Radiology: Magnetic Resonance Imaging of Musculoskeletal Tumors

The Scientific Board of the California Medical Association presents the following inventory of items of progress in radiology. Each item, in the judgment of a panel of knowledgeable physicians, has recently become reasonably firmly established, both as to scientific fact and important clinical significance. The items are presented in simple epitome, and an authoritative reference, both to the item itself and to the subject as a whole, is generally given for those who may be unfamiliar with a particular item. The purpose is to assist busy practitioners, students, researchers, or scholars to stay abreast of these items of progress in radiology that have recently achieved a substantial degree of authoritative acceptance. Whether in their own field of special interest or another.The items of progress listed below were selected by the Advisory Panel to the Section on Radiology of the California Medical Association, and the summaries were prepared under its direction.     

Dynamic Contrast-Enhanced and Diffusion-Weighted Magnetic Resonance Imaging Noninvasive Evaluation of Vascular Disrupting Treatment on Rabbit Liver Tumors

Evaluation of vascular disrupting treatment (VDT) is generally based on tumor size and enhancement on conventional magnetic resonance imaging (MRI) which, unfortunately, may be limited in providing satisfactory information. The purpose of the study is to evaluate consecutive changes of 20 rabbit VX2 liver tumors after VDT by dynamic contrast-enhanced MRI (DCE-MRI) and diffusion-weighted imaging (DWI) at a 3.0 T MR unit. Twenty four hours after intravenous injection of Combretastatin A-4-phosphate (CA4P) at 20 mg/kg, DCE-MRI derived Maximum Slope of Increase (MSI) and Positive Enhancement Integral (PEI) decreased sharply due to sudden shutting down of tumor feeding vessels. DWI derived Apparent Diffusion Coefficient (ADC) in tumor periphery decreased because of ischemic cell edema. On day 4, an increase of MSI was probably caused by the recovery of blood supply. A remarkable increase of ADC represented a large scale of necrosis among tumors. On day 8, the blood perfusion further decreased and the extent of necrosis further increased, reflected by lower MSI and PEI values and higher ADC value. On day 12, a second decrease of ADC was noticed because the re-growth of periphery tumor. The experimental data indicate that the therapeutic effects of VDT may be noninvasively monitored with DCE-MRI (reflecting tumor blood perfusion) and DWI (reflecting the changes of histology), which provide powerful measures for assessment of anticancer treatments.     

Detection of Lung Tumors in Mice Using a 1-Tesla Compact Magnetic Resonance Imaging System

Due to their small size, lung tumors in rodents are typically investigated using high-field magnetic resonance (MR) systems (4.7 T or higher) to achieve higher signal-to-noise ratios, although low-field MR systems are less sensitive to susceptibility artifacts caused by air in the lung. We investigated the feasibility of detecting lung tumors in living, freely breathing mice with a 1-T compact permanent magnet MR system. In total, 4 mice were used, and MR images of mouse lungs were acquired using a T1-weighted three-dimensional fast low-angle shot sequence without cardiac or respiratory gating. The delineation and size of lung tumors were assessed and compared with histopathological findings. Submillimeter lesions were demonstrated as hyperintense, relative to the surrounding lung parenchyma, and were delineated clearly. Among the 13 lesions validated in histopathological sections, 11 were detected in MR images; the MR detection rate was thus 84.6%. A strong correlation was obtained in size measurements between MR images and histological sections. Thus, a dedicated low-field MR system can be used to detect lung tumors in living mice noninvasively without gating.     

