基于相位展开的磁敏感加权图像中相位伪影处理方法的研究

针对Hanning滤波器难以有效解决磁敏感加权成像过程中产生的相位伪影问题,提出一种基于相位展开技术的相位伪影处理方法。采用两个步骤有效消除磁敏感加权成像过程中产生的相位伪影。首先,采用传统的Hanning滤波器对相位伪影进行初步处理;然后,采用相位展开技术,对由Hanning滤波器处理后的残余伪影进行进一步处理,从而达到完全消除相位伪影的目的。对扫描层厚为0.6 mm的100层脑部SWI原始图像进行相位伪影的处理,结果表明,该方法能有效消除磁敏感加权图像中的相位伪影。采用该方法处理SWI图像中的相位伪影,可为后续采用最小密度投影方法显示清晰的血管影像奠定基础。     

磁敏感加权成像在高血压性脑出血患者诊断中的应用

目的:探讨磁敏感加权成像(Susceptibility Weighted Imaging,SWI)在高血压性脑出血(hypertensive cerebral hemorrhage,HICH)患者诊断中的应用价值.方法:选择2018年2月至12月本院收治的60例HICH患者,均行SWI序列及核磁共振弥散加权成像(Magnetic resonance imaging diffusion weighted imaging,MRI-DWI)扫描,并以手术结果为对照,分析SWI序列扫描、MRI-DWI序列扫描诊断HICH患者病灶分布情况的准确率与图像质量.结果:经手术结果明确60例HICH患者中共检测出94处病灶.与MRI-DWI序列诊断HICH患者病灶分布的准确率相比,SWI序列诊断病灶分布的准确率更高(P<0.05).经Kappa一致性度量,SWI序列和MRI-DWI序列诊断HICH患者的病灶分布与手术结果的一致性均较好(Kappa>0.8,P<0.01);SWI序列与MRI-DWI序列诊断HICH患者中病灶分布情况的呼吸伪影评分、运动伪影评分、冈上肌边缘的清晰和锐利度评分、影像的总体质量评分都比较高(P>0.05).结论:两种序列诊断HICH患者病灶分布情况的图像质量相当,但SWI序列诊断准确性更高,和手术结果的一致性也更好.     

相位解缠绕算法在磁敏感加权图像中的应用与比较

为了找到能有效解决磁敏感加权成像(SWI)相位信息缠绕问题的方法,针对8种空域解缠算法进行分析和比较,其中:选取5种全局优化算法,分别为加权最小二乘法(WLS)、解缠离散估计的相位区域扩张标记法(PRELUDE)、最大流/最小切相位解缠法(PUMA)、差值映射累加法(ARM)、排序多聚类法(SL-MC);3种积分算法,分别为枝切法(Branch-cut)、基于傅里叶滤波的质量图引导法(WFF-QG)、递归正交参考相位解缠法(PUROR)。采用两组Matlab仿真图像和两组来自Alltech公司提供的1.5 T真实SWI数据进行实验,以原始缠绕相位与再缠绕相位之间的突变点统计值和算法运行时间作为量化指标,评价8种算法的优越性。结果显示,PUROR的P±|M|值为0,运行时间最短,鲁棒性较强,解缠绕结果可靠,在实际临床应用中可尝试采用PUROR法。     

丘纹静脉及其属支的可视化磁敏感加权成像

目的利用3.0T磁共振磁敏感加权成像(SWI)序列探索丘纹静脉及其属支的解剖形态,为丘纹静脉性脑血管疾病的诊治和神经外科微创手术提供依据。方法选取40名健康志愿者行3.0T磁共振系常规序列以及磁敏感加权成像序列头部扫描,利用最小密度投影(m Ips)技术对原始图像进行后处理,得到横断面、矢状面及冠状面3个断层的图像。将丘纹静脉分为Ⅰ型(静脉角)和Ⅱ型(假静脉角),同时将尾状核前静脉分为1型(支数为1)、2型(支数为2)以及A型(注入丘纹静脉)、B型(注入透明隔前静脉)、C型(注入两者夹角)。通过SWI序列的原始图像以及重建后图像,对丘纹静脉及其属支的解剖形态进行观察分析。结果丘纹静脉的引流区域包括尾状核、内囊、豆状核、外囊、屏状核、最外囊以及额顶叶脑髓质深部,但丘脑除外。丘纹静脉、尾状核前静脉、尾状核横静脉的显示率依次为92.5%、82.5%、58.75%。丘纹静脉Ⅰ型和Ⅱ型的显示率分别为79.7%、20.3%;并且右侧大脑Ⅰ型更多见(P0.05)。尾状核前静脉分型中以1支型(89.4%)和A型(69.7%)最常见。结论 SWI能清晰显示活体脑深部丘纹静脉及其细小属支的解剖形态。     

