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Surface Coil (surface + coil)
Selected AbstractsHigh-resolution MRI Enhances Identification of Lesions Amenable to Surgical Therapy in Children with Intractable EpilepsyEPILEPSIA, Issue 8 2004Monisha Goyal Summary:,Purpose: Many children with refractory epilepsy can achieve better seizure control with surgical therapy. An abnormality on magnetic resonance imaging (MRI), along with corroborating localization by other modalities, markedly increases chances of successful surgical outcome. We studied the impact of high-resolution MRI on the surgical outcome of intractable epilepsy. Methods: High-resolution MRI using four-coil phased surface array was obtained as part of the comprehensive presurgical protocol for children with focal onset intractable seizures evaluated by our epilepsy center during the first half of 2002. Results: Thirteen consecutive children, ages 5 to 18 years, entered this prospective study. For four patients with a lesion on a recent MRI examination with a standard head coil, management did not change with high-resolution MRI. Standard MRI in the other nine patients did not identify a lesion. However, high-resolution MRI with the phased-array surface coil found previously undiagnosed focal abnormalities in five of nine patients. These abnormalities included hippocampal dysplasia, hippocampal atrophy, and dual pathology with frontal cortical dysplasia. In four of nine patients, no identifiable lesion was identified on the high-resolution MRI. All patients underwent invasive monitoring. In three of five patients, newly diagnosed lesions correlated with EEG abnormalities, and resection was performed. Conclusions: In our center, high-resolution MRI identified lesions not detected by standard MRI in more than half the children (56%). Technical advances such as four-coil phased surface array MRI can help identify and better delineate lesions, improving the diagnosis of patients who are candidates for surgical treatment of refractory epilepsy. [source] Improved homogeneity of the transmit field by simultaneous transmission with phased array and volume coilJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 2 2010Nikolai I. Avdievich PhD Abstract Purpose: To improve the homogeneity of transmit volume coils at high magnetic fields (,4 T). Due to radiofrequency (RF) field/tissue interactions at high fields, 4 T to 8 T, the transmit profile from head-sized volume coils shows a distinctive pattern with relatively strong RF magnetic field B1 in the center of the brain. Materials and Methods: In contrast to conventional volume coils at high field strengths, surface coil phased arrays can provide increased RF field strength peripherally. In theory, simultaneous transmission from these two devices could produce a more homogeneous transmission field. To minimize interactions between the phased array and the volume coil, counter rotating current (CRC) surface coils consisting of two parallel rings carrying opposite currents were used for the phased array. Results: Numerical simulations and experimental data demonstrate that substantial improvements in transmit field homogeneity can be obtained. Conclusion: We have demonstrated the feasibility of using simultaneous transmission with human head-sized volume coils and CRC phased arrays to improve homogeneity of the transmit RF B1 field for high-field MRI systems. J. Magn. Reson. Imaging 2010;32:476,481. © 2010 Wiley-Liss, Inc. [source] Evaluation of intrarenal oxygenation in mice by BOLD MRI on a 3.0T human whole-body scanner,JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2007Lu-Ping Li PhD Abstract Purpose To extend observations on intra-renal oxygenation with blood oxygen level-dependent (BOLD) MRI in human and rats to mouse kidneys imaged with a human whole-body scanner. Materials and Methods Renal BOLD MRI studies were performed on a 3.0T scanner using a multiple gradient-echo (mGRE) sequence with a custom-designed 2.0-cm surface coil to acquire six T2*-weighted images in mice (N = 8) at an in-plane resolution of 156 × 156 ,m2. BOLD MRI data were obtained before and after administration of furosemide (10 mg/kg intravenously [i.v.]). Results The mean weight of eight mice was 24.6 ± 1.0 g. The baseline renal R2* (mean ± standard error [SE]) was 28.6 ± 2.1 seconds,1 in the renal cortex (CO), 35.4 ± 2.2 in the outer medulla (OM), and 21.2 ± 2.1 seconds,1 in the inner medulla (IM). The BOLD response to furosemide (,R2*) was 4.1 ± 1.4 in the CO, 10.1 ± 2.1 seconds,1 in the OM, and 3.4 ± 0.8 seconds,1 in the IM in mice. Conclusion Intrarenal BOLD MR images with sufficiently high resolution can be obtained on a human whole-body scanner when combined with a small receiver coil to allow studies in mice. Both baseline R2* and ,R2* values following administration of furosemide were consistent with previous experience in humans and rats. J. Magn. Reson. Imaging 2007. © 2007 Wiley-Liss, Inc. [source] Adding another spectral dimension to 1H magnetic resonance