移植肾磁共振成像研究进展

近年来随着成像技术的进步,磁共振在移植肾中的应用逐渐增多,本文旨在介绍磁共振血管成像、扩散加权成像、磁共振灌注成像、血氧水平依赖成像、磁共振弹性成像在移植肾功能评估及并发症诊断中的应用和价值.     

磁共振尿路成像诊断肾移植输尿管病变的价值

目的 :探讨磁共振尿路成像对肾移植输尿管病变的诊断价值。材料和方法 :16例肾移植后输尿管并发症患者 ,临床诊断移植肾盂积水 13例 ,移植肾周积液 3例 ,用重T2加权快速自旋回波序列和脂肪抑制技术作磁共振尿路成像。结果 :16例均清楚显示移植肾实质及泌尿系集合系统高质量图像 ,输尿管病变得到确诊 ,其中移植肾输尿管狭窄 11例 ,输尿管坏死漏尿致移植肾周积尿 3例 ,输尿管结石 1例 ,输尿管返流 1例。结论 :磁共振尿路成像对肾移植后输尿管病变具有极高诊断价值。     

肾移植血流灌注的影像学研究进展

肾移植术后并发症主要有急性排斥反应、急性肾小管坏死、慢性排斥反应等,其病理改变可引起移植肾血流灌注的变化．此为国内外研究的热点。影像学检查在肾移植术后并发症的监测中发挥重要的作用,目前主要以超声作为移植肾的基本检测手段,磁共振成像作为进一步的补充检查。三维超声容积自动测量技术和超声成像是目前发展较快的超声新技术,磁共振灌注成像用于检测移植肾早期病变作为研究热点,三者在评价移植肾血流灌注方面具有非常重要的作用。有望使移植肾术后并发症的检测从定性、半定量水平发展到定量水平,提高影像学检查的特异性和敏感性,为临床提供更进一步的帮助。     

肾移植血流灌注的影像学研究进展

肾移植术后并发症主要有急性排斥反应、急性肾小管坏死、慢性排斥反应等,其病理改变可引起移植肾血流灌注的变化,此为国内外研究的热点.影像学检查在肾移植术后并发症的监测中发挥重要的作用,目前主要以超声作为移植肾的基本检测手段,磁共振成像作为进一步的补充检查.三维超声容积自动测量技术和超声成像是目前发展较快的超声新技术,磁共振灌注成像用于检测移植肾早期病变作为研究热点,三者在评价移植肾血流灌注方面具有非常重要的作用,有望使移植肾术后并发症的检测从定性、半定量水平发展到定量水平,提高影像学检查的特异性和敏感性,为临床提供更进一步的帮助.     

卵巢实性肿块功能磁共振成像研究进展

动态对比增强成像、扩散加权成像及磁共振波谱等功能磁共振成像技术能反映卵巢肿块的血供特点、肿瘤细胞密度和生物代谢行为。在常规磁共振检查的基础上联合应用多种功能磁共振成像技术,对临床诊断、治疗方案选择及预后判断具有重要价值。就上述几种功能磁共振成像技术的优缺点及对卵巢实性肿块的影像学诊断价值进行综述。     

移植肾的磁共振检查

近年来磁共振技术的迅速发展,使得评估移植肾功能成为可能.本文旨在介绍常规磁共振成像(MRI),磁共振血管成像(MRA),磁共振泌尿系统成像(MRU),MR灌注加权成像(PWI),MR弥散加权成像(DWI)和血氧水平依赖成像(BOLD)在移植肾检查中的应用和意义.     

非对比剂增强磁共振血管成像技术在评估移植肾血管并发症方面的研究

目的:探讨基于多翻转脉冲空间标记技术(SLEEK)的非对比剂增强磁共振血管成像序列在显示移植肾血管并发症方面的价值.方法:对23例移植肾血管并发症患者行SLEEK及彩色多普勒超声扫描.由两位放射医师对SLEEK显示移植肾血管并发症情况进行评估,并将SLEEK结果与彩色多普勒超声、DSA及手术结果进行对照.结果:23例患者均成功进行了SLEEK扫描,其中移植肾动脉狭窄11例,移植肾动脉闭塞3例,移植肾动脉扭曲3例,移植肾静脉狭窄2例,动静脉瘘2例,假性动脉瘤1例,肌纤维发育不良1例.SLEEK检出了所有23例并发症,彩色多普勒超声检查出了其中19例,两者检出率差异无统计学意义(P＞0.05).结论:基于SLEEK的非对比剂增强磁共振血管成像序列无创、无辐射,在显示移植肾血管并发症方面具有很高的应用价值.     

