Standard Coil Research Articles

Diffusion tensor imaging in carpal tunnel syndrome

We aimed to investigate the efficacy of diffusion tensor imaging in the diagnosis of carpal tunnel syndrome and to obtain a quantitative parameter that may contribute to the diagnosis. The median nerves in 57 wrists of 38 patients diagnosed as carpal tunnel syndrome and 30 wrists of 24 normal subjects were prospectively evaluated with a 3T Philips scanner, using standard 8-channel SENSE head coil. Diffusion tensor imaging was performed using spin echo-echo planar imaging. For anatomical reference, a T1-weighted sequence was acquired. Fractional anisotropy and apparent diffusion coefficient measurements were done focally at the carpal tunnel level and from whole median nerve. In carpal tunnel syndrome patients, both focal carpal tunnel and whole nerve measurements demonstrated statistically significantly lower fractional anisotropy values than normal subjects (P < 0.001). No statistically significant difference was observed in apparent diffusion coefficient measurements. The cut-off value obtained by receiver operator characteristics analysis was 0.554 for focal carpal tunnel fractional anisotropy (sensitivity, 80%; specificity, 80%) and 0.660 for whole nerve fractional anisotropy (sensitivity, 82%; specificity, 80%) measurement. Diffusion tensor imaging may contribute to the diagnosis of carpal tunnel syndrome on the basis of fractional anisotropy measurements.

The depth of the olfactory sulcus is an indicator of congenital anosmia

Background and Purpose: In congenital anosmia, the olfactory bulb and olfactory tract can be both aplastic or hypoplastic. In clinical routine they are sometimes difficult to assess. We thus want to investigate morphologic differences of the olfactory sulcus in patients with isolated anosmia (IA) since birth or early childhood in comparison to controls in a large group of subjects; to investigate whether the depth of the olfactory sulcus (OS) indicates IA. Materials and Methods: Within the context of a two-center study we investigated 36 IA patients in comparison to 40 controls. Imaging was performed with a standard quadrature head coil (1.5 T; T1 and T2-weighted spin echo sequences were used (coronal plane perpendicular to frontal skull base). We assessed olfactory bulb volume by planimetric contouring, and OS depth in the plane of the posterior tangent through the eyeballs (PPTE). Results: Looking at the OS depth in the PPTE, none of the healthy controls exhibited a depth of less than 8 mm. In IA patients, 10 had an OS deeper than 8 mm, while 26 had OS depth lower than 8 mm. Thus, if we consider an OS depth lower than 8 mm it clearly indicates IA, with a specificity of 1 while the sensitivity is 0.72. Conclusions: In IA, the OS depth in the PPTE is a useful clinical indicator. Indeed, if it is ≤ 8 mm, it clearly indicates IA, with a specificity of 1. If it is deeper, the measure does not clearly predict IA.

Adenosine Stress Perfusion Cardiac MRI: Improving Image Quality Using a 32-Channel Surface Coil

Purpose: Adenosine stress CMR is commonly used to assess myocardial ischaemia. Obtaining high quality images requires maximising signal to noise ratio (SNR) over a large double-oblique field of view (FOV) whilst minimising artefacts. A 32-channel surface coil may provide a higher SNR over a larger FOV compared to standard coils, possibly leading to improved image quality. Materials and Methods: 50 adenosine perfusion CMR scans were performed on a Philips Achieva CV 1.5T, with either a 5 or 32-channel coil (25 patients each) using standardised acquisition protocols. 3 short axis slices were acquired per cardiac cycle and the resulting cine images were scored by two blinded CMR specialists on a quality scale of 1 to 5. Phantom studies were performed using similar acquisition parameters and the SNR was calculated and compared across a range of acceleration factors. Results: The mean patient age was 62 ± 11 years and 50% of patients were male. The image quality scores were higher using the 32-channel coil (mean 3.8 ± 0.7 vs 3.2 ± 0.9 p = 0.002). The average phantom SNR was greater for the 32-element coil across the range of acceleration factors measured (103 vs 86 p = <0.001). Conclusions: The 32-channel coil produces significantly higher quality images and a higher SNR than the 5-channel coil in routine perfusion CMR.