spectroscopy of hepatic encephalopathy,JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2005Nader Binesh PhD Abstract Purpose To evaluate a localized two-dimensional correlated magnetic resonance spectroscopic (L-COSY) technique in patients with hepatic encephalopathy (HE) and healthy subjects, and to correlate the cerebral metabolite changes with neuropsychological (NP) test scores. Materials and Methods Eighteen minimal hepatic encephalopathy (MHE) patients and 21 healthy controls have been investigated. A GE 1.5-T magnetic resonance (MR) scanner was used in combination with a body MR coil for transmission and a 3-inch surface coil for reception. A 27-mL voxel was localized by three slice-selective radio frequency (RF) pulses (90°-180°-90°) in the anterior cingulate region. The total duration of each two-dimensional L-COSY spectrum was approximately 25 minutes. The NP battery included a total of 15 tests, which were grouped into six domains. Results MR spectroscopic results showed a statistically significant decrease in myo-inositol (mI) and choline (Ch) and an increase in glutamate/glutamine (Glx) in patients when compared to healthy controls. There was also an increase in taurine (Tau) in patients. The NP results indicated a significant correlation between motor function assessed by NP tests and mI ratios recorded using two-dimensional L-COSY. Conclusion The study demonstrated the feasibility of evaluating the two-dimensional L-COSY sequence in a clinical environment. The results showed additional cerebral metabolites that can be measured with the technique in comparison to one-dimensional study. J. Magn. Reson. Imaging 2005;21:398,405. © 2005 Wiley-Liss, Inc. [source] Central brightening due to constructive interference with, without, and despite dielectric resonance,JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 2 2005Christopher M. Collins PhD Abstract Purpose To aid in discussion about the mechanism for central brightening in high field magnetic resonance imaging (MRI), especially regarding the appropriateness of using the term dielectric resonance to describe the central brightening seen in images of the human head. Materials and Methods We present both numerical calculations and experimental images at 3 T of a 35-cm-diameter spherical phantom of varying salinity both with one surface coil and with two surface coils on opposite sides, and further numerical calculations at frequencies corresponding to dielectric resonances for the sphere. Results With two strategically placed surface coils it is possible to create central brightening even when one coil alone excites an image intensity pattern either bright on one side only or bright on both sides with central darkening. This central brightening can be created with strategic coil placement even when the resonant pattern would favor central darkening. Results in a conductive sample show that central brightening can similarly be achieved in weakly conductive dielectric materials where any true resonances would be heavily damped, such as in human tissues. Conclusion Constructive interference and wavelength effects are likely bigger contributors to central brightening in MR images of weakly conductive biological samples than is true dielectric resonance. J. Magn. Reson. Imaging 2005;21:192,196. © 2005 Wiley-Liss, Inc. [source] Time course of 23Na signal intensity after myocardial infarction in humansMAGNETIC RESONANCE IN MEDICINE, Issue 3 2004Joern J.W. Sandstede Abstract Experimental studies demonstrated persistently increased 23Na content in nonviable myocardium post-myocardial infarction (MI). We hypothesized that nonviable myocardium in humans would show elevated 23Na content at all stages of infarct development, and therefore could be imaged with 23Na MRI. Ten patients were examined on days 4, 14, and 90 after infarction, and five of these patients participated in a 12-month follow-up. Double angulated short-axis cardiac 23Na images were obtained with the use of a 23Na surface coil and an ECG-triggered, 3D gradient-echo sequence. 1H T2 -weighted imaging (N = 9) was performed on days 4, 14, and 90. Wall motion was assessed by cine MRI, and the infarct size was determined by late enhancement on day 90. The 23Na signal intensity (SI) of infarcted myocardium was expressed as the percentage increase over 23Na SI of noninfarcted myocardium. All of the patients showed an area of elevated SI on 23Na and 1H T2 -weighted images that correlated with wall motion abnormalities and late enhancement. 23Na SI was highest on day 4. It then decreased until day 90, but remained elevated (39% ± 18%, 31% ± 17%, 28% ± 13% on days 4, 14, and 90, respectively, P = 0.001). No further decrease was found 1 year after infarction (25% ± 7%, P = 0.89 vs. day 90). 