Single-Shot Magnetic Resonance Imaging: Applications to Angiography

Recently developed technologies that allow the collection of magnetic resonance imaging (MRI) in as little as 26 msec have been explored in their application to angiography. Advantages are demonstrated in scan time reduction, insensitivity to patient motion (especially in abdominal applications), flow quantification, and temporal resolution. We demonstrate that because such single-shot techniques are inherently resistant to flow dephasing during acquisition that allow for sustained high signal intensities to be achieved when images must be combined through the cardiac cycle. Such high temporal resolution scans may be utilized for the collection of time-resolved angiograms. With these techniques we demonstrate the collection of complete MR angiograms in the course of reasonable 10–25 sec breath holds. The relative simplicity of the technique, coupled with its overall short acquisition time, allows us to incorporate angiography into other imaging protocols without adding significant time burdens. Results to date are promising for further improvements in spatial resolution, without extension of scan time.     

Parallel Imaging Artifacts in Body Magnetic Resonance Imaging

Objective

To familiarize the reader with the fundamental concepts of partial parallel imaging (PPI); to review the technical aspects of PPI including calibration scan, coil geometry, and field of view (FOV); and to illustrate artifacts related to parallel imaging and describe solutions to minimize their negative impact.

Results

PPI has led to a significant advance in body magnetic resonance imaging by reducing the time required to generate an image without loss of spatial resolution. Although PPI can improve image quality, it is not free of artifacts, which can result in significant image degradation. Knowledge of these artifacts and how to minimize their effect is important to optimize the use of parallel imaging for specific body magnetic resonance imaging applications.

Conclusions

The reader will be introduced to the fundamental principles of PPI. Common imaging characteristics of PPI artifacts will be displayed with an emphasis on those seen with image-based methods, the principles behind their generation presented, and measures to minimize their negative impact will be proposed.     

The effect of image resolution on vessel signal in high-resolution magnetic resonance angiography

In this paper, the theoretical dependence of the signal of flowing fluids is considered in terms of the imaging parameters and the physical condition of the flowing fluid. For the vessel sizes, flow ranges, and imaging conditions studied, it is demonstrated that the fluid signal can be predicted from the solution of Bloch equations. For vessels on the order of the imaging resolution or smaller, the effects of the image resolution must be included.     

Voxel sensitivity function description of flow-induced signal loss in MR imaging: implications for black-blood MR angiography with turbo spin-echo sequences.

The conditions in which the image intensity of vessels transporting laminar flow is attenuated in black-blood MR angiography (BB-MRA) with turbo spin-echo (TSE) and conventional spin-echo (CSE) pulse sequences are investigated experimentally with a flow phantom, studied theoretically by means of a Bloch equation-voxel sensitivity function (VSF) formalism, and computer modeled. The experiments studied the effects of: a) flow velocity, b) imaging axes orientation relative to the flow direction, and c) phase encoding order of the TSE train. The formulated Bloch equation-VSF theory describes flow effects in two-dimensional (2D)- and 3D-Fourier transform magnetic resonance imaging. In this theoretical framework, the main attenuation mechanism instrumental to BB-MRA, i.e., transverse magnetization dephasing caused by flow in the presence of the imaging gradients, is described in terms of flow-induced distortions of the individual voxel sensitivity functions. The computer simulations predict that the intraluminal homogeneity and extent of flow-induced image intensity attenuation increase as a function of decreasing vessel diameter, in support of the superior image quality achieved with TSE-based BB-MRA in the brain.     

IFIR技术在肺动脉成像的可行性研究

目的 探讨插入有限脉冲响应(IFIR)技术行肺动脉成像的可行性.方法 对28例受试者行IFIR肺动脉成像序列扫描,在ADW 4.6工作站上行最大密度投影(MIP)重建.对肺动脉主干及其各分支显示程度进行评分,与肺动脉的信噪比、年龄、有无呼吸运动伪影等因素对比分析.结果 26例(92.9％)可显示肺动脉主干血管,24例(85.7％)能清晰观察到肺动脉主干及一、二级分支,20例(71.4％)可清晰显示到肺动脉主干及一、二、三、四级分支.呼吸运动影响肺动脉评分,有无呼吸伪影组评分平均秩次分别为58.25及36.42(P =0.005).不同年龄组间血管评分不同,＜70岁组及≥70岁组血管评分平均秩次为60.42及46.58(P =0.008).信噪比与肺动脉评分无关(P =0.124).结论 磁共振IFIR非对比剂增强序列可清楚显示肺动脉主干及其各级分支,是一种具有很好临床应用前景的无创、安全、可行的肺动脉血管成像技术.     