Loop Antennas for Near-Field Multipolar-Expansion Identification: First Experimental Validations

In this paper, electromagnetic compatibility is assessed using novel magnetic induction sensors based on the standard CISPR16-1 coils. The new coil shape allows the sensors to be sensitive only to specific components of the multipolar expansion, which is similar to a spatial filtering. The aim is to simplify the geometry of sensor coils introduced in the previous work by rotating the spherical-harmonic functions. This paper describes the mathematical tools required as well as the design method and concludes with the first experimental studies.

Simple analytical dual-band spectral-spatial RF pulses for B(1) + and susceptibility artifact reduction in gradient echo MRI.

Susceptibility artifacts and transmission radio frequency (RF) field (B(1) +) inhomogeneity are major limitations in high-field gradient echo MRI. Previously proposed numerical 2D spectral-spatial RF pulses have been shown to be promising for reducing the through-plane signal loss susceptibility artifact by incorporating a frequency-dependent through-plane phase correction. This method has recently been extended to 4D spectral-spatial RF pulse designs for reducing B(1) + inhomogeneity as well as the signal loss. In this manuscript, we present simple analytical pulse designs for constructing 2D and 4D spectral-spatial RF pulses as an alternative to the numerical approaches. The 2D pulse capable of exciting slices with reduced signal loss and is lipid suppressing. The 4D pulse simultaneously corrects signal loss as well as the B(1) + inhomogeneity from a body coil transmitter. The pulses are demonstrated with simulations and with gradient echo phantom and brain images at 3T using a standard RF body coil. The pulses were observed to work well for multiple slices and several volunteers.

RF coil considerations for short‐T2 MRI

With continuing hardware and pulse sequence advancements, modern MRI is gaining sensitivity to signals from short-T(2) (1)H species under practical experimental conditions. However, conventional MRI coils are typically not designed for this type of application, as they often contain proton-rich construction materials that may contribute confounding (1)H background signal during short-T(2) measurements. An example of this is shown herein. Separately, a loop-gap style coil was used to compare different coil construction materials and configurations with respect to observed (1)H background signal sizes in a small animal imaging system. Background signal sources were spatially identified and quantified in a number of different coil configurations. It was found that the type and placement of structural coil materials around the loop-gap resonator, as well as the coil's shielding configuration, are critical determinants of the coil's background signal size. Although this study employed a loop-gap resonator design, these findings are directly relevant to standard volume coils commonly used for MRI.

Using repetitive transcranial magnetic stimulation for the treatment of tinnitus

Transcranial magnetic stimulation (TMS) has recently emerged as a potential treatment option for tinnitus.1–6 TMS induces electrical stimulation of cortical neurons by creating a brief, focused magnetic field over the surface of the brain.7 When magnetic pulses are delivered repetitively and rhythmically, the process is called repetitive TMS (rTMS). The magnetic field induced by rTMS is brief (microseconds), relatively weak (except directly under the coil, where 1–3 cm of tissue is stimulated, depending on coil configuration),8 and declines rapidly with distance from the coil (falling off sharply after 2 cm).7,9 Pulse trains can be delivered at low (≤1 Hz) or high (>1 Hz) frequencies, which tend to decrease or increase neural activity beneath the coil, respectively. Standard TMS coils are only able to directly stimulate the superficial cortex, but deeper brain structures and structures in the opposite cerebral hemisphere may be affected by TMS via connecting neural pathways.10,11 Most studies using rTMS for the treatment of tinnitus have used low-frequency magnetic pulses applied to one temporal lobe for 30 minutes, once daily, for 3–10 consecutive days. Some have used functional imaging with neuronavigation to select the treatment site based on asymmetrical cortical activation, while others have targeted the left superior temporal lobe in all cases or the side opposite the loudest tinnitus. Regardless of targeting technique, beneficial results are obtained in about 50% of patients who receive active treatment. While treatment effects have been reported to persist for 6 months in some cases,2 most treatment studies have demonstrated tinnitus suppression effects lasting only a few days to a few weeks.3,5,6 This article will briefly review rTMS, the rationale for its use to treat tinnitus, and data relevant to its efficacy in treating tinnitus.

