前列腺磁共振检查技术的探讨

目的 通过选择合理的扫描线圈、扫描计划以获得清晰的前列腺图像。方法 选择１８例病人首次使用体线圈得前裂腺ＭＲＩ检查,在１８个月内再次复诊扫描时使用盆腔相控表面线圈以相同的扫描计划进行检查。比较两种扫描方法所获得的图像之间的差异（ｔ检验）。结果 通过对所获得的图像进行分析、比较,可知盆腔相控线圈所获图像优于体线圈（有显著差异）。结论 为了获得良好的前列腺磁共振检查图像,需根据病人民政部尽量使用盆腔相     

中轴骨转移瘤的背景抑制磁共振弥散成像多线圈对比研究

目的:研究磁体内置BODY线圈与全脊柱相控阵线圈获取的背景抑制磁共振弥散图像对中轴骨转移瘤显示的敏感性和特异性,探讨磁共振全身弥散技术( WB - DWI)临床应用价值.材料与方法:搜集本院有明确恶性肿瘤病史并辅助检查(包括X光平片及常规CT、MRI)诊断中轴骨转移患者39例,其中采用磁体内置BODY线圈行磁共振全身弥散扫描患者16例(实验A组),采用全脊柱相控阵线圈行背景抑制磁共振弥散成像扫描患者23例(实验B组);所有患者在3个月之后至少一次全脊柱MRI随访扫描(包括STIR序列扫描).比较实验A组和B组背景抑制磁共振弥散图像的阳性率、病灶数目及所能现实的骨转移灶的最小直径,并进一步分析两组图像对病灶显示的敏感性和特异性.结果:实验A组和B组显示骨转移灶阳性率均为100％;实验A组显示病灶的数目、最小直径不如实验B组;实验A组和B组对骨转移灶显示的敏感性分别为87.14％和91.31％,特异性分别为90.36％和89.07％.结论:体部正交线圈获取的WB - DWI图像虽然空间分辨率和信号分辨率较局部体表相控阵线圈低,但对骨转移灶显示能力的差异无显著性统计学意义,而且具有大范围全身扫描的优势,值得在临床恶性肿瘤骨转移患者的诊断中推广使用;但临床应用该序列诊断时对可疑区域应采用局部线圈,如全脊柱相控阵线圈,加扫背景抑制磁共振弥散成像,以提高病变诊断的敏感性和小病灶的显示能力.     

利用颅脑射频线圈进行大鼠磁共振成像

目的 研究3.0T磁共振成像系统中大鼠脑部射频线圈.方法 提出一种设计线圈结构的方案,采用高等于直径的鞍型线圈,研究直径为5 cm的大鼠脑部线圈减小电容和分布电容,可使线圈带宽减小,提高线圈品质的因素(Q).将线圈与人体头部线圈和体部线圈分别对自制的模型利用同一序列进行扫描,对三组图像选择同一位置的图像,比较各线圈的信噪比(SNR).观察图像的质量,应用大鼠颅脑模型分别进行轴位、矢状位和冠状位T1W FLAIR或T2W扫描.结果 线圈的SNR比现有的头部线圈高5倍以上.大鼠图像能很好地显示脑室结构,可清楚分辨脑部的灰质和白质.结论 利用所设计的线圈可获得具有很高SNR的图像,在大鼠脑部影像研究中取得了很好的效果.     

临床用肢端柔性表面线圈和相控阵线圈在小动物磁共振成像中的性能比较

目的对比肢端柔性线圈和相控阵线圈非并行采集及并行采集技术在小动物实验中对图像质量的影响。方法10只Wistar大鼠,分别用西门子标配的临床用正交柔性肢端线圈和相控阵肢端线圈在同一扫描参数的条件下用于头部信号采集,同时在肢端相控阵线圈采集中采用并行采集技术再获得相同的图像,然后对三组图像选择同一层面进行SNR的比较。结果正交柔性线圈和4通道肢端相控阵线圈采集的图像信噪比有明显的差异,正交柔性线圈能获得更高的图像信噪比,而肢端相控阵线圈非并行采集与并行采集技术(R=2)所获得的图像信噪比没有差异,但采用并行采集技术能极大地减少扫描时间。结论小动物实验在线圈的选用上,线圈的填充因数对图像质量的影响更大,但相控阵线圈与并行采集技术合用可以极大地减少成像时间。     

磁共振3D成像技术在眼眶部扫描的应用价值

目的:探讨磁共振3D成像技术在眼眶部扫描中的应用价值。材料与方法:采用我院奥泰1.5T超导磁共振成像仪在2013年8月份-12月份期间对30例志愿者的眼眶部分别进行2D成像技术与3D成像技术扫描并进行对比。并比较2D成像技术与3D成像技术扫描前后对病变的显示情况。结果:应用3D成像技术与2D成像技术相比较:(1)扫描时间:3D成像技术扫描时间明显缩短;(2)两种技术所做图像信噪比和对比噪声比比较:3D成像技术图像明显高于2D成像技术图像;(3)两种成像技术MR图像质量情况:3D成像技术图像质量明显好于2D成像技术。结论:磁共振3D成像扫描技术能更清楚的显示眼眶部的解剖结构、提高病变的诊断价值,减小运动伪影。     

常规磁共振对裸鼠成像的可行性及参数优化

目的探讨临床常规磁共振在裸鼠成像中的可行性。方法采用小关节线圈及专用小动物线圈对裸鼠肝脏进行MR成像,根据伪影、均匀度与对比度,评价两种线圈对裸鼠成像的质量。对裸鼠进行T1mapping和T2mapping成像,根据肝脏的T1、T2值确定扫描序列中的TE值,然后采用浮动的TR值进行扫描,最后调整扫描的其它参数实现序列的优化。结果在FSE T1WI、SE T1WI、FSE T2WI、GRE T2*WI序列中,小动物线圈和3英寸双环形线圈的图像质量评分分别为2.6±0.54、3.2±0.84、2.6±0.89、2.4±0.55和3.6±0.55、3.8±0.45、3.2±0.84、2.6±0.55,小动物线圈图像的信噪比明显高于3英寸双环形线圈(P0.05)。经过序列优化后,图像的细节分辨率,对比度明显提高,图像信号显示更均匀。结论通过线圈的优选及序列的优化,常规临床磁共振可以进行活体裸鼠磁共振成像。     

以直肠内线圈进行前列腺扩散加权成像的可行性研究

目的以腹部相控阵线圈获得的前列腺常规DWI成像为标准,研究以1.5T磁共振系统进行直肠内线圈DWI成像所得前列腺ADC值的准确性。方法随机选择20例同时进行了常规DWI和直肠内DWI的前列腺病例,比较两种DWI图像的空间分辨率和信噪比。以第三方软件逐点测量前列腺的ADC值,并手动测量ADC值,与常规方法所得ADC值进行对比,分析直肠内线圈所得ADC值的可用性。结果直肠内DWI的空间分辨率明显高于常规DWI,两种DWI信噪比无显著性差异。观察获得的散点图,发现与直肠内线圈表面相距22.9 mm以内的ADC值与常规ADC值差异不大。在前列腺外周带手工测量两种ADC值,无统计学差异,相关系数为0.820。结论前列腺直肠内线圈DWI图像分辨率高,但仅距离线圈前表面约22.9 mm以内的ADC值与常规ADC值具有可比性。     

前列腺癌的磁共振成像:直肠内线圈与腹部相控阵线圈的比较

目的比较直肠内线圈(endorectalcoil，ERC)和腹部相控阵线圈(torsophasedarray，TORs0PA)对前列腺检查的图像质量及对前列腺癌显示的差别。方法对123位患者行前列腺MRl检查，每位患者先用TORSOPA检查，然后行ERC检查。对30例病理证实为前列腺癌患者的MRI图像进行评价。将前列腺分为6个区，左、右侧的底部、中部和尖部，由阅片者对每个分区是否有癌作出评价。结果123位受检者中有1位未完成ERC检查。两组图像质量无明显差别(Y2=2．562，P=0．278)。MRI和穿刺病理对照，ERC与TORSOPA比较，对肿瘤定位的敏感性和阴性预期值明显升高(由58．8％和82．6％上升为86．2％和93．0％)，诊断的特异性、准确度和阳性预期值无明显变化。结论直肠内线圈比腹部相控阵线圈MRI对前列腺癌的定位更敏感。     

肠道磁共振水成像检查技术探讨

目的通过选择合理的对比剂、扫描计划以获得清晰满意的肠道MR图像。方法随机选择无消化系统疾病的健康志愿者20名(年龄20～40岁),采用Siemens Symphony 1.5T磁共振成像系统,分别使用阳性对比剂(水)和阴性对比剂(钡剂)以相同的扫描条件行肠道磁共振成像,比较两种扫描方法所获图像之间的差异。结果通过对所获图像进行比较、分析,发现阳性对比剂(水)所获图像优于阴性对比剂(钡剂);两者之间存在显著的统计学差异(P<0.01)。结论为了获得清晰满意的肠道磁共振图像,应尽量使用阳性对比剂(水)的检查方法(即肠道磁共振水成像)。     

脑功能磁共振成像的质量控制标准

自1972年第一台磁共振扫描仪问世以来,磁共振作为一项重要的临床检查手段得到了飞速的发展[1]。同时,磁共振的成像方式也与日俱进:multi-echo SE,fast spin-echo,gradient-echo,EPI,ASSET,DTI等序列的相继问世[2,3],开辟了磁共振科研的新天地。但是,作为一种非常复杂的系统,磁共振仪器的成像受很多因素和环节的影响[4,5]。任何一个环节的出错,都可能影响图像质量。在国外,从事磁共振质量控制的是专门的磁共振工程师[6,7]。国内通常由放射技师和物理师共同完成该工作。据统计显示,我国目前磁共振仪器的运行状况并未完全达标[8]。这就迫切需要一套专门针对磁共振仪器质量控制的、简单易行的标准。由于磁共振成像的复杂性,磁共振的质量控制也涉及诸多方面[9]。1 signal to noise ratio(SNR)磁共振是一种信号成像,包括了有用的图像的整体噪声,用图像中心区域的信号值作为整体信号[10]。1&#183;1常规SNR的测量方式(图1):信号(信息)和无用的信号(噪声)。SNR越高,则图像质量越好。目前磁共振头部线圈多采用相控阵线圈,这种线圈有多个信号接收单元,图像各个部...     

Dynamic MR urography in urinary tract obstruction: implementation and preliminary results

Background Recent studies have demonstrated magnetic resonance (MR) capabilities in evaluating renal morphology and function in patients with urinary obstruction. The objective of this report is to support the introduction of dynamic MR renography on any MR equipment. Methods A custom-made device of vials filled with different concentrations of gadolinium was studied by combinations of T1-weighted gradient-echo sequences and coils. We compared the capabilities of two coils (phased array vs. standard body), the properties of dynamic sequences, and the effects of increasing concentrations of gadolinium on signal intensity. In a second section, we designed MR urography plug-ins of Image J (DICOM image software) for the analysis of dynamic studies. Results Optimized gradient-echo sequences acquired with a phased array body coil produced acceptable quality images with a linear relation between signal intensity and the lowest concentrations of gadolinium. In vitro measurements showed loss of linearity above 8 mmol/L. Conclusion Theoretical calculation and data from the literature suggest that the gadolinium dose to the patient should not exceed one-fourth of the usual one (0.025 mmol/kg). Postprocessing using Image J software and the specifically designed plug-ins was validated. The collection of plug-ins is now available on the Internet.     

基于射频场测量的去耦技术在磁共振相控阵线圈中的应用

目的将基于射频场测量的去耦技术应用于核磁共振相控阵线圈以消除核磁共振图像由于阵列单元之间耦合引起的伪影.方法利用测量得到的单个线圈和阵列单元的射频场计算阵列中各个单元之间的耦合系数矩阵以及相应的去耦系数矩阵,并将后者作用于阵列中各单元线圈射频场,以消除各个单元之间的耦合.结果此方法用基于有限元的高频结构仿真软件HFSS进行了仿真,并对仿真结果用计算机模拟核磁共振图像进行了验证, 两者之间具有很好的一致性.结论证明该方法有效驱除了阵列单元之间的耦合效应.     

Improving whole brain structural MRI at 4.7 Tesla using 4 irregularly shaped receiver coils

Both higher magnetic field strengths (> or =3 T) and multiple receiver "array coils" can provide increased signal-to-noise ratio (SNR) for MRI. This increase in SNR can be used to obtain images with higher resolution, enabling better visualisation of structures within the human brain. However, high field strength systems also suffer from increased B(1) non-uniformity and increased power deposition, reaching specific absorption rate (SAR) limits more quickly. For these problems to be mitigated, a careful choice of both the pulse sequence design and transmit RF coil is required. This paper describes the use of a prototype array coil consisting of 4 irregularly shaped coils within a standard configuration for neuroimaging at 4.7 T (a head transmit/receive volume coil to minimise SAR and a head gradient insert for maximum gradient performance). With a fast spin echo (FSE) pulse sequence optimised for 4.7 T, this provides dramatically increased quality and resolution over a large brain volume. Using the array coil, a SNR improvement relative to the volume coil of 1-1.5 times in central brain areas and 2-3 times in cortical regions was obtained. Array coil images with a resolution of 352 x 352 x 2000 mum had a SNR of 16.0 to 26.2 in central regions and 19.9 to 34.8 in cortical areas. Such images easily demonstrate cortical myeloarchitecture, while still covering most of the brain in a approximately 12 min scan.     

Clinical Implementation of Magnetic Resonance Imaging Systems for Simulation and Planning of Pediatric Radiation Therapy

AimTo describe the clinical implementation and optimization of magnetic resonance imaging (MRI) systems installed in a radiation oncology department for dedicated use in radiotherapy (RT) simulation and treatment planning for pediatric patients.MethodsTwo wide-bore MRI systems were installed and commissioned in 2016. Patient setups, coil placements, and scan protocols were developed to image various anatomic sites in children. Patients with brain tumors were routinely imaged using a pair of flexible loop coils and a posterior receiver coil integrated into the patient couch. The integrated posterior coil and the flexible anterior torso coil supported by the coil bridge were used together when imaging the abdomen, pelvis, or spine. A three-dimensional acquisition was most often performed, given the benefit of high-resolution multiplanar reformation as well as elimination of B0-related distortions in the slice selection direction.ResultsWe performed 542 MRI studies (265 for planning and 277 for monitoring on-treatment tumor changes) on pediatric patients in the first year after system installation. Multisequence images of pediatric RT patients with ependymoma, medulloblastoma, craniopharyngioma, rhabdomyosarcoma, or Ewing sarcoma were shown to illustrate the image quality obtainable with optimized planning sequences.ConclusionsMagnetic resonance imaging (MRI) of pediatric patients in their treatment positions with setup devices in place can be performed with coil arrangements that include flexible coils. The resulting image quality is suitable for treatment planning and on-treatment monitoring. We provide optimized site-specific sequence parameters to support the continued improvement of MRI for pediatric RT planning.     

Investigation of multichannel phased array performance for fetal MR imaging on 1.5T clinical MR system

Fetal MRI on 1.5T clinical scanner has been increasingly becoming a powerful imaging tool for studying fetal brain abnormalities in vivo. Due to limited availability of dedicated fetal phased arrays, commercial torso or cardiac phased arrays are routinely used for fetal scans, which are unable to provide optimized SNR and parallel imaging performance with a small number coil elements, and insufficient coverage and filling factor. This poses a demand for the investigation and development of dedicated and efficient radiofrequency (RF) hardware to improve fetal imaging. In this work, an investigational approach to simulate the performance of multichannel flexible phased arrays is proposed to find a better solution to fetal MR imaging. A 32 channel fetal array is presented to increase coil sensitivity, coverage and parallel imaging performance. The electromagnetic field distribution of each element of the fetal array is numerically simulated by using finite-difference time-domain (FDTD) method. The array performance, including B(1) coverage, parallel reconstructed images and artifact power, is then theoretically calculated and compared with the torso array. Study results show that the proposed array is capable of increasing B(1) field strength as well as sensitivity homogeneity in the entire area of uterus. This would ensure high quality imaging regardless of the location of the fetus in the uterus. In addition, the paralleling imaging performance of the proposed fetal array is validated by using artifact power comparison with torso array. These results demonstrate the feasibility of the 32 channel flexible array for fetal MR imaging at 1.5T.     

