Imaging artifacts at 3.0T

Clinical MRI at a field strength of 3.0T is finding increasing use. However, along with the advantages of 3.0T, such as increased SNR, there can be drawbacks, including increased levels of imaging artifacts. Although every imaging artifact observed at 3.0T can also be present at 1.5T, the intensity level is often higher at 3.0T and thus the artifact is more objectionable. This review describes some of the imaging artifacts that are commonly observed with 3.0T imaging, and their root causes. When possible, countermeasures that reduce the artifact level are described.     

3.0T MRI对血管母细胞瘤的诊断

血管母细胞瘤是一种良性肿瘤,手术切除肿瘤是根治血管母细胞瘤的最佳途径,一旦肿瘤完全切除可以获得治愈.对残留肿块有必要进行术后辅助放疗 ,可以达到控制肿瘤的目的[1].术前的明确诊断对治疗有很大的临床意义.因此本文回顾性分析血管母细胞瘤MRI表现,并结合文献讨论对本病诊断及鉴别诊断.     

Imaging characteristics of PROPELLER T2-weighted imaging

As the PROPELLER sequence is a combination of the radial scan and fast-spin-echo (FSE) sequence, it can be considered an FSE sequence with a motion correlation. However, there are some differences between PROPELLER and FSE owing to differences in k-space trajectory. We clarified the imaging characteristics of PROPELLER T2-weighted imaging (T2WI) for different parameters in comparison with usual FSE T2WI. When the same parameters were used, PROPELLER T2WI showed a higher signal-to-noise ratio (SNR) and lower spatial resolution than usual FSE. Effective echo time (TE) changed with different echo train lengths (ETL) or different bandwidths on PROPELLER, and imaging contrast changed accordingly to be more effective.     

High-Resolution 3 T MR Microscopy Imaging of Arterial Walls

Purpose To achieve a high spatial resolution in MR imaging that allows for clear visualization of anatomy and even histology and documentation of plaque morphology in in vitro samples from patients with advanced atherosclerosis. A further objective of our study was to evaluate whether T2-weighted high-resolution MR imaging can provide accurate classification of atherosclerotic plaque according to a modified American Heart Association classification. Methods T2-weighted images of arteries were obtained in 13 in vitro specimens using a 3 T MR unit (Medspec 300 Avance/Bruker, Ettlingen, Germany) combined with a dedicated MR microscopy system. Measurement parameters were: T2-weighted sequences with TR 3.5 sec, TE 15–120 msec; field of view (FOV) 1.4 × 1.4; NEX 8; matrix 192; and slice thickness 600 μm. MR measurements were compared with corresponding histologic sections. Results We achieved excellent spatial and contrast resolution in all specimens. We found high agreement between MR images and histology with regard to the morphology and extent of intimal proliferations in all but 2 specimens. We could differentiate fibrous caps and calcifications from lipid plaque components based on differences in signal intensity in order to differentiate hard and soft atheromatous plaques. Hard plaques with predominantly intimal calcifications were found in 7 specimens, and soft plaques with a cholesterol/lipid content in 5 cases. In all specimens, hemorrhage or thrombus formation, and fibrotic and hyalinized tissue could be detected on both MR imaging and histopathology. Conclusion High-resolution, high-field MR imaging of arterial walls demonstrates the morphologic features, volume, and extent of intimal proliferations with high spatial and contrast resolution in in vitro specimens and can differentiate hard and soft plaques.     

3.0T磁共振弥散加权成像在直肠病变的应用

目的 探讨3T磁共振弥散加权成像(diffusion-weighted imaging,DWI)在直肠病变诊断中的价值.方法 使用3T双梯度短磁体全身磁共振系统,8通道相控阵表面线圈,对55例直肠癌及直肠周围病变患者进行DWI.选用5个不同的b值(200、400、600、800、1000 s/mm2),采用Single shot DWI EPI序列,扫描层数6～11层,层厚7 mm,层间距1 mm,扫描时间17～35 s.测量不同直肠病变在不同b值下DWI图像上的信号强度值和表观弥散系数(apparent diffusion coefficient,ADC),并进行比较.所有数据利用SPSS11.5软件包进行处理.结果 随b值的升高,各类直肠病变在DWI图像上的平均信号强度呈 下降趋势,b值为400 s/mm2时病变显示最明显.随b值的升高,各类直肠病变的ADC值逐渐减小,并渐趋稳定.不同直肠病变的ADC值的差别随b值的增加逐渐明显,至b值为800 s/mm2和1000 s/mm2时出现显著性差异(P<0.05),存在于间质瘤与其他病种.不同T分期的直肠癌ADC值差别明显,随肿瘤浸润深度的增加,ADC值明显降低(P<0.05).结论 DWI及ADC值可以作为直肠癌诊断和鉴别诊断、评价预后的指标.     

