MR-based respiratory and cardiac motion correction for PET imaging

Purpose: To develop a motion correction for Positron-Emission-Tomography (PET) using simultaneously acquired magnetic-resonance (MR) images within 90 s.Methods: A 90 s MR acquisition allows the generation of a cardiac and respiratory motion model of the body trunk. Thereafter, further diagnostic MR sequences can be recorded during the PET examination without any limitation. To provide full PET scan time coverage, a sensor fusion approach maps external motion signals (respiratory belt, ECG-derived respiration signal) to a complete surrogate signal on which the retrospective data binning is performed. A joint Compressed Sensing reconstruction and motion estimation of the subsampled data provides motion-resolved MR images (respiratory + cardiac). A 1-POINT DIXON method is applied to these MR images to derive a motion-resolved attenuation map. The motion model and the attenuation map are fed to the Customizable and Advanced Software for Tomographic Reconstruction (CASToR) PET reconstruction system in which the motion correction is incorporated. All reconstruction steps are performed online on the scanner via Gadgetron to provide a clinically feasible setup for improved general applicability. The method was evaluated on 36 patients with suspected liver or lung metastasis in terms of lesion quantification (SUVmax, SNR, contrast), delineation (FWHM, slope steepness) and diagnostic confidence level (3-point Likert-scale).Results: A motion correction could be conducted for all patients, however, only in 30 patients moving lesions could be observed. For the examined 134 malignant lesions, an average improvement in lesion quantification of 22%, delineation of 64% and diagnostic confidence level of 23% was achieved.Conclusion: The proposed method provides a clinically feasible setup for respiratory and cardiac motion correction of PET data by simultaneous short-term MRI. The acquisition sequence and all reconstruction steps are publicly available to foster multi-center studies and various motion correction scenarios.     

Direct three-dimensional myocardial strain tensor quantification and tracking using zHARP

Images of myocardial strain can be used to diagnose heart disease, plan and monitor treatment, and to learn about cardiac structure and function. Three-dimensional (3D) strain is typically quantified using many magnetic resonance (MR) images obtained in two or three orthogonal planes. Problems with this approach include long scan times, image misregistration, and through-plane motion. This article presents a novel method for calculating cardiac 3D strain using a stack of two or more images acquired in only one orientation. The zHARP pulse sequence encodes in-plane motion using MR tagging and out-of-plane motion using phase encoding, and has been previously shown to be capable of computing 3D displacement within a single image plane. Here, data from two adjacent image planes are combined to yield a 3D strain tensor at each pixel; stacks of zHARP images can be used to derive stacked arrays of 3D strain tensors without imaging multiple orientations and without numerical interpolation. The performance and accuracy of the method is demonstrated in vitro on a phantom and in vivo in four healthy adult human subjects.     

Three- and four-dimensional reconstruction of intra-cardiac anatomy from two-dimensional magnetic resonance images

The present study was designed to evaluate the feasibility and clinical usefulness of three-dimensional (3D) reconstruction of intra-cardiac anatomy from a series of two-dimensional (2D) MR images using commercially available software. Sixteen patients (eight with structurally normal hearts but due to have catheter radio-frequency ablation of atrial tachyarrhythmias and eight with atrial septal defects (ASD) due for trans-catheter closure) and two volunteers were imaged at 1T. For each patient, a series of ECG-triggered images (5 mm thick slices, 2–3 mm apart) were acquired during breath holding. Depending on image quality, T ₁- or T ₂-weighted spin-echo images or gradient-echo cine images were used. The 3D reconstruction was performed off-line: the blood pools within cardiac chambers and great vessels were semi-automatically segmented, their outer surface was extracted using a marching cube algorithm and rendered. Intra- and inter-observer variability, effect of breath-hold position and differences between pulse sequences were assessed by imaging a volunteer. The 3D reconstructions were assessed by three cardiologists and compared with the 2D MR images and with 2D and 3D trans-esophagal and intra-cardiac echocardiography obtained during interventions. In every case, an anatomically detailed 3D volume was obtained. In the two patients where a 3 mm interval between slices was used, the resolution was not as good but it was still possible to visualize all the major anatomical structures. Spin-echo images lead to reconstructions more detailed than those obtained from gradient-echo images. However, gradient-echo images are easier to segment due to their greater contrast. Furthermore, because images were acquired at least at ten points in the cardiac cycles for every slice it was possible to reconstruct a cine loop and, for example, to visualize the evolution of the size and margins of the ASD during the cardiac cycle. 3D reconstruction proved to be an effective way to assess the relationship between the different parts of the cardiac anatomy. The technique was useful in planning interventions in these patients.     

