高场强MR仪结合小动物线圈在小鼠神经系统疾病中的应用

【摘要】目的：研究临床常规高场强MR仪结合8通道小孔径专用线圈用于小鼠神经系统常见疾病成像的可行性。方法：采用3.0T MR仪结合8通道横向放置小孔径线圈及小柔线圈扫描小鼠脑组织，调整T1WI、 T2WI冠状面及横轴面参数，优化各个序列图像质量，最终确定扫描参数。取15只C57小鼠，采用8通道横向放置线圈和小柔线圈依次扫描。扫描结束对图像质量行主观评分，测量并计算大脑皮层及中心区域信噪比（SNR）及对比噪声比（CNR），并采用配对t检验法比较两种线圈各个序列的主观评分及SNR、CNR值。采用8通道横向放置小孔径线圈扫描永久性脑缺血模型及脑胶质瘤模型并观察病灶显示情况。结果：8通道横向放置线圈T1WI及T2WI冠状面及横轴面图像主观评分均高于小柔线圈（P均<0.001）。8通道横向线圈T1WI及T2WI冠状面图像（皮层及中心）SNR高于小柔线圈（P均<0.01）。8通道横向线圈T1WI及T2WI冠状面图像（皮层及中心）CNR高于小柔线圈，差异不具有统计学意义（P均>0.05）。8通道横向线圈T1WI及T2WI横轴面图像（皮层及中心）SNR和CNR高于小柔线圈（P均<0.01）。使用8通道横向放置线圈结合高场强MR仪能清晰显示缺血灶及胶质瘤部位及范围，增强后可见肿瘤明显强化。结论：使用8通道横向放置线圈结合高场强MR仪能很好的进行小鼠脑部MR成像，T1WI、T2WI图像成像质量佳，图像质量明显优于小柔线圈，对脑卒中及脑胶质瘤病灶显示清晰，可以用于小鼠脑缺血疾病及肿瘤疾病的成像。     

3.0 T MR扫描仪联合8通道相控阵眼表面线圈提高眼部肿块显示能力的多中心研究

目的探讨在3.0 T MR扫描仪上联合使用8通道相控阵眼表面线圈提高眼部图像质量及眼部肿块显示能力的价值。方法前瞻性收集2018年7月至2020年1月6个中心的692例拟行眼部MRI的眼部肿块初诊患者, 均采用3.0 T MR扫描仪, 以简单随机法分为2组, 表面线圈组413例, 使用8通道相控阵眼表面线圈进行扫描;头线圈组279例, 使用8通道相控阵头线圈行相同序列扫描。评价2组图像的图像质量, 客观评价为计算眼眶正常结构(眼睑、玻璃体、泪腺和视神经眶内段)和各部位肿块(眼睑肿块、眼球内肿块、泪腺窝肿块及眼眶肿块)图像的信噪比(SNR)和对比噪声比(CNR);主观评价为主观评分, 指标包括运动伪影、肿块边缘及肿块与邻近结构关系的显示情况, 并计算图像质量总体评分。采用独立样本t检验或Wilcoxon秩和检验比较2组图像间客观指标和主观评分的差异。结果表面线圈组所有图像的SNR、CNR高于头线圈组, 差异有统计学意义(P<0.05), 运动伪影评分低于头线圈组, 差异有统计学意义(P<0.05)。表面线圈组眼球内肿块边缘、肿块与邻近结构关系评分及图像总体质量评分高于头线圈组...     

小孔径正交相控阵线圈与临床表面柔性线圈小动物MRI成像质量的比较研究

目的:比较小孔径小动物实验专用正交相控阵线圈与单通道表面柔性线圈的MRI成像质量。方法:采用1.5 T磁共振成像系统,同一扫描参数,测量比较2种线圈在大鼠头颅MRI平扫的信噪比、图像质量及脑波谱成像质量。结果:小孔径正交相控阵线圈采集的大鼠头部脑组织的信噪比明显优于表面柔性线圈采集图像的信噪比,2组间有明显差异(P<0.01),小孔径正交相控阵线圈采集的图像质量评分及脑波谱成像优于表面柔性线圈(P<0.01)。结论:小孔径正交相控阵动物实验线圈在大鼠头部MRI检查成像质量优于表面柔性线圈,小孔径动物实验用正交相控阵线圈能较好地应用于临床实验。     

