Accurate magnetic resonance imaging of atherosclerotic plaques: change future strategies for the diagnosis and therapy of atherosclerotic disease

In recent years, magnetic resonance imaging (MRI) have been developed to image atherosclerosis and is emerging as a useful tool to assess the burden of atherosclerosis, whereas the potential influence on the diagnosis and therapy of atherosclerotic disease have not been fully determined. MRI allows for three-dimensional evaluation of vascular structures and outstanding depiction of various components of the atherosclerotic plaque. The self-contained intravascular MRI probe appears to hold promise in the identification of high-risk coronary and peripheral atherosclerotic lesions. Molecular and targeted contrast MRI can offer exciting possibilities of direct visualization of biologic processes within atherosclerotic tissue. The addition of quantitative hydrogen 1 magnetic resonance spectroscopy and diffusion weighted imaging within atherosclerotic plaques can provide important data on the biological activity of potentially vulnerable lesions. Therefore, we hypothesized that accurate magnetic resonance imaging of atherosclerotic plaques maybe further affect and change future strategies for the diagnosis and therapy of atherosclerotic disease.     

Deformable and rigid registration of MRI and microPET images for photodynamic therapy of cancer in mice

We are investigating imaging techniques to study the tumor response to photodynamic therapy (PDT). Positron emission tomography (PET) can provide physiological and functional information. High-resolution magnetic resonance imaging (MRI) can provide anatomical and morphological changes. Image registration can combine MRI and PET images for improved tumor monitoring. In this study, we acquired high-resolution MRI and microPET 18F-fluorodeoxyglucose (FDG) images from C3H mice with RIF-1 tumors that were treated with Pc 4-based PDT. We developed two registration methods for this application. For registration of the whole mouse body, we used an automatic three-dimensional, normalized mutual information algorithm. For tumor registration, we developed a finite element model (FEM)-based deformable registration scheme. To assess the quality of whole body registration, we performed slice-by-slice review of both image volumes; manually segmented feature organs, such as the left and right kidneys and the bladder, in each slice; and computed the distance between corresponding centroids. Over 40 volume registration experiments were performed with MRI and microPET images. The distance between corresponding centroids of organs was 1.5 +/- 0.4 mm which is about 2 pixels of microPET images. The mean volume overlap ratios for tumors were 94.7% and 86.3% for the deformable and rigid registration methods, respectively. Registration of high-resolution MRI and microPET images combines anatomical and functional information of the tumors and provides a useful tool for evaluating photodynamic therapy.     

Laser-induced thermal therapy for tumor ablation

Image-guided ablation of tumors is assuming an increasingly important role in many oncology services as a minimally invasive alternative to conventional surgical interventions for patients who are not good candidates for surgery. Laser-induced thermal therapy (LITT) is a percutaneous tumor-ablation technique that utilizes high-power lasers placed interstitially in the tumor to deliver therapy. Multiple laser fibers can be placed into the treatment volume and, unlike other interstitial heating techniques, can be fired simultaneously to rapidly treat large volumes of tissue. Modern systems utilize small, compact, high-power laser diode systems with actively cooled applicators to help keep tissue from charring during procedures. Additionally, because this approach to thermal therapy is easily made magnetic resonance (MR) compatible, the incorporation of magnetic resonance imaging (MRI) for treatment planning, targeting, monitoring, and verification has helped to expand the number of applications in which LITT can be applied safely and effectively. We provide an overview of the clinically used technology and algorithms that provide the foundations for current state-of-the-art MR-guided LITT (MRgLITT), including procedures in the brain, liver, bone, and prostate as examples. In addition to advances in imaging and delivery, such as the incorporation of nanotechnology, next-generation MRgLITT systems are anticipated to incorporate an increasing presence of in silico-based modeling of MRgLITT procedures to provide human-assisted computational tools for planning, MR model-assisted temperature monitoring, thermal-dose assessment, and optimal control.     

