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.     

Evolution of the continuity equation in the Doppler echocardiographic assessment of the severity of valvular aortic stenosis

The use of Doppler techniques has greatly enhanced the noninvasive ultrasound technique for evaluation of valvular aortic stenosis. M-mode and two-dimensional echocardiography could not reliably distinguish patients with severe aortic stenosis from those with milder obstructions. The hemodynamic information offered by Doppler complemented echocardiographic imaging and provided an alternative modality for evaluation of patients with aortic stenosis. By application of the modified Bernoulli equation, the pressure gradient across the stenotic aortic valve could be estimated by Doppler echocardiography. Though helpful and widely used, the information provided by the pressure gradient across the valve about the severity of the obstruction was not complete. The assessment of valvular aortic stenosis therefore includes an estimation of the valve area by application of the continuity equation. This review examines the maturation of the continuity equation by Doppler techniques and discusses the implications of the procedure.     

Diffusion and perfusion MR imaging of the prostate

Conventional anatomic MR imaging has evolved to a superior modality in the evaluation of prostate carcinoma and is now a widely established technique in the detection and staging of this disease, aiding in clinical decision making on treatment and therapy evaluation. Recent improvements in functional MR techniques, such as diffusion-weighted MR imaging and dynamic contrast-enhanced MR imaging, have greatly increased the impact of MR imaging in prostate cancer. The combination of T2-weighted imaging, diffusion-weighted MR imaging, and dynamic contrast-enhanced MR imaging may overcome the limitations of conventional T2-weighted MR imaging of the prostate and may be able accurately to detect, localize, stage, and grade prostate carcinoma and guide biopsies.     

Magnetic-resonance velocity mapping of the central circulation

Summary. In magnetic-resonance (MR) velocity mapping there exists a linear relationship between the velocity and signal in each element of a tomographic image. The technique can be used for quantitative measurements of linear velocities (m s^_1) and flow rates (1 min^-1). By using cinematographic images the flow profile during the cardiac cycle can be determined. This allows quantification of forward flow, regurgitant volume and regurgitant fraction in cases of heart-valve insufficiency. In valvular stenosis the transvalvular pressure gradient and valve area can be determined. Magnetic-resonance velocity mapping may also provide information about diastolic function of left ventricular function. Together with other MR imaging techniques, velocity mapping gives an accurate assessment of the severity of aortic dissection. Recent studies indicate that MR velocity mapping provides quantification of renal blood flow, and that MR imaging may be used even for coronary angiography and measurements of coronary blood flow. Therefore MR velocity mapping has the potential to become an important clinical tool for examination of the cardiovascular system providing high accuracy and quantitative measurements.     

Contrast-enhanced MRI of the small bowel in Crohn��s disease

Recently, magnetic resonance imaging has emerged as a valuable tool in evaluation of small bowel Crohn’s disease. MRI provides several advantages to other imaging modalities, including the lack of ionizing radiation, multiplanar capability, and functional information. Intravenous contrast administration is a routine portion of MR enterography protocol, and aids in detection of disease extent, extramural complications such as fistula and abscess, and assessment of activity. Additionally, promising techniques such as dynamic contrast-enhanced MRI may provide quantitative measures to assess bowel perfusion, which may enhance evaluation of disease activity. This article will provide an overview of the technical aspects of contrast-enhanced MR enterography, describe common pathologic findings involving the small bowel in Crohn’s disease, summarize its role in determination of activity with an emphasis on endoscopic and histologic correlation, and compare its efficacy with other imaging modalities.     

The current state of imaging the articular cartilage of the upper extremity

MR imaging has increasingly been used to image joints since its inception. Historically, there has been more emphasis on the evaluation of internal derangement rather than cartilaginous disease. This article reviews cartilaginous diseases of the upper extremity emphasizing those that can be assessed using current clinical MR imaging protocols and addresses the limitations of current imaging techniques in evaluating the articular cartilage of smaller joints. It also provides a brief overview of novel techniques that may be instituted in the future to improve the diagnostic performance of MR imaging in the evaluation of the articular cartilage of the upper extremity.     

心血管磁共振成像临床应用和新进展

近年来由于MRI的进展,现已成为医学成像技术的主要组成部分,心血管MRI已广泛、有效地应用于心脏、大血管、内脏和外周血管成像及诊治工作.本文简要叙述心血管MRI临床应用概况,如对胸主动脉疾患、缺血性心脏病、心肌病、心脏肿瘤、先心病、心包疾患和心脏瓣膜病的诊断评价等.重点讨论一些新进展,如MR心肌灌注成像和心肌存活的评价;MR冠脉造影和斑块成像;深静脉血栓和肺栓塞的MR诊断以及MR血管造影对腹主-髂股-下肢动脉狭窄性病变的诊断及效果分析.     

