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.     

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.     

Improved BOLD detection in the medial temporal region using parallel imaging and voxel volume reduction

Using gradient-echo EPI, signal dropout due to macroscopic off resonance effects can prevent blood-oxygenation-level-dependent (BOLD) signal change detection. The anterior medial temporal lobe (MTL) is located near these susceptibility gradients and therefore shows considerable signal dropout with GE-EPI. Reducing the volume of the image voxel reduces susceptibility-related signal dropout. However, this is accompanied by a prohibitive reduction in signal-to-noise ratio (SNR). To compensate for SNR loss with smaller voxels, we used a multi-channel MRI receiver with an array of receive-only 16-element surface coils at 3 T. We demonstrate that the reduction of susceptibility artifacts, through use of high resolution images, coupled with the gains in image SNR from the array coil improves the temporal signal-to-noise ratio (TSNR) and enhances the contrast-to-noise ratio (CNR). Furthermore, a comparison of 2 mm with 4-mm-thick axial images both with the same in-plane resolution showed that thinner slices enhanced TSNR and CNR throughout the ventral-medial regions of the temporal lobes, with the greatest improvement in the most anterior regions of the MTL. Further improvements were seen when adjacent 2 mm slices were combined to match overall voxel volume. These results demonstrate that BOLD investigation of anterior MTL function can be enhanced by decreasing voxel size but only in combination with the SNR gained by using the 16-channel head coil system.     

An implanted 8-channel array coil for high-resolution macaque MRI at 3T

An 8-channel receive coil array was constructed and implanted adjacent to the skull in a male rhesus monkey in order to improve the sensitivity of (functional) brain imaging. The permanent implant was part of an acrylic headpost assembly and only the coil element loop wires were implanted. The tuning, matching, and preamplifier circuitry was connected via a removable external assembly. Signal-to-noise ratio (SNR) and noise amplification for parallel imaging were compared to single-, 4-, and 8-channel external receive-only coils routinely used for macaque fMRI. In vivo measurements showed significantly improved SNR within the brain for the implanted versus the external coils. Within a region-of-interest covering the cerebral cortex, we observed a 5.4-, 3.6-fold, and 3.4-fold increase in SNR compared to the external single-, 4-, and 8-channel coils, respectively. In the center of the brain, the implanted array maintained a 2.4×, 2.5×, and 2.1× higher SNR, respectively compared to the external coils. The array performance was evaluated for anatomical, diffusion tensor and functional brain imaging. This study suggests that a stable implanted phased-array coil can be used in macaque MRI to substantially increase the spatial resolution for anatomical, diffusion tensor, and functional imaging.     

自制线圈辅助支架及表面线圈组合用于新生儿颅脑1.5T MR检查北大核心CSCD

目的观察自制线圈辅助支架及相控阵表面线圈组合(简称组合线圈)用于新生儿颅脑1.5T MRI的价值。方法针对水模分别以组合线圈及常规头颅线圈以相同参数采集T1WI进行体外实验。采用组合线圈(试验组)及常规头颅线圈(对照组)以相同参数对10名健康足月新生儿采集颅脑T1WI、T2WI和T2液体衰减反转恢复(T2-FLAIR)序列图像,比较图像信噪比(SNR)、对比噪声比(CNR)和信号一致性(Cs),综合分析新生儿颅脑各序列图像,比较组间图像主观评分的差异。结果体外实验中,相比常规头颅线圈,以组合线圈采集的T1WI中,各区域SNR均有所增加(P均<0.05),前后部及左右侧Cs值均降低(P均<0.01)。临床试验中,相比对照组,试验组新生儿颅脑T1WI、T2WI及T2-FLAIR序列图像的前额部SNR均提高(P均<0.05),T1WI基底节及左右颞部SNR均降低(P均<0.05),其余区域各序列图像SNR差异均无统计学意义(P均>0.05);组间新生儿颅脑各序列图像所示各区域CNR差异均无统计学意义(P均>0.05);试验组图像质量主观评分(4.45±0.27)高于对照组[(3.01±0.42),t=35.25,P<0.01]。结论自制线圈辅助支架及表面线圈组合有利于提高新生儿颅脑1.5T MR图像质量。     