乳腺纤维腺瘤的3.0T MRI表现

目的：探讨乳腺纤维腺瘤3.0T MRI表现,提高对乳腺疾病的诊断准确性。方法：回顾性分析19例（21个病灶）经手术或穿刺病理证实的乳腺纤维腺瘤患者的MRI资料。分析病灶的MRI形态学特征、信号强度及动态增强特征。结果：所有病灶边界清晰,14个病灶可见分叶状改变,T2WI上11个病灶显示不完整的包膜,病灶内可见低信号分隔：T2WI显示4个,TIRM-T2WI显示10个,增强后显示11个。增强扫描示病灶强化均匀17个,不均匀4个。病灶的时间-信号强度曲线分为4种类型：Ⅰ型曲线17个,Ⅱ型曲线2个,Ⅳ型曲线2个。结论：清晰的边界、分叶状形态、不完整的包膜、无强化的内部间隔和持续均匀的强化是纤维腺瘤的MRI特征性表现,3.0T MRI能清晰地显示上述细微结构,对乳腺纤维腺瘤的诊断具有重要意义。     

正常肾脏3.0 T磁共振扩散张量成像研究

目的 评估肾脏扩散张量成像(DTI)检查的可行性,观察正常肾脏3.0 T MR DTI参数值特点及扩散张量示踪图表现.方法 采用3.0 T MR成像系统,结合呼吸触发技术,对30名健康志愿者行双侧肾脏斜冠状面DTI检查,在6个非共线性方向施加扩散敏感梯度场,b值采用0、300 s/mm2,分别测量双肾皮髓质各异性分数(FA)值及表观扩散系数(ADC)值,采用配对样本t检验比较双肾皮质间、双肾髓质间及每侧肾皮髓质间的FA值、ADC值,同时重建双肾扩散张量示踪图,观察其图像特征.结果 (1)双肾皮质间、双肾髓质间FA值及ADC值差异均无统计学意义(P＞0.05);(2)肾脏皮质FA值(0.32±0.04)明显低于髓质(0.70±0.05),皮质ADC值[(2.83±0.20)×10-3mm2/s]明显高于髓质[(2.50±0.18)×10-3mm2/s],差异均有统计学意义(t=-43.87,P＜0.001;t=11.14,P＜0.001);(3)扩散张量示踪图显示肾髓质内由肾门指向皮髓质交界的放射状分布的纤维束样结构.结论 采用3.0 T MR结合呼吸触发技术可以获得良好的肾脏DTI图像;肾脏DTI是描述肾脏皮髓质扩散特征并直观显示肾髓质微观结构的有效检查技术.     

0.35T开放式磁共振扫描仪肩关节扫描技术研究

目的:探讨0.35T开放式磁共振扫描仪肩关节扫描技术及其图像质量评价.材料和方法:对18例肩关节患者行横轴位T1、12、斜矢状位T2、斜冠状位T1、T2加权像(所有T2加权像脂肪抑制用FSE-IR脉冲序列代替)、水脂分离像,其中6例行关节造影.结果:所有图像质量较高,特别是水脂分离成像技术的二三种图像,对于观察骨髓内信号改变、关节软骨、关节囊、软骨下骨病变、周嗣软组织及肌肉内病变效果较好.结论:永磁0.35T开放式磁共振扫描肩关节有众多优势,能够获得较高的图像质量和操作方便,可提供更多的诊断依据.     