基于幅度图像引导的磁敏感加权图像相位解缠算法

为了更好地利用相位信息补偿血流造成的影响,本文对磁敏感加权成像(SWI)中存在的相位缠绕问题展开了研究。为提高解缠绕的准确性,本文提出了幅度图像引导的磁敏感加权图像相位解缠算法。基本思路如下:(1)通过改进旋转不变非局部主成分分析滤波(PRI-NL-PCA)降低噪声影响;(2)结合C-V模型水平集提取相位图像中对应的实性组织区域,从而规避背景噪声对相位解缠方法的影响;(3)采用相位补偿的方法约束K空间重建出的相位图像。最后,利用四种统计量作为量化指标,评价解缠绕方法的可靠性:相位误差的突变点个数、均值(M)、方差(Var),以及阳性百分比(Pos)和阴性百分比(Neg)。通过对比仿真数据和226组真实头部磁敏感数据,结果表明,本文算法相对于经典的枝切法和最小二乘法,解缠绕结果具有较高的准确性。     

MR图像Ghost伪影的校正

原始K空间奇偶回波单独重建图像数据时，根据二维多项式拟合参考扫描各点相位漂移估计值对图像进行相位校证，可减轻伪影的影响。但在噪声较严重的情况下，校正后的图像仍含有较严重的残余伪影。按相位编码方向对图像数据采用基于最小二乘法多项式拟合的方法可减轻噪声对图像的干扰，再利用二维抑制Ghost伪影算法能更有效地消除EPI成像过程中由于涡流引起的伪影。该算法的缺点是会引起图像信息强度的变化及造成图像高频信息的衰减。但由于MRI图像主要集中为低频信息，且Ghost伪影信息强度不超过图像信息最大强度20％时，该方法对图像信息的损失不会影响对病灶的识别。     

MRI常规扫描及SWI、DWI序列在新生儿缺氧缺血性脑病诊断中的应用价值研究

目的研究磁共振成像(MRI)常规扫描及磁敏感加权成像(SWI)、弥散加权成像(DWI)序列在新生儿缺氧缺血性脑病(HIE)诊断中的应用价值。方法回顾性分析本院2016年8月至2020年8月收治的86例HIE患儿的临床资料,观察病灶密度、边界、与周围组织关系等特征,比较不同MRI序列诊断HIE的临床价值。结果 86例HIE患儿共检出病灶245枚,其中以SWI扫描检查病灶数最多(86.12%),其次为DWI(70.20%),常规MRI序列中以T2WI检出病灶数最高(55.92%);其中86例HIE患者经常规MRI检查检出阳性39例(45.35%),经常规MRI+DWI检查检出阳性50例(58.14%),经常规MRI+SWI检查检出阳性61例(70.93%),经常规MRI+DWI+SWI检查检出阳性77例(89.53%),以三者联合检查检出HEI阳性率最高(P<0.05)。结论常规MRI序列、DWI序列及SWI序列在诊断HIE上具有一定价值,但三者联合扫描诊断阳性率更高,可为临床治疗方案的优化提供可靠意见。     

7.0 T高场磁共振磁敏感倍增成像效应研究

磁敏感性可以看作是物质的一种固有属性,不同的组织由于成分与结构的差异,磁敏感性往往各不相同,有效地利用磁化率的差异可为组织结构与功能提供额外的信息.基于这种新的成像对比机制,磁敏感加权成像技术(SWI)诞生.研究发现,在一定的条件下,由于磁敏感性差异的存在,特定组织在MR成像过程中会出现"成像倍增",这种现象被称为磁敏...     