UTE-T2∗ mapping of human articular cartilage in vivo: a repeatability assessment

Ultrashort echo-time enhanced T2∗ (UTE-T2∗) mapping of articular cartilage is a novel quantitative MRI technique with the potential to visualize deep cartilage characteristics better than standard T2 mapping. The feasibility and intersession repeatability of UTE-T2∗ mapping of cartilage in vivo has not previously been evaluated. Eleven asymptomatic subjects underwent repeat UTE-T2∗ imaging on a whole-body 3T MRI scanner on three consecutive days. Full-thickness, superficial and deep regions of interest (ROIs) were evaluated in the central weight-bearing zones of the medial femoral condyle (cMFC) and tibial plateau (cMTP). Intersession precision error across subjects was evaluated by the root-mean-square average coefficients of variation (RMSA-CV) and by the median of intra-subject standard deviations (SDs) of UTE-T2∗ values in each ROI. UTE-T2∗ values in vivo were found to be repeatable with relative (RMSA-CV) intersession precision errors of 8%, 6%, 16% for full-thickness, superficial and deep cMFC ROIs, corresponding to absolute errors (SD) of 1.2, 1.5, 1.5 ms, respectively. In cMTP tissue, UTE-T2∗ relative repeatability was 8%, 8%, 13%, corresponding to absolute repeatability of 1.0, 1.5, 2.1 ms (full-thickness, superficial, deep). UTE-T2∗ values were higher in superficial cartilage compared to deep in both cMFC (P≪0.001) and cMTP (P=0.0004) regions. In vivo 3D UTE-T2∗ mapping at 3T is feasible and can be implemented using a standard clinical MRI scanner and knee coil. Intersession precision error of UTE-T2∗ values in full-thickness ROIs in the weight-bearing regions of asymptomatic subjects is under 1.2 ms or 8% (RMSA-CV). Significant zonal and regional variations of UTE-T2∗ were seen.

H-coil repetitive transcranial magnetic stimulation for the treatment of bipolar depression: an add-on, safety and feasibility study

Objectives. The H1-Coil is a novel transcranial magnetic stimulation (TMS) device capable of inducing a magnetic field with a deeper and wider distribution than standard coils. This pilot study evaluated the safety and feasibility of the H1-Coil as adjuvant treatment for bipolar depression (BPD). Methods. Nineteen patients diagnosed as having BPD and under treatment with psychotropic medication were enrolled in the study. They received daily prefrontal repetitive TMS (rTMS: 20 Hz, 2 s on, 20 s off, totaling 1680 stimuli) every weekday for four consecutive weeks. The primary outcome measure was the change from baseline in the Hamilton Depression Rating Scale (HDRS-24) score a week after the last treatment session. Results. A significant mean decrease of 12.9 points in the HDRS-24 scale (P< 0.001) was found. Response rate was 63.2% and remission rate was 52.6%. Treatment was well tolerated in terms of headache and overall discomfort, and there were no significant change in cognitive functioning or mood switches. One patient had a short induced generalized seizure without complications. Conclusions. An add-on H-coil rTMS treatment protocol in BPD subjects indicated improvement in bipolar depression symptoms. Sham-control studies to further determine the efficacy and safety of the H-Coil for BPD are warranted.

A theoretical and experimental study on transverse field radio frequency surface coils

We have analysed, theoretically and experimentally, transverse field RF surface coils comprising two parallel linear current elements (figure-of-eight, FO8). A quasi-static numerical integration of the Biot–Savart law was used to simulate the B 1 field distribution of FO8 coils comprising a range of coil diameters and linear element separations. RF coil prototypes, suitable for 1H and 31P magnetic resonance imaging/spectroscopy at 1.5 T, that closely match the simulated models, were built and tested using workbench and MRI methods. A comparison with standard loop RF coils was made. Testing with phantoms showed a good agreement between the theoretical and experimental RF field distributions. Our findings should be useful to optimize the sensitivity and spatial selectivity of FO8 coils by a careful choice of the geometrical parameters. A number of applications where the use of FO8 RF coils could be of benefit are discussed, these include in vivo nuclear magnetic resonance imaging/spectroscopy.