1H T2 -weighted SI decreased between days 4 and 14, but on day 90 only six of nine patients had a residual elevated SI. Thus, 23Na SI is elevated in nonviable infarction at all time points following MI, and 23Na MRI may become a suitable technique for imaging nonviable myocardium in humans. Magn Reson Med 52:545,551, 2004. © 2004 Wiley-Liss, Inc. [source] Functional perfusion imaging using continuous arterial spin labeling with separate labeling and imaging coils at 3 TMAGNETIC RESONANCE IN MEDICINE, Issue 5 2003Toralf Mildner Abstract Functional perfusion imaging with a separate labeling coil located above the common carotid artery was demonstrated in human volunteers at 3 T. A helmet resonator and a spin-echo echo-planar imaging (EPI) sequence were used for imaging, and a circular surface coil of 6 cm i.d. was employed for labeling. The subjects performed a finger-tapping task. Signal differences between the condition of finger tapping and the resting state were between ,0.5% and ,1.1 % among the subjects. The imaging protocol included a long post-label delay (PLD) to reduce transit time effects. Labeling was applied for all repetitions of the functional run to reduce the sampling interval. Magn Reson Med 49:791,795, 2003. © 2003 Wiley-Liss, Inc. [source] In vivo imaging of the neutron capture therapy agent BSH in mice using 10B MRIMAGNETIC RESONANCE IN MEDICINE, Issue 1 2001Peter Bendel Abstract Boron neutron capture therapy (BNCT) is an experimental cancer treatment modality requiring the targeting of 10B-enriched compounds to the tumor, which is then irradiated by low-energy neutrons. One of the boron-containing compounds used for this purpose is the mercaptoborane Na2B12H11SH (BSH). The first in vivo MR images of 10B-enriched BSH are presented here. BSH, injected into the tail vein of mice with implanted M2R melanoma xenografts, was imaged using 3D gradient echo 10B MRI. 10B NMR spectroscopy, localized mainly to the tumor by virtue of the use of a small surface coil, was applied to measure the T1 (2.9 ± 0.3 ms) and T2 (1.75 ± 0.25 ms) values of the 10B signal. The MRI experiments detected levels of about 20 ppm (,g boron / g tissue) at 6 × 6 × 6 mm spatial resolution in a total scan time of 16 min. Magn Reson Med 46:13,17, 2001. © 2001 Wiley-Liss, Inc. [source] Accurate phosphorus metabolite images of the human heart by 3D acquisition-weighted CSIMAGNETIC RESONANCE IN MEDICINE, Issue 5 2001Rolf Pohmann Abstract Fourier imaging modalities suffer from significant signal contamination between adjacent voxels, especially when the spatial resolution is comparable to the size of the anatomical structures. This contamination can be positive or negative, depending on the spatial response function and the geometry of the object. Such a situation arises in human cardiac 31P chemical shift imaging (CSI). Acquisition-weighted CSI reduces this contamination substantially, which is demonstrated by comparing conventional CSI to Hanning-weighted 3D 31P-CSI experiments in 13 healthy volunteers at 2 T. The nominal spatial resolution and the total number of scans were identical for both experiments. The improved spatial response function of the acquisition-weighted experiment led to a significantly (P < 0.0001) higher myocardial PCr/ATP ratio (2.05 ± 0.31, mean ± SD, N = 33, corrected for saturation and blood contribution) compared to the conventional CSI experiment (1.60 ± 0.46). This is explained by the absence of negative contamination from skeletal muscle, which also resulted in an increase of the observed SNR (from 5.4 ± 1.4 to 7.2 ± 1.4 for ATP). With acquisition-weighted CSI, metabolic images with a nominal resolution of 16 ml could be obtained in a measurement time of 30 min. After correction for the inhomogeneous B1 field of the surface coil, these images show uniform ATP distribution in the entire myocardium, including the posterior wall. Magn Reson Med 45:817,826, 2001. © 2001 Wiley-Liss, Inc. [source] Comparison of oxidative capacity among leg muscles in humans using gated 31P 2-D chemical shift imagingNMR IN BIOMEDICINE, Issue 10 2009Sean C. Forbes Abstract In many small animals there are distinct differences in fiber-type composition among limb muscles, and these differences typically correspond to marked disparities in the oxidative capacities. However, whether there are similar differences in the oxidative capacity among leg muscles in humans is less clear. The purpose of this study was to compare the rate of phosphocreatine (PCr) recovery, a functional in vivo marker of oxidative capacity, in the lateral and medial gastrocnemius, soleus, and the anterior compartment of the leg (primarily the tibialis anterior) of humans. Subjects performed plantar flexion and dorsiflexion gated exercise protocols consisting of 70 sets of three rapid dynamic contractions (<2.86,s) at 20,s intervals (total: 23.3,min). Starting after the sixth set of contractions, 31P 2-D CSI (8,×,8 matrix, 14,16,cm FOV, 3,cm slice, TR 2.86,s) were acquired via a linear transmit/receive surface coil using a GE 3T Excite System. The CSI data were zero-filled (32,×,32) and a single FID was produced for each time point in the lateral and medial gastrocnemius, soleus, and anterior compartment. The time constant for PCr recovery was calculated