Design of a dedicated circular coil for Magnetic Resonance Spectroscopy studies in small phantoms and animal acquisition with a 3 Tesla Magnetic Resonance clinical scanner

Abstract Introduction: Magnetic Resonance Spectroscopy (MRS) is a very powerful tool to explore the tissue components, by allowing a selective identification of molecules and molecular distribution mapping. Due to intrinsic Signal-to-Noise Ratio limitations (SNR), MRS in small phantoms and animals with a clinical scanner requires the design and development of dedicated radiofrequency (RF) coils, a task of fundamental importance. In this article, the authors describe the simulation, design, and application of a 1H transmit/receive circular coil suitable for MRS studies in small phantoms and small animal models with a clinical 3T scanner. In particular, the circular coil could be an improvement in animal experiments for tumor studies in which the lesions are localized in specific areas. Material and methods: The magnetic field pattern was calculated using the Biot–Savart law and the inductance was evaluated with analytical calculations. Finally, the coil sensitivity was measured with the perturbing sphere method. Successively, a prototype of the coil was built and tested on the workbench and by the acquisition of MRS data. Results: In this work, we demonstrate the design trade-offs for successfully developing a dedicated coil for MRS experiments in small phantoms and animals with a clinical scanner. The coil designed in the study offers the potential for obtaining MRS data with a high SNR and good spectral resolution. Conclusions: The paper provides details of the design, modelling, and construction of a dedicated circular coil, which represents a low cost and easy to build answer for MRS experiments in small samples with a clinical scanner

A Practical Guide to Estimating Coil Inductance for Magnetic Resonance Applications

Radiofrequency (RF) coils are employed to transmit and/or receive signals in Magnetic Resonance (MR) systems. The design of home-made, organ-specific RF coils with optimized homogeneity and/or Signal-to-Noise Ratio (SNR) can be a plus in many research projects. The first step requires accurate inductance calculation, this depending on the conductor's geometry, to later define the tuning capacitor necessary to obtain the desired resonance frequency. To fulfil such a need it is very useful to perform a priori inductance estimation rather than relying on the time-consuming trial-and-error approach. This paper describes and compares two different procedures for coil inductance estimation to allow for a fast coil-prototyping process. The first method, based on calculations in the quasi-static approximation, permits an investigation on how the cross-sectional geometry of the RF coil conductors affects the total inductance and can be easily computed for a wide variety of coil geometries. The second approach uses a numerical full-wave method based on the Finite-Difference Time-Domain (FDTD) algorithm, and permits the simulation of RF coils with any complex geometry, including the case of multi-element phased array. Comparison with workbench measurements validates both the analytical and numerical results for RF coils operating within a wide field range (0.18–7 T)

Echinoderm larvae as bioindicators for the assessment of marine pollution: Sea urchin and sea cucumber responsiveness and future perspectives

Echinoderms play a crucial role in the functioning of marine ecosystems and due to their extensive distribution, rapid response, and the high sensitivity of their planktonic larvae to a large range of stressors, some species are widely used as biological indicators. In addition to sea urchins, sea cucumbers have recently been implemented in embryotoxicity bioassays showing high potential in ecotoxicological studies. However, the use of this species is still hindered by a lack of knowledge regarding their comparative responsiveness. The present study aimed to investigate the responsiveness of different echinoderm species to environmental pollution in order to develop their integration in batteries of ecotoxicological bioassays. To this end, the embryos of two sea urchins (Paracentrotus lividus and Arbacia lixula) and two sea cucumbers (Holothuria polii and Holothuria tubulosa) were incubated with inorganic and organic toxicants (cadmium, copper, mercury, lead, sodium dodecyl sulphate and 4-n-Nonhyphenol) and elutriates from contaminated marine sediments, chosen as a case study model. The results obtained, expressed through the percentage of abnormal embryos and Integrative Toxicity Indices (ITI), indicated species-specific sensitivities to pollutants, with comparable and correlated responsiveness between sea urchins and sea cucumbers. More specifically, sea cucumber larvae exposed to elutriates appear to be more sensitive than sea urchins, especially when incubated with samples containing trace metals, PCB and TBT. These results indicate that toxic responses in embryos exposed to environmental matrices are probably modulated by interactions between different variables, including additive, synergistic and antagonistic effects. These findings suggest that performing a larval test using different echinoderm classes can integrate the interactive effects of bioavailable fraction of contaminants on various levels, providing sensitive, representative and all year-round batteries of bioassays to apply in ecotoxicological studies