Combination of compressed sensing and parallel imaging for highly accelerated first‐pass cardiac perfusion MRI

First-pass cardiac perfusion MRI is a natural candidate for compressed sensing acceleration since its representation in the combined temporal Fourier and spatial domain is sparse and the required incoherence can be effectively accomplished by k-t random undersampling. However, the required number of samples in practice (three to five times the number of sparse coefficients) limits the acceleration for compressed sensing alone. Parallel imaging may also be used to accelerate cardiac perfusion MRI, with acceleration factors ultimately limited by noise amplification. In this work, compressed sensing and parallel imaging are combined by merging the k-t SPARSE technique with sensitivity encoding (SENSE) reconstruction to substantially increase the acceleration rate for perfusion imaging. We also present a new theoretical framework for understanding the combination of k-t SPARSE with SENSE based on distributed compressed sensing theory. This framework, which identifies parallel imaging as a distributed multisensor implementation of compressed sensing, enables an estimate of feasible acceleration for the combined approach. We demonstrate feasibility of 8-fold acceleration in vivo with whole-heart coverage and high spatial and temporal resolution using standard coil arrays. The method is relatively insensitive to respiratory motion artifacts and presents similar temporal fidelity and image quality when compared to Generalized autocalibrating partially parallel acquisitions (GRAPPA) with 2-fold acceleration.

Assessment of standard coil positioning in transcranial magnetic stimulation in depression

Transcranial magnetic stimulation (TMS) is a non-invasive technique used in the treatment of major depression. Meta-analyses have shown that it is more efficient than a placebo and that its efficacy is enhanced by the optimum tuning of stimulation parameters. However, the stimulation target, the dorsolateral prefrontal cortex (DLPFC), is still located using an inaccurate method. In this study, a neuronavigation system was used to perform a comprehensive quantification of target localization errors. We identified and quantified 3 sources of error in the standard method: cap repositioning, interexpert variability in coil positioning and distance between the stimulated point and the expected target. For cap repositioning, the standard deviation was lower than 5mm in the 3 axes. For interexpert variability in coil positioning, the spatial dispersion of the points was higher than 10mm in 2 of the 3 axes. For interindividual anatomical variability, the distance between the actual “reference” DLPFC and its standard determination was greater than 20mm for 54% of the subjects, while one subject out of eleven was correctly targeted which means 10mm or less from the reference. Results showed that interindividual anatomical variability and interexpert variability were the two main sources of error using the standard method. Results demonstrate that a neuronavigation system is mandatory to conduct reproducible and reliable studies.

Determination of pre-emphasis constants for eddy current reduction

Magnetic field gradients play a fundamental role in fast magnetic resonance imaging (MRI) methods and spectroscopy imaging. Precise information on gradient waveform shape and rise times is often very useful in experimental MRI. We present a simple method for the measurement of the gradient time course and static magnetic field changes. The method does not require any specialized hardware and can be used with a standard volume coil and a special phantom filled with deionized or doped water. The method is based on an analysis of the instantaneous frequency variation of an MR signal in the time domain, acquired from a mechanically selected thin slice of phantom located at the gradient isocentre. The measurement and approximation of the course of time gradients and of the changes in the static magnetic field result in pre-emphasis constants that substitute the constants determined manually in a time-consuming manner. The described method facilitates the determination of pre-emphasis constants for the compensation of eddy current effects in MR systems. Our results show that residual gradients in the region of interest within 0.5 ms after the gradient is switched off are smaller than 5 µT m−1 (for an applied test gradient of 72 mT m−1) and the shift of the static field is smaller than 0.2 µT. This accuracy is very important for the development of MR spectroscopic imaging technologies using samples with very short relaxation times, and for EPI pulse sequences.