from ,,=,-,t/ln[D/(D,+,Q)], where Q is the percentage change in PCr due to contraction during the steady-state portion of the protocol, D the additional drop in PCr from rest, and ,t is the interval between contractions. The , of PCr recovery was longer (p,<,0.05) in the anterior compartment (32,±,3,s) than in the lateral (23,±,2,s) and medial gastrocnemius muscles (24,±,3,s) and the soleus (22,±,3,s) muscles. These findings suggest that the oxidative capacity is lower in the anterior compartment than in the triceps surae muscles and is consistent with the notion that fiber-type phenotypes vary among the leg muscles of humans. Copyright © 2009 John Wiley & Sons, Ltd. [source] Transrectal ultrasound-guided biopsy of prostate voxels identified as suspicious of malignancy on three-dimensional 1H MR spectroscopic imaging in patients with abnormal digital rectal examination or raised prostate specific antigen level of 4,10 ng/mlNMR IN BIOMEDICINE, Issue 1 2007Virendra Kumar Abstract Results of the evaluation of transrectal ultrasound (TRUS) guided needle biopsy of voxels identified as suspicious of malignancy on magnetic resonance spectroscopic imaging (MRSI) in a large cohort of men (n,=,83) with abnormal digital rectal examination (DRE) [prostate specific antigen (PSA) 0,4,ng/ml] or PSA less than 10,ng/ml, are reported. Three-dimensional 1H MRSI was carried out at 1.5 T using a pelvic-phased array coil in combination with an endorectal surface coil. Voxels were classified as suspicious of malignancy based on Cit/(Cho,+,Cr) metabolite ratio. TRUS-guided biopsy of suspicious voxels was performed using the z - and x -coordinates obtained from MR images and two to three cores were taken from the suspected site. A systematic sextant biopsy was also carried out. MRSI showed voxels suspicious of malignancy in 44 patients while biopsy revealed cancer in 11 patients (25%). Patients who were negative for malignancy on MRSI were also negative on biopsy. An overall sensitivity of 100%, specificity of 54%, negative predictive value of 100% and accuracy of 60% were obtained. The site of biopsy was confirmed (n,=,20) as a hypo-intense area on repeat MRI while repeat MRSI revealed high choline and low citrate. The overall success rate of MRI-directed TRUS-guided biopsy of 25% was higher compared with a 9% success rate achieved without MR guidance in another group of 120 patients. Our results indicate that TRUS-guided biopsy of suspicious area identified as malignant from MRSI can be performed using the coordinates of the voxel derived from MR images. This increases the detection rate of prostate cancer in men with PSA level <10,ng/ml or abnormal DRE and also demonstrates the potential of MR in routine clinical practice. Copyright © 2006 John Wiley & Sons, Ltd. [source] An additional phase in PCr use during sustained isometric exercise at 30% MVC in the tibialis anterior muscleNMR IN BIOMEDICINE, Issue 4 2002C. J. Houtman Abstract The occurrence of an abrupt acceleration in phosphocreatine hydrolysis in the tibial anterior muscle during the last part of a sustained isometric exercise at 30% maximal voluntary contraction until fatigue is demonstrated in seven out of eight healthy subjects by applying in vivo31P NMR spectroscopy at 1.5,T field strength. This additional third phase in PCr hydrolysis, is preceded by a common biphasic pattern (first fast then slow) in PCr use. The NMR spectra, as localized by a surface coil and improved by proton irradiation, were collected at a time resolution of 16 s. Mean rates of PCr hydrolysis during exercise were ,0.44,±,0.19% s,1, ,0.07,±,0.04% s,1, and ,0.29,±,0.10% s,1 for the three successive phases. The increased rate of PCr hydrolysis, and also the loss of fine force control evident in the force records are consistent with increased involvement of large, fast-fatiguable units later in the contraction. Copyright © 2002 John Wiley & Sons, Ltd. [source] Central brightening due to constructive interference with, without, and despite dielectric resonance,JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 2 2005Christopher M. Collins PhD Abstract Purpose To aid in discussion about the mechanism for central brightening in high field magnetic resonance imaging (MRI), especially regarding the appropriateness of using the term dielectric resonance to describe the central brightening seen in images of the human head. Materials and Methods We present both numerical calculations and experimental images at 3 T of a 35-cm-diameter spherical phantom of varying salinity both with one surface coil and with two surface coils on opposite sides, and further numerical calculations at frequencies corresponding to dielectric resonances for the sphere. Results With two strategically placed surface coils it is possible to create central brightening even when one coil alone excites an image intensity pattern either bright on one side only or bright on both sides with central darkening. This central brightening can be created with strategic coil placement