Neuroimaging findings in a case of cerebral fat embolism syndrome with delayed recovery

A young male with multiple lower limb fractures admitted to our Intensive Care Unit was diagnosed with cerebral fat embolism syndrome (FES) based on clinical features and initial magnetic resonance imaging (MRI) which showed multiple hyperintensities on T2-weighted imaging, involving bilateral cerebral and cerebellar hemispheres, predominantly in the watershed territory. The serial MRI done at 3 weeks showed more prominent and larger sized lesions which were in line with the patient''s initial low Glasgow Coma Score and indicated severe cerebral insult. The patient responded well to supportive intensive care therapy; his neurological recovery though slow was consistent as he could return to his full functional status after 6 months. The follow-up MRI showed resolution of the most of earlier lesions. This indicates potentially good outcomes even in severe cases of cerebral FES with appropriate medical care.     

High resolution computed tomography and MRI for monitoring lung tumor growth in mice undergoing radioimmunotherapy: correlation with histology

A model lung tumor system has been developed in mice for the evaluation of vascular targeted radioimmunotherapy. In this model, EMT-6 mammary carcinoma tumors growing in the lung are treated with 213Bi, an alpha particle emitter, which is targeted to lung blood vessels using a monoclonal antibody. Smaller tumors (< 100 microm in diameter) are cured, but larger tumors undergo a period of regression and then regrow and ultimately prove lethal. The goal of this work was to determine if external imaging with MRI or CT could be used routinely to monitor the growth/ regression of lung tumors in live mice. To attempt to evaluate individual tumors in vivo, animals were initially imaged with magnetic resonance imaging (MRI). High resolution MRI images could be obtained only after sacrifice when lungs were not moving. In contrast, high resolution computed tomography (CT) produced evaluable images from anesthetized animals. Serial CT images (up to 5/animal) were collected over a 17 day period of tumor growth and treatment. When tumored animals became moribund, animals were sacrificed and lungs were inflated with fixative, embedded in paraffin, and then sectioned serially to compare the detection of tumors by high resolution CT with detection by histology. CT proved most useful in detecting lung tumors located in the hilar area and least useful in detecting serosal surface and anterior lobe tumor foci. Overall, CT images of live animals revealed tumors in approximately 2/3 of cases detected in histologic serial sections when relatively few tumors were present per lung. Detection of lesions and their resolution post therapy were complicated due to residual hemorrhagic, regressing tumor nodules and the development of lung edema both of which appeared as high density areas in the CT scans. We conclude that the microCT method used could identify some lung tumors as small as 100 microm in diameter; however, no concrete evaluation of therapy induced regression of the tumors could be made with CT analyses alone.     

Spatial integration of multimodal brain images in cerebral infarction

Summary Different structural as well as functional imaging techniques are becoming increasingly important in the investigation of patients suffering from an ischemic stroke. Available imaging procedures usually provide complementary data, but the images can not easily be compared due to differences in patient positioning, angulation, and slice thickness. We studied the value of spatial integration of images from different modalities in a patient with an ischemic stroke and used skin markers to integrate the obtained information. Computed tomography (CT), magnetic resonance imaging (MRI),^99mTc HMPAO-single photon emission computed tomography (SPECT) and magnetic resonance spectroscopic imaging (MRSI) were performed in a patient, presenting with a right sided hemiparesis caused by an ischemic stroke. Combination of MRI with CT demonstrated that the infarction visible on CT and MRI corresponded in size and volume. Furthermore, structural and functional images could readily be integrated, thus allowing us to obtain accurate information in this stroke patient. Different imaging modalities provide complementary information in the acute phase of cerebral infarction and multimodality matching can be of great value for improvement of our understanding of the pathophysiology and course of ischemic stroke.     