Minimally invasive repair of the mitral valve: Technological and clinical developments

Abstract

The present article will review new technology in the invasive approach to mitral valvular disease. Mitral valve pathology continues to present an important challenge to the cardiac surgeon and interventionalist. From the early days of closed mitral valvular commisurotomy, a number of new approaches to this valve have been developed. Mitral stenosis was previously approached through a minimally invasive beating heart surgical approach, but may now be treated with either catheter-based or open surgical techniques. Regurgitation, which has become the leading pathology of the mitral valve in the developed world, may be approached through traditional cardiac surgery or through catheter-based techniques. New imaging techniques and device innovation will cause drastic changes in therapy for mitral valvular disease in the foreseeable future.     

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.     

Crohn disease of the small bowel: MR enteroclysis versus conventional enteroclysis

Enteroclysis has been suggested as the technique of choice for the evaluation of Crohn disease of the small intestine. Adequate distention of the entire small bowel with barium suspension allows the radiologic demonstration of mucosal abnormalities and provides functional information by defining distensibility or fixation of the small bowel loops. The principal disadvantage of conventional enteroclysis is the limited indirect information on the state of the bowel wall and extramural extension of Crohn disease, and its effectiveness may be hindered owing to overlapping bowel loops. Moreover, the radiation dose administered to patients, mostly at a young age, should be considered. Magnetic resonance (MR) enteroclysis is an emerging technique for small bowel imaging and was introduced to overcome the limitations of conventional enteroclysis and MR cross-sectional imaging by combining the advantages of both into one technique. MR enteroclysis has the potential to change how the small bowel is assessed because of the functional information, soft tissue contrast, direct multiplanar imaging capabilities, and lack of ionizing radiation.     

Techniques for liver MR imaging.

MR imaging provides exquisite, versatile, and unique soft tissue contrast, which allows for an effective evaluation of a wide range of liver disorders. A careful selection of imaging strategies can yield a comprehensive assessment of the liver in a reasonable examination time. Recent advances in MR hardware and software allow for rapid acquisition times that can bypass many of the motion artifacts that previously posed limitations to abdominal MR imaging. The ability to obtain artifact-free images with sufficient contrast-to-noise ratios across a broad range of techniques is now feasible with rapid scanning. This capability has emerged as the result of the implementation of high-performance gradient systems and localized phased-array body coils. In this article, the authors review the current status of MR imaging strategies for the evaluation of the liver, with an emphasis on the use of fast scanning techniques.     

Ischemic heart disease: value of MR techniques

Background. The cardiovascular applications of magnetic resonance (MR) techniques in coronary artery disease have increased considerably in recent years. Technical advantages of MR imaging are the excellent spatial resolution, the characterization of myocardial tissue, and the potential for three-dimensional imaging. These characteristics allow the accurate assessment of left ventricular mass and volume, the differentiation of infarcted from normal tissue, and the determination of systolic wall thickening and regional wall motion abnormalities. Methods. In addition to the conventionally used spin-echo and cine-echo techniques, newer techniques such as myocardial tagging, ultrafast MR imaging and MR coronary angiography have been developed. These newer techniques allow a more accurate assessment of ventricular function (tagging), myocardial perfusion (ultrafast imaging), and evaluation of stenosis severity (MR coronary angiography). Particularly early detection and flow assessment of stenosed coronary arteries and bypasses by MR angiography would constitute a major breakthrough in cardiovascular MR imaging. Apart from the MR imaging techniques, cardiac metabolism may be well assessed using MR spectroscopy. This provides unique information on the metabolic behaviour of the myocardium under conditions stress-induced ischemia. However, the definite niche of cardiac MR spectroscopy has still to be settled. Conclusion. Currently, MR techniques allow the evaluation of anatomy and function (accepted use), perfusion and viability (development phase), and coronary angiography (experimental phase). A particular strength of MR imaging is that one single MR test may encompass cardiac anatomy, perfusion, function, metabolism and coronary angiography. The replacement of multiple diagnostic tests with one MR test may have major effects on cardiovascular healthcare economics and would outweigh the cost inherent to the MR angiography procedure.     

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.     