改进心脏磁共振成像的定位方法

目的探讨心脏磁共振成像定位的改进方法。方法对18例心血管病患者及82名正常志愿者行心脏MR平扫,以改进的定位方法获得美国心脏协会(AHA)推荐的标准心脏断层成像层面,包括标准水平长轴位(HLA)、垂直长轴位(VLA)及短轴位(SA)图像,在此基础上探索左、右心室流入道和流出道,主动脉弓斜矢状位及各瓣膜横断位层面图像。结果采用此法可获得标准层面的图像及左心室功能参数。结论改进的心脏磁共振成像定位方法可保证各基本成像平面及各瓣膜成像平面的标准性,为观察心脏及大血管的形态和结构提供可靠依据。     

An endoscopic micromanipulator for multiplanar transesophageal imaging

We have developed an esophageal probe with a precision micromanipulator and a transversely oriented 32 element ultrasonic array which operates at 3.5 MHz. The probe allows us to obtain multiple two-dimensional images of the heart with known angular relationships between them over a series of cardiac cycles. Our ultimate purpose is to acquire images for left ventricular volume estimation with a three-dimensional reconstruction method. Technical details of the probe design are given. In vitro tests have shown that the imaging plane can be angulated within 1.5° root mean square error. In vivo results with dogs have demonstrated its ability to obtain multiplanar short axis images of the heart.     

Estimation of 3D left ventricular deformation from echocardiography

The quantitative estimation of regional cardiac deformation from 3D image sequences has important clinical implications for the assessment of viability in the heart wall. Such estimates have so far been obtained almost exclusively from Magnetic Resonance (MR) images, specifically MR tagging. In this paper we describe a methodology for estimating cardiac deformations from 3D echocardiography (3DE). The images are segmented interactively and then initial correspondence is established using a shape-tracking approach. A dense motion field is then estimated using a transversely isotropic linear elastic model, which accounts for the fiber directions in the left ventricle. The dense motion field is in turn used to calculate the deformation of the heart wall in terms of strain in cardiac specific directions. The strains obtained using this approach in open-chest dogs before and after coronary occlusion, show good agreement with previously published results in the literature. They also exhibit a high correlation with strains produced in the same animals using implanted sonomicrometers. This proposed method provides quantitative regional 3D estimates of heart deformation from ultrasound images.     

Accurate two-dimensional cardiac strain calculation using adaptive windowed Fourier transform and Gabor wavelet transform

Purpose

Cardiac strain calculated from tagged magnetic resonance (MR) images provides clinicians information about abnormalities of heart-wall motion in patients. It is important to develop an accurate method to determine the cardiac strain efficiently. An adaptive windowed harmonic phase (AWHARP) method is proposed for cardiac strain calculation.

Materials and methods

AWHARP is based on adaptive windowed Fourier transform (AWFT) and 2D Gabor wavelet transform (2D-GWT). The AWFT provides a spatially varying representation of the signal spectra, which allows the harmonic phase (HARP) image to be extracted with high accuracy. Instantaneous spatial frequencies are calculated using 2D-GWT, and the widths of the adaptive windows are then determined according to the instantaneous spatial frequencies for multi-resolution analysis of phase extraction. The proposed method was studied using simulated images and patients’ MR images. Both single tagged images (SPAMM) and subtracted tagged images (CSPAMM) were generated using our simulation method, and their results calculated using AWHARP and HARP methods were compared. Normal and pathological tagged MR images were also processed to evaluate the performance of our method.