Diffusion MR Imaging with T2-based Water Suppression (T2wsup-dMRI)

Purpose: This study proposes and assesses a new diffusion MRI (dMRI) technique to solve problems related to the quantification of parameter maps (apparent diffusion coefficient [ADC] or mean diffusivity [MD], fractional anisotropy [FA]) and misdrawing of fiber tractography (FT) due to cerebrospinal fluid (CSF)-partial volume effects (PVEs) for brain tissues by combining with the T2-based water suppression (T2wsup) technique.Methods: T2wsup–diffusion-weighted imaging (DWI) images were obtained by subtracting those images from the acquired multi-b value (b) DWI images after correcting the signal intensities of multiecho time (TE) images using long TE water signal-dominant images. Quantitative parameter maps and FT were obtained from minimum data points and were compared with those using the standard (without wsup) DWI method, and partly compared with those obtained using other alternative DWI methods of applying fluid attenuation inversion recovery (FLAIR), non-b-zero (NBZ) by theoretical or noise-added simulation and MR images.Results: In the T2wsup-dMRI method, the hyperintense artifacts due to CSF-PVEs in MRI data were dramatically suppressed even at lower b (≲ 500 s/mm²) while keeping the tissue SNR. The quantitative parameter map values became precisely close to the pure tissue values precisely even in water (CSF) PVE voxels in healthy brain tissues (T2 ≲ 100 ms). Furthermore, the fiber tracts were correctly connected, particularly at the fornix in closest contact to the CSF.Conclusion: Solving the problem of CSF-PVE in the current dMRI technique using our proposed T2wsup-dMRI technique is easy, with higher SNR than those obtained with FLAIR or NBZ methods when applying to healthy brain tissues. The proposed T2wsup–dMRI could be useful in clinical settings, although further optimization of the pulse sequence and processing techniques and clinical assessments are required, particularly for long T2 lesions.     

3.0T MR扩散加权成像对膀胱癌T分期的诊断价值

目的探讨MR扩散加权成像(DWI)对膀胱癌T分期的诊断价值。资料与方法使用Philips Achieva3.0 T高场强超导型MR机,应用腹部多通道相控阵线圈,对44例膀胱癌患者,共71处病灶行MR检查,观察其DWI表现,并与手术病理分期结果进行对照分析。结果 71处病灶中,有蒂型病灶占60.56%(43/71),在DWI上均表现为C形或拱形样结构,其T分期的诊断符合率为95.35%(41/43)。DWI诊断膀胱癌T分期的准确度非常高,其准确度、敏感度和特异度分别为88.73%、84%、91.3%。DWI对膀胱癌T分期准确性优于T2WI(71.83%),但联合T2WI,可提高其对分期诊断的准确性(90.14%)。结论 3.0 T高场强MR DWI所表现C形或拱形样结构,可作为早期膀胱癌较特征性的诊断征象。联合其他序列,可提高DWI对分期的诊断准确性。     

1.5.T和3.0T磁共振检查在直肠癌术前分期价值的比较

目的:探讨1.5T和3.0T磁共振检查在直肠癌诊断和术前分期中的作用,分析两者在直肠癌术前分期的应用价值.方法:选择经肠镜活检证实为直肠癌病人60例,随机盲法均分为两组.分别行1.5T和3.0T磁共振检查及术前直肠癌影像分期,并与病理分期对照.结果:1.5T MRIT分期总准确性为80%,N分期总准确率为67%,N0分...     

3.0 T MR全身扩散加权成像联合全身冠状位T2-tirm脂肪抑制序列对全身转移瘤筛查临床应用价值

目的 探讨全身扩散加权成像(WB-DWI)联合全身冠状位T2-firm脂肪抑制序列对全身转移瘤筛查价值.方法 对124例有原发肿瘤病史患者进行WB-DWI及冠状位T2-tirm脂肪抑制序列检查,对上述检查可疑病变部位进行CT或MRI检查(包括增强),分3组进行研究,A组行背景抑制扩散加权成像(DWIBS);B组行DWIBS联合全身冠状位T2-tirm脂肪抑制序列检查;C组,B组+CT或MRI检查.将三者检查结果对比分析,分别计算3种检查方法对病灶显示的敏感度、特异度、准确率,统计B组及C组全身各部位病灶显示数目,并对B组及C组数据做一致性检验分析.结果 B组与C组对病灶准确率均比A组高,A组与B组之间的差异有统计学意义(x2=16.09,P=0.000),B、C两组间配对卡方kappa一致性检验结果K=0.841,P=0.038＜0.05,表明两者诊断一致性很高,但存在差异,全身DWI联合全身MR检查在脊柱、骨盆、股骨上段成骨性及溶骨性转移病灶、肝脏(呼吸均匀者)检出及诊断准确性较高,B组与C组无统计学差异(P＞0.05),但对脑内、肺、纵隔、盆腔髂血管周围直径＜10mm较小转移灶、肋骨局部＜10 mm成骨性转移灶假阴性较高,C组更有优势,B组对肝脏(脓肿、血管瘤等)、肺(肉芽肿、结核球等)、椎体内血管瘤、股骨头坏死、非病理性压缩骨折、多发性骨髓瘤等易造成假阳性,C组准确率更高.结论 WB-DWI联合T2-tirm脂肪抑制序列对全身转移瘤筛查有较高检出率和准确率,同时结合CT或MRI检查能进一步提高病灶检出率和准确率.     