磁共振磁敏感加权成像在颅脑疾病中的应用研究

目的 探讨磁敏感加权成像在脑部疾病中的临床应用价值.方法 对65例临床疑是脑血管病变患者行常规 T1WI、T2WI、DWI、SWI 序列及增强T1WI、MRA,探讨SWI序列在显示小出血灶、小静脉及含铁血黄素、钙化等顺磁性物质的优越性.结果 ①海绵状血管瘤,SWI能鉴别出血与血管,发现更多的小出血灶;②动静脉畸形,SWI能够发现更多的细小静脉向大静脉引流;③急性脑梗死,SWI可发现小的出血灶;④脑肿瘤,SWI显示出小的引流静脉;⑤帕金森病,SWI能显示脑内多发异常低信号铁沉积.结论 SWI对低流量血管畸形、小静脉结构、多发细小出血以及铁钙沉积十分敏感,为常规MRI的重要补充,应用于中枢神经系统疾病的诊断和鉴别诊断.     

星形细胞肿瘤磁敏感成像与动态对比剂MR灌注加权成像的相关性研究

目的：探讨星形细胞肿瘤磁敏感加权成像（ SWI)半量化与动态对比剂增强MR灌注加权成像（ PI)的相关性。方法回顾性分析98例经手术病理证实星形细胞肿瘤患者的术前SWI及PI检查资料。测量SWI中肿瘤内磁敏感低信号区（ ITSHIA)半量化数据,以及PI中肿瘤内实性部分最大相对脑血流量值（ rrCBV瘤内max )和瘤周区最大相对CBV值（ rrCBV瘤周max )。应用Kruskal-Wallis H检验比较不同病理分级星形细胞肿瘤间rrCBV瘤内max与rrCBV瘤周max的差异,比较不同级别肿瘤间灌注热点区与ITSHIA形态的对应情况;应用Spearman相关性检验比较不同级别肿瘤间SWI中各半量化指标与PI中rrCBV瘤内max与rrCBV瘤周max的相关性。结果星形细胞肿瘤rrCBV瘤内max值（ rs =0．662,P<0．01)及rrCBV瘤周max值（rs =0．794,P<0．01)与其分级显著相关。毛细胞型星形细胞瘤rrCBV瘤内max高于Ⅱ级星形细胞瘤,与Ⅲ级肿瘤类似;而 rrCBV瘤周max与Ⅱ级星形细胞瘤差异无统计学意义（ P >0．05),却低于高级别肿瘤。星形细胞肿瘤的ITSHIA半量化指标与rrCBV瘤内max与rrCBV瘤周max值呈显著线性正相关。星形细胞肿瘤内灌注热点区与ITSHIA不完全对应。结论星形细胞肿瘤SWI指标与PI指标密切相关,二者对于术前评估星形细胞肿瘤的病理分级同样具有较高价值。灌注热点区与ITSHIA并不完全相同,可能与二者显示肿瘤内血管生成的机制不同有关。     

大脑内静脉系的超高场强磁敏感加权成像研究现状

目的观察大脑内静脉及其属支的分布、引流及吻合规律，探讨超高场强磁敏感加权成像（SWI）技术的临床应用及优点。方法查阅近几年来国内外关于大脑内静脉、大脑深静脉以及超高场强SWI的文献，进行归纳总结。结果超高场强SWI的主要特点是高信噪比、短时间成像和高分辨率，可对直径50μm以上的微小静脉显影。结论超高场强SWI在脑肿瘤及其他脑部疾病的诊治方面有很好的应用前景，将为脑部疾病的早发现、早治疗提供更准确的影像学依据。     

Measurement of the magnetic susceptibility effect in high-field NMR imaging

The magnetic susceptibility effect often obtained in clinical NMR imaging is analysed and a measurement method of the magnetic susceptibility effect is proposed. The method of extraction of the susceptibility effect alone in high-field NMR imaging where usually the chemical shift and main magnetic field inhomogeneity effects are intermingled with the susceptibility effect is discussed. The proposed susceptibility measurement uses the susceptibility weighted echo-time encoding technique (SWEET) to modulate the NMR signal as a function of echo time with which the image intensity can be weighted. Both phantom-oriented physical experiments and human volunteer experiments were performed to demonstrate the usefulness of the technique for human imaging.     