Results

Our experimental results show that the accuracies of phase and strain images calculated using the AWHARP method are higher than that calculated using the HARP method especially for large tag line deformation. The improvement in accuracies can be up to 3.2 strain (E1) and 17.3 calculation from MR images reveals that the cardiac strain in the end-systolic state is significantly reduced for patients with hypertrophic cardiomyopathy (HCM) compared to that of healthy subjects.

Conclusion

The proposed AWHARP is an accurate and efficient method for cardiac strain estimation from MR images. This new algorithm can help clinicians to detect left ventricle dysfunctions and myocardial diseases with accurate cardiac strain analysis.     

5.0T MR心脏成像:与3.0T MR对比

目的 观察5.0T MR用于心脏成像的可行性。方法 前瞻性对3例心脏疾病患者和17名健康志愿者行5.0T及3.0T 心脏MR(CMR)电影序列和黑血序列成像;比较5.0T与3.0T CMR图像质量和伪影程度分级,并分析以其所获左心室参数的一致性。结果 5.0T与3.0T CMR图像质量和伪影程度分级差异均无统计学意义(P均>0.05),基于不同场强电影图像获得的左心室舒张末期容积(EDV)、收缩末期容积(ESV)、射血分数(EF)、每搏输出量(SV)及舒张末期心肌质量(EDM)的一致性均好(ICC均>0.75,P均<0.001)。结论 5.0T MR可用于心脏成像,其电影序列及黑血序列图像质量与3.0T MR相当。     

经食管超声心动图纵向扫描切面三维重建

在双平面经食管超声心动图研究的基础上，借鉴经胸壁三维超声心动图研究的经验，开展新的经食管超声心动图三维重建系统的研究。介绍了经食管超声心动图三维重建系统的硬件装置和图像处理的流程框图。结果表明。本系统可以对心脏和大血管多区域结构进行三维重建，结构显示清晰、直观、立体感强，并且能以不同层次立体剖面和不同方位的立体旋转图像显示各区域的结构，为心脏立体形态学研究提供了准确的三维解剖学资料，有助于确定病变的空间位置和大小。     

Morroniside alleviates coxsackievirus B3-induced myocardial damage apoptosis via restraining NLRP3 inflammasome activation

Coxsackievirus B3 (CVB3)-induced myocardial damage always leads to serious heart failure by inducing cardiac injury. NLRP3 inflammasome activation has been identified as a central player in the pathogenesis of CVB3-induced viral myocarditis. Therefore, restraining NLRP3 inflammasome activation has been supposed to significantly alleviate the severity of myocardial damage and improve cardiac function. Morroniside (MR), one of the main iridoid glycosides, has the ability to depress the production of reactive oxygen species (ROS) and restrain the expression of caspase-3 and -9. Of importance, ROS and caspase are essential for NLRP3 inflammasome activation in response to CVB3 infection. Therefore, in the present study, MR was selected as a model drug to alleviate CVB3-induced myocardial damage. The results of cardiac function index determination showed that abnormal indexes including mean arterial pressure, heart rate, and left ventricular systolic pressure of myocardial damage rats could be recovered by treating with MR. Such results can be further verified by histopathological evaluation, with the heart tissues of CVB3-infected rats displaying the most amount of H&E and TUNEL positive cells. The underlying mechanism by which MR improves the cardiac function was subsequently investigated. The detection of various gene levels indicated that NLRP3 inflammasome activation was inhibited by MR through down-regulating the expression of pro-inflammatory cytokines: interleukin (IL)-β and IL-18, the pivotal factors that lead to inflammatory responses. More importantly, the related genes, cardiac function indexes, and various myocardial damage markers of normal rats treated with MR did not exhibit any obvious changes compared with the control group, indicating a satisfactory biocompatibility of MR. In summary, MR holds a great potential in the alleviation of CVB3-induced myocardial damage with a negligible cytotoxicity to normal heart tissues.

Coxsackievirus B3 (CVB3)-induced myocardial damage always leads to serious heart failure by inducing cardiac injury.     