Condon-domain phase diagram and hysteresis size for beryllium

The Condon domain phase diagram for beryllium is determined in magnetic fields up to 10 T and at temperatures down to 1.3 K using a standard ac pick-up coil method to measure the de Haas-van Alphen (dHvA) effect. The detection of the transition point from the homogeneous state to the Condon domain state (CDS) is based on the extremely non-linear response to the modulation field resulting from a small irreversibility in the dHvA magnetization. The experimental results are compared with theoretical predictions calculated from the Fermi surface (FS) of beryllium. The width h_m of the hysteresis loop in the CDS is measured in a wide temperature and field region. A model for the hysteresis size is proposed and numerically calculated for the whole phase diagram.

Experimental and Numerical Studies of Megagauss Magnetic-Field Generation at LANL-NHMFL

The LANL-NHMFL Megagauss Facility has a well-established history of generating ultrahigh magnetic fields beyond 200 T for a broad range of applications. Using the 2-D Loughborough filamentary modeling, a detailed numerical analysis of the single-turn technique was performed. Single-turn calculations for the standard coil (10 × 10 × 3.2 mm) proved to be extremely accurate up to 40-kV capacitor bank charging, corresponding to a field of 185 T, and also revealed important aspects to be observed during experimentation. For pushing the boundaries toward 500 T, a major effort is under way to perform <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fast</i> electromagnetic flux compression using a pulsed-power system mainly based on the same capacitor bank. Full details of the design for the new arrangement are given, and based on a well-proven 2-D filamentary modeling, the complex phenomena expected during the flux-compression process are highlighted.

Improved 1.5 T Magnetic Resonance Spectroscopy in the Human Calf with a Spatially Selective Radio Frequency Surface Coil

We describe the use of a transverse field RF surface coil that improves 1.5 T proton MR spectroscopy in the human calf. A 2-element figure-of-eight (FO8) transverse field RF surface coil (diameter 2R=10 cm; separation between the two linear current elements 2s=1cm) and a circular loop (CL) coil of equal diameter where built and tested with proton PRESS spectra at 1.5 T. The 1 H PRESS spectra obtained in the resting calf muscle of healthy volunteers showed that the FO8 coil allows a higher PRESS SNR (up to a factor 4.5) within a region of about 20 mm centred at about 12 mm from the coil plane, as compared to a standard CL coil. We found also a faster PRESS SNR decrease in the muscle tissue for anterior/posterior distance >20 mm using the FO8 coil. The measured PRESS SNR in the fat tissues of the calf showed a signal mostly localised within 10 mm from the coils surface and with an improved SNR (up to 5.5 times) observed in the presence of the FO8 coil as compared to the CL coil of equal diameter. The FO8 coil design can be advantageous for MRS applications, since it allows higher SNR from a small VOI positioned centrally within a relatively narrow region at a given depth in the human calf. The reported spatial SNR features of the FO8 coil design should also be useful for 1 H and 31 P MRS metabolites quantification in the human brain.

A rapid and robust numerical algorithm for sensitivity encoding with sparsity constraints: Self‐feeding sparse SENSE

The method of enforcing sparsity during magnetic resonance imaging reconstruction has been successfully applied to partially parallel imaging (PPI) techniques to reduce noise and artifact levels and hence to achieve even higher acceleration factors. However, there are two major problems in the existing sparsity-constrained PPI techniques: speed and robustness. By introducing an auxiliary variable and decomposing the original minimization problem into two subproblems that are much easier to solve, a fast and robust numerical algorithm for sparsity-constrained PPI technique is developed in this work. The specific implementation for a conventional Cartesian trajectory data set is named self-feeding Sparse Sensitivity Encoding (SENSE). The computational cost for the proposed method is two conventional SENSE reconstructions plus one spatially adaptive image denoising procedure. With reconstruction time approximately doubled, images with a much lower root mean square error (RMSE) can be achieved at high acceleration factors. Using a standard eight-channel head coil, a net acceleration factor of 5 along one dimension can be achieved with low RMSE. Furthermore, the algorithm is insensitive to the choice of parameters. This work improves the clinical applicability of SENSE at high acceleration factors.