Differential diagnostic approach to MR imaging of white matter diseases

OBJECTIVES: The purpose of this article is to explore the magnetic resonance (MR) imaging features and the advanced MR techniques for differential diagnosis of white matter diseases of the brain. RESULTS: Magnetic resonance imaging is exquisitely sensitive for detecting brain abnormalities. Particularly in the evaluation of white matter diseases, MR far outperforms any other imaging technique. Lesions that may be quite subtle or even invisible on computed tomography are often clearly seen on the MR scan. The MR signal characteristics of white matter lesions are similar and relatively nonspecific, but other distinguishing features are often present to assist in diagnosis, such as the pattern of the abnormality, location, signal intensities, and enhancement features. Advanced MR techniques, such as diffusion-weighted imaging, MR spectroscopy, and perfusion imaging, provide additional specificity to the diagnosis of demyelinating diseases. CONCLUSIONS: Conventional MR images and advanced MR techniques are very helpful in distinguishing various types of white matter disease, for assessing disease burden, and for separating acute and chronic lesions.     

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.     

Female pelvis

MR is the diagnostic imaging modality of choice for many disorders of the female pelvis. Benign uterine disease is well-demonstrated using rapid sequences and minimal examination time,whereas evaluation of malignancy is best performed with high-resolution techniques. Wide-spread availability of ultrafast sequences has expanded MR imaging applications to include evaluation of pelvic floor relaxation and fetal anomalies. Promising developments, such as new contrast agents, MR-guided focused ultrasound,and 3 tesla imaging, suggest continued advancement of MR imaging in the care of patients who have gynecologic disease.     

超声心动图评估主动脉瓣置换术后早期并发症的临床应用

主动脉瓣置换术(AVR)是目前治疗有症状的主动脉瓣病变的标准手术。AVR可明显改善主动脉瓣狭窄或反流患者的临床症状及血流动力学,手术效果好,远期生存率高。尽管经导管主动脉瓣置入术(TAVI)也被认可为治疗主动脉瓣病变的有效手段,但目前AVR仍然是最可靠的手术方式。超声心动图是主动脉瓣狭窄或反流最重要的诊断方法,是一种安全可靠的无创检测技术,在术前评估、明确手术指证、选择手术方式、判断预后等方面有重要的价值。AVR术后30d内发生的早期并发症影响患者预后,目前主要依靠超声心动图来检测和诊断。常规超声心动图的应用最为广泛,近年来超声心动图新技术如组织多普勒显像(TDI)、二维或三维斑点追踪显像、负荷超声心动图的应用也得到越来越多的临床医师重视。然而,超声心动图对AVR术后早期并发症的预测价值尚无充分的证据证明。笔者对AVR术后主要早期并发症及超声心动图检测方法进行系统回顾,以期为探究超声心动图指标预测术后早期并发症的价值提供参考。     

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.     

MR Imaging in the Management of Patients with Breast Cancer

Magnetic resonance (MR) imaging has high sensitivity in detecting and determining the extent of breast cancer and the information provided by this modality has proven valuable in patient management. Investigations defining the strengths of MR imaging, technical advances, and greater standardization of protocols have led to its increased use in patients with breast cancer, both before and following treatment. This article reviews techniques and procedures used in the performance and interpretation of breast MR examinations. Applications of MR imaging in the management of patients with breast cancer are also summarized, including preoperative evaluation of extent of disease, postoperative assessment of residual disease, and the detection of recurrent carcinoma. The use of MR imaging to evaluate patient response to chemotherapy and to assess patients with axillary lymph node metastases with an unknown primary lesion will also be discussed.     

Molecular MRI of Atherosclerosis Burden

Atherosclerosis is a systemic vascular disease predominantly affecting the intima of central and peripheral arteries. Its complications, myocardial infarction and stroke, remain the leading cause of morbidity and mortality in the Western world and developing countries. Angiographic imaging methods are the current gold standard for the clinical graduation of coronary and carotid artery disease and the guidance of treatment. These techniques are however limited to the assessment of the extent of luminal narrowing. MRI is a noninvasive modality, which allows the direct evaluation of the thin arterial vessel wall with excellent soft tissue contrast and high spatial resolution. Targeted MR contrast agents enable the evaluation of specific cellular and subcellular markers on a molecular level. This review will introduce and discuss novel molecular MR imaging techniques for the assessment of plaque and inflammatory burden in the context of atherosclerosis. Both measures can provide additional information beyond the assessment of luminal stenosis alone.