MR各成像序列对脑弥漫性轴索损伤的诊断价值

目的比较MR各序列成像诊断脑弥漫性轴索损伤(DAI)的价值。方法对21例临床诊断DAI的患者行常规自旋回波(SE)T1WI、快速自旋回波(TSE)T2WI、流动衰减反转恢复序列(FLAIR)、扩散加权成像(DWI)和小角度激发快速梯度回波序列(FLASH)扫描,比较各序列脑内病灶的显示率,分析其信号特征。结果FLASH为显示DAI病灶最敏感的序列,能显示常规序列所不能显示的DAI小针尖样大小的出血灶。21例各序列脑内各部位DAI病灶平均检出数依次为:T1WI(0.78±0.58)个、T2WI(1.96±1.30)个、FLAIR(2.98±2.39)个、DWI(3.67±2.75)个、FLASH(6.24±5.46)个。FLASH的DAI病灶检出数最高,与SE T1WI、TSE T2WI的差异有统计学意义(q值分别为3.14、2.47,P值均<0.05)。结论FLASH序列能提高DAI病灶的检出数及早期诊断率,应作为MR诊断DAI的首选序列。     

使用3.0T磁共振成像技术二维反转恢复超短回波时间和三维超短回波时间对半月板钙化形态和定量评价的可行性研究

摘要目的评价超短回波时间(UTE)MRI技术对不同类型半月板钙化的形态评估效果,将这些序列与标准的临床序列进行比较并测量半月板钙化的T2*值。方法该研究由机构审查委员会豁免,知情同意不是必需的。10具尸体的半月板行高空间分辨力X线摄影和3.0T的磁共振形态成像[T1加权快速自旋回波序列(FSE),T2加权FSE序列,质子密度加权(PD)的FSE序列,二维(2D)快速毁损梯度回波序列(FSPGR),三维(3D)FSPGR序列和3DUTE序列]以及定量成像[2D反转恢复(IR)UTE序列和3DUTE序列]。     

三维薄层梯度回波动态增强扫描在胰腺疾病中的诊断价值

目的明确三维薄层磁共振小角度快速激发梯度回波序列动态增强扫描在胰腺疾病诊断中的价值.材料和方法对70例经证实胰腺疾病病人进行磁共振检查,采用的扫描序列分别为2D FS-FLASH T1WI、HASTE T2WI和3DFLASH动态增强扫描等.测量肿块与正常胰腺组织信号值,计算胰腺/病灶对比噪声比(CNR).结果动态增强3D FLASH扫描良好显示胰腺疾病的血流动力学特征,胰腺癌各期的CNR值分别为4.46±2.21,12.71±2.91,6.17±1.66,慢性胰腺炎分别为4.15±1.25,9.27±1.38,4.96±10.85,壶腹周围癌分别为5.49±1.35,11.52±2.24,5.55±1.33.30例胰腺癌、11例慢性胰腺炎、14例壶腹周围癌出现胰管扩张.70例胰腺疾病的敏感性为100%(70/70),诊断准确性为98.6%(69/70).结论三维梯度回波序列动态增强扫描能良好显示胰腺病变的解剖细节及血流动力学特征,在胰腺疾病的定性诊断中有较高的应用价值.     

脑微出血:运用定量磁敏感图谱行负荷评估

目的运用定量磁敏感图减少标准磁共振序列在对大脑微量出血的负荷评估中的误差。材料与方法此项回顾性研究符合HIPAA法案,获机构审查委员会批准。在178例疑有卒中病史且行3.0T多回波梯度回波序列检查,T2*加     

磁共振成像短时间反转恢复序列在鼻咽癌中的应用

目的　比较磁共振成像短时间反转恢复序列 (short tauinversionrecovery ,STIR)与快速自旋回波T2加权 (fastspinechoT2weightedimaging ,FSET2WI)在鼻咽癌成像中的应用。方法　 5 0例经手术和病理证实的鼻咽癌病人进行磁共振STIR序列和FSET2WI扫描 ,对两者进行对比度 噪音比值 (C Ns)比较和肿瘤影像征像 (包括肿块边界和肿块内部细节 )清晰程度的比较。结果　STIR序列的C Ns为 2 0 4 1± 3 87,FSET2WI的C Ns为 8 2 4± 1 74。STIR序列比FSET2WI有更高的C Ns ,t=2 0 2 9,P <0 0 1。STIR序列成像对鼻咽癌的边界和内部结构的显示比FSET2WI成像更清楚 ,两者影像征像比较 :鼻咽癌肿块边界 χ2 =2 3 19,P <0 0 1、肿块内部细节 χ2 =16 2 3,P <0 0 1。结论STIR序列在鼻咽癌成像效果比FSET2WI更敏感、更能有效显示鼻咽癌。     

膝关节软骨缺损性病变的MR成像序列研究

目的　评价各种临床常用MR扫描序列诊断关节软骨病变的价值。方法　实验猪膝关节 5只 ,在股骨内外髁关节面软骨上制成缺损模型 ,分别采用各种常用序列扫描 ,测量各种扫描序列上关节软骨的信噪比 (SNR)、软骨相对周围组织的对比噪声比 (CNR) ,采用一致性评价指标 (ICC)评价软骨缺损MRI测量值与实际测量值的一致性。采用实验中优选的MR序列对 2 3例膝关节病变患者进行检查 ,并与关节镜分级诊断结果比较。结果　实验膝关节软骨SNR良好者有质子和T2 WI快速自旋双回波 (FSEPD/T2 WI)、附加脂肪抑制的三维快速扰相梯度回波 (FS 3DFSPGR)和附加脂肪抑制的质子和T2 WI快速自旋双回波 (FSFSEPD/T2 WI)。CNR表现“极佳”者 ,对骨皮质 :FS 3DFSPGR、FSFSEPD/T2 WI;对关节液 :脂肪抑制快速自旋回波 (FSFSE)T2 WI、FS 3DFSPGR ;对半月板和韧带 :FS 3DFSPGR、FSFSEPD/T2 WI、SET1WI、反转时间为 70 0ms的T1WI反转恢复 (IRTI70 0 )序列 ;对脂肪 :FS 3DFSPGR、SET1WI。ICC只有IRTI70 0序列有统计学上的意义 (P <0 .0 5 ) ,且一致性评价为“极佳”。对2 3例膝关节病变患者MR检查结果 :FS 3DFSPGR序列的敏感性为 86 %、特异性为 96 %、表示准确度的Kappa值为 0 .8;IRTI70 0序列的敏感性为 6 8%、特异性为 99%、Kappa值为 0     

利用脂肪抑制三维扰相梯度回波(T1-FFE)序列进行膝关节软骨3D打印的可行性分析

目的 研究脂肪抑制三维扰相梯度回波(T1-FFE)序列在膝关节软骨3D打印中的应用价值及可行性分析.方法 利用脂肪抑制三维扰相梯度回波(T1-FFE)序列进行膝关节软骨成像,并将图像数据进行处理转换成3D打印机可识别的STL格式,然后利用高精度3D打印机进行膝关节软骨打印建模,根据模型的质量以及精确度分析该序列的应用价值.结果 脂肪抑制三维扰相梯度回波(T1-FFE)序列可清晰地显示关节软骨,利用该序列得到的图像数据进行软骨3D打印,可完整精确的打印出软骨模型.结论 利用脂肪抑制三维扰相梯度回波(T1-FFE)序列进行膝关节软骨3D打印可得到理想的三维软骨模型,具有非常实用的临床价值.     

ADC图和动态增强平面回波MR序列评价头颈部癌的颈部淋巴结转移

目的：评价ADC图和动态增强平面回波MR序列对诊断头颈部癌颈部淋巴结转移的临床应用价值。方法：对51名头颈部癌伴颈部淋巴结病变的患行扩散加权（DWI）和动态增强T2。灌注加权。DWI采用单次激发EPI序列，b值为500和1000s／mm^2，并重建出ADC图。多层面MR灌注成像采用单次激发平面回波T2WI，在首过团注Gadolinium-DTPA（0．2ml mol／kgBW）后每两秒采集一次，共采集2min以获得信号强度时间曲线。计算出淋巴结的ADC值和最大信号强度下降的百分比，并与组织病理学进行对照。     