乳腺MR检查的常见伪影及解决方案

目的:分析乳腺MR检查中的常见伪影,探讨合理的解决方案,以提高乳腺MR图像质量及诊断准确性。方法:随机抽取我院100例行乳腺MR检查的图像资料,观察图像中出现的各种伪影及其表现,分析其产生的原因和影响因素。结果:乳腺MR图像的影像细节显示能力较强,图像质量与扫描技术关系密切,影响图像质量的常见伪影有:硬件相关伪影、图像处理相关伪影、运动相关伪影。结论:加强MR设备的使用管理,选择合理的扫描序列及参数,做好乳腺MR扫描的检查前准备及扫描,有助于提高乳腺病变的检出率。     

Diaphragm Postural Function Analysis Using Magnetic Resonance Imaging

We present a postural analysis of diaphragm function using magnetic resonance imaging (MRI). The main aim of the study was to identify changes in diaphragm motion and shape when postural demands on the body were increased (loading applied to a distal part of the extended lower extremities against the flexion of the hips was used). Sixteen healthy subjects were compared with 17 subjects suffering from chronic low back pain and in whom structural spine disorders had been identified. Two sets of features were calculated from MRI recordings: dynamic parameters reflecting diaphragm action, and static parameters reflecting diaphragm anatomic characteristics. A statistical analysis showed that the diaphragm respiratory and postural changes were significantly slower, bigger in size and better balanced in the control group. When a load was applied to the lower limbs, the pathological subjects were mostly not able to maintain the respiratory diaphragm function, which was lowered significantly. Subjects from the control group showed more stable parameters of both respiratory and postural function. Our findings consistently affirmed worse muscle cooperation in the low back pain population subgroup. A clear relation with spinal findings and with low back pain remains undecided, but various findings in the literature were confirmed. The most important finding is the need to further address various mechanisms used by patients to compensate deep muscle insufficiency.     

Brain Characterization Using Normalized Quantitative Magnetic Resonance Imaging

Objectives

To present a method for generating reference maps of typical brain characteristics of groups of subjects using a novel combination of rapid quantitative Magnetic Resonance Imaging (qMRI) and brain normalization. The reference maps can be used to detect significant tissue differences in patients, both locally and globally.

Materials and Methods

A rapid qMRI method was used to obtain the longitudinal relaxation rate (R₁), the transverse relaxation rate (R₂) and the proton density (PD). These three tissue properties were measured in the brains of 32 healthy subjects and in one patient diagnosed with Multiple Sclerosis (MS). The maps were normalized to a standard brain template using a linear affine registration. The differences of the mean value ofR₁, R₂ and PD of 31 healthy subjects in comparison to the oldest healthy subject and in comparison to an MS patient were calculated. Larger anatomical structures were characterized using a standard atlas. The vector sum of the normalized differences was used to show significant tissue differences.

Results

The coefficient of variation of the reference maps was high at the edges of the brain and the ventricles, moderate in the cortical grey matter and low in white matter and the deep grey matter structures. The elderly subject mainly showed significantly lower R₁ and R₂ and higher PD values along all sulci. The MS patient showed significantly lower R₁ and R₂ and higher PD values at the edges of the ventricular system as well as throughout the periventricular white matter, at the internal and external capsules and at each of the MS lesions.

Conclusion

Brain normalization of rapid qMRI is a promising new method to generate reference maps of typical brain characteristics and to automatically detect deviating tissue properties in the brain.     

Imaging Lymphatic System in Breast Cancer Patients with Magnetic Resonance Lymphangiography

Objective

To investigate the feasibility of gadolinium (Gd) contrast-enhanced magnetic resonance lymphangiography (MRL) in breast cancer patients within a typical clinical setting, and to establish a Gd-MRL protocol and identify potential MRL biomarkers for differentiating metastatic from non-metastatic lymph nodes.

Materials and Methods

32 patients with unilateral breast cancer were enrolled and divided into 4 groups of 8 patients. Groups I, II, and III received 1.0, 0.5, and 0.3 ml of intradermal contrast; group IV received two 0.5 ml doses of intradermal contrast. MRL images were acquired on a 3.0 T system and evaluated independently by two radiologists for the number and size of enhancing lymph nodes, lymph node contrast uptake kinetics, lymph vessel size, and contrast enhancement patterns within lymph nodes.

Results

Group III patients had a statistically significant decrease in the total number of enhancing axillary lymph nodes and lymphatic vessels compared to all other groups. While group IV patients had a statistically significant faster time to reach the maximum peak enhancement over group I and II (by 3 minutes), there was no other statistically significant difference between imaging results between groups I, II, and IV. 27 out of 128 lymphatic vessels (21%) showed dilatation, and all patients with dilated lymphatic vessels were pathologically proven to have metastases. Using the pattern of enhancement defects as the sole criterion for identifying metastatic lymph nodes during Gd-MRL interpretation, and using histopathology as the gold standard, the sensitivity and specificity were estimated to be 86% and 95%, respectively.

Conclusion

Gd-MRL can adequately depict the lymphatic system, can define sentinel lymph nodes, and has the potential to differentiate between metastatic and non-metastatic lymph nodes in breast cancer patients.     

磁共振成像对乳腺肿瘤的诊断价值

乳腺癌是危及女性健康的常见恶性肿瘤之一,病死率较高,且发病年龄呈年轻化趋势。目前临床对乳腺疾病的检查方法很多,既往检查主要包括钼靶、超声等,因价格便宜、操作方便,已成为常规的乳腺疾病检查方法,但两者的敏感性和特异性较低并有自身的局限性。CT软组织分辨率较高,但检查过程中的X线剂量较大,并且动态增强时间较长,故作为乳腺钼靶的补充检查手段。这些检查方法对乳腺疾病均有不同的诊断意义,在当前众多诊断乳腺疾病方法中,具有无辐射,较高软组织分辨力及可多方位多层面成像的乳腺磁共振(MRI)成像有其独到的优势,某些方面能弥补超声和钼靶检查的局限性,乳腺磁共振可提供病灶形态学和增强血流动力学表现,可用于常规检查方法不能确诊病灶的鉴别诊断。乳腺肿瘤MRI成像对临床诊断、鉴别诊断及手术方案的选择有着极其重要的作用。本文就乳腺MRI影像技术、MRI影像学表现及其临床应用予以综述,探讨MRI在乳腺肿瘤中的应用。     

Noninvasive Cardiac Flow Assessment Using High Speed Magnetic Resonance Fluid Motion Tracking

Cardiovascular diseases can be diagnosed by assessing abnormal flow behavior in the heart. We introduce, for the first time, a magnetic resonance imaging-based diagnostic that produces sectional flow maps of cardiac chambers, and presents cardiac analysis based on the flow information. Using steady-state free precession magnetic resonance images of blood, we demonstrate intensity contrast between asynchronous and synchronous proton spins. Turbulent blood flow in cardiac chambers contains asynchronous blood proton spins whose concentration affects the signal intensities that are registered onto the magnetic resonance images. Application of intensity flow tracking based on their non-uniform signal concentrations provides a flow field map of the blood motion. We verify this theory in a patient with an atrial septal defect whose chamber blood flow vortices vary in speed of rotation before and after septal occlusion. Based on the measurement of cardiac flow vorticity in our implementation, we establish a relationship between atrial vorticity and septal defect. The developed system has the potential to be used as a prognostic and investigative tool for assessment of cardiac abnormalities, and can be exploited in parallel to examining myocardial defects using steady-state free precession magnetic resonance images of the heart.     

Characterization of Breast Tumors Using Diffusion Kurtosis Imaging (DKI)

Aim

The aim of this study was to investigate and evaluate the role of magnetic resonance (MR) diffusion kurtosis imaging (DKI) in characterizing breast lesions.

Materials and Methods

One hundred and twenty-four lesions in 103 patients (mean age: 57±14 years) were evaluated by MR DKI performed with 7 b-values of 0, 250, 500, 750, 1,000, 1,500, 2,000 s/mm² and dynamic contrast-enhanced (DCE) MR imaging. Breast lesions were histologically characterized and DKI related parameters—mean diffusivity (MD) and mean kurtosis (MK)—were measured. The MD and MK in normal fibroglandular breast tissue, benign and malignant lesions were compared by One-way analysis of variance (ANOVA) with Tukey''s multiple comparison test. Receiver operating characteristic (ROC) analysis was performed to assess the sensitivity and specificity of MD and MK in the diagnosis of breast lesions.

Results

The benign lesions (n = 42) and malignant lesions (n = 82) had mean diameters of 11.4±3.4 mm and 35.8±20.1 mm, respectively. The MK for malignant lesions (0.88±0.17) was significantly higher than that for benign lesions (0.47±0.14) (P<0.001), and, in contrast, MD for benign lesions (1.97±0.35 (10⁻³ mm²/s)) was higher than that for malignant lesions (1.20±0.31 (10⁻³ mm²/s)) (P<0.001). At a cutoff MD/MK 1.58 (10⁻³ mm²/s)/0.69, sensitivity and specificity of MD/MK for the diagnosis of malignant were 79.3%/84.2% and 92.9%/92.9%, respectively. The area under the curve (AUC) is 0.86/0.92 for MD/MK.

Conclusions

DKI could provide valuable information on the diffusion properties related to tumor microenvironment and increase diagnostic confidence of breast tumors.     

Noninvasive Assessment of Cardiac Abnormalities in Experimental Autoimmune Myocarditis by Magnetic Resonance Microscopy Imaging in the Mouse

Myocarditis is an inflammation of the myocardium, but only ~10% of those affected show clinical manifestations of the disease. To study the immune events of myocardial injuries, various mouse models of myocarditis have been widely used. This study involved experimental autoimmune myocarditis (EAM) induced with cardiac myosin heavy chain (Myhc)-α 334-352 in A/J mice; the affected animals develop lymphocytic myocarditis but with no apparent clinical signs. In this model, the utility of magnetic resonance microscopy (MRM) as a non-invasive modality to determine the cardiac structural and functional changes in animals immunized with Myhc-α 334-352 is shown. EAM and healthy mice were imaged using a 9.4 T (400 MHz) 89 mm vertical core bore scanner equipped with a 4 cm millipede radio-frequency imaging probe and 100 G/cm triple axis gradients. Cardiac images were acquired from anesthetized animals using a gradient-echo-based cine pulse sequence, and the animals were monitored by respiration and pulse oximetry. The analysis revealed an increase in the thickness of the ventricular wall in EAM mice, with a corresponding decrease in the interior diameter of ventricles, when compared with healthy mice. The data suggest that morphological and functional changes in the inflamed hearts can be non-invasively monitored by MRM in live animals. In conclusion, MRM offers an advantage of assessing the progression and regression of myocardial injuries in diseases caused by infectious agents, as well as response to therapies.     

Selective Histochemical Identification of Nerve Cell Populations Using Fucose-Specific Lectins

We studied lectin-histochemical properties of the components of caudal ganglia of the vagus nerve and ganglion of the trigeminal nerve in white rats using fucose-specific lectin–peroxidase conjugates. Morphological preparations were processed using a computer video analyzer. Metrical and optical indices of the afferent neurons were analyzed. The results demonstrated differences in the composition and topography of glycoconjugates in the afferent ganglia. Application of recent image-processing techniques made it possible to identify the neurocyte populations undetectable by conventional morphological methods in the afferent ganglia of rats.     

A Polymer-Based Magnetic Resonance Tracer for Visualization of Solid Tumors by 13C Spectroscopic Imaging

Morphological imaging precedes lesion-specific visualization in magnetic resonance imaging (MRI) because of the superior ability of this technique to depict tissue morphology with excellent spatial and temporal resolutions. To achieve lesion-specific visualization of tumors by MRI, we investigated the availability of a novel polymer-based tracer. Although the ¹³C nucleus is a candidate for a detection nucleus because of its low background signal in the body, the low magnetic resonance sensitivity of the nucleus needs to be resolved before developing a ¹³C-based tracer. In order to overcome this problem, we enriched polyethylene glycol (PEG), a biocompatible polymer, with ¹³C atoms. ¹³C-PEG40,000 (¹³C-PEG with an average molecular weight of 40 kDa) emitted a single ¹³C signal with a high signal-to-noise ratio due to its ability to maintain signal sharpness, as was confirmed by in vivo investigation, and displayed a chemical shift sufficiently distinct from that of endogenous fat. ¹³C-PEG40,000 intravenously injected into mice showed long retention in circulation, leading to its effective accumulation in tumors reflecting the well-known phenomenon that macromolecules accumulate in tumors because of leaky tumor capillaries. These properties of ¹³C-PEG40,000 allowed visualization of tumors in mice by ¹³C spectroscopic imaging. These findings suggest that a technique based on ¹³C-PEG is a promising strategy for tumor detection.     

磁共振成像设备发展趋势

本文主要叙述了磁共振设备的原理、构造、产品发展趋势。并对提高磁共振图像分辨的新技术,如Tim全景矩阵成像、自由浪潮技术、高清晰MRI技术和双梯度技术作了综述。     

乳腺癌功能磁共振成像与生物学预后因子的研究进展

乳腺癌已成为女性最为常见的恶性肿瘤,如何对乳腺癌进行早期诊断、合理化治疗及判断预后意义重大。雌激素受体(ER)、孕激素受体(PR)、Ki-67、人表皮生长因子受体2(HER-2)等免疫组化指标在判断乳腺癌临床类型、转移情况及预后等方面具有重要作用。随着功能磁共振的发展,氢质子磁共振波谱(1H-MRS)、动态增强磁共振成像(DCE-MRI)、扩散加权成像(DWI)等被越来越广泛的用于乳腺组织的检查。研究功能磁共振与乳腺癌预后因子的相关性,对乳腺癌的临床分型、治疗及预后等方面有一定的指导作用。本文就相关进展进行综述。     

核磁功能成像在前列腺癌诊断中的应用

磁共振成像是诊断早期前列腺癌及评价分期最好的影像学技术之一,然而常规MRI-T2WI在诊断中存在较低的特异性缺陷.随着核磁技术的发展,对前列腺癌的诊断发展到从定性到定量、从形态到功能的变化,本文主要就近年来的磁共振功能成像技术在前列腺癌诊断中的研究进展作一论述.     

Vibrant技术在磁共振双侧乳腺动态增强检查中的应用及优势

目的：探讨Vibrant 软件技术在磁共振双侧乳腺动态增强检查中的应用及优势。方法：回顾性分析我院经手术或穿刺病理证 实的乳腺疾病患者70 例,均为女性,按照Vibrant 动态增强检查扫描的时间不同,分为A、B 两组,每组35 例。两组病例均采用 1.5T MR 机行动态增强检查。A 组病例行Vibrant 动态增强的扫描时间为9 分24 秒,B组病例行Vibrant 动态增强的扫描时间为 7 分42 秒。结果：A 组病例动态增强MRI 诊断的敏感性为94.74%,特异性为85%,准确性为89.74%;B 组病例动态增强MRI诊 断的敏感性为91.3%,特异性为89.47%,准确性为90.48%。两组病例动态增强MRI对病灶诊断的敏感性、特异性和准确性无显著 性差异（P>0.05）。结论：Vibrant乳腺动态增强扫描技术在乳腺疾病的诊断中具有较高的诊断敏感性、特异性和准确性。Vibrant技 术在缩短增强扫描时间的情况下不降低其诊断效能。     

Accelerating Fibre Orientation Estimation from Diffusion Weighted Magnetic Resonance Imaging Using GPUs

With the performance of central processing units (CPUs) having effectively reached a limit, parallel processing offers an alternative for applications with high computational demands. Modern graphics processing units (GPUs) are massively parallel processors that can execute simultaneously thousands of light-weight processes. In this study, we propose and implement a parallel GPU-based design of a popular method that is used for the analysis of brain magnetic resonance imaging (MRI). More specifically, we are concerned with a model-based approach for extracting tissue structural information from diffusion-weighted (DW) MRI data. DW-MRI offers, through tractography approaches, the only way to study brain structural connectivity, non-invasively and in-vivo. We parallelise the Bayesian inference framework for the ball & stick model, as it is implemented in the tractography toolbox of the popular FSL software package (University of Oxford). For our implementation, we utilise the Compute Unified Device Architecture (CUDA) programming model. We show that the parameter estimation, performed through Markov Chain Monte Carlo (MCMC), is accelerated by at least two orders of magnitude, when comparing a single GPU with the respective sequential single-core CPU version. We also illustrate similar speed-up factors (up to 120x) when comparing a multi-GPU with a multi-CPU implementation.