Functional magnetic resonance imaging aided radiation treatment planning

Functional MRI (magnetic resonance imaging) allows one to noninvasively identify various eloquent cortices in the brain. The integration of cortical activation information into radiosurgical treatment planning may provide an alternative to prevent or minimize radiation damage to eloquent cortex. A novel approach of directly integrating the fMRI (functional magnetic resonance imaging) brain map into treatment planning is proposed. Three brain tumor patients have been studied using this method with motor and/or visual paradigms. Brain activation was demonstrated in eloquent cortex at the precentral gyrus (motor area) and medial occipital lobe (visual area). The activation maps were transferred to a treatment planning workstation, (XKnife), and 3D (three-dimensional) activation maps were generated and co-registered to a 3D CT (computed tomography) anatomical data set, which provided the calibration localizer, for treatment planning. Radiosurgery was designed based on both functional and structural information by the medical team consisting of a radiation oncologist, a neurosurgeon and a physicist. The average maximum dose for the tumor was 2113 cGy. The average maximum dose for tissue surrounding the tumor was 1600 cGy. The average dose with fMRI information to the eloquent cortex was 163.4 cGy over three patients, while without fMRI information it was 240.5 cGy. The average percentage dose reduction over three patients is 32%. The results suggest that using this method can reduce the dose to the eloquent cortex. This approach provides the physician with additional information for treatment planning and may spare the patient unnecessary radiation exposure to adjacent eloquent cortices.     

Optic Chiasmatic-Hypothalamic Glioma

Optic chiasmatic-hypothalamic gliomas (OCHGs) have been considered benign tumors and self-limiting in growth potential because of their histological appearance. Unfortunately, most clinical series have reported significant morbidity and mortality especially with the more extensive, posteriorly positioned tumors. The biological behavior of OCHGs is age-dependent, with patients younger than five years and older than 20 years typically having tumors that exhibit aggressive growth. There are no specific pathological features to help differentiate the clinical behavior of such tumors. The emergence of modern imaging techniques, including magnetic resonance imaging (MRI), has facilitated the monitoring of the natural history of the disease and the determination of the effects of therapy. Most patients with OCHGs survive for many years. While the natural history of an OCHG for any individual may be indeterminate, enough data are now available from large series to make recommendations for treatment. Our current treatment policy for patients with OCHGs in the context of NF-I without visual failure is a conservative one involving CSF shunting for hydrocephalus if present and medical therapy for endocrinologic dysfunction. Patients with or without NF-I with visual deterioration or progressive neurological deficits and a rapidly expanding suprasellar mass lesion are treated surgically. After tumor resection, patients whose vision is significantly compromised or who show progression of their disease on serial neuroimaging scans receive chemotherapy. If chemotherapy proves ineffective in disease stabilization, then considerations of radiation therapy are given to children over five years old.     

Combination of feature-reduced MR spectroscopic and MR imaging data for improved brain tumor classification

The purpose of this paper is to evaluate the effect of the combination of magnetic resonance spectroscopic imaging (MRSI) data and magnetic resonance imaging (MRI) data on the classification result of four brain tumor classes. Suppressed and unsuppressed short echo time MRSI and MRI were performed on 24 patients with a brain tumor and four volunteers. Four different feature reduction procedures were applied to the MRSI data: simple quantitation, principal component analysis, independent component analysis and LCModel. Water intensities were calculated from the unsuppressed MRSI data. Features were extracted from the MR images which were acquired with four different contrasts to comply with the spatial resolution of the MRSI. Evaluation was performed by investigating different combinations of the MRSI features, the MRI features and the water intensities. For each data set, the isolation in feature space of the tumor classes, healthy brain tissue and cerebrospinal fluid was calculated and visualized. A test set was used to calculate classification results for each data set. Finally, the effect of the selected feature reduction procedures on the MRSI data was investigated to ascertain whether it was more important than the addition of MRI information. Conclusions are that the combination of features from MRSI data and MRI data improves the classification result considerably when compared with features obtained from MRSI data alone. This effect is larger than the effect of specific feature reduction procedures on the MRSI data. The addition of water intensities to the data set also increases the classification result, although not significantly. We show that the combination of data from different MR investigations can be very important for brain tumor classification, particularly if a large number of tumors are to be classified simultaneously.     