急性卒中病人3D多回波梯度回波与2D T_2~* MR序列动脉血栓检出的对照研究

正摘要目的比较急性卒中病人多回波梯度回波MR序列[磁敏感加权血管成像(SWAN)]与T2*序列对动脉血栓的检出。方法连续74例急性卒中病人被纳入研究。采用时间     

利用自旋回波平面成像T_2加权序列提高肝脏实性病变的检出率

目的　评价自旋回波平面成像 (SE EPI)T2 W序列对肝脏实性病变的检出能力。方法74例病人 (2 0 2个病灶 )接受肝脏 3种SE EPIT2 W序列磁共振扫描 ,评价其图像信噪比 (SNR)、肝脾对比噪声比 (L SCNR)、病灶对比噪声比 (CNR)及病变检出率 ,并与真实稳态进动快速成像 (true FISP)、快速自旋回波 (TSE)及半傅立叶采集单次激发快速自旋回波 (HASTE)等屏气T2 W序列相比较。结果SE EPI的SNR高于TSE (P <0 0 5 ) ,与true FISP相近 (P >0 0 5 ) ,但低于HASTE(P <0 0 1)。SE EPI序列的L SCNR及实性病变的CNR均显著高于true FISP、HASTE及TSE(P <0 0 1)。对于囊性病变 ,各序列间的检出率无明显差异 (P >0 0 5 )。各序列均检出所有直径大于 5cm的实性病变。直径 2～ 5cm的实性病变 ,SE EPI序列的检出率略高于true FISP、HASTE及TSE ,但无显著性差异 (P >0 0 5 )。直径小于 2cm的实性病灶 ,SE EPI序列的检出率 (93 9% )明显高于true FISP(5 7 6 % )、HASTE(71 2 % )及TSE(6 8 2 % ) (P <0 0 1)。结论　与其他屏气T2 W序列相比 ,SE EPIT2 WI有较高的病灶对比 ,能提高肝脏实性病变的检出率     

Comparison of echo planar imaging, gradient echo and fast spin echo MR scans of knee menisci.

In order to reduce the acquisition time, we compared a three-dimensional multi-shot echo-planar imaging (EPI) sequence with fat-suppression with two widely used sequences, the fat-suppressed gradient echo (GRE) and the proton-density weighted turbo spin-echo (FSE) in imaging the menisci of the knee. Sixty patients with various indications were studied prospectively with MRI. The menisci were imaged in the sagittal plane with all three sequences using a 1T MR scanner with 15mT/m gradients. The signal-to-noise ratio (SNR) of bone (b), cartilage (c), and meniscus (m) as well as contrast-to-noise ratio (CNR) and relative contrast (ReCon) between menisci and cartilage and between bone and cartilage were measured. A qualitative analysis was performed on grading of meniscal pathology (0-IV). The imaging accuracy of meniscal pathology was assessed compared to arthroscopy in 13 patients. The EPI provided the highest SNR in cartilage and meniscus (p<0.001), the highest CNR and the highest ReCon between bone and cartilage (p< or =0.001). MR grading of meniscal abnormalities showed overestimation compared to GRE and FSE. The EPI sequence could not be included in the routine protocol in imaging the menisci since the overestimation of meniscal abnormalities could lead to unnecessary arthroscopy.     

Gradient echo imaging

Magnetic resonance imaging (MRI) based on gradient echoes is used in a wide variety of imaging techniques and clinical applications. Gradient echo sequences form the basis for an essential group of imaging methods that find widespread use in clinical practice, particularly when fast imaging is important, as for example in cardiac MRI or contrast‐enhanced MR angiography. However, the term “gradient echo sequence” is somewhat unspecific, as even images acquired with the most common sequences employing the gradient echo for data acquisition can significantly differ in signal, contrast, artifact behavior, and sensitivity to, eg, flow. This is due to the different use of sequence timing and basic sequence building blocks such as spoiler gradients or specific radiofrequency (RF) pulse phase patterns. In this article the basic principles of gradient echo formation compared to spin echo imaging are reviewed and the properties of gradient echo imaging in its simplest form (TR ? T₂) are described. Further, the most common three variants of fast gradient echo sequences (TR < T₂), namely, unbalanced gradient echo, RF spoiled gradient echo, and balanced steady state free precession; are discussed. For each gradient echo sequence type, examples of applications exploiting the specific properties of the individual technique are presented. J. Magn. Reson. Imaging 2012;35:1274–1289. © 2012 Wiley Periodicals, Inc.     

Dual‐echo Dixon imaging with flexible choice of echo times

In this work, a new two‐point method for water–fat imaging is described and explored. It generalizes existing two‐point methods by eliminating some of the restrictions that these methods impose on the choice of echo times. Thus, the new two‐point method promises to provide more freedom in the selection of protocol parameters and to reach higher scan efficiency. Its performance was studied theoretically and was evaluated experimentally in abdominal imaging with a multigradient‐echo sequence. While depending on the choice of echo times, it is generally found to be favorable compared to existing two‐point methods. Notably, water images with higher spatial resolution and better signal‐to‐noise ratio were attained with it in single breathholds at 3.0 T and 1.5 T, respectively. The use of more accurate spectral models of fat is shown to substantially reduce observed variations in the extent of fat suppression. The acquisition of in‐ and opposed‐phase images is demonstrated to be replaceable by a synthesis from water and fat images. The new two‐point method is finally also applied to autocalibrate a multidimensional eddy current correction and to enhance the fat suppression achieved with three‐point methods in this way, especially toward the edges of larger field of views. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Transverse relaxometry with reduced echo train lengths via stimulated echo compensation