Physiological noise and signal-to-noise ratio in fMRI with multi-channel array coils

Sensitivity in BOLD fMRI is characterized by the signal to noise ratio (SNR) of the time-series (tSNR), which contains fluctuations from thermal and physiological noise sources. Alteration of an acquisition parameter can affect the tSNR differently depending on the relative magnitude of the physiological and thermal noise, therefore knowledge of this ratio is essential for optimizing fMRI acquisitions. In this study, we compare image and time-series SNR from array coils at 3T with and without parallel imaging (GRAPPA) as a function of image resolution and acceleration. We use the "absolute unit" SNR method of Kellman and McVeigh to calculate the image SNR (SNR(0)) in a way that renders it comparable to tSNR, allowing determination of the thermal to physiological noise ratio, and the pseudo-multiple replica method to quantify the image noise alterations due to the GRAPPA reconstruction. The Kruger and Glover noise model, in which the physiological noise standard deviation is proportional to signal strength, was found to hold for the accelerated and non-accelerated array coil data. Thermal noise dominated the EPI time-series for medium to large voxel sizes for single-channel and 12-channel head coil configurations, but physiological noise dominated the 32-channel array acquisition even at 1 mm × 1mm × 3 mm resolution. At higher acceleration factors, image SNR is reduced and the time-series becomes increasingly thermal noise dominant. However, the tSNR reduction is smaller than the reduction in image SNR due to the presence of physiological noise.     

Fast high resolution whole brain T2* weighted imaging using echo planar imaging at 7T

Magnetic susceptibility based (T(2)* weighted) contrast in MRI at high magnetic field strength is of great value in research on brain structure and cortical architecture, but its use is hampered by the low signal-to-noise ratio (SNR) efficiency of the conventional spoiled gradient echo sequence (GRE) leading to long scan times even for a limited number of slices. In this work, we show that high resolution (0.5mm isotropic) T(2)* weighted images of the whole brain can be obtained in 6min by utilizing the high SNR efficiency of echo-planar imaging (EPI). A volumetric (3D) EPI protocol is presented and compared to conventional 3D GRE images acquired with the same resolution, amount of T(2)* weighting, and imaging duration. Spatial coverage in 3D EPI was increased by a factor of 4.5 compared to 3D GRE, while also the SNR was increased by a factor of 2. Image contrast for both magnitude and phase between gray and white matter was similar for both sequences, with enhanced conspicuity of anatomic details in the 3D EPI images due to the increased SNR. Even at 7T, image blurring and distortion is limited if the EPI train length remains short (not longer than the T(2)* of the imaged tissue). 3D EPI provides steps (speed, whole brain coverage, and high isotropic resolution) that are necessary to utilize the benefits of high field MRI in research that employs T(2)* weighted imaging.     

Multi-projection magnetic resonance inverse imaging of the human visuomotor system

Using highly parallel radiofrequency (RF) detection, magnetic resonance inverse imaging (InI) can achieve 100 ms temporal resolution with whole brain coverage. This is achieved by trading off partition encoding steps and thus spatial resolution for a higher acquisition rate. The reduced spatial information is estimated by solving under-determined inverse problems using RF coil sensitivity information. Here we propose multi projection inverse imaging (mInI) to combine different projection images to improve the spatial resolution of InI. Specifically, coronal, sagittal, and transverse projection images were acquired from different runs of the fMRI acquisitions using a 32-channel head coil array. Simulations show that mInI improves the quality of the instantaneous image reconstruction significantly. Going from one projection to three projections, the spatial resolution quantified by the full width at half maximum of the point-spread function (PSF) is improved from 2.6 pixels to 1.4 pixels (4 mm nominal resolution per pixel). Considering the shape of the PSF, the effective spatial resolution is improved from 16.9 pixels to 4.7 pixels. In vivo fMRI experiments using a two-choice reaction time tasks show visual and sensorimotor cortical activities spatially consistent with typical EPI data, yet mInI offers 100 ms temporal resolution with the whole brain coverage. The mInI data with three projections revealed that the sensorimotor cortex was activated 700 ms after the visual cortex. mInI can be applied to BOLD-contrast fMRI experiments to characterize the dynamics of the activated brain areas with a high spatiotemporal resolution.     