Optimisation of the 3D MDEFT sequence for anatomical brain imaging: technical implications at 1.5 and 3 T

An algorithm for the optimisation of 3D Modified Driven Equilibrium Fourier Transform (MDEFT) sequences for T1-weighted anatomical brain imaging is presented. Imaging parameters are optimised for a clinical whole body scanner and a clinical head scanner operating at 1.5 and 3 T, respectively. In vivo studies show that the resulting sequences allow for the whole brain acquisition of anatomical scans with an isotropic resolution of 1 mm and high contrast-to-noise ratio (CNR) in an acceptable scan time of 12 min. Typical problems related to the scanner-specific hardware configurations are discussed in detail, especially the occurrence of flow artefacts in images acquired with head transmit coils and the enhancement of scalp intensities in images acquired with phased array receive coils. It is shown both theoretically and experimentally that these problems can be avoided by using spin tagging and fat saturation.     

采用神经血管线圈和体线圈测量颈部良性淋巴结表观弥散系数值的稳定性

目的 观察神经血管线圈和体线圈接收信号测量的颈部良性淋巴结的ADC值与指数化ADC(eADC)值是否存在差异。 方法 对15名健康志愿者于同日内分别采用8通道神经血管线圈和体线圈行颈部DWI扫描,b值均取0、800 s/mm²,对比双侧(30个)及左右分侧(各15个)良性淋巴结DWI图、ADC图及eADC图特点,分别测量两种线圈测量出的淋巴结ADC及eADC值,并进行比较。 结果 对15名受检者采用两种线圈扫描均获得可测量ADC的图像。神经血管线圈测量出的淋巴结平均ADC值为(0.892±0.165)×10^-3 mm²/s,平均eADC值为(0.425±0.068)×10^-3 mm²/s;体线圈测量出的淋巴结的平均ADC值为(0.857±0.142)×10^-3 mm²/s,平均eADC值为(0.432±0.057)×10^-3 mm²/s。采用两种线圈所获双侧或左右分侧淋巴结的ADC值、eADC值之间差异均无统计学意义(P>0.05)。 结论 采用神经血管线圈或体线圈接收信号对颈部良性淋巴结DWI ADC值的测量无影响。     

在体肝脏质子3.0T MR波谱谱线后处理的应用研究

目的：探讨在体肝脏单体素3.0T 1H-MRS谱线后处理方法。材料和方法：46例受检者,男26例,女20例,年龄19～67岁,中位年龄39岁,包括正常29例、慢性乙型肝炎4例、脂肪肝10例和脂肪肝合并慢性乙型肝炎3例。使用GE Signa Excite HD 3.0T超导型磁共振扫描仪,8通道相控阵线圈。1H-MRS采集使用单体素PRESS序列,参数为TR/TE：1 500 ms/30 ms,NSA：64次,VOI：2 cm×2 cm×2 cm。采用专用波谱后处理软件SAGE 7.3对谱线进行分析。同一谱线采用Spectrum及Probe后处理方法。评价后处理截趾对基线稳定性和SNR的影响及采用配对样本秩和检验。后处理截趾对拟合线宽、峰高及峰下面积的影响采用配对样本t检验。结果：Spectrum方法为要水峰的后处理,显示的代谢物峰较少,主要为4.7 ppm处的水峰与1.3 ppm处的亚甲基峰;Probe方法为不要水峰的后处理,显示代谢物峰个数较多。两种方法均可获得各种化合物峰高、峰下面积及其相互间的比率。5 Hz较1.25 Hz指数函数处理的波谱原始数据所获谱线SNR好,但谱线宽度及峰下面积增加。结论：对脂肪含量进行以水为内参照绝对定量分析可以使用Spectrum方法,而Probe方法有助于含量较少的化合物的显示。相较于1.25 Hz,推荐使用5 Hz的指数函数处理在体肝脏波谱原始数据。     

Multiturn surface coil: Theoretical considerations on unloaded to loaded Q ratio and SNR

Radiofrequency coils in magnetic resonance systems are used for exciting the nuclei in the object to be imaged and for picking up the signals emitted by the nuclei. The quality of obtained images strongly depends on the correct choice of the coils geometry and type. Although the coils' performance are influenced by the cross‐sectional shape of the coil conductors, for multiturn surface coils proximity effects between conductors can significantly influence coil behavior. This work describes how the use of a multiturn conductor affects a coil's performance in terms of unloaded to loaded quality factors ratio and signal‐to‐noise ratio, taking into account for the proximity effect between conductors of the coil. © 2014 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 44B: 27–31, 2014