The capability of detecting small vessels beyond the conventional MRI sensitivity using iron‐based contrast agent enhanced susceptibility weighted imaging

Imaging brain microvasculature is important in cerebrovascular diseases. However, there is still a lack of non‐invasive, non‐radiation, and whole‐body imaging techniques to investigate them. The aim of this study is to develop an ultra‐small superparamagnetic iron oxide (USPIO) enhanced susceptibility weighted imaging (SWI) method for imaging micro‐vasculature in both animal (~10 μm in rat) and human brain. We hypothesized that the USPIO‐SWI technique could improve the detection sensitivity of the diameter of small subpixel vessels 10‐fold compared with conventional MRI methods. Computer simulations were first performed with a double‐cylinder digital model to investigate the theoretical basis for this hypothesis. The theoretical results were verified using in vitro phantom studies and in vivo rat MRI studies (n = 6) with corresponding ex vivo histological examinations. Additionally, in vivo human studies (n = 3) were carried out to demonstrate the translational power of the USPIO‐SWI method. By directly comparing the small vessel diameters of an in vivo rat using USPIO‐SWI with the small vessel diameters of the corresponding histological slide using laser scanning confocal microscopy, 13.3‐fold and 19.9‐fold increases in SWI apparent diameter were obtained with 5.6 mg Fe/kg and 16.8 mg Fe/kg ferumoxytol, respectively. The USPIO‐SWI method exhibited its excellent ability to detect small vessels down to about 10 μm diameter in rat brain. The in vivo human study unveiled hidden arterioles and venules and demonstrated its potential in clinical practice. Theoretical modeling simulations and in vitro phantom studies also confirmed a more than 10‐fold increase in the USPIO‐SWI apparent diameter compared with the actual small vessel diameter size. It is feasible to use SWI blooming effects induced by USPIO to detect small vessels (down to 10 μm in diameter for rat brain), well beyond the spatial resolution limit of conventional MRI methods. The USPIO‐SWI method demonstrates higher potential in cerebrovascular disease investigations.     

Application of arterial spin labeling and susceptibility weighted imaging in the diagnosis of ischemic cerebrovascular diseases

Objective: To investigate the application value of arterial spin labeling (ASL) and susceptibility weighted imaging (SWI) in the diagnosis of acute ischemic cerebrovascular disease (CVDs). Methods: A total of 124 patients who received fluid attenuated inversion recovery (FLAIR), diffusion weighted imaging (DWI), ASL, time of flight magnetic resonance angiography (TOF-MRA) and SWI scan sequentially were included in this study. The area of the abnormal perfusion region was compared with that of the restricted diffusion region. The cerebral blood flow (CBF) value and apparent diffusion coefficient (ADC) value were compared in ischemic penumbra (IP), infarct core and mirror region. The susceptibility vessel sign (SVS) detection rate was compared with the major vessel severe stenosis or occlusion rate as revealed by MRA. A receiver operating characteristic curve (ROC) was used to analyze the value of SVS as revealed by SWI. Results: In total, 124 cases were included in this study, and 77 cases showed acute cerebral infarction. Among the 77 cases, 59 cases showed an IP. There were significant differences in ADC and CBF values between the infarct core and mirror region (P < 0.01). There was no significant difference in ADC value between IP and mirror region (P = 0.176), but there was significant difference in CBF value between IP and mirror region (P < 0.01). There was no significant difference in SVS detection rate compared with the vessel severe stenosis or occlusion rate in MRA (P = 0.111). Based on the MRA standards, the area under curve (AUC) of ROC for the SVS as revealed by SWI was 0.86 (95% CI: 0.753-0.962). Conclusions: ASL combined with DWI contributed to IP evaluation of acute cerebral infarction. SWI showed higher diagnostic value for intravascular thrombus in acute cerebral infarction.     