3.0T MRI胸椎扫描中联合线圈单元开放对图像质量的影响

目的:探讨不同的联合线圈单元开放方法在3.0T MRI胸椎扫描中对图像质量的影响,筛选最佳扫描方案。方法:应用3.0T MR机联合线圈(NV线圈及SPINE线圈)对20例患者行胸椎扫描,分别获得不同线圈单元开放的T1WI压脂增强(SPIR)序列图像,测量图像的信噪比(SNR)及对比度噪声(CNR),比较其图像质量是否存在差异。结果:20例中使用NV线圈开放NPC单元结合SPINE线圈开放ABC单元(即NPC-ABC,A组)图像的SNR-Ⅰ(上段胸椎)及CNR-Ⅰ均高于使用NV线圈开放PC单元结合SPINE线圈开放ABCD单元(即PC-ABCD,B组),SNR-Ⅰ分别为70.11±5.38和16.37±4.76(P<0.05),CNR-Ⅰ分别为15.11±4.62和7.90±4.48,两组间差异有统计学意义(P<0.05);而NPC-ABC与PC-ABCD的SNR-Ⅱ(即中段胸椎)及NPC-ABC与PC-ABCD的SNR-Ⅲ(即下段胸椎)间差异均无统计学意义。A组序列上段胸椎图像的主观评分为3.6±0.4,B组为2.7±0.5。结论:使用NV线圈开放NPC单元结合SPINE线圈开放ABC单元得出的上段胸椎图像质量最好,可作为常规扫描方案。     

前列腺MRI检查:直肠内表面线圈与体线圈的对比研究

目的　研究直肠线圈对前列腺病变的诊断价值。方法　对前列腺癌 9例 ,前列腺增生 4例 ,正常 2例 ,共 15例前列腺检查作了体线圈与直肠线圈自旋回波 (SET1WI、FSET2 WI)序列扫描的对照研究。评分比较体线圈与直肠线圈横轴位的图像质量 ,并进行诊断分析。结果　T2 WI图像的平均评分 :体线圈 ( 2 .97± 0 .61)分 ,表面线圈 ( 3.4± 0 .60 )分 ,Ρ <0 .0 5。T1WI图像的平均评分 :体线圈 ( 2 .70± 0 .46)分 ,直肠表面线圈 ( 3.2 7± 0 .68)分 ,Ρ <0 .0 5。图像诊断分析显示 :前列腺癌 9例中 ,直肠线圈图像观察病灶范围 7例较体线圈清楚 ,包膜外侵犯 2例较体线圈清楚 ,精囊侵犯 1例常规图像未能显示。前列腺增生及正常病例中直肠线圈图像观察增生结节及合并的小囊肿更为清楚。结论　直肠表面线圈提高前列腺病变的分辨率 ,有助于前列腺癌的诊断和分期     

头颅柔性线圈改善MRS图像质量的可行性

目的:探讨头颅柔性12通道线圈(AHC12)改善MRS图像质量的可行性。方法:招募30例健康受试者,采用相同MRI扫描仪及头颅硬质常规16通道线圈(HNC16)、硬质24通道线圈(HC24)、AHC12线圈行MRS成像。采用LCModel软件计算各代谢物与肌酸(Cr)+磷酸肌酸(PCr)的浓度比值,估计标准差值(SD%),并利用联影工作站获得代谢产物峰值、半高全宽值、图像SNR进行客观评价。采用主观评分法评价谱线基线、谱线线型及伪影。结果:图像质量客观评价中,使用HC24及AHC12线圈MRS图像的Cr与Cr+PCr比值、N-乙酰天冬氨酸(NAA)及Cr的SNR均高于HNC16线圈,Cr的SD%值均小于HNC16线圈(均P<0.05);HC24与AHC12间差异无统计学意义(P>0.05)。主观评价中,HC24及AHC12线圈MRS图像的谱线基线、谱线线型评分均高于HNC16线圈(均P<0.05),HC24与AHC12间差异无统计学意义(P>0.05)。结论:在MRS成像中,改良的AHC12线圈可获得与HC24线圈相同的图像质量。     