Shape analysis of hypertrophic and hypertensive heart disease using MRI-based 3D surface models of left ventricular geometry

The focus of this study was to develop advanced mathematical tools to construct high-resolution 3D models of left-ventricular (LV) geometry to evaluate focal geometric differences between patients with hypertrophic cardiomyopathy (HCM) and hypertensive heart disease (HHD) using cardiac magnetic resonance (MR) cross-sectional images. A limiting factor in 3D analysis of cardiac MR cross-sections is the low out-of-plane resolution of the acquired images. To overcome this problem, we have developed a mathematical framework to construct a population-based high-resolution 3D LV triangulated surface (template) in which an iterative matching algorithm maps a surface mesh of a normal heart to a set of cross-sectional contours that were extracted from short-axis cine cardiac MR images of patients who were diagnosed with either HCM or HHD. A statistical analysis was conducted on deformations that were estimated at each surface node to identify shape differences at end-diastole (ED), end-systole (ES), and motion-related shape variation from ED to ES. Some significant shape difference in radial thickness was detected at ES. Differences of LV 3D surface geometry were identified focally on the basal anterior septum wall. Further research is needed to relate these findings to the HCM morphological substrate and to design a classifier to discriminate among different etiologies of LV hypertrophy.     

Magnetic resonance imaging of congenital heart disease

MRI has assumed an important role in the noninvasive evaluation of patients with congenital cardiac lesions. In this article, the authors examine basic technical considerations, an approach to analysis of MR images in congenital heart disease patients, and review major applications of MRI as they apply to patients with congenital heart disease.     

基于MRI图像的主动脉分割与三维建模

目的基于MRI图像序列建立主动脉的三维几何模型并进行计算网格的划分,以用于主动脉血流动力学特性的模拟。方法采用心电R波触发和呼吸控制的方式在体扫描得到心动周期20个时相760幅MRI图像,利用Mimics软件对所获取的图像序列进行图像预处理、分割和三维重建,然后将所建立的三维模型导入到ADINA软件中进行计算网格的划分。结果建立了20个主动脉三维模型,分别代表主动脉在心动周期不同时相的状态,同时,还实现了计算网格的划分。结论该方法可得到进行主动脉血流动力学仿真所需的三维几何模型和计算网格;同时,该方法也可用于人体其他组织的三维建模和网格划分。     

Intracardiac echocardiography: gross anatomy and magnetic resonance correlations and validations

Purpose: The feasibility and safety of intracardiac echocardiography (ICE) in humans, using low frequency transducers, and its excellent tissue contrast capabilities that enhances the differentiation of intracardiac structures have been previously demonstrated. However, correlations among ICE imaging and anatomic sections or magnetic resonance (MR) scan planes have never been described before. This study was designed to correlate a simplified ICE approach with the anatomy of the right atrium and great vessels obtained by serial post-mortem sections and cardiac MR images. Methods: A stepwise approach to ICE, which is based on our experience on over 300 consecutive patients with interatrial communications, has been correlated with anatomic sections from pressure-perfused-fixed hearts and spin echo cardiac MR imaging. A 9F-9 MHz mechanical device was used to record four transverse and one longitudinal sections for an extensive evaluation of the intracardiac architecture. Results: ICE transverse and longitudinal views allowed the detection of all the required information. Moreover, the anatomic sections and cardiac MR scan planes allowed validation of all the structures imaged by ICE. The potential clinical applications of the ICE technique are further discussed. Conclusion: This paper demonstrates the basic accuracy of this new imaging modality. Therefore, mechanical ICE might be considered an active investment in cardiac catheterization laboratories, specifically in the percutaneous interventional procedure setting, discovering a new route (let’s see and treat) to sophisticated interventions. In this respect, there can be little doubt that the knowledge of cross-sectional mechanical ICE imaging provides the basis for understanding the heart anatomy.     