even when the resonant pattern would favor central darkening. Results in a conductive sample show that central brightening can similarly be achieved in weakly conductive dielectric materials where any true resonances would be heavily damped, such as in human tissues. Conclusion Constructive interference and wavelength effects are likely bigger contributors to central brightening in MR images of weakly conductive biological samples than is true dielectric resonance. J. Magn. Reson. Imaging 2005;21:192,196. © 2005 Wiley-Liss, Inc. [source] Inductively coupled helmholtz coil on a dedicated imaging platform for the in vivo1H-MRS measurement of intramyocellular lipids in the hind leg of ratsMAGNETIC RESONANCE IN MEDICINE, Issue 4 2009Michael Neumaier PhD Abstract Skeletal muscle triglycerides are markers for insulin resistance in type 2 diabetes. Recently, MR spectroscopy was adapted for in vivo measurement of triglycerides in animal models and for the characterization of new therapeutic approaches. Because of small MR spectroscopy voxel sizes used in skeletal muscles, surface coils are used for signal reception. Furthermore, to obtain well-resolved and undistorted lipid spectra, muscle fibers must be aligned parallel to the magnetic field. Consequently, to achieve a high signal-to-noise ratio and spectral quality, a coil setup must combine high sensitivity with a reliable and reproducible positioning of muscle and voxel. These demands are difficult to match using surface coils. Here, a coil platform is described, which uses inductively coupled Helmholtz coil setup combined with a leg retainer system for rats. The new system allows for measurement of intramyocellular lipids with high signal-to-noise ratio and for significantly improved animal handling, positioning, and throughput. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [source] Saturated double-angle method for rapid B1+ mappingMAGNETIC RESONANCE IN MEDICINE, Issue 6 2006Charles H. Cunningham Abstract For in vivo magnetic resonance imaging at high field (,3 T) it is essential to consider the homogeneity of the active B1 field (B1+), particularly if surface coils are used for RF transmission. A new method is presented for highly rapid B1+ magnitude mapping. It combines the double angle method with a B1 -insensitive magnetization-reset sequence such that the choice of repetition time (TR) is independent of T1 and with a multislice segmented (spiral) acquisition to achieve volumetric coverage with adequate spatial resolution in a few seconds. Phantom experiments confirmed the accuracy of this technique even when TR , T1, with the side effect being lowered SNR. The speed of this method enabled B1+ mapping in the chest and abdomen within a single breath-hold. In human cardiac imaging, the method enabled whole-heart coverage within a single 16-s breath-hold. Results from phantoms and healthy volunteers at 1.5 T and 3 T are presented. Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc. [source] Real-time accelerated interactive MRI with adaptive TSENSE and UNFOLD,MAGNETIC RESONANCE IN MEDICINE, Issue 2 2003Michael A. Guttman Abstract Reduced field-of-view (FOV) acceleration using time-adaptive sensitivity encoding (TSENSE) or unaliasing by Fourier encoding the overlaps using the temporal dimension (UNFOLD) can improve the depiction of motion in real-time MRI. However, increased computational resources are required to maintain a high frame rate and low latency in image reconstruction and display. A high-performance software system has been implemented to perform TSENSE and UNFOLD reconstructions for real-time MRI with interactive, on-line display. Images were displayed in the scanner room to investigate image-guided procedures. Examples are shown for normal volunteers and cardiac interventional experiments in animals using a steady-state free precession (SSFP) sequence. In order to maintain adequate image quality for interventional procedures, the imaging rate was limited to seven frames per second after an acceleration factor of 2 with a voxel size of 1.8 × 3.5 × 8 mm. Initial experiences suggest that TSENSE and UNFOLD can each improve the compromise between spatial and temporal resolution in real-time imaging, and can function well in interactive imaging. UNFOLD places no additional constraints on receiver coils, and is therefore more flexible than SENSE methods; however, the temporal image filtering can blur motion and reduce the effective acceleration. Methods are proposed to overcome the challenges presented by the use of TSENSE in interactive imaging. TSENSE may be temporarily disabled after changing the imaging plane to avoid transient artifacts as the sensitivity coefficients adapt. For imaging with a combination of surface and interventional coils, a hybrid reconstruction approach is proposed whereby UNFOLD is used for the interventional coils, and TSENSE with or without UNFOLD is used for the surface coils. Magn Reson Med 50:315,321, 2003. Published 2003 Wiley-Liss, Inc. [source] | ||||||||||