头线圈与眼表面线圈对眼球MR成像质量影响的对比研究

目的通过筛选环形眼表面线圈对眼球成像的最佳扫描参数、对比头线圈与眼表面线圈对眼球MRI质量的影响,优化眼球MRI扫描参数。材料与方法应用环形眼表面线圈采用不同参数组合对体模进行FSET1WI、T2WI（FOV分别为18cm×18cm、10cm×10cm、8cm×8cm,层厚分别为4.0mm、3.0mm、2.0mm）和FSPGR序列（FOV分别为18cm×18cm、10cm×10cm、8cm×8cm,层厚分别为3.2mm、2.8mm、2.4mm）扫描,筛选出环形眼表面线圈的最佳扫描参数,然后分别用环形眼表面线圈和头线圈对10名健康志愿者行横断面FSET2WI,计算图像的SNR、CNR和空间分辨率,并进行统计学处理。结果 （1）体模实验结果：FSE序列采用层厚/间距4.0mm/0.5mm、矩阵288×224、NEX2、FOV分别为18cm×18cm、10cm×10cm、8cm×8cm时体模图像空间分辨率分别是0.80mm、0.45mm、0.36mm,FSET2WI的SNR分别是241.10、94.01、56.90,FSET1WI的SNR分别是805.22、234.71、156.88;FSE序列采用FOV10cm×10cm、矩阵288×224、NEX2、层厚/间距分别为4.0mm/0.5mm、3.0mm/0.3mm、2.0mm/0.2mm时,FSET2WI的SNR分别是94.01、71.57、51.40,FSET1WI的SNR分别是223.34、183.80、130.43;FSPGR序列采用层厚/间距3.2mm/0mm、矩阵288×224、NEX2、FOV分别为18cm×18cm、10cm×10cm、8cm×8cm时,图像SNR分别是263.69、95.40、67.35;FSPGR序列扫描参数FOV10cm×10cm、矩阵288×224、NEX2不变,层厚/间距分别为3.2mm/0mm、2.8mm/0mm、2.4mm/0mm时SNR分别是95.40、93.44、67.39。（2）健康志愿者实验结果：FSE序列T2WIFOV分别为18cm×18cm、10cm×10cm时,所得环形眼表面线圈图像SNR分别是166.22±45.17、65.17±4.99,CNR分别是142.09±43.58、54.98±5.48,头线圈图像SNR分别是70.53±6.58、9.79±0.87,CNR分别是57.20±2.58、6.35±0.34;环形眼表面线圈FOV分别为18cm×18cm、10cm×10cm时,所得图像SNR分别是相应头线圈的2.36倍（P〈0.01）、6.66倍（P〈0.01）,CNR分别是2.48倍（P〈0.01）、8.66倍（P〈0.01）,环形眼表面线圈FOV为10cm×10cm时,所得图像SNR与头线圈FOV为18cm×18cm时的图像无显著性差异（P〉0.05）,但此时环形眼表面线圈图像的空间分辨率（0.45mm）高于头线圈图像（0.8mm）。结论眼球MRI检查推荐使用环形眼表面线圈（FOV10cm×10cm）或头线圈（FOV18cm×18cm）,采用FSE序列、层厚/间距：4mm/0.5mm、矩阵288×224、NEX2。3..     