3.0T T2*WI磁共振成像技术在脑内病变的应用

目的 探讨T2*WI磁共振成像技术在脑部疾病中的临床应用价值.方法 收集疑有脑部血管性病变患者84例,其中脑内血管畸形6例,脑外伤5例,脑出血慢性期10例,脑梗塞36例,脑肿瘤27例.均行常规T1WI、T2WI、T2FLAIR、3DTOFMRA、DWI及T2*WI成像,脑血管畸形及脑肿瘤加扫增强序列.结果 T2*WI在脑内血管畸形,能清楚显示病灶内小出血,较细小血管走行及分布;脑梗塞患者脑内发现更多微小的出血灶,脑肿瘤内可显示小的引流静脉及出血.结论 在脑内血管性病变,T2*WI可提供更多影像信息,可作为 MRI常规序列的有力补充,在中枢神经系统疾病的诊断和鉴别诊断中具有较高临床实用价值.     

FLASH序列T1加权成像在脊柱转移性肿瘤的应用价值

目的　评价FLASH序列T1 WI对脊柱转移性肿瘤的检出能力及其限度。方法　 5 9例病人 (2 79个病灶 )接受脊柱FLASH-T1 WI序列磁共振扫描 ,评价其图像信噪比 (SNR) ,脊椎—肌肉对比噪声比 (S -MCNR) ,病灶对比噪声比 (CNR)及病变检出率 ,并与SE -T1 WI ,TSE -T2 WI作比较。结果　FLASH -T1 WI的SNR低于SE -T1 WI、TSE -T2 WI ,两者Ρ <0 .0 0 1;其病灶CNR明显高于后两者 ,两者Ρ <0 .0 0 1;其S -MCNR高于SE -T1 WI ,Ρ <0 .0 0 1,近似于TSE -T2 WI,Ρ值 >0 .5。FLASH -T1 WI病变检出率 (98.6% )略高于SE -T1 WI(95 .3 % ) ,0 .0 2 5 <Ρ <0 .0 5 ;明显高于TSE -T2 WI(63 .4% ) ,Ρ <0 .0 0 5。椎体内局灶性黄骨髓 ,良性椎体压缩性骨折 ,脊柱结核在FLASH -T1 WI像上均表现为高信号。结论　与SE -T1 WI、TSE -T2 WI作比较 ,FLASH -T1 WI对脊柱转移性肿瘤有较高的病灶对比 ,能提高其检出率。其具有较高的敏感性 ,但特异性差。     

Imaging of urea using chemical exchange-dependent saturation transfer at 1.5T

The purpose of this study was to screen for slow proton chemical exchange between water and kidney metabolites using a standard clinical 1.5-T scanner. Imaging was performed using a fast spin-echo sequence with a magnetization transfer (MT) preparation pulse train. Off-resonance saturation ranging from +/-50 to +/-1000 Hz was used on urea and urine phantoms and normal human subjects imaged through the kidneys. The positive frequency was used as the control for each frequency pair. Results of frequency sweeps show an asymmetric MT effect peaking at approximately 100 Hz ( thick similar1 ppm) for urea, urine, and renal parenchyma. Varying differences (5%-25%) occurred with different human subjects. Few differences were observed from phantom water or subject muscle tissue. Chemical exchange is detectable in the kidney near 1 ppm at 1.5 T, attributable to urea. This technique was used to produce in vivo distribution maps of this metabolite in vivo.     

大范围扩散加权成像在3.0T MR的正常表现

恶性肿瘤具有向骨及其他组织侵犯的倾向,骨及其他组织转移瘤的诊断对于肿瘤的精确分期、确定预后及合理化治疗非常重要[1,2].骨扫描是目前最常用的检测骨转移瘤的方法,但特异性受限,敏感性也仅约62%～89%[3,4].