Magnetic resonance imaging measures of brain atrophy in multiple sclerosis

Magnetic resonance imaging (MRI) has been widely used to diagnose and monitor multiple sclerosis (MS). Although MRI-visible lesions are a key feature of MS, they are thought to correlate poorly with clinical progression. Neurodegeneration is increasingly being recognized as an important factor in the pathogenesis of MS, and MRI measures of brain atrophy have been suggested as surrogate markers of neuroaxonal loss and disease progression. This pathology may be more relevant to the progression of disability than focal inflammation. A number of MRI-based methods have been developed for the measurement of global and regional brain atrophy. Natural-history studies of MS and clinically isolated syndromes suggestive of MS have observed atrophy in these subjects above that seen in controls, over periods ranging from three months to years. Brain atrophy has also been incorporated as an outcome measure in therapeutic trials of disease-modifying treatments. This paper considers neuroaxonal loss and the pathological basis of brain atrophy, methods developed to quantify brain atrophy, the findings of natural-history and therapeutic studies, the relationship of brain atrophy to disability and cognition, and the future research directions and clinical applications of brain atrophy measurements.     

Focal liver lesion detection and characterization with GD-EOB-DTPA

Superior soft-tissue contrast affords magnetic resonance imaging (MRI) some advantages compared to computed tomography (CT) in both detection and characterization of focal liver lesions. Because of its relatively recently introduction into clinical practice, a growing number of articles in the literature have demonstrated the usefulness of the hepatobiliary-specific MRI contrast agent gadoxetic acid disodium (Gd-EOB-DTPA) in liver imaging. The purpose of this review is to demonstrate the typical enhancement patterns of the most common liver lesions using Gd-EOB-DTPA in daily clinical scenarios and briefly describe its mechanism of action. Radiologists interpreting liver MRI studies with this agent must be familiar with the appearance of focal lesions in the hepatocyte phase to avoid misinterpretation.     

The value of magnetic resonance tomography in the detection and differential diagnosis of focal liver lesions]

Magnetic resonance imaging (MRI) of the liver has made considerable progress due to improvements in the examination technique. Sensitivity for the detection of focal liver lesions is higher for MRI than for CT. In the differential diagnosis of liver tumors MRI is remarkably accurate. This is particularly true for hemangiomas, liver cell carcinomas and focal nodular hyperplasias. From a clinical view point differentiation between hemangiomas and metastases is of utmost importance. Future improvements in MR diagnosis of liver diseases are expected due to fast imaging techniques and liver-specific contrast agents.     

Magnetic resonance imaging of the liver: New imaging strategies for evaluating focal liver lesions

The early detection of focal liver lesions, particularly those which are malignant, is of utmost importance. The resection of liver metastases of some malignancies (including colorectal cancer) has been shown to improve the survival of patients. Exact knowledge of the number, size, and regional distribution of liver metastases is essential to determine their resectability. Almost all focal liver lesions larger than 10 mm are demonstrated with current imaging techniques but the detection of smaller focal liver lesions is still relatively poor. One of the advantages of magnetic resonance imaging (MRI) of the liver is better soft tissue contrast (compared to other radiologic modalities), which allows better detection and characterization of the focal liver lesions in question. Developments in MRI hardware and software and the availability of novel MRI contrast agents have further improved the diagnostic yield of MRI in lesion detection and characterization. Although the primary modalities for liver imaging are ultrasound and computed tomography, recent studies have suggested that MRI is the most sensitive method for detecting small liver metastatic lesions, and MRI is now considered the pre-operative standard method for diagnosis. Two recent developments in MRI sequences for the upper abdomen comprise unenhanced diffusion-weighted imaging (DWI), and keyhole-based dynamic contrast-enhanced (DCE) MRI (4D THRIVE). DWI allows improved detection (b = 10 s/mm(2)) of small (< 10 mm) focal liver lesions in particular, and is useful as a road map sequence. Also, using higher b-values, the calculation of the apparent diffusion coefficient value, true diffusion coefficient, D, and the perfusion fraction, f, has been used for the characterization of focal liver lesions. DCE 4D THRIVE enables MRI of the liver with high temporal and spatial resolution and full liver coverage. 4D THRIVE improves evaluation of focal liver lesions, providing multiple arterial and venous phases, and allows the calculation of perfusion parameters using pharmacokinetic models. 4D THRIVE has potential benefits in terms of detection, characterization and staging of focal liver lesions and in monitoring therapy.     