Advances in computational and statistical diffusion MRI

Computational methods are crucial for the analysis of diffusion magnetic resonance imaging (MRI) of the brain. Computational diffusion MRI can provide rich information at many size scales, including local microstructure measures such as diffusion anisotropies or apparent axon diameters, whole‐brain connectivity information that describes the brain's wiring diagram and population‐based studies in health and disease. Many of the diffusion MRI analyses performed today were not possible five, ten or twenty years ago, due to the requirements for large amounts of computer memory or processor time. In addition, mathematical frameworks had to be developed or adapted from other fields to create new ways to analyze diffusion MRI data. The purpose of this review is to highlight recent computational and statistical advances in diffusion MRI and to put these advances into context by comparison with the more traditional computational methods that are in popular clinical and scientific use. We aim to provide a high‐level overview of interest to diffusion MRI researchers, with a more in‐depth treatment to illustrate selected computational advances.     

Segmentation and visualization of nasopharyngeal carcinoma using MRI

In this study, a semi-automatic system was developed for nasopharyngeal carcinoma (NPC) tumor segmentation, volume measurement and visualization using magnetic resonance imaging (MRI). Some novel algorithms for tumor segmentation from MRI and inter-slice interpolation were integrated in this medical diagnosis system. This system was applied to 10 MR image data sets of NPC patients and satisfactory results were achieved. This system can be used as a clinical image analysis tool for doctors or radiologists to obtain tumor location from MRI, tumor volume estimation, and 3D information.     

Registration of 2D x-ray images to 3D MRI by generating pseudo-CT data

Spatial and soft tissue information provided by magnetic resonance imaging can be very valuable during image-guided procedures, where usually only real-time two-dimensional (2D) x-ray images are available. Registration of 2D x-ray images to three-dimensional (3D) magnetic resonance imaging (MRI) data, acquired prior to the procedure, can provide optimal information to guide the procedure. However, registering x-ray images to MRI data is not a trivial task because of their fundamental difference in tissue contrast. This paper presents a technique that generates pseudo-computed tomography (CT) data from multi-spectral MRI acquisitions which is sufficiently similar to real CT data to enable registration of x-ray to MRI with comparable accuracy as registration of x-ray to CT. The method is based on a k-nearest-neighbors (kNN)-regression strategy which labels voxels of MRI data with CT Hounsfield Units. The regression method uses multi-spectral MRI intensities and intensity gradients as features to discriminate between various tissue types. The efficacy of using pseudo-CT data for registration of x-ray to MRI was tested on ex vivo animal data. 2D-3D registration experiments using CT and pseudo-CT data of multiple subjects were performed with a commonly used 2D-3D registration algorithm. On average, the median target registration error for registration of two x-ray images to MRI data was approximately 1 mm larger than for x-ray to CT registration. The authors have shown that pseudo-CT data generated from multi-spectral MRI facilitate registration of MRI to x-ray images. From the experiments it could be concluded that the accuracy achieved was comparable to that of registering x-ray images to CT data.     

极度非均匀磁场下的低场核磁共振成像技术研究进展

传统的磁共振成像设备系统庞大笨重、价格昂贵、检查噪声大、摆位困难等,因此限制其普及应用,而低场可移动式磁共振成像设备可以克服这些缺点。传统核磁共振成像采取大磁体包围小样品的模式,对高度均匀磁场环境(<5×10^-6/40 mm DSV)中的样品进行成像,相应的硬件设计和许可技术相对都比较成熟和完善。开放式核磁共振成像系统基于极度不均匀的磁场条件(>1 000×10^-6/mm DSV),相关的硬件设计、成像技术与传统的核磁共振成像系统差距很大,难度也急剧增加。全面论述低场开放式磁共振成像技术的起源、发展、关键技术,包括磁体、射频线圈、梯度线圈等硬件和射频脉冲设计、成像序列、图像后处理等方法,旨在为可移动式核磁共振成像设备的研发抛砖引玉。     

Noninvasive monitoring of orthotopic glioblastoma therapy response using RGD-conjugated iron oxide nanoparticles