Multi‐echo susceptibility‐weighted imaging and histology of open‐field blast‐induced traumatic brain injury in a rat model

Blast‐induced traumatic brain injury is on the rise, predominantly as a result of the use of improvised explosive devices, resulting in undesirable neuropsychological dysfunctions, as demonstrated in both animals and humans. This study investigated the effect of open‐field blast injury on the rat brain using multi‐echo, susceptibility‐weighted imaging (SWI). Multi‐echo SWI provided phase maps with better signal‐to‐noise ratio (SNR) and contrast‐to‐noise ratio (CNR), making it a sensitive technique for brain injury. Male Sprague‐Dawley rats were subjected to a survivable blast of 180 kPa. The visibility of blood vessels of varying sizes improved with multi‐echo SWI. Reduced signal intensity from major vessels post‐blast indicates increased deoxyhaemoglobin. Relative cerebral blood flow was computed from filtered phase SWI images using inferred changes in oxygen saturation from major blood vessels. Cerebral blood flow decreased significantly at day 3 and day 5 post‐blast compared with that pre‐blast. This was substantiated by the upregulation of β‐amyloid precursor protein (β‐APP), a marker of ischaemia, in the neuronal perikaya of the cerebral cortex, as observed by immunofluorescence, and in the cortical tissue by western blot analysis. Our findings indicate the presence of brain ischaemia in post‐blast acute phase of injury with possible recovery subsequently. Our results from cerebrovascular imaging, histology and staining provide an insight into the ischaemic state of the brain post‐blast and may be useful for prognosis and outcome. Copyright © 2015 John Wiley & Sons, Ltd.     

大脑内静脉及其属支的磁敏感加权成像研究进展 

磁敏感加权成像(SWI)是利用不同组织间磁化率的差异产生图像对比。顺磁性的脱氧血红蛋白是静脉显影的内源性对比剂,故对于静脉血管有特殊敏感性,甚至可以检测到小于1个体素(200～300μm)的细微静脉结构。这一新技术的应用,将大大提高隐匿性大脑疾病的检出率。然而,疾病的诊断始终是建立在对正常解剖结构的认识之上的,我们通过     

超顺磁性氧化铁标记骨髓间充质干细胞移植治疗大鼠脑梗死的在体磁敏感加权成像研究

目的 超顺磁性氧化铁(SPIO)体外标记骨髓间充质干细胞(BMSC)移植治疗大鼠脑梗死,使用磁敏感加权成像(SWI)监测BMSC在脑内的分布与迁移.方法 原代培养大鼠BMSC,SPIO体外标记第3代BMSC,倒置显微镜及普鲁士蓝染色观察.改良Longa法制作大鼠左侧脑梗死模型,缺血对侧顶叶脑皮层移植SPIO标记的BMSC.分别在移植后1d、1周、2周和4周进行SWI序列MRI动态观察,移植后4周脑组织普鲁士蓝染色观察.结果 移植后1d、1周、2周和4周SWI序列MRI检测均可显示缺血对侧半球移植的SPIO标记BMSC所致的低信号;移植后2周可见沿胼胝体腹侧走行的线状低信号影;移植后4周移植细胞所致的“彗星状”改变更为明显,彗星尾向缺血侧延伸.移植后4周脑组织切片普鲁士蓝染色显示胼胝体内迁移的蓝染细胞呈条带状排列.结论 SWI序列可显示移植部位SPIO标记BMSC所致的低信号,且可以明确显示其在大鼠脑组织内的迁移.     

急性脑梗死大脑皮、髓静脉的磁敏感加权成像解剖研究

目的　利用磁敏感加权成像(susceptibility weighted imaging, SWI)技术分析脑梗死患者大脑皮、髓质静脉的不对称征与脑梗死严重度和梗死灶解剖学特征的相关性，为临床急性脑梗死诊断、治疗提供影像参考。 方法　选取38例超急性期、62例急性期脑梗死患者，采用磁共振扫描，比较静脉不对称组与对称组的脑梗死严重度差异以及梗死灶解剖学特征差异。 结果 对于超急性期，静脉不对称组与对称组NIHSS评分分别为8（4~8.8）、5.5（3~8），两组评分无显著性差异（P=0.058）。对于急性期，静脉不对称组与对称组NIHSS评分分别为5（2~7）、1.5（1~2），两组评分有显著性差异（P=0.043）。大脑前循环和后循环动脉梗塞静脉不对称出现率分别为48(82.8%)、 12(28.6%)，两者有显著性差异（P<0.001）。 结论 急性期脑梗死的静脉不对称征可反映卒中更高的严重度，而超急性期则不然。大脑前循环梗塞更趋向于形成静脉不对称征。