Volume distribution of cerebrospinal fluid using multispectral MR imaging

The goal of this study was to design a reliable method to quantify and visualize the anatomical distribution of cerebrospinal fluid (CSF) intracranially. The method should be clinically applicable and based on multispectral analysis of three-dimensional (3D) magnetic resonance images. T1-weighted, T2-weighted and proton density-weighted fast 3D gradient pulse sequences were used to form high resolution multispectral 3D images of the entire head. Training on single 2D slices, the Mahalanobis distances between the resulting multivariate tissue-specific densities were studied as functions of the feature vector composition and dimension. Multispectral analysis was applied to the images of four human brains. One feature vector with three components gave CSF volumes that were in the normal range and corresponding anatomical distributions that largely agreed with general anatomical knowledge. The exception was CSF missing around the basal parts of the brain due to signal artifacts. These artifacts were almost certainly due to the coil effect and magnetic field inhomogeneities induced by the imaged head. Such misclassifications could probably be reduced by bias field estimation and proper image restoration. Most CSF voxels formed large connected components that were found automatically, so the manual post-processing of the classified 3D image to locate CSF voxels was moderate. It is concluded that some of the fast, high resolution 3D gradient echo pulse sequences that have become available on conventional clinical scanners can be used to obtain good estimates of brain cerebrospinal fluid anatomical distribution and volume.     

fMRI at 7 T: whole-brain coverage and signal advantages even infratentorially?

fMRI is one of the most likely applications to benefit from high field MRI. It profits from the higher signal-to-noise ratio (SNR) and increased BOLD contrast itself. However, this sensitivity to susceptibility brings with it problems, e.g. in-plane dephasing and signal dropouts near tissue-air boundaries. Therefore, most fMRI studies at 7 T focus on high resolution in supratentorial areas. Nine volunteers were measured at both 1.5 and 7 T using finger tapping with fMRI in a block design fashion. An EPI sequence with short TE (28 ms at 7 T) was chosen for covering the whole brain. A CP transmit/receive head coil was used for image acquisition. Statistical analyses were performed using SPM 02. The activated images were superimposed on both individual images and a standard T1-normalized brain dataset. All cerebral areas involved in finger tapping could be revealed using 7 T: SI, MI, SII, SMA, thalamus, and cerebellar areas. At 1.5 T the activation in the thalamus was only detectable in one subject using the same corrected p value for all analyses. Furthermore, the BOLD signal change was significantly higher at 7 T than at 1.5 T (factor 2 to 3). A well fitted response curve could be detected in all sensory-motor areas at 7 T in whole-brain coverage, even in areas suffering from susceptibility like the cerebellum. Supra- and infratentorial sensory-motor areas are consistently and reliably detectable using whole-brain fMRI at 7 T with good quality response functions and, as expected, higher signal compared to 1.5 T.     

Extensive heterogeneity in white matter intensity in high-resolution T2*-weighted MRI of the human brain at 7.0 T

MRI at high magnetic field strength potentially allows for an increase in resolution and image contrast. The gains are particularly dramatic for T(2)(*)-weighted imaging, which is sensitive to susceptibility effects caused by a variety of sources, including deoxyhemoglobin, iron concentration, and tissue microstructure. On the other hand, the acquisition of high quality whole brain MRI at high field is hampered by the increased inhomogeneity in B(o) and B(1) fields. In this report, high-resolution gradient echo MRI was performed using an 8-channel detector to obtain T(2)(*)-weighted images over large brain areas. The high SNR achieved with the multi-channel array enabled T(2)(*)-weighted images of the brain with an unprecedented spatial resolution of up to 0.2 x 0.2 x 0.5 mm(3). This high resolution greatly facilitated the detection of microscopic susceptibility effects. In addition to the expected contrast between gray, white matter, cerebral spinal fluid, and veins, a large degree of heterogeneity in contrast was observed throughout the white matter of normal brain. The measured T(2)(*) values in white matter varied as much as 30% with some of the variation apparently correlating with the presence of large fiber bundles.     