Transverse relaxation (T₂) mapping has many applications, including imaging of iron accumulation in grey matter. Using the typical multiecho spin‐echo sequence with long echo trains, stimulated echo compensation can enable T₂ fitting under conditions of variable radio frequency homogeneity arising from slice profile and in‐plane radio frequency variation. Substantial reduction in the number of refocusing pulses could enable use at high magnetic fields where specific absorption rate is a major limitation, and enable multislice use with reduced incidental magnetization transfer at all field strengths. We examine the effect of reduced echo train lengths and multislice imaging on T₂ fitting using stimulated echo compensation applied to iron‐rich subcortical grey matter in human brain at 4.7 T. Our findings indicate that reducing from 20 echoes to as few as four echoes can maintain consistent T₂ values when using stimulated echo compensation in grey and white matter, but not for cerebrospinal fluid. All territories produce marginal results when using standard exponential fitting. Savings from reduced echoes can be used to substantially increase slice coverage. In multislice mode, the resulting incidental magnetization transfer decreased brain signal but had minimal effect on measured T₂ values. Magn Reson Med 70:1340–1346, 2013. © 2013 Wiley Periodicals, Inc.     

Fast spin echo vs conventional spin echo in cervical spine imaging

The major attraction of fast-spin-echo (FSE) imaging is reduced acquisition time; however, careful review of the literature reveals many weaknesses: phase-encoded blurring, truncation artefact, bright fat signal, reduced magnetic susceptibility and increased motion artefact. Our aim was a prospective, blinded comparison of FSE and conventional spin echo (CSE) in the cervical spine. Both sequences were performed in 43 patients (19 males and 24 females; mean age 45 years, range 15–66 years). Twenty-eight patients were studied at 1.5 T and 15 at 0.5 T. Typical sequence parameters were: at 1.5 T, TR/TE 2000/90 CSE and 3000/120 FSE, and at 0.5 T, 2200/80 CSE and 2800/120 FSE. Time saved on the FSE was used to increase the matrix and the number of acquisitions. Two neuroradiologists evaluated the images for pathology, artefacts, disc signal intensity, thecal sac compression and image quality. Ten patients had cord lesions; 2 (20 %) were missed on CSE. In 4 of 10 patients with moderate/severe thecal sac compression, the degree of stenosis was apparently exaggerated on CSE. The mean degree of confidence for the CSE sequences was 1.8 and for the FSE 1.1, where 1 is optimal. For cervical spine imaging, FSE should be preferred to CSE. Received 6 May 1996; Revision received 19 July 1996; Accepted 26 February 1997     

Fast SSFP gradient echo sequence for simultaneous acquisitions of FID and echo signals

Recently, the gradient echo imaging sequence in conjunction with small flip angle excitations and short repetition times has been widely used for fast NMR imaging. As the repetition time decreases to an extent comparable to the spin-spin relaxation time T2, the residual phase coherency of the transverse spin magnetization tends to form another nuclear signal which is heavily weighted by T2 and similar to a long TR/long TE spin-echo signal. This effect, although expected, has not been utilized in the conventional fast gradient echo imaging. When this residual phase coherency is utilized in conjunction with the fast SSFP (steady-state free precession) technique, both the FID and the echo signals can be obtained. In this paper, we have proposed a new technique by which simultaneous acquisitions of both the FID and the echo signals are possible. Experiments on this fast SSFP mode imaging have shown that the FID signal is T1-weighted while the echo signal is strongly T2-weighted. The flip angle optimal for maximizing signal and related contrast are also studied in conjunction with the proposed sequence and the experimental results are presented.     

Fast spin echo and fast gradient echo MRI with low acoustic noise

It has been shown previously that a significant reduction of the acoustic noise in standard, slow magnetic resonance imaging (MRI) sequences is achieved when the gradient pulses have long sinusoidal ramps. An improvement of this method is now presented for fast gradient echo (FLASH) and fast spin echo (RARE) sequences. The new strategy consists of using a sinusoidal readout pulse with no plateau and extending the phase encoding pulses to the entire readout period. The distribution of k-space samples is no longer equidistant, and images have to be reconstructed with gridding. A reduction of the acoustic noise by 20-40 dBA was obtained with respect to standard sequences installed by the scanner manufacturer, which is 10-20 dBA better than that with the previously proposed method of sinusoidal ramps. J. Magn. Reson. Imaging 2001;13:960-966.