Solenoid Radiofrequency Coil Research Articles

Segmented solenoid RF coils for MRI of ex vivo brain samples at ultra-high field preclinical and clinical scanners

Magnetic resonance imaging (MRI) is a well-known and widespread imaging modality for neuroscience studies and the clinical diagnoses of neurological disorders, mainly due to its capability to visualize brain microstructures and quantify various metabolites. Additionally, its noninvasive nature makes possible the correlation of high-resolution MRI from ex vivo brain samples with histology, supporting the study of neurodegenerative disorders such as Alzheimer's or Parkinson's disease. However, the quality and resolution of ex vivo MRI highly depend on the availability of specialized radiofrequency coils with maximized filling factors for the different sizes and shapes of the samples to be studied. For instance, small, dedicated radiofrequency (RF) coils are not always commercially available in ultrahigh field whole-body MRI scanners. Even for ultrahigh field preclinical scanners, specific RF coils for ex vivo MRI are expensive and not always available. Here, we describe the design and construction of two RF coils based on the solenoid geometry for ex vivo MRI of human brain tissues in a 7T whole-body scanner and for ex vivo MRI of marmoset brain samples in a 9.4T preclinical scanner. We designed the 7T solenoid RF coil to maximize the filling factor of human brain samples conditioned on cassettes for histology, while the 9.4T solenoid was constructed to accommodate marmoset brain samples conditioned in 50 ml centrifuge tubes. Both solenoid designs operate in transceiver mode. The measured B1+ maps show a high level of homogeneity in the imaging volume of interest, with a high signal-to-noise ratio over the imaging volume. High-resolution (80 µm in plane, 500 µm slice thickness) images of human brain samples were acquired with the 7T solenoid, while marmoset brain samples were acquired with an isotropic resolution of 60 µm using the 9.4T solenoid coil.

Thermostatted micro-reactor NMR probe head for monitoring fast reactions

A novel nuclear magnetic resonance (NMR) probe head for monitoring fast chemical reactions is described. It combines micro-reaction technology with capillary flow NMR spectroscopy. Two reactants are fed separately into the probe head where they are effectively mixed in a micro-mixer. The mixed reactants then pass through a capillary NