Functional magnetic resonance imaging of the liver: parametric assessments beyond morphology

There is growing interest in exploring and using functional imaging techniques to provide additional information on structural alterations in the liver, which often occur late in the disease process. This article presents a summary of the different functional MR imaging techniques currently in use, focusing on dynamic contrast-enhanced MR imaging, diffusion-weighted MR imaging, MR spectroscopy, in- and oppose-phase MR imaging, and T2*-weighted imaging. For each technique, the biologic underpinning for the technique is explained, the clinical applications surveyed, and the challenges for their application enumerated. Developing and less frequently used techniques such as MR elastography, blood oxygenation level dependent imaging, dynamic susceptibility contrast-enhanced MR imaging, and diffusion-tensor imaging are reviewed. The challenges widespread adoption of functional MR imaging and the translation of such techniques to high field strengths are also discussed.     

MR imaging and spectroscopy of brain development

MR imaging provides an invaluable tool for the study of brain development in vivo. Current MR imaging techniques allow noninvasive methodologies, without ionizing radiation, that provide a diversity of information on structure, metabolism, and function of the developing brain. This article focuses on the application of conventional and advanced MR imaging techniques, including quantitative morphometric MR imaging, diffusion-weighted, functional MR, and MR spectroscopic imaging to the study of early human brain development.     

Advances in magnetic resonance neuroimaging techniques in the evaluation of neonatal encephalopathy

Magnetic resonance (MR) imaging has become an essential tool in the evaluation of neonatal encephalopathy. Magnetic resonance-compatible neonatal incubators allow sick neonates to be transported to the MR scanner, and neonatal head coils can improve signal-to-noise ratio, critical for advanced MR imaging techniques. Refinement of conventional imaging techniques include the use of PROPELLER techniques for motion correction. Magnetic resonance spectroscopic imaging and diffusion tensor imaging provide quantitative assessment of both brain development and brain injury in the newborn with respect to metabolite abnormalities and hypoxic-ischemic injury. Knowledge of normal developmental changes in MR spectroscopy metabolite concentration and diffusion tensor metrics is essential to interpret pathological cases. Perfusion MR and functional MR can provide additional physiological information. Both MR spectroscopy and diffusion tensor imaging can provide additional information in the differential of neonatal encephalopathy, including perinatal white matter injury, hypoxic-ischemic brain injury, metabolic disease, infection, and birth injury.     

DWI与1H MRS基本原理及其在脑肿瘤中的应用

磁共振扩散加权成像（DWI）及磁共振波谱（MRS）是目前较先进的磁共振成像技术,二者能提供常规MRI所不能获得的信息。DWI及MRS在脑肿瘤的鉴别诊断、分级、肿瘤边界的界定、疗效及预后评估等方面的研究发展很快,本文就DWI及1HMRS的基本原理及其在脑肿瘤中的临床应用作一综述。     

Assessment of valve disease: qualitative and quantitative

Evaluation of valve disease has changed significantly with the development of color Doppler echocardiography. Nevertheless, this technique has limitations, particularly in the assessment of valvular regurgitation. MR imaging, with its ability to provide three-dimensional morphologic data, dynamic cine information, and functional evaluation with flow-sensitive techniques, can be envisioned as a complementary noninvasive modality, able to provide the complete information required for planning therapeutic options. With MR imaging, qualitative as well as accurate and reproducible quantitative information such as volume measurements, cardiac function, and flow velocity profiles are unique for the evaluation of the severity of valve disease. This article reviews the different MR imaging techniques used in assessing valvular heart disease and discusses the advantages and limitations of these techniques in current clinical applications in comparison with classical imaging methods.     

Novel techniques for MR imaging of pulmonary airspaces

Hyperpolarized gas- and molecular oxygen-enhanced MR imaging are two new techniques for high-resolution MR imaging of pulmonary airspaces. Both techniques produce excellent images in a safe, reproducible, and technically feasible manner. Because morphologic and functional information is obtained, and radiation is not used, these techniques may prove ideal for serially evaluating patients with a variety of lung diseases that affect pulmonary ventilation, such as cystic fibrosis, emphysema, asthma, or bronchiolitis obliterans syndrome in lung transplant recipients. At present, the greatest clinical experience is with hyperpolarized He-3-enhanced MR imaging. This technique is limited, however, by the limited availability of He-3, by its polarization requirements, and by the need to tune the MR system to the resonant frequency of the gas. There is less clinical experience with oxygen-enhanced MR imaging. Although this technique produces images with more inherent noise than hyperpolarized He-3 imaging, this problem can be overcome by signal averaging. Oxygen-enhanced imaging has the major advantages of lower cost and ready availability. For oxygen-enhanced imaging, the MR imaging system does not need to be readjusted; imaging is performed at the conventional hydrogen proton frequency.     

MR imaging of malignant uterine disease

The role of MR imaging in the diagnosis and management of patients who have uterine malignancy continues to evolve. MR imaging has been shown to be effective for preoperative characterization and staging of endometrial and cervical carcinoma, and for the evaluation of posttreatment changes and recurrent disease. Because of its potential to provide detailed information about local extent and metastatic disease, MR imaging has enormous potential to help triage patients to appropriate treatment groups and provide imaging surveillance after therapy. This article reviews the MR imaging technique and the imaging characteristics of malignant disease of the uterine corpus and cervix.     

MRI电影对月经过多子宫肌瘤患者子宫蠕动的研究

目的应用MR电影成像技术(cine MRI)探讨月经过多子宫肌瘤患者排卵期子宫蠕动情况及肌瘤位置对子宫蠕动的影响。材料与方法采用1.5 T MRI仪对30名健康志愿者及30例月经过多子宫肌瘤患者于排卵期行盆腔T1轴面、T2-抑脂轴面、T2矢状面及子宫cine MR扫描。比较健康志愿者与月经过多肌瘤患者子宫正常蠕动存在率及蠕动频率,分析肌瘤位置与蠕动形式的关系。结果月经过多子宫肌瘤患者排卵期子宫正常蠕动存在率及蠕动频率较健康志愿者显著降低,两者均有统计学意义(P值均0.01),黏膜下肌瘤患者主要表现为无蠕动,肌壁间肌瘤患者蠕动形式多样。结论月经过多子宫肌瘤患者排卵期子宫正常蠕动显著减少,不利于排卵期精子快速进入输卵管;Cine MRI有助于月经过多子宫肌瘤患者子宫蠕动的评价,为临床提供子宫蠕动的功能信息。     

MR imaging of the neonatal musculoskeletal system

Experience in magnetic resonance (MR) imaging of the neonatal musculoskeletal system is rapidly increasing. The exquisite ability of MR to image the soft tissues, especially cartilage, without radiation is its key strength. Although it is not practical or sensible to undertake MR imaging in conditions in which radiography and ultrasound provide adequate information, MR is proving to be a useful adjunct and problem-solving tool in many neonatal musculoskeletal conditions.     

MR imaging of the thyroid and parathyroid glands

Whereas scintigraphy and ultrasonography are the primary imaging modalities used for the investigation of thyroid disorders, MR imaging is generally used for specific indications, including evaluating the extent of substernal goiters, assessing the effect on adjacent structures, imaging the local extent of thyroid carcinomas, and localizing recurrent sites of thyroid neoplasia. MR imaging also has been used for the investigation of congenital disorders of the thyroid gland and the evaluation of diffuse thyroid disease, such as Grave's disease, Hashimoto's and Riedel thyroiditis, and hemochromatosis. MR imaging of the parathyroid glands is generally used for patients with recurrent or persistent hyperparathyroidism following neck exploration. MR imaging provides useful information about morphologic abnormalities of the thyroid and parathyroid glands. MR imaging has good sensitivity and positive predictive value for the identification of non-ectopic and ectopic abnormal parathyroid glands. The detailed anatomic information provided by MR imaging is useful in planning a surgical approach and is complementary to other imaging methods used in the investigation of recurrent or persistent hyperparathyroidism.     

The role of magnetic resonance in the evaluation of functional results after CABG/PTCA

Magnetic resonance imaging (MRI) is a non-invasive modality which can be used for direct visualization of coronary artery bypass grafts. Spin-echo and gradient-echo (cine-MRI) techniques are now available on standard MR machines and provide information on graft morphology and graft patency with a 90% accuracy. By combining the standard techniques with MR phase velocity mapping, the flow rate in the graft can be measured, thereby offering a unique non-invasive assessment of the graft function. Newer techniques include MR coronary angiography, pharmacologically induced stress MRI, ultrafast MRI of the first-pass (perfusion) of a paramagnetic contrast agent through the myocardium, and³¹P MR spectroscopy of high-energy phosphate metabolism of the myocardium. All of these may develop into valuable diagnostic tools for the assessment of functional results after CABG or PTCA, but still require clinical validation. At present, MRI is a useful screening procedure for assessment of graft patency and function in post-operative pain syndromes and in late graft occlusion or stenosis.     

MR imaging of mediastinal masses

Although ongoing developments in MR imaging have resulted in improved image quality and decreased acquisition time, MR imaging is largely used as an adjunct to CT scanning in the evaluation of mediastinal abnormalities. In this role, MR imaging often provides additional information about the nature, location, and extent of disease. MR imaging is useful in confirming the cystic nature of mediastinal lesions that appear solid on CT and, by revealing small amounts of intralesional fat, can suggest the diagnosis of hemangioma, teratoma, or extramedullary hematopoesis. MR imaging is the preferred modality for imaging neurogenic tumors, because its multiplanar capability and high contrast resolution can best demonstrate the number and nature of the lesions (differentiating cysts from neoplasms), intraspinal extension, and craniocaudad extent. MR imaging is also especially useful for evaluating the mediastinum of patients for whom the administration of iodinated contrast material is contraindicated.     

Cardiothoracic magnetic resonance angiography.

At the current state of the art, cardiothoracic MR angiography offers the clinician information that is supplemental to that provided by other noninvasive imaging techniques. Indeed, in some areas MR angiography will likely surpass currently used methods as the technique of choice. Specifically, measurement of cardiac output, pulmonary blood flow, and lung perfusion can be performed relatively accurately and simply during a brief MR examination. Both standard spin-echo and angiographic evaluation of the thoracic aorta provide qualitative images with superior resolution. Additionally, development of pulmonary artery angiography is progressing rapidly and may soon be clinically useful. Phase incoherence caused by complex flow and resulting in a signal void is useful for location and qualitative assessment of abnormal flow jets induced by stenoses. However, this phenomenon represents the major limitation to quantitative assessment of flow abnormalities. Methods to increase signal to noise and/or reduce phase incoherence must be developed before MR angiography can be used effectively to assess abnormal flow conditions.     

Functional MR imaging of the lung

Recent development of MR techniques has overcome many problems, such as susceptibility artifacts or motion artifact, allowing both static and dynamic MR lung imaging and providing quantitative information of pulmonary function, including perfusion, ventilation, and respiratory motion. Dynamic contrast-enhanced MR perfusion imaging is suitable for the evaluation of angiogenesis of pulmonary solitary nodules. (129)Xe MR imaging is potentially a robust technique for the evaluation of various pulmonary function and may replace (3)He. The information provided by these new MR imaging methods is proving useful in research and in clinical applications in various lung diseases.     

Renal MR angiography

The high accuracy of renal MR angiography makes it well suited for diagnosing renal vascular disease. A comprehensive examination includes three-dimensional gadolinium MR angiography to assess lumenal anatomy and functional techniques to assess the hemodynamic significance of any stenosis identified. Postprocessing is critical to provide reformations, maximum intensity projections, and optional volume-rendered images to display arteries in an angiographic format for optimal demonstration of any vascular lesions. It is important to review source images to avoid missing pathologic findings. As MR imaging continues to develop, the renal MR angiography examination will likely expand to include extensive functional information about creatinine clearance, flow, and response to pharmacologic agents as well as spectroscopy, diffusion, perfusion, phase contrast, and other techniques.     

Assessment of cardiac function with MR imaging

A variety of black or white blood imaging techniques are available for assessing global and regional LV and RV function during cardiovascular MR imaging examinations. In addition to providing information about LV function at rest, these techniques provide diagnostic and prognostic information regarding myocardial ischemia and viability during MR imaging stress tests.     

西门子磁共振技术在乳腺疾病诊断中的应用

随着西门子磁共振技术的飞速发展,磁共振乳腺成像已经能够满足高空间分辨率和高时间分辨率的要求,并与先进的运动校正技术一起可以得到真实、准确的病变信息。乳腺波谱技术对于乳腺良恶性病变的鉴别起到非常重要的作用,并用于乳腺病变治疗后的疗效评估和追踪随访。另外,近些年磁共振乳腺活检技术应用于乳腺病变的鉴别诊断大大提高病变定性的准确性,对于乳腺疾病的治疗起到很大的指导作用。     

MR urography: technique and results for the evaluation of urinary obstruction in the pediatric population

MR urography has the potential to revolutionize imaging of the urinary tract in both adults and children, because of its ability to provide an unprecedented level of anatomic information and quantitative functional evaluation of each kidney. MR urography can now provide useful assessment of obstructive uropathy and may provide predictive information about which children will benefit from surgery. It has the potential to identify parameters that indicate a significant obstruction as opposed to self-limited hydronephrosis. Further technical developments in the field will produce greater insights into the pathophysiology of not only urologic disorders but also disorders of the kidney itself.     

Newer MR imaging techniques for head and neck

Dynamic and functional imaging techniques are being developed to improve the evaluation of various pathologic processes of the head and neck region. These techniques include dynamic contrast-enhanced MR imaging for evaluating soft tissue masses and cervical lymph nodes, the use of ultrasmall superparamagnetic iron oxide contrast agent, and functional techniques such as in vivo and in vitro MR spectroscopy of head and neck cancer and lymph nodes and apparent diffusion coefficient mapping of parotid glands. These techniques can help to differentiate nonmalignant tissue from malignant tumors and lymph nodes and can aid in differentiating residual malignancies from postradiation changes. From methodological development, they are making the critical transition to preclinical and clinical validating methods and eventually to widespread clinical tools.     

MR imaging of nephropathies

Acute and chronic nephropathies are responsible for morphologic and functional renal changes. However, radiologic techniques currently play a minor role in imaging of parenchymal nephropathies in native or transplanted kidneys. From a morphologic point of view, three-dimensional magnetic resonance (MR) volumetric biomarkers of kidney function, such as renal and cortical volumes or cystic volume, in polycystic kidney diseases play a growing role in nephrologic practice. From a functional point of view, if scintigraphic techniques remain the major sources of renal performance assessment, new MR imaging systems and specific MR contrast agents may soon provide significant developments in the evaluation of renal performance (glomerular filtration rate measurement), in the search for prognostic factors (hypoxia, inflammation, cell viability, degree of tubular function, and interstitial fibrosis), and for monitoring new cell therapies. New developments that have provided higher signal-to-noise ratio and higher spatial and/or temporal resolutions have the potential to direct new opportunities for obtaining morphologic and functional information on tissue characteristics that are relevant for various renal diseases with respect to diagnosis, prognosis, and treatment follow-up.