Use of contrast agents for liver MRI

Contrast-enhanced MRI is recognised as one of the most accurate imaging methods for investigating diseases of the liver. Uniquely several different types of contrast agents are available for liver MRI. They can be divided into non-specific extracellular fluid space (ECF), hepatocyte specific and reticulo-endothelial system (RES) specific agents. They are used to improve the detection of focal liver lesions by increasing normal-abnormal tissue contrast and to assist in lesion characterisation by demonstrating tissue perfusion and cellular function. ECF-gadolinium (Gd) chelates have been widely used in abdominal MRI for many years. They provide valuable information regarding the vascularisation and perfusion characteristics of lesions and assist in lesion detection, particularly of hypervascular lesions. The hepatocyte and RES-specific agents further improve lesion detection, provide important functional information and allow the distinction between hepatocellular and non-hepatocellular tumours. This article describes the different MR contrast agents and discusses their current status for diagnosing focal liver lesions. The importance of optimised technique and appropriate selection of contrast agent is emphasised.     

Die letzten Entwicklungen beim Ultraschall der Leber

Abdominal ultrasound (US) is often the first-line imaging modality used to assess focal liver lesions. Due to various new gray-scaled US techniques, such as tissue harmonic imaging (THI), spatial compounding technique and speckle reduction technique, as well as contrast-enhanced techniques, abdominal ultrasound nowadays has great potential regarding detection and characterization of focal liver lesions. Furthermore, image fusion with computed tomography (CT), magnetic resonance imaging (MRI) and 3D ultrasound will most likely help to improve clinical management before and after interventional procedures. This article illustrates the principles and clinical impact of recently developed techniques in the field of ultrasound.     

Ultrasound of focal liver lesions

This paper gives a comprehensive overview of ultrasound of focal liver lesions. Technical aspects such as examination technique and the use of Doppler modes as well as recent developments such as tissue harmonic imaging and microbubble contrast agents are discussed. The clinical significance and sonographic features of various liver lesions such as haemangioma, focal nodular hyperplasia, adenoma, regenerative nodule, metastasis, hepatocellular carcinoma and various types of focal infections are described. With the exception of cysts and typical haemangiomas, definitive characterisation of a liver lesion is often not possible on conventional ultrasound. This situation has changed with the recent advent of ultrasound contrast agents, which permit definitive diagnosis of most lesions. Contrast-enhanced sonography using recently developed contrast-specific imaging modes dramatically extends the role of liver ultrasound by improving its specificity in the detection and characterisation of focal lesions to rival CT and MRI.     

Diffusion and perfusion imaging of the liver

MRI of the liver is an important tool for the detection and characterization of focal liver lesions, for assessment of tumor response to treatment, and for the evaluation of diffuse liver disease. With recent advances in technology, functional MRI methods such as diffusion-weighted (DW) and perfusion-weighted (PW)-MRI are increasingly used in the abdomen with promising results, particularly in the evaluation of diffuse and focal liver diseases. In this review, we will discuss background, technical considerations, acquisition, applications, limitations and future applications of DW-MRI and PW-MRI applied in evaluation of diffuse and focal liver diseases.     

Contrast agents for MR imaging of the liver

Imaging of the liver is performed most often to detect and characterize focal liver lesions. MR imaging has been the method of choice to assess focal liver lesions accurately. Nonspecific intravenous contrast agents have been used for routine abdominal MR imaging protocols including liver imaging. Over the last 10 to 15 years new contrast agents have been developed that combine the excellent contrast resolution of MR imaging with improved tissue specificity. This article reviews various contrast agents that are in clinical use for liver MR imaging and discusses their potential clinical role.     

Advances in ultrasound

Ultrasound (US) has undergone dramatic changes since its inception three decades ago; the original cumbersome B-mode gantry system has evolved into a high resolution real-time imaging system. This review describes both recent advances in ultrasound and contrast media and likely future developments. Technological advances in electronics and computing have revolutionized ultrasound practice with ever expanding applications. Developments in transducer materials and array designs have resulted in greater bandwidths with improvements in spatial and contrast resolution. Developments in digital signal processing have produced innovations in beam forming, image display and archiving. Technological advances have resulted in novel imaging modes which exploit the non-linear behaviour of tissue and microbubble contrast agents. Microbubble contrast agents have dramatically extended the clinical and research applications of ultrasound. Not only can Doppler studies be enhanced but also novel non-linear modes allow vessels down to the level of the microcirculation to be imaged. Functional and quantitative studies allow interrogation of a wide spectrum of tissue beds. The advent of tissue-specific agents promises to improve the sensitivity and specificity of ultrasound in the detection and characterization of focal liver lesions to rival that of computed tomography (CT) and magnetic resonance imaging (MRI). Ultrasound has recently moved into therapeutic applications with high intensity focused ultrasound (HIFU) and microbubble assisted delivery of drugs and genes showing great promise.     