Event-related single-shot volumetric functional magnetic resonance inverse imaging of visual processing

Developments in multi-channel radio-frequency (RF) coil array technology have enabled functional magnetic resonance imaging (fMRI) with higher degrees of spatial and temporal resolution. While modest improvement in temporal acceleration has been achieved by increasing the number of RF coils, the maximum attainable acceleration in parallel MRI acquisition is intrinsically limited only by the amount of independent spatial information in the combined array channels. Since the geometric configuration of a large-n MRI head coil array is similar to that used in EEG electrode or MEG SQUID sensor arrays, the source localization algorithms used in MEG or EEG source imaging can be extended to also process MRI coil array data, resulting in greatly improved temporal resolution by minimizing k-space traversal during signal acquisition. Using a novel approach, we acquire multi-channel MRI head coil array data and then apply inverse reconstruction methods to obtain volumetric fMRI estimates of blood oxygenation level dependent (BOLD) contrast at unprecedented whole-brain acquisition rates of 100 ms. We call this combination of techniques magnetic resonance Inverse Imaging (InI), a method that provides estimates of dynamic spatially-resolved signal change that can be used to construct statistical maps of task-related brain activity. We demonstrate the sensitivity and inter-subject reliability of volumetric InI using an event-related design to probe the hemodynamic signal modulations in primary visual cortex. Robust results from both single subject and group analyses demonstrate the sensitivity and feasibility of using volumetric InI in high temporal resolution investigations of human brain function.     

Longitudinal stability of MRI for mapping brain change using tensor-based morphometry

Measures of brain change can be computed from sequential MRI scans, providing valuable information on disease progression, e.g., for patient monitoring and drug trials. Tensor-based morphometry (TBM) creates maps of these brain changes, visualizing the 3D profile and rates of tissue growth or atrophy, but its sensitivity depends on the contrast and geometric stability of the images. As part of the Alzheimer's Disease Neuroimaging Initiative (ADNI), 17 normal elderly subjects were scanned twice (at a 2-week interval) with several 3D 1.5 T MRI pulse sequences: high and low flip angle SPGR/FLASH (from which Synthetic T1 images were generated), MP-RAGE, IR-SPGR (N = 10) and MEDIC (N = 7) scans. For each subject and scan type, a 3D deformation map aligned baseline and follow-up scans, computed with a nonlinear, inverse-consistent elastic registration algorithm. Voxelwise statistics, in ICBM stereotaxic space, visualized the profile of mean absolute change and its cross-subject variance; these maps were then compared using permutation testing. Image stability depended on: (1) the pulse sequence; (2) the transmit/receive coil type (birdcage versus phased array); (3) spatial distortion corrections (using MEDIC sequence information); (4) B1-field intensity inhomogeneity correction (using N3). SPGR/FLASH images acquired using a birdcage coil had least overall deviation. N3 correction reduced coil type and pulse sequence differences and improved scan reproducibility, except for Synthetic T1 images (which were intrinsically corrected for B1-inhomogeneity). No strong evidence favored B0 correction. Although SPGR/FLASH images showed least deviation here, pulse sequence selection for the ADNI project was based on multiple additional image analyses, to be reported elsewhere.     

An RF breast coil for 0.2T MRI

Breast cancer is the most frequently diagnosed cancer in women. High field studies have shown the diagnostic value of breast MRI, but the examination costs greatly exceed those of competing conventional mammography. Low field MRI offers typical MRI contrast at substantially lower cost, but has suffered from lower spatial resolution. Specificity of breast MRI can potentially be increased by acquiring MR imaging with higher spatial or temporal resolution, but the signal‐to‐noise ratio (SNR) achievable in a given imaging time becomes limiting. SNR for the particular pulse sequence and magnet field strength is strongly influenced by the characteristics of the radio‐frequency coil. An optimal breast coil should yield excellent SNR but also generate a homogeneous B₁ field, while allowing imaging of the both breasts simultaneously and maintaining patient comfort. RF receiver coil design is a key determinant of image quality, thus to address this we have designed and constructed a low field breast imaging coil. The coil was tested with a 4‐post 0.2T MRI providing high quality breast images. Designed and constructed saddle rf coil allows to obtain good quality image of the breast using low 0.2 T MRI system within 2 minutes. The coil provides patient comfort as breast compression is not required and minimizes artefacts caused by respiration or motion. A high contrast, low‐cost and pain‐free breast examination using optimized low field MRI system has the potential to serve a large patient population for whom current technologies have deficiencies. © 2015 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 46B: 3–7, 2016     