高场强头颅柔性线圈的颅脑成像质量的应用价值研究

【摘要】目的：通过与头颅16通道硬质线圈（HC16）比较，评价头颅12通道柔性磁共振线圈（AHC12）的颅脑成像效果。方法：首先对二个线圈进行物理测试，之后招募20例健康志愿者，分别采用同一磁共振仪、同一成像序列，先后采用AHC12和HC16线圈进行头颅成像，成像序列包括横轴面T2WI 、矢状面3D T1WI及扩散加权成像。对两组中各序列图像质量进行主观评分，测量及计算图像信噪比，并进行统计学分析。结果：AHC12线圈组中T2WI、3D-T1WI、DWI图像的信噪比均高于HC16线圈组，组间差异均具有统计学意义（P<0.05）。AHC12线圈组T2WI图像质量的主观评分明显高于HC16线圈（4.77±0.43 vs. 4.41±0.50，P<0.05)；两个线圈组中T1WI和DWI图像质量的主观评分差异君无统计学意义（4.82±0.39 vs. 4.64±0.49，4.70±0.47 vs. 4.40±0.50；P均>0.05）。结论：高场强下AHC12 柔性线圈可获得优于HC16硬质线圈的图像质量，可应用于临床常规头颅MRI检查中。     

串联线圈大鼠MR成像的初步应用研究

目的 探讨串联线圈进行大鼠3.0 T MR扫描的效果.方法 应用研制的串联线圈与随机所配的3个线圈,分别对自制的水溶液模型运用相同的快速恢复快速自旋回波序列(FRFSE-XL)进行扫描,选择4组图像中同一位置的层面,采用单幅图像测量信噪比(SNR).12只SD大鼠平均分为3个模型组和1个正常组.运用FRFSE-XL序列、快速扰相梯度回波(FSPGR)和多体素波谱(Probe-SI)序列,分别对大鼠脑损伤、脑氢质子MR波谱(1H-MRS)、脊髓损伤(SCI)和大鼠腹部进行了初步应用研究.结果 串联线圈的SNR(39.7)比随机所配的3个线圈中SNR(6.41)最好的膝关节线圈高出6倍以上.大鼠颅脑损伤的T2WI和T1WI能清楚分辨灰质和白质,很好地显示脑室的结构和血肿的位置及大小.注射6-羟基多巴胺(6-OHDA)2周后,大鼠脑部1H-MRS能显示氮-乙酰天冬氨酸/肌酸(NAA/Cr)的比值减小(注射6-OHDA前为1.240,注射2周后为0.781).大鼠胸髓T2WI可清楚显示卵圆形的脊髓,显示"H"形脊髓白质;大鼠SCI模型T2WI清楚显示大鼠胸部脊髓损伤的部位和程度.大鼠腹部扫描,FSPGR序列T1WI时间为8 s,有利于克服呼吸等运动的影响,清楚显示大鼠腹部的结构.结论 应用3.0 T MR结合串联线圈为活体大鼠模型的MR检查提供了很好的方法.     