移植肾功能不全的影象学研究现状

本简述了影象学技术在移植肾功能不全时的应用现状，认为普勒超声，ＣＴ及磁共振成象对急性肾排异、环孢霉素毒性及急性肾小管坏死的鉴别诊断有一定帮助，但指标为非特异性。结合临床及环孢霉素浓度测定，影象学技术对移植肾功能不全的鉴别可提供有意义的信息。     

改良胰肾联合移植术后MR检查的价值

目的 探讨磁共振成像在胰肾联合移植术后的应用价值。方法 5例改良胰肾联合移植术后患者均用MR SE序列，磁共振胆管成像（MR cholangiopancreatography,MRCP)和磁共振尿路成像（MR urography,MRU)，动态钆喷替酸葡甲胺（Gd-DTPA)增强三维快速扰相梯度顺波磁共振血管成像（3D fast spoiled gradient recalled MRA,3D FSPGR MRA)和三维相位对比法磁共振血管成像（3D PC MRA）检查 分析各序列图像特点，并计算胰腺与腰大肌信号比（PPR）和胰腺实质强化平均在百分比（MPPE）。结果 5例中有2例移植体形态及信号完全正常，其中1例并发脾动脉末端动脉瘤。术后并发肾脏迟发性超急性排斥反应，胰腺急性排斥反应和胰腺慢性排斥反应各1例。肾脏迟发性超急性排斥反应MRI表现为皮髓质界线（CMD）消失，MRU未见肾集合系统及输尿管扩张，MRA见肾血管仅限于肾窦内。胰腺急性排斥反应MRI表现为胰腺增大，信号不均匀，MRA见胰腺血管吻合口通畅，PPR及MPPE分别为6．2和160％。胰腺慢性排斥反应MRI表现为胰腺体积缩小，实质信号尚均匀，MRCP示胰管扩张，MRA见胰腺血管稍细，PPR及MPPE分别为4．9和160％。结论 正确完善的MR扫描方法可客观反映移植体的形态及功能，是移植术后监测移植体的有效方法。     

活体肾移植供肾血管术前MRA评估的研究进展

术前评估供肾者血管解剖情况对于供肾筛选以及减少移植过程中潜在并发症的风险至关重要。目前多种磁共振血管成像(MRA),如对比增强MRA(CE-MRA)、时间飞跃法(TOF)、相位对比法(PC)及平衡稳态自由进动(SSFP)等技术已应用于供肾血管术前评估,可对肾动脉和肾静脉的复杂变异分型进行诊断。就肾血管解剖及各种MRA方法在供肾血管评估中的研究进展予以综述。     

fMRI评价移植肾功能异常的研究进展

肾移植术后及时准确地评价移植肾功能受损至关重要,并发症的早期准确鉴别有助于及时干预及治疗,从而进一步提高移植肾的长期存活率。目前多种扩散成像、血氧水平依赖成像（BOLD）、动脉自旋标记（ASL）等功能MRI技术已用于评价移植肾功能,可以从肾脏水分子扩散、血氧水平及血流灌注微观角度等方面对肾功能进行评估。就多种功能MRI技术对移植肾功能的评价、肾移植术后并发症的鉴别作一综述,为临床诊断及治疗提供依据及思路。     

Magnetic resonance imaging of the transplanted kidney. Correlation to function and histopathology

Interstitial fibrosis is a frequent finding in biopsies from long-term renal allografts, and may be due to chronic cyclosporine nephrotoxicity or chronic rejection. In this study, long-term renal transplants were investigated with magnetic resonance (MR) imaging, and the results were correlated to histopathology and graft function. Seventeen patients were investigated with MR one to 10 years after transplantation and with simultaneous ultrasonographically guided cortical needle biopsy and function tests. Histopathology included semiquantitative grading of degree of fibrosis and quantitation of ratios of tubular structures to interstitial tissue. The correlation between the histopathological assessment of interstitial fibrosis and graft function was good. Poor differentiation between the renal cortex and the renal medulla at MR imaging was correlated to high degree of interstitial fibrosis in the kidney transplants as well as to reduced graft function. MR examination may thus be of value in the evaluation of long-term renal transplants with chronic functional changes.     