相控线圈在上腹部磁共振检查中的作用

目的 选择合适的脉冲线圈以获得清晰的腹部磁共振图像。方法 14例病人采用体线圈和体部相控阵线圈分别进行腹部磁共振扫描，两种线圈 的扫描序列完全一致，比较两种线圈所获图像的质量。结果 用相控阵线圈采集的腹部磁共振图像的平均信噪比明显高于体线圈所获图像（P＜0．05）。结论 利用体部相控阵线圈可明显提高腹部磁共振图像的质量。     

Studies of RF Shimming Techniques with Minimization of RF Power Deposition and Their Associated Temperature Changes

In ultrahigh field (UHF), human magnetic resonance imaging (MRI) concerns related to the homogeneity of the B1+ field [the radiofrequency (RF) magnetic field component responsible for the excitation of the spins] and the local/average specific absorption rate (SAR) are highly evident. In this work, through RF shimming techniques, a full-wave electromagnetic model that treats a coupled-RF coil and the load (an 18-tissue anatomically detailed human head model) as a single system is utilized to simultaneously (1) improve the homogeneity of B1+ field in various regions of interest across the volume of the human head and (2) minimize the total RF power deposition at 7 and 9.4 T. The numerical results illustrate that the B1+ field homogeneity (evaluated by the coefficient of variance) can be greatly improved in 3D slabs that vary in orientations and sizes, in the brain, and in the entire head volume without increasing the total RF power deposition in the head to exceed that obtained with quadrature excitation. The RF shimming simulation results are experimentally validated (by performing RF shimming without experimental B(1) measurements) on a head-sized phantom using a 7-T human MRI scanner equipped with a transmit array excitation system. The SAR and associated temperature changes under quadrature and RF shimming excitation conditions are calculated and compared.     

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。     

Theoretical analysis of magnetic wall decoupling method for radiative antenna arrays in ultrahigh magnetic field MRI

Radiative antenna techniques, e.g., dipole and monopole, have been proposed for radiofrequency (RF) coil array designs in ultrahigh field MRI to obtain stronger B₁ field and higher signal‐to‐noise ratio (SNR) gain in the areas deep inside human head or body. It is known that element decoupling performance is crucial to SNR and parallel imaging ability of array coil and has been a challenging issue in radiative antenna array designs for MR imaging. Magnetic wall or induced current elimination (ICE) technique has proven to be a simple and effective way of achieving sufficient decoupling for radiative array coils experimentally. In this study, this decoupling technique for radiative coil array was analyzed theoretically and verified by a simulation study. The decoupling conditions were derived and obtained from the theory. By applying the predicated decoupling conditions, the isolation of two radiative elements could be improved from about ? 8 dB to better than ? 35 dB. The decoupling performance has also been validated by current distribution along the radiative elements and magnetic field profiles in a water phantom. © 2015 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 45B: 183–190, 2015     

Design of a quadrature surface coil for hyperpolarized 13C MRS cardiac metabolism studies in pigs

This work describes the design of a quadrature surface coil constituted by a circular loop and a butterfly coil, employed in transmit/receive (TX/RX) mode for hyperpolarized ¹³C studies of pig heart with a clinical 3T scanner. The coil characterization is performed by developing an SNR model for coil performance evaluation in terms of coil resistance, sample‐induced resistance and magnetic field pattern. Experimental SNR‐vs.‐depth profiles, extracted from the [1–13C]acetate phantom chemical shift image (CSI), showed good agreement with the theoretical SNR‐vs.‐depth profiles. Moreover, the performance of the quadrature coil was compared with the single TX/RX circular and TX/RX butterfly coil, in order to verify the advantage of the proposed configuration over the single coils throughout the volume of interest for cardiac imaging in pig. Finally, the quadrature surface coil was tested by acquiring metabolic maps with hyperpolarized [1–13C]pyruvate injected i.v. in a pig. © 2013 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 43B: 69–77, 2013