Noninvasive imaging techniques have been considered important strategies in the clinic to monitor tumor early response to therapy. In the present study, we applied RGD peptides conjugated to iron oxide nanoparticles (IONP-RGD) as contrast agents in magnetic resonance imaging (MRI) to noninvasively monitor the response of a vascular disrupting agent VEGF(121)/rGel in an orthotopic glioblastoma model. RGD peptides were firstly coupled to IONPs coated with a crosslinked PEGylated amphiphilic triblock copolymer. In vitro binding assays confirmed that cellular uptake of particles was mainly dependent on the interaction between RGD and integrin α(v)β(3) of human umbilical vein endothelial cells (HUVEC). The tumor targeting of IONP-RGD was observed in an orthotopic U87 glioblastoma model. Finally, noninvasive monitoring of the tumor response to VEGF(121)/rGel therapy at early stages of treatment was successfully accomplished using IONP-RGD as a contrast agent for MRI, a superior method over common anatomical approaches which are based on tumor size measurements. This preclinical study can accelerate anticancer drug development and promote clinical translation of nanoprobes.     

Tumour gene therapy monitoring using magnetic resonance imaging and spectroscopy

Recent progress in gene therapy has increased the need for non-invasive imaging methods that would allow early diagnosis of successful treatment. Magnetic resonance methods, magnetic resonance imaging (MRI) and spectroscopy (MRS), have shown great promise to achieve this goal. The current mini-review describes recent advances in experimental MRI and MRS to detect individual treatment steps in gene therapy of tumours from gene transfection to therapy response. Limitations of the current techniques are also discussed.     

Assessment of therapeutic response and treatment planning for brain tumors using metabolic and physiological MRI

MRI is routinely used for diagnosis, treatment planning and assessment of response to therapy for patients with glioma. Gliomas are spatially heterogeneous and infiltrative lesions that are quite variable in terms of their response to therapy. Patients classified as having low-grade histology have a median overall survival of 7 years or more, but need to be monitored carefully to make sure that their tumor does not upgrade to a more malignant phenotype. Patients with the most aggressive grade IV histology have a median overall survival of 12-15 months and often undergo multiple surgeries and adjuvant therapies in an attempt to control their disease. Despite improvements in the spatial resolution and sensitivity of anatomic images, there remain considerable ambiguities in the interpretation of changes in the size of the gadolinium-enhancing lesion on T(1) -weighted images as a measure of treatment response, and in differentiating between treatment effects and infiltrating tumor within the larger T(2) lesion. The planning of focal therapies, such as surgery, radiation and targeted drug delivery, as well as a more reliable assessment of the response to therapy, would benefit considerably from the integration of metabolic and physiological imaging techniques into routine clinical MR examinations. Advanced methods that have been shown to provide valuable data for patients with glioma are diffusion, perfusion and spectroscopic imaging. Multiparametric examinations that include the acquisition of such data are able to assess tumor cellularity, hypoxia, disruption of normal tissue architecture, changes in vascular density and vessel permeability, in addition to the standard measures of changes in the volume of enhancing and nonenhancing anatomic lesions. This is particularly critical for the interpretation of the results of Phase I and Phase II clinical trials of novel therapies, which are increasingly including agents that are designed to have anti-angiogenic and anti-proliferative properties as opposed to having a direct effect on tumor cell viability.     

Nosologic imaging of the brain: segmentation and classification using MRI and MRSI

A new technique is presented to create nosologic images of the brain based on magnetic resonance imaging (MRI) and magnetic resonance spectroscopic imaging (MRSI). A nosologic image summarizes the presence of different tissues and lesions in a single image by color coding each voxel or pixel according to the histopathological class it is assigned to. The proposed technique applies advanced methods from image processing as well as pattern recognition to segment and classify brain tumors. First, a registered brain atlas and a subject‐specific abnormal tissue prior, obtained from MRSI data, are used for the segmentation. Next, the detected abnormal tissue is classified based on supervised pattern recognition methods. Class probabilities are also calculated for the segmented abnormal region. Compared to previous approaches, the new framework is more flexible and able to better exploit spatial information leading to improved nosologic images. The combined scheme offers a new way to produce high‐resolution nosologic images, representing tumor heterogeneity and class probabilities, which may help clinicians in decision making. Copyright © 2008 John Wiley & Sons, Ltd.     