Hepatocellular carcinoma in the cirrhotic liver with helical CT and MRI: imaging spectrum and pitfalls of cirrhosis-related nodules

OBJECTIVE: This article reviews the imaging spectrum of cirrhosis-related nodules on CT and MRI and differentiates between hepatocellular carcinoma (HCC) and common focal lesions that can simulate HCC in the cirrhotic liver. CONCLUSION: Knowledge of cirrhotic nodules and focal lesions and how they mimic HCC will improve the diagnosis and characterization of focal lesions in cirrhotic liver on CT and MRI.     

MRT der Leber

The liver is a common site for various benign and malignant focal lesions. The initial modality for assessing liver lesions is ultrasound or CT. MRI with its superior soft tissue contrast offers multiple advantages over other imaging modalities. Contrast agents have been developed that increase the detection rate and provide more specific information in comparison to unenhanced techniques. In the mean time three classes are available for MR imaging of the liver: extracellular gadolinium chelates, hepatobiliary and reticulo-endothelia, superparamagnetic agents. We describe in this review the most common focal lesions, their diagnostic possibilities, and the imaging protocols. Clinical use of these contrast agents facilitates detection and differential diagnosis of focal liver lesions that may help to avoid invasive procedures such as biopsy for lesion characterization.     

Fast MR imaging techniques: Impact in the abdomen

The increased efficiency of MRI data acquisition has had a substantial impact on clinical MRI of the abdomen. Five particular applications that have thus been affected include breath-hold imaging of liver lesions (including detection, characterization, and biopsy), MR cholangiopan- creatography, practical chemical shift imaging (including liver and adrenal glands), dynamic imaging after contrast media injection, and MR angiography.     

菲立磁增强MRI在肝脏局灶性病变诊断中的价值

目的 评价菲立磁增强MRI在肝脏实性占位性病变诊断中的应用价值。材料与方法 对21例怀疑有肝脏局灶性占位病变患者行MR平行及菲立磁增强MRI检查。扫描序列包括频率选择脂肪抑制及非脂肪抑制ASTE T2WI、True FISP T2WI、频率选择脂肪抑制FLASH T1WI。比较增强前后T2WI及T2WI病灶及肝脏的信噪比（SNR）及对比噪声比（CNR）;观察增强前后病灶数量及形态;结合MR平扫及增强MRI表现进行定性诊断。结果 菲立磁增强T2WI及T2WI肝脏信号强度较平扫明显下降,病灶与肝脏的CNR较平扫明显提高,差异具有统计学意义。结论 菲立磁增强T2WI及T2WI可明显提高肝脏实性占位性病灶的检出率。菲立磁增强T1WI在脏局灶性病变的定性诊断中具有潜在价值,有待于进一步开发与研究。     

Focal nodular hyperplasia of the liver in longterm survivors of neuroblastoma: How much diagnostic imaging is necessary?

Objectives

Focal nodular hyperplasia of the liver is a tumor-like lesion, uncommon in children, but it has recently been more frequently observed in children treated for malignant diseases, especially neuroblastoma. The aetiology is unclear, the pathogenesis remains controversial. Focal nodular hyperplasia of the liver is suspected to be a sequela of tumor therapy.

Methods

Besides the clinical data we evaluated the imaging modalities needed to diagnose focal nodular hyperplasia of the liver in children with neuroblastoma who have been followed in our institution for more than 5 years.

Results

Out of 60 children six developed focal nodular hyperplasia at a median time of 10.5 years after diagnosis of neuroblastoma and 9.4 years after the end of treatment. The diagnosis of focal nodular hyperplasia was based on imaging criteria which are variable in ultrasonography and specific in MRI. Only one child underwent surgical biopsies to rule out liver metastases.

Conclusions

Longterm survivors of neuroblastoma are at risk of developing focal nodular hyperplasia, especially if they underwent toxic chemotherapy and/or radiotherapy to the liver during initial treatment. The recommended diagnostic imaging tools are ultrasonography for detecting liver lesions and MRI for confirming and characterizing these lesions as focal nodular hyperplasia.     

Infantile hepatic hemangiomas: clinical and imaging findings and their correlation with therapy