SU‐GG‐J‐135: Exploring the Neuroprotective Effects of Bee Venom in a Mouse Parkinson Model with Immunohistochemistry, Magnetization Transfer Ratio Imaging and Spectroscopy

Purpose: Neuroprotective therapeutics stop or slowdown the degeneration process in animal models of Parkinson's disease (PD). In the present study, we investigated the anti‐inflammatory effect of bee venom (BV) on lipopolysaccharide (LPS)‐stimulated microglia. Method and Materials: To investigate whether MR techniques have added value in neuroprotection research in the MPTP mouse model, both MRI and MRS were applied to investigate the neuroprotective effects of BV. BV is suggested to stimulate anti‐inflammatory processing indirectly via DA‐dependent mechanisms or γ‐aminobutyric acid (GABA) and glutamate release. Magnetization transfer ratio (MTR) and 1H‐MRS studies were performed on control mice, MPTP‐intoxicated mice and BV treatment mice. The successfully induced lesions were verified by tyrosine hydroxylase immunolabelling on the substantia nigra (SN) and striatum (ST) performed on perchloric extracts of mice brains, after the control mice and the MPTP‐intoxicated mice were killed. All the MTR and 1H‐MRS experiments were performed on a 9.4 T MRI/MRS system using a standard head coil. Outer volume suppression combined with the ultra‐short echo‐time stimulated echo acquisition mode was used for the localized 1H‐MRS. The quantitative analysis of metabolites was determined using jMRUI from the 1H spectra obtained in vivo on the striatum. Results: The peak height of the MTR histograms in the PD model group was significantly lower than that in the BV treatment group (P&lt;0.05). The present study revealed that the peak height of the MTR histogram was significantly decreased in the ST and SN, and a significant increase of the Glx/Cr ratio was found in the striatum of the PD group, as compared with that of the BV treatment group. Conclusion: These results demonstrate that BV possess a potent suppressive effect on proinflammatory responses of microglia and suggest that these compounds may offer substantial therapeutic potential for treatment of neurodegenerative diseases that are accompanied by microglial activation.

Relative cost comparison of embolic materials used for treatment of wide-necked intracranial aneurysms

IntroductionEmbolization of wide-necked intracranial aneurysms can be associated with excessive expense, especially for large/giant aneurysms. Depending on the material used, endovascular treatment may be cost prohibitive. The goal of this...

Changes in the Frontotemporal Cortex and Cognitive Correlates in First-Episode Psychosis

BackgroundLoss of cortical volume in frontotemporal regions has been reported in patients with schizophrenia and their relatives. Cortical area and thickness are determined by different genetic processes, and measuring these parameters separately may clarify disturbances in corticogenesis relevant to schizophrenia. Our study also explored clinical and cognitive correlates of these parameters.MethodsThirty-seven patients with first-episode psychosis (34 schizophrenia, 3 schizoaffective disorder) and 38 healthy control subjects matched for age and sex took part in the study. Imaging was performed on an magnetic resonance imaging 1.5-T scanner. Area and thickness of the frontotemporal cortex were measured using a surface-based morphometry method (Freesurfer). All subjects underwent neuropsychologic testing that included measures of premorbid and current IQ, working and verbal memory, and executive function.ResultsReductions in cortical area, more marked in the temporal cortex, were present in patients. Overall frontotemporal cortical thickness did not differ between groups, although regional thinning of the right superior temporal region was observed in patients. There was a significant association of both premorbid IQ and IQ at disease onset with area, but not thickness, of the frontotemporal cortex, and working memory span was associated with area of the frontal cortex. These associations remained significant when only patients with schizophrenia were considered.ConclusionsOur results suggest an early disruption of corticogenesis in schizophrenia, although the effect of subsequent environmental factors cannot be excluded. In addition, cortical abnormalities are subject to regional variations and differ from those present in neurodegenerative diseases.