动态增强MRI在骨关节中的热点研究

文题释义： 动态增强MRI：是一种MRI功能成像技术,采用快速MRI序列连续采集静脉注射对比剂前、中、后的图像,显示对比剂进入靶器官或组织血管、通过毛细血管床并最终被清除过程中的信息。与常规核磁增强不同的是,动态增强能够提供每一个时间点的强化信息,目前在肿瘤病灶的检出、良恶性病变的鉴别、肿瘤分级、肿瘤放化疗疗效监测、治疗后的预后评价等方面有重要的价值。 偶极-偶极作用：极性分子因电荷分布不均产生偶极矩,当极性分子靠近时,会造成电性的吸引,这种作用力称为偶极-偶极力。分子的偶极矩愈大,分子间的作用力愈大。 背景：动态增强MRI作为一种无创性检测方法,目前在肿瘤领域运用广泛,可进行肿瘤良恶性的鉴别、肿瘤级别的分级以及预后的预测与评估等。近年其在骨关节领域的运用研究逐渐成为热点,可用于骨髓血流灌注的测定、骨组织活性的评估、骨灌注异常的早期发现以及关节炎性病变血运的评估等。 目的：总结动态增强MRI的技术概况及其目前在骨关节方面的应用进展。 方法：英文检索式为“(bone OR joint) AND (dynamic contrast-enhanced MRI) OR dynamic contrast-enhanced magnetic resonance imaging)”,中文检索式为“(骨OR关节)AND动态增强磁共振”“(骨OR关节)AND 动态增强MRI”“(骨OR关节)AND DCE-MRI”,由第一作者检索1984至2019年PubMed、Springerlink以及中国期刊全文数据库(CNKI),查阅近年动态增强MRI在骨关节方面应用的相关文献,最终保留55篇文献进行总结分析。 结果与结论：①目前动态增强MRI成像技术及数据处理尚未标准化,在骨关节主要采用T1WI成像,可行定性、半定量及全定量分析;②定性分析及半定量分析操作简便,量化指标明确,能客观地描述曲线形态,但不能反映组织间、血管内的对比剂浓度,且容易受扫描参数序列的影响,无法检测组织药物代谢动力学信息;而定量分析能获得组织内亚结构间的对比剂浓度变化并生成参数,评估组织的微血管生成及其功能;③动态增强MRI可无创性评估骨关节的微循环灌注,对许多骨关节疾病发病机制的探讨、诊断及鉴别诊断、预后预测、疗效评估以及治疗方式的选择都有一定参考价值。 ORCID: 0000-0002-0093-9910(黄雪洁) 中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程     

Diagnosis of cerebrovascular disorders using nuclear magnetic resonance tomography

Regarding cerebrovascular diseases magnetic resonance imaging (MRI) provides informations which could not be obtained before by any other imaging method. MRI permits an early detection of ischemic infarctions, exact delineation of lesions near to skull base, and microangiopathy. Further diagnosis of arteriovenous malformations and venous thromboses can be done without using contrast media. Exclusion of acute hemorrhage or subarachnoidal hemorrhage is still a domain of computed tomography (CT). Other MR methods, like magnetic resonance angiography (MRA) and magnetic resonance spectroscopy (MRS) are expected to replace angiography and positron emission tomography (PET) in the near future, at least for some purposes.     

A review of diffusion tensor magnetic resonance imaging computational methods and software tools

In this work we provide an up-to-date short review of computational magnetic resonance imaging (MRI) and software tools that are widely used to process and analyze diffusion-weighted MRI data. A review of different methods used to acquire, model and analyze diffusion-weighted imaging data (DWI) is first provided with focus on diffusion tensor imaging (DTI). The major preprocessing, processing and post-processing procedures applied to DTI data are discussed. A list of freely available software packages to analyze diffusion MRI data is also provided.