不同抑脂序列在3.0 T乳腺MR扩散加权成像中的应用比较

目的 比较4种不同脂肪抑制序列的3.0T MR正常乳腺扩散加权成像(DWI)的图像质量,从而优化和筛选3.0T乳腺MR DWI的最佳脂肪抑制技术.方法 在3.0 T MRI上,分别对44例女性乳腺受检者应用选择性水激励技术(water excitation)、频率选择脂肪饱和技术(Fatsat)、反转恢复技术(IR)、频率选择反转脉冲脂肪抑制技术(Fatsat+ IR)4种不同脂肪抑制序列行DWI,其他参数相同.比较不同抑脂序列的DWI图像质量,测量并计算不同抑脂序列DWI图像的乳腺组织信噪比(SNR),并进行统计学分析.结果 应用water excitation的DWI图像质量平均评分为3.07±0.79,主观质量评分达到3分(可以诊断)及以上者34例,占总检查例数的77.27％;应用Fatsat的DWI图像质量平均评分为2.43±0.82,主观质量评分达到3分及以上者20例,占总检查例数的45.45％;应用IR的DWI图像质量平均评分为1.32±0.60,主观质量评分达到3分及以上者3例,占总检查例数的6.82％;应用Fatsat+IR的DWI图像质量平均评分为2.07±0.99,主观质量评分达到3分及以上者15例,占总检查例数的34.09％.统计结果显示不同抑脂序列的DWI图像质量比较差异有统计学意义(P =0.0001 ＜0.01),两两比较显示应用Water excitation的DWI图像质量明显优于Fatsat、IR及Fatsat+ IR(P值分别为0.002、0.000及0.000).应用water excitation的DWI图像乳腺组织SNR平均为52.28±19.34,应用Fatsat的DWI图像乳腺组织SNR平均为39.93±15.07,应用IR的DWI图像乳腺组织SNR平均为23.00±7.34,应用Fatsat+IR的DWI图像乳腺组织SNR平均为28.55±9.36.统计结果显示不同抑脂序列DWI图像乳腺组织SNR差异有统计学意义(F=90.73,P=0.0000＜ 0.01),两两比较显示应用water excitation的DWI图像乳腺组织SNR明显优于其他3组(P值均为0.000). 结论 在3.0T乳腺MR检查中,应用water excitation抑脂序列有助于改善DWI的图像质量,提高SNR.     

脑肿瘤T_1WI-FLASH 3D序列直接增强扫描的伽玛刀定位价值

目的探讨T1WI-FLASH 3D(fast low angle shot,FLASH)序列直接增强扫描作为伽玛刀定位图像的价值。方法回顾性的分别对60例颅脑肿瘤患者的增强扫描SE T1WI图像与T1WI-FLASH 3D图像对比研究。由2名放射主任医师、2名放射技师双盲法对两组图像进行分析,分别测量病灶个数、信噪比(SNR)、对比噪声比(CNR),并对两组图像显示程度进行评分。两组图像SNR、CNR比较采用配对样本t检验。结果 T1WI-FLASH 3D图像SNR为87.2±18.8,SE T1WI图像SNR为60.3±9.4,低于T1WI-FLASH3D图像,差异具有统计学意义(t值=9.913,P0.05)。T1WI-FLASH3D图像CNR为40.3±12.6,SE T1WI图像CNR为30.2±3.1,低于T1WI-FLASH3D图像,差异有统计学意义(t值=6.029,P值0.05)。结论以T1WI-FLASH 3D序列直接增强扫描图像作为伽玛刀定位序列优于SE T1WI图像。     

Comparison of volume, four- and eight-channel head coils using standard and parallel imaging

Array coils can potentially offer increased signal-to-noise ratio (SNR) over standard coils adjacent to the array elements, while preserving the SNR at the center of the volume. The SNR advantage should theoretically increase with the number of array elements. Parallel acquisition techniques (PAT), on the other hand, can benefit acquisition times or spatial resolution at a cost to SNR as well as image quality. This study examines the question of whether SNR and image quality are still acceptable with two different array coils (four and eight channels) in conjunction with PAT when compared to standard imaging with a volume coil. All imaging was on a 1.5 T MR scanner. T2-weighted, FLAIR, diffusion-weighted, and time of flight (TOF) angiography images were performed with and without PAT in a phantom and in ten healthy volunteers. The phantom measurements demonstrated superior SNR for the eight-channel coil versus the four-channel and standard head coils. Using the eight-channel head coil for in vivo imaging, image quality with PAT (acceleration factor=2) was scored similar to images without PAT using the volume coil. The four-channel head coil suffered from inhomogeneity, lower SNR and poorer image quality when using PAT compared to standard imaging with the volume head coil. Both the in vivo and the phantom results indicate that the eight-channel head coil should be used for the highest quality brain images; this coil can be combined with PAT sequences for shorter acquisition time without a significant decrease in image quality relative to a volume coil without PAT.     

A comparison of an inductively coupled implanted coil with optimized surface coils for in vivo NMR imaging of the spinal cord

A study was performed to determine whether an implanted, inductively coupled nuclear magnetic resonance (NMR) imaging spine coil could provide a significant gain in signal-to-noise ratio (SNR) on images of the spinal cord relative to the SNR of optimized surface coils. Implanted coils were surgically affixed to the upper lumbar spine (first lumbar through third lumbar vertebrae) in a total of four adult cats. The implanted coil was inductively coupled to an external 12 × 12 cm square surface coil that was mounted on a 14-cm diameter Plexiglas® cradle (Townsend Industries, Des Moines, IA). Two similar cradles were prepared with transmit-only 12 × 12 cm surface coils and either a receive-only 6 × 6 cm square surface coil or a receive-only quadrature coil pair (two 4 × 6 cm coils overlapped slightly to minimize their mutual inductance) with 'the same surface area (6 × 6 cm). A total of five single-slice, T1-weighted spin-echo images (TR = 500 ms, TE = 30 ms, 4-mm slice thickness) were acquired from a 1-liter saline phantom and from the second lumbar spinal level in an adult cat with a normal, uninjured spinal cord. On the spinal cord images, the quadrature coil exhibited a factor of 1.65 increase in SNR relative to the single-turn surface coil, whereas the implanted coil achieved a factor of 2.19 increase in SNR. The improved SNR for the quadrature and implanted coils was observed as a dramatic improvement in the clarity of the images. The high SNR available with the implanted coils allows the acquisition of higher resolution NMR images and opens up the possibility of measuring localized spectroscopy in vivo within the spinal cord.     

Three‐element phased‐array coil for imaging of rat spinal cord at 7T

To overcome some of the limitations of an implantable coil, including its invasive nature and limited spatial coverage, a three‐element phased‐array coil is described for high‐resolution magnetic resonance imaging (MRI) of rat spinal cord. This coil allows imaging both thoracic and cervical segments of rat spinal cord. In the current design, coupling between the nearest neighbors was minimized by overlapping the coil elements. A simple capacitive network was used for decoupling the next neighbor elements. The dimensions of individual coils in the array were determined based on the signal‐to‐noise ratio (SNR) measurements performed on a phantom with three different surface coils. SNR measurements on a phantom demonstrated higher SNR for the phased array coil relative to two different volume coils. In vivo images acquired on rat spinal cord with our coil demonstrated excellent gray and white matter contrast. To evaluate the performance of the phased array coil under parallel imaging, g‐factor maps were obtained for acceleration factors of 2 and 3. These simulations indicate that parallel imaging with an acceleration factor of 2 would be possible without significant image reconstruction–related noise amplifications. Magn Reson Med 60:1498–1505, 2008. © 2008 Wiley‐Liss, Inc.     

Sensitivity of an eight-element phased array coil in 3 Tesla MR imaging: a basic analysis.

PURPOSE: To evaluate the performance advantages of an 8-element phased array head coil (8 ch coil) over a conventional quadrature-type birdcage head coil (QD coil) with regard to the signal-to-noise ratio (SNR) and image uniformity in 3 Tesla magnetic resonance (MR) imaging. MATERIALS AND METHODS: We scanned a phantom filled with silicon oil using an 8 ch coil and a QD coil in a 3T MR imaging system and compared the SNR and image uniformity obtained from T(1)-weighted spin echo (SE) images and T(2)-weighted fast SE images between the 2 coils. We also visually evaluated images from 4 healthy volunteers. RESULTS: The SNR with the 8 ch coil was approximately twice that with the QD coil in the region of interest (ROI), which was set as 75% of the area in the center of the phantom images. With regard to the spatial variation of sensitivity, the SNR with the 8 ch coil was lower at the center of the images than at the periphery, whereas the SNR with the QD coil exhibited an inverse pattern. At the center of the images with the 8 ch coil, the SNR was somewhat lower, and that distribution was relatively flat compared to that in the periphery. Image uniformity varied less with the 8 ch coil than with the QD coil on both imaging sequences. CONCLUSION: The 8 ch phased array coil was useful for obtaining high quality 3T images because of its higher SNR and improved image uniformity than those obtained with conventional quadrature-type birdcage head coil.     

Cardiac imaging at 4 Tesla.

Although higher magnetic field strength is a means to increase SNR in MRI, cardiac imaging has been difficult at high fields due to decreased RF penetration. Using a tailored cardiac coil constructed of two transmit surface coils with a four-element multicoil for signal reception, the authors demonstrate high-quality heart images acquired on a 4-T scanner. These images show an increase in SNR of approximately 2.5-fold over imaging at 1.5 T. This improvement in image quality can be used to increase in-plane resolution, reduce slice thickness, or reduce total scan time. Magn Reson Med 45:176-178, 2001.     

Superconducting RF coils for clinical MR imaging at low field

RATIONALE AND OBJECTIVES: A number of recent reports in the MRI literature have established that substantial signal-to-noise ratio (SNR) gains can be achieved with small samples or low resonance frequencies, through the use of high-quality factor high-temperature superconducting (HTS) RF receive coils. We show the application of HTS coils to the imaging of human subjects with improved SNR compared with copper coils. MATERIALS AND METHODS: HTS coils were constructed from 7.62-cm YBa2Cur3O7-delta thin films on LaAlO3 substrate and cooled in a liquid nitrogen cryostat. Human and phantom images were acquired on a 0.2-T scanner. The SNR improvements compared with equivalent-sized copper coils are reported. RESULTS: SNR gains of 2.8-fold and 1.4-fold were observed in images of a phantom acquired with an HTS coil versus a room temperature copper coil and a liquid nitrogen-cooled copper coil, respectively. Preliminary results suggest higher image quality can be obtained in vivo with an HTS coil compared with copper coil imaging. Images of human orbit, brain, temporomandibular joint, and wrist are presented. CONCLUSION: The experimental results show that benefits can be expected from application of HTS surface coils in human MR imaging with low-field scanners. These potential benefits justify the continued development of practical HTS coil imaging systems despite the considerable technical difficulties involved in cryostat and coil design.     

A three-coil comparison for MR angiography

The purpose of this work was to compare intracranial magnetic resonance angiography (MRA) image quality using three different radiofrequency coils. The three coil types included a reduced volume quadrature birdcage coil with endcap, a commercially available quadrature birdcage head coil, and a four-element phased-array coil. Signal-to-noise ratio (SNR) measurements were obtained from comparison studies performed on a uniform cylindrical phantom. MRA comparisons were performed using data acquired from 15 volunteers and applying a thick-slab three-dimensional time-of-flight sequence. Analysis was performed using the signal difference-to-noise ratio, a quantitative measure of the relative vascular signal. The reduced-volume endcap and phased-array coils, which were designed specifically for imaging the intracranial volume of the head, improved the image SNR and vascular detail considerably over that obtained using the commercially available head coil. The endcap coil configuration provided the best vascular signal overall, while the phased-array coil provided the best results for arteries close to the coil elements.     

Performance assessment of phased-array coil in breast MR imaging.

PURPOSE: To compare the performance of the phased-array coil (PAC) with that of the single-loop coil (SLC) in magnetic resonance (MR) imaging of the breast. MATERIALS AND METHODS: MR imaging was performed with a 1.5T MR imager. A phantom study was performed with the right element of the two coils to obtain their signal-to-noise ratio (SNR). MR images of the breasts of 12 patients with breast lesions were obtained with the PAC and SLC, and these images were reviewed by five readers in a blind evaluation employing a scoring system for assessing overall image quality. RESULTS: In the phantom study, the SLC exhibited a SNR 1.82 times higher than that of the PAC at the center of the coil; however, the SLC exhibited an inhomogeneous sensitivity profile and its SNR varied with the distance from the center of the coil in the horizontal and vertical directions. In most of the 12 patients, the MR images obtained with the PAC showed more noise than did those obtained with the SLC, and the PAC obtained lower scores than the SLC in the assessment of overall image quality; however, the difference was significant (p < 0.05) only in coronal imaging. On the other hand, the uniformity of fat saturation in the MR images obtained with the PAC was judged to be significantly superior to that obtained with the SLC (p < 0.05). CONCLUSION: Compared with the SLC, the PAC exhibited a lower SNR and was less advantageous at depicting the breast. However, the PAC provided more homogeneous fat saturation and might be useful for reducing artifacts.