能够估计局部肺组织力学，但仅限于二维信息。本文提出一种基于三维（3D）肺血管对比增强磁共振血管造影和非刚性图像配准技术的方法，用于量化肺区域变形，该方法有可能用于评估肺实质力学和区域通气以辅助疾病诊断，且无需电离辐射。
对三名志愿者，在注射钆剂几分钟后，使用三维屏气对比增强MRI序列依次为每位志愿者采集呼气末扫描和吸气末扫描图像。随后，为每次呼气末扫描手动选择一个矩形框肺掩码，应用以三次B样条曲线作为变换的非刚性配准算法来对齐每对图像。这将归一化相关系数相似度与弯曲能量项结合作为代价函数，并采用多分辨率多网格方法。最后，使用通过配准获得的变换来获取肺区域三维变形。通过将一组肺血管分支点用作每对图像的解剖标志，来估计非刚性配准后的对齐精度。
通过对比增强，肺血管信号增强，这极大地促进了肺实质内的非刚性配准。通过非刚性配准，三对数据集中平均标志点距离分别从17.9、20.3和16.3毫米减小到1.0、1.6和1.2毫米。配准后，每对数据集在左右（RL）方向的平均距离误差小于0.6毫米，在上下（IS）方向小于0.9毫米，在前后（AP）方向小于1.2毫米。
结果表明，所提出的方法能够准确地对具有大变形的肺进行配准，以评估肺区域变形。它可用于三维肺区域通气的定量评估，避免电离辐射。