Functional renal imaging: new trends in radiology and nuclear medicine

The objective of this work is to compare the characteristics of various techniques for functional renal imaging, with a focus on nuclear medicine and magnetic resonance imaging. Even with low spatial resolution and rather poor signal-to-noise ratio, classical nuclear medicine has the advantage of linearity and good sensitivity. It remains the gold standard technique for renal relative functional assessment. Technetium-99m ((99m)Tc)-labeled diethylenetriamine penta-acetate remains the reference glomerular tracer. Tubular tracers have been improved: (123)I- or (131)I-hippuran, (99m)Tc-MAG3 and, recently, (99m)Tc-nitrilotriacetic acid. However, advancement in molecular imaging has not produced a groundbreaking tracer. Renal magnetic resonance imaging with classical gadolinated tracers probably has potential in this domain but has a lack of linearity and, therefore, its value still needs evaluation. Moreover, the advent of nephrogenic systemic fibrosis has delayed its expansion. Other developments, such as diffusion or blood oxygen level-dependent imaging, may have a role in the future. The other modalities have a limited role in clinical practice for functional renal imaging.     

血氧水平依赖磁共振成像在肾功能不全中的应用

目的：探讨血氧水平依赖磁共振成像（BOLD MRI）在诊断肾功能不全以及鉴别不同分级肾功能不全的应用价值。方法对15名健康志愿者和55名不同分级肾功能不全患者进行BOLD MRI扫描,测量各组肾脏皮质、髓质的R2＊值并计算髓质／皮质R2＊值,对比分析各组数据。结果①正常对照组及不同分级的肾功能不全患者的皮质、髓质以及髓质／皮质R2＊值间均存在统计学差异（ P ＜0．05）;②皮质R2＊值与肾功能分级呈正相关,而髓质R2＊值及髓质／皮质R2＊比值与肾功能分级呈负相关。结论血氧水平依赖磁共振成像作为反映肾脏功能改变程度的敏感指标在肾功能不全的诊断及分级鉴别中起到重要的作用。     

Update of renal imaging

Significant technical improvements have allowed the use of radiological techniques to play a growing role in the imaging of renal diseases. Noninvasive ultrasound methods (ie, sonography and Doppler) are now positioned as first-line methods for the evaluation of renovascular diseases. Multidetector computed tomography is able to provide high spatial resolution images of the kidneys and renal arterial vessels. Magnetic resonance imaging, which provides higher signal-to-noise ratio and higher spatial and/or temporal resolution, can display both morphological information about renal parenchyma and vessels and functional data, including perfusion, filtration, diffusion, or oxygenation. In renovascular diseases, these techniques have the potential to drive new strategies, including Doppler sonography as a first-line method, followed by computed tomography angiography or magnetic resonance angiography, depending mainly on renal function. Imaging of parenchymal renal diseases is developing toward more quantitative (volumetric and functional measurements) and more specific (through in vivo cell targeting) acquisitions for obtaining the adequate information on tissue characteristics relevant either for diagnosis or for prognosis or treatment follow-up.     

Quantification of pulmonary perfusion with MR imaging: recent advances

Recent advances in magnetic resonance pulmonary perfusion imaging are reviewed, focusing on magnetic resonance perfusion imaging using gadolinium contrasts agents or spin labeling of blood using naturally flowing spins as the source of intravascular signal. These recent developments in magnetic resonance imaging have made it possible to analyze data quantitatively which holds significant potential for clinical imaging of lung perfusion and opens windows to functional MR imaging of the lung. We believe that fast magnetic resonance functional imaging will play an important role in the assessment of pulmonary function and the pulmonary disease process.     

Non-invasive assessment of renal artery stenosis: current concepts and future directions in magnetic resonance angiography

Magnetic resonance angiography is undergoing rapid development as a non-invasive technique to reliably assess renal artery stenosis. Invasive X-ray angiography is currently the gold standard imaging technique and gives excellent spatial resolution. However, its disadvantages include a necessary exposure to radiation and the need for iodinated contrast media. While magnetic resonance angiography does not have these disadvantages, its spatial resolution is inherently lower. On the other hand, magnetic resonance angiography enables true three-dimensional imaging. The use of rapid imaging techniques allows multiple image acquisition within one breath-hold thereby permitting the visualization of distinct vascular phases. The limitation in spatial resolution can be overcome readily by combining morphologic imaging with functional information on the hemodynamic relevance. This can be achieved by means of magnetic resonance phase contrast flow measurements. The use of such a combined approach enables the grading of vascular stenosis based on the combination of morphology and functional information. Magnetic resonance angiography is already able to demonstrate a clinical utility equivalent to that of invasive procedures, indicating that it is likely to become a premier method for the diagnosis and follow up of renovascular disease.     

Magnetic resonance imaging in renal transplantation.

End stage renal disease is common and can result from a variety of diseases. The expense and morbidity of dialysis has made renal transplantation the preferred treatment when it is available. In the United States, 11,000 renal transplants are performed annually. Because of the limited supply of donor organs, every effort is made to salvage the transplanted kidney that has began to fail. Imaging modalities that are currently used to evaluate transplanted kidneys are ultrasound (US), computed tomography (CT), scintigraphy, intravenous urography (IVU), contrast angiography, and magnetic resonance imaging (MRI). MRI offers multiple advantages. MRI provides cross sectional and vascular information without the risks of ionizing radiation, iodinated contrast, or arterial catheterization. This article describes the role of MR imaging in renal transplantation, technical aspects of image acquisition, and MR findings of post-transplantation complications.     

Nierenfunktionsdiagnostik mittels Magnetresonanztomographie

Due to progress in the development of sequences and techniques magnetic resonance imaging (MRI) methods, such as functional MR urography (fMRU), arterial spin labeling (ASL), diffusion-weighted imaging (DWI), diffusion tension imaging (DTI) and blood oxygen level dependent MRI (BOLD-MRI) have become available for renal functional evaluation. In recent years research of these imaging techniques has demonstrated that they provide valid functional data with respect to renal perfusion, oxygenation and interstitial diffusion as well as glomerular filtration and the extent of an obstructive uropathy. Many pathophysiological renal processes, e.?g. in transplanted kidneys, in the setting of chronic kidney disease and in the diagnostics of renal tumors, can therefore be fully evaluated. The fMRU, which enables a reliable assessment of renal function combined with high-resolution morphological evaluation of the kidneys and the entire urinary tract, has already become an inherent component in the clinical setting, at least in specialized pediatric radiology centers. To establish the new imaging methods in the clinical routine, further technical improvements and large-scale prospective clinical studies are necessary to validate the determined functional parameters, to generate standard protocols and to unify and facilitate data post-processing.     

Functional assessment of transplanted kidneys with magnetic resonance imaging

Kidney transplantation has emerged as the treatment of choice for many patients with end-stage renal disease, which is a significant cause of morbidity and mortality. Given the shortage of clinically available donor kidneys and the significant incidence of allograft dysfunction, a noninvasive and accurate assessment of the allograft renal function is critical for postoperative management. Prompt diagnosis of graft dysfunction facilitates clinical intervention of kidneys with salvageable function. New advances in magnetic resonance imaging (MRI) technology have enabled the calculation of various renal parameters that were previously not feasible to measure noninvasively. Diffusion-weighted imaging provides information on renal diffusion and perfusion simultaneously, with quantification by the apparent diffusion coefficient, the decrease of which reflects renal function impairment. Diffusion-tensor imaging accounts for the directionality of molecular motion and measures fractional anisotropy of the kidneys. Blood oxygen level-dependent MR evaluates intrarenal oxygen bioavailability, generating the parameter of R2* (reflecting the concentration of deoxyhemoglobin). A decrease in R2* could happen during acute rejection. MR nephro-urography/renography demonstrates structural data depicting urinary tract obstructions and functional data regarding the glomerular filtration and blood flow. MR angiography details the transplant vasculature and is particularly suitable for detecting vascular complications, with good correlation with digital subtraction angiography. Other functional MRI technologies, such as arterial spin labeling and MR spectroscopy, are showing additional promise. This review highlights MRI as a comprehensive modality to diagnose a variety of etiologies of graft dysfunction, including prerenal (e.g., renal vasculature), renal (intrinsic causes) and postrenal (e.g., obstruction of the collecting system) etiologies.