OBJECTIVE: This study was undertaken to determine different imaging patterns in infantile hepatic hemangiomas and to explore the relationship between clinical presentations, imaging findings, and response to therapy. MATERIALS AND METHODS: The imaging studies and clinical records of all patients with infantile hepatic hemangiomas from two tertiary children's hospitals were reviewed. Univariate and multivariate stepwise logistic regression techniques were used to determine whether clinical presentation and imaging variables differentiated the type of treatment required. RESULTS: Typical hemangiomas appeared as focal or multifocal T2-hyperintense spheres with centripetal contrast enhancement and dilated feeding and draining vessels. Three atypical patterns included focal mass lesions with central varix with or without direct shunts, focal mass with central necrosis or thrombosis, and massive hemangiomatous involvement of the liver with abdominal vascular compression. In general, patients with focal lesions without high flow needed no treatment, and those with central varix and direct shunts developed severe high-output cardiac failure that responded quickly to embolization. The pattern of massive replacement of liver was associated with hypothyroidism, abdominal compartment syndrome, and a high mortality rate. Multivariate analysis of 55 patients indicated that congestive heart failure was the only independent predictor of treatment (p = 0.005). The presence of a shunt was the only independent factor associated with embolization or surgery (p = 0.002). CONCLUSION: Although the imaging features of infantile hepatic hemangiomas vary to some extent, MRI features are typical in most patients and certain imaging findings are predictive of the clinical course. MRI is the technique of choice in diagnosing infantile hepatic masses.     

Magnetic resonance imaging of the liver: consensus statement from the 1st International Primovist User Meeting

The role of contrastenhanced liver MRI using the hepatocyte-specific agent gadoliniumethoxybenzyl-diethylene triamine penta-acetic acid (Gd-EOB-DTPA, Primovist, Bayer Schering Pharma, Berlin, Germany) is considered, based on the discussion at the Forum of Liver MRI: The 1st International Primovist User Meeting. Current clinical evidence supports Gd-EOB-DTPA’s use in non-invasive diagnosis of benign and malignant liver lesions and staging of focal and diffuse liver disease. The information thus gained assists in the provision of cost-effective patient management. The pharmacological properties of Gd-EOB-DTPA facilitate the imaging of both the vascular and hepatobiliary phases in the cirrhotic and non-cirrhotic liver and may provide an opportunity for one-stop diagnosis of liver lesions, such as focal nodular hyperplasia, adenomas, haemangiomas, hepatocellular carcinoma and metastases. The currently recommended protocols using Gd-EOB-DTPA are appropriate for the majority of patients, but imaging time points may require modification in specific patient groups. Further experience in routine clinical practice, as opposed to that gained from rigidly designed clinical studies, may provide greater understanding of the potential of Gd-EOB-DTPA for the evaluation of the cirrhotic and non-cirrhotic liver. Additional studies may substantiate the potential of Gd-EOB-DTPA in the imaging of other abdominal organs and in the evaluation of liver function and fibrosis.     

Current state of the use of sonographic contrast agents with low acoustic pressure techniques in the study of focal liver lesions

Ultrasonography is the most commonly used screening modality for focal liver lesions in Europe. Over the past few years, to overcome the inherent limitations of B-mode imaging and colour-Doppler ultrasound in identifying and characterising focal liver lesions, intravenous agents capable of enhancing the ultrasound signal emitted by vascular and parenchymal structures have been developed. From December 1999 to December 2001, about 400 patients with a known tumour, HCV-related chronic cirrhotic liver disease, or with an indeterminate focal liver lesion discovered incidentally were evaluated by ultrasound of the liver parenchyma both in baseline conditions and after administration of contrast material. The ultrasound contrast agents used were: SonoVue (Bracco, Milan-Italy) and Optison (Mallinckrodt, London - UK). Our experience is based on low mechanical-index contrast-enhanced imaging, which acts conservatively, performed with different commercially available algorithms, in grey-scale mode alone (B-mode). We report the morphological patterns displayed by the main benign and malignant liver lesions after the administration of second-generation ultrasound contrast material, and review the main imaging patterns able to provide effective and practical guidance in formulating a diagnosis of benignity or malignancy. Our clinical experience confirmed the literature findings that the introduction of low mechanical index methods in grey-scale imaging has allowed qualitatively better results for detecting and characterising focal liver lesions than those obtained with baseline and colour-Doppler imaging. The ease of use, substantial repeatability and predictability of the enhancement effects obtainable with low mechanical index methods are the main reasons for the success of this approach. Broadening the scope of studies to obtain controlled data and comparisons with the other imaging modalities is crucial for the definitive validation of the method.     

梯度回波化学位移MRI诊断脂肪肝的研究

目的　评价梯度回波化学位移MRI对脂肪肝的诊断价值和探讨梯度回波化学位移MRI的技术特点和原理。方法　对 12例脂肪肝患者 (轻、中度弥漫性脂肪肝 6例 ,局限性脂肪肝 6例 )均行MRI的常规SE序列、梯度回波同相 (in -phase ,IP)和反相 (out-phase ,OP)序列扫描 ,对比观察这些病灶在常规SET1WI、IP和OP像上的显示情况。结果　全部的脂肪肝在OP像上信号强度比IP像有明显下降 ,而在常规SET1WI上信号强度无明显变化。结论　梯度回波化学位移MRI简单实用 ,对脂肪肝的诊断具有较高的敏感性和特异性 ,是诊断脂肪肝最好的检查方法之一