A Novel Approach for Determining the Electromagnetic Properties of a Colloidal Fluid With Magnetic Nanoparticles for Hyperthermia Applications

The paper presents a general analytical method for evaluating the magnetic properties of colloidal fluid with magnetic nanoparticles and agar through in vitro specific absorption rate (SAR) measurements. The approach for the determination of magnetic complex susceptibility herein presented reveals itself as simple, rapid, broadband, and accurate enough to compete with alternative conventional direct methods requiring complex and expensive instrumentation. In particular, it makes use of indirect equations based on the single-order Debye model [linear response theory (LRT)] combined with a punctual set of in vitro SAR measurements. The procedure is effective inside the range of validity of the LRT theory, and it can be easily applied in the up-growing field of magnetic hyperthermia studies

Simulation, design, and test of an elliptical surface coil for magnetic resonance imaging and spectroscopy

AbstractThe simplest design of surface coils for magnetic resonance imaging (MRI) applications is circular and square loops, both producing a magnetic field perpendicular to the coil plane in the central region‐of‐interest (ROI), with an amplitude that decreases along the coil axis. However, a surface coil constituted by a loop with different geometry could be necessary when particular field‐of‐views (FOVs) are desired, especially for performing imaging in an elongated region. This can be achieved by using an elliptical loop, which can guarantee a wide longitudinal FOV and a good penetration in deep sample regions. This work proposes the application of a method for elliptical coil Signal‐to‐Noise Ratio (SNR) estimation previously developed for circular and square loop design, in which coil inductance and resistance are analytically calculated and the magnetic field pattern is estimated using the magnetostatic approach, while the sample‐induced resistance is calculated with the vector potential calculation method. In the second part of the paper, we propose the simulation and the design of a transmit/receive elliptical coil for MRI in mice with a 3T clinical scanner. We also evaluated the coil performance in a preliminary magnetic resonance spectroscopy (MRS) study in phantom

Detection of 3D Cardiac metabolism after injection of hyperpolarized [1-13C]pyruvate

Introduction MRI with hyperpolarised 13C represents a promising modality for in-vivo spectroscopy and provides a unique opportunity for non-invasive assessment of cardiac regional metabolism. Purpose We present a method based on a volumetric IDEAL spiral CSI acquisition for obtaining spatial information on the metabolism of the whole heart after intravenous injection of hyperpolarized [1-13C]pyruvate in a large animal model with a clinical 3T scanner. Methods Three healthy male mini-pigs (38±2 kg) were maintained under deep sedation; a dose of 20 mL of 230 mM [1-13C]pyruvate was administered over about 10 s by manual injection. Animal experiments were performed on a 3T GE Signa HDx scanner with a 13C quadrature birdcage coil. [1-13C]pyruvate was polarized using a HyperSense DNP polariser with subsequent dissolution. The final injection solution contained 230 mM sodium [1-13C]pyruvate, 100 mM TRIS buffer, 0.27 mM Na2EDTA and 20 μM Dotarem with T≈37°C and pH ≈ 7.6. Anatomical reference images were acquired in the axial plane with standard FIESTA sequence (body coil FOV=30x30 cm2, FA=20°, TE/TR=3.8ms/7.52ms, matrix 224x160, slice thickness 5 mm, 20 slices). Metabolic information covering the heart were obtained using a 3D IDEAL spiral CSI prescribed on the same region imaged by the reference anatomical sequence (FOV= 30x30 cm, slab thickness=100mm) starting 20 seconds after the beginning of the hyperpolarized [113C]-pyruvate injection. The IDEAL spiral CSI concept was implemented into a multi-slice, pulse-and-acquire sequence with a 2D spiral readout and phase encoding along the third dimension. A constant echo time shift of TE=0.9ms, 11 encoding steps and FA=7° were used to optimize the study for the considered frequencies. The data was reconstructed using spectrally-preconditioned, minimum-norm CS inversion followed by gridding reconstruction implemented in Matlab. The reconstruction on cardiac short axis (SA) and image fusion was performed by PMOD software. Results Pyruvate and its metabolic products lactate and bicarbonate were detected in the heart. Metabolic maps overlaid on anatomical images are shown in Figure 1. On SA sections the metabolites signal resulted correctly localized in cardiac structures: pyruvate more evident in ventricular cavity, bicarbonate in myocardial wall