MR evaluation of cardiac and pericardial malignancy

The accurate evaluation of cardiac masses by MR imaging was established in the infancy of cardiac MR imaging. From its advent, MR imaging was believed to be diagnostically superior to echocardiography in the evaluation of suspected cardiac masses. Though excellent in its assessment of the left side of the heart, echocardiography is limited in its evaluation of the right heart, mediastinum, and paracardiac structures. It is also of limited use in patients with emphysema and chest wall deformities. With the advent of ECG gating, MR imaging's ability to assess the presence and anatomy of cardiac and paracardiac masses was well established by a number of studies. This research also demonstrated MR imaging's capacity to exclude a cardiac mass when the echocardiogram was equivocal.     

心肌及心血管系统的四维可视化技术研究与实现

目的为克服二维医学图像和三维重建无法实时、多方位和多角度观察心脏运动形态的不足,提出一种全新的四维可视化解决方案来实现心肌及心血管系统的动态显示。方法以三维实时显示技术为基础,编程实现序列体数据的读入、显示和管理,将心脏运动模型离散化,使序列体数据显示的时间间隔与真实的心动周期时间间隔保持一致,实时显示心脏离散化序列体数据,实现心肌四维可视化;通过改变不同部位的透明度来实现心血管系统的四维可视化。结果该四维可视化技术主要有两大优点:①采用心脏CT图像重建得到心脏体数据模型,效果逼真;②采用异步纹理绘制技术动态、四维显示心血管系统,避免了延时现象,使得心血管系统四维可视化更加真实、流畅。结论心肌及心血管系统的四维可视化技术可多方位、多角度显示心脏的实时搏动。     

基于MRI的动物肝脏脉管分割与三维重建

目的探索基于磁共振成像的肝脏脉管(血管、胆管)三维重建的方法,以显示肝脏中血管、胆管走行立体图像,从而指导劈离式肝脏移植手术.方法综合利用二维图像的多种平滑和分割方法,得到肝实质和肝脉管二维图像序列,并在此基础上三维重建肝实质和肝脉管.结果由MR图像序列可三维重建清晰的肝实质和肝血管立体图像,并且可得到肝叶、段间血管及胆管的走行及相互关系.结论利用MRI和图像分割以及图像三维重建技术指导劈离式肝移植手术,具有重要的临床意义.     

Setting up a clinical cardiac MR imaging program: practical issues and economics

Use of MR imaging to assess the heart has grown rapidly in recent years. MR imaging can assess cardiac anatomy, quantify ventricular and valvular function, identify regions of infarcted myocardium, and evaluate flow-limiting coronary artery stenoses better than any other single imaging modality. Despite its superior capabilities, cardiac MR imaging has yet to be adopted widely in clinical practice, in part because of the many obstacles to developing a clinical cardiac MR imaging program. The purpose of this article is to provide information that may be helpful in developing such a program. The information is based on the authors' experience in an inpatient hospital setting and an outpatient private practice. The recommendations reflect personal opinions and donot represent requirements of any organization or society unless otherwise indicated.     

心脏CT重建时相对冠状动脉钙化积分危险分级的影响

目的 观察心脏CT重建时相对冠状动脉钙化积分(CACS)危险分级的影响.方法 对70名存在冠心病高风险因素的成人志愿者行心脏回顾性心电门控多时相重建,观察以5％为间隔重建的11个时相CACS、最佳舒张及收缩期时相CACS及心率相关指标,对比不同时相CACS危险分级,以多因素岭回归分析分级与各指标间相关性.结果 系统自识...     

基于纹理分析的带标记线心脏MR图像分割

背景：左心室边界的准确分割是对左心室运动及形变进行分析的前提。由于受带标记线心脏核磁共振图像中标记线强梯度的影响,对左心室内膜的提取变得非常困难。目的：为了抑制标记线对图像分割的影响,提出了一种基于最小值-方差能量图的纹理分析方法。方法：首先对局部最小值和方差进行加权求和,得到能量图;然后利用中值滤波滤除能量图中的伪影并保持边界;最后,应用GVF-snake模型提取左心室内膜。结果与结论：针对标记线在心脏MR图像中的分布特征,提出了一种基于最小值-方差的纹理分析方法,该方法有效地去除了标记线。结果提示,对使用该纹理分析方法生成的能量图应用GVF-snake模型可以较好地提取左心室内膜。