Vulnerable Atherosclerotic Carotid Plaque Evaluation by Ultrasound,Computed Tomography Angiography,and Magnetic Resonance Imaging: An Overview

Ischemic syndromes associated with carotid atherosclerotic disease are often related to plaque rupture. The benefit of endarterectomy for high-grade carotid stenosis in symptomatic patients has been established. However, in asymptomatic patients, the benefit of endarterectomy remains equivocal. Current research seeks to risk stratify asymptomatic patients by characterizing vulnerable, rupture-prone atherosclerotic plaques. Plaque composition, biology, and biomechanics are studied by noninvasive imaging techniques such as magnetic resonance imaging, computed tomography, ultrasound, and ultrasound elastography. These techniques are at a developmental stage and have yet to be used in clinical practice. This review will describe noninvasive techniques in ultrasound, magnetic resonance imaging, and computed tomography imaging modalities used to characterize atherosclerotic plaque, and will discuss their potential clinical applications, benefits, and drawbacks.     

MRI对先天性心脏病解剖及功能评价

目的　探讨MRI对先天性心脏病 (CHD)解剖及功能评价的临床应用价值。方法　对 1 5例经手术证实的CHD患者超声心动图 (ECG)与MRI诊断结果进行对比分析 ,研究 2种技术检测心脏解剖与功能的作用。结果　 1 5例患者 2 4个畸形中 ,MRI诊断正确 2 0个 (2 0 / 2 4 ) ,ECG诊断正确 2 1个 (2 1 / 2 4 )。MRI显示心外大血管病变较ECG有优势 ,而ECG显示心脏瓣膜病变较清晰 ;MRI和ECG在检测左心室舒张末期横径、容积 ,左心室收缩末期容积 ,左心室搏出量以及射血分数时 ,2种技术无显著性差异。结论　MRI可较准确地检测CHD的解剖和功能异常     

三维磁共振管壁成像与数字减影血管造影诊断颈动脉闭塞的对照研究

目的通过与数字减影血管造影(DSA)比较,评价三维磁共振管壁成像(3D-MR-VWI)技术诊断颈动脉闭塞形态学特征的可行性。资料与方法纳入经超声诊断为颅外段颈动脉闭塞(CAO),并于1周内完成3D-MR-VWI和DSA检查的124例患者。评价3D-MR-VWI与DSA在诊断CAO类型和闭塞发生部位的一致性。结果3D-MR-VWI对于颈动脉完全闭塞及闭塞起始部位的诊断与DSA结果均有较高的一致性(Cohen’s κ=0.85,95%CI 0.71~0.94;Cohen’s κ=0.85,95%CI 0.71~0.97)。3DMR-VWI诊断颈动脉完全闭塞的敏感度为97.0%,特异度为86.7%,准确率为94.6%。结论3D-MR-VWI能够准确诊断CAO并判定闭塞的形态学特征,可为临床诊治颈动脉闭塞性病变提供参考。     

Magnetic Resonance Imaging in Diplopia: Neural Pathway,Imaging, and Clinical Correlation

The role of magnetic resonance imaging (MRI) in diplopia is to diagnose various diseases that occur along the neural pathway governing eye movement. However, the lesions are frequently small and subtle and are therefore difficult to detect on MRI. This article presents representative cases of diseases that cause diplopia. The purpose of this article was to 1) describe the anatomy of the neural pathway governing eye movement, 2) recommend optimal MRI targets and protocols for the diagnosis of diseases causing diplopia, 3) correlate MRI findings with misalignment of the eyes (i.e., strabismus), and 4) help familiarize the reader with the imaging diagnosis of diplopia.     

膝部骨胳隐匿性病灶的磁共振成像分析

目的：分析膝部骨结构隐匿性病灶的ＭＲＩ特点以及与关节损伤的关系。资料与方法：膝关节ＭＲＩ检查连续资料中发现７０例明确骨内信号异常，其ＭＲＩ表现分为五种类型。按临床表现不同分为三组。１９例施行关节镜检查，９例同时做ＣＴ检查。结果：膝关节急性损伤组的骨内ＭＲＩ异常信号多呈Ⅰ～Ⅲ型表现，即主要表现为片状模糊的Ｔ１ＷＩ低信号和Ｔ２ＷＩ高信号，反映骨挫伤、隐匿性骨折或骨软骨骨折。慢性损伤组的骨内信号改变多为Ⅳ～Ⅴ型表现，病灶紧贴关节软骨下，Ｔ１ＷＩ和Ｔ２ＷＩ以低信号为主，反映骨软骨慢性损伤或退变。亚急性组的骨内病灶ＭＲＩ表现类型则介于上述二者之间。结论：膝部骨内隐匿性病灶的ＭＲＩ表现类型与关节损伤状况密切相关     

磁共振扩散相关成像技术在宫颈癌诊治中的研究进展

宫颈癌因其发病率高、恶性程度高成为威胁女性健康的第一大杀手。早期诊断和准确分期对宫颈癌治疗方案的选择、治疗效果及预后至关重要。扩散相关成像技术是新兴的MRI方法,以其高敏感性、完全无创等特点迅速成为宫颈癌诊断的重要方法,并通过参数分析对宫颈癌的治疗进行疗效评估。本文旨在对扩散相关成像技术应用于宫颈癌诊治的研究进展进行综述。     

Hemodynamic Change in Pulmonary Vein Stenosis after Radiofrequency Ablation: Assessment with Magnetic Resonance Angiography

We present a case of pulmonary vein (PV) stenosis after radio-frequency (RF) ablation, in which a hemodynamic change in the pulmonary artery was similar to that of congenital PV atresia on time-resolved contrast-enhanced magnetic resonance angiography (TR-MRA). A 48-year-old man underwent RF ablation due to atrial fibrillation. The patient subsequently complained of hemoptysis, dyspnea on exertion, and right chest pain. Right PV stenosis after catheter ablation was diagnosed through chest computed tomography and lung perfusion scan. Pulmonary TR-MRA revealed the pulmonary artery via systemic arterial collaterals and draining systemic collateral veins. On a velocity-encoded cine image, the flow direction of the right pulmonary artery was reversed in the diastolic phase and the left pulmonary artery demonstrated continuous forward flow throughout the cardiac cycle. These hemodynamic changes were similar to those seen in congenital unilateral PV atresia.     

膝骨关节炎软骨MRI信号强度与基质成分表达相关性研究

目的 分析膝骨关节炎(OA)软骨MRI信号强度(SI)与软骨Ⅱ型胶原、蛋白多糖表达的相关性,探讨软骨MR序列反映OA软骨组分变化的能力. 资料与方法 对26例膝关节置换手术患者术前行关节软骨MRI,采用序列为快速自旋回波(FSE)T2WI、三维脂肪抑制扰相梯度回波序列(3D-FS-SPGR)和脂肪抑制质子加权序列(FS-PDWI).观察各序列上软骨SI.术后对截骨标本进行软骨采样,以鼠抗人单克隆抗体进行Ⅱ型胶原和蛋白多糖免疫组织化学染色和分级评价.对软骨缺损旁区域SI值与基质Ⅱ型胶原、蛋白多糖表达等级进行多个独立样本的秩和检验和Spearman相关性分析. 结果 OA软骨基质的不同Ⅱ型胶原表达等级间FSE T2WI和FS-SPGR序列上软骨SI差异无统计学意义(FSPGR=0.771,PSPGR＝0.474;FT2WI＝1.075,PT2WI＝0.358),FS-PDWI序列上软骨SI差异有统计学意义(FPD= 28.739,PPD<0.001);软骨基质蛋白多糖的不同表达等级的MR各序列软骨SI差异均无统计学意义(FT2WI＝1.275,PT2WI＝0.299;FPD= 2.045,PPD=0.152; FSPGR＝1.057,PSPGR＝0.364).FS-PDWI上OA缺损旁区域软骨SI与Ⅱ型胶原表达呈负相关(P<0.001,r＝-0.825),软骨SI随Ⅱ型胶原破坏程度升高而降低;其他序列上软骨SI虽有随Ⅱ型胶原和蛋白多糖缺失而变化的趋势,但统计学上无相关性. 结论 在常用软骨MRI序列中,FS-PDWI与OA软骨基质Ⅱ型胶原表达具有相关性,但常规MRI序列无法反映OA软骨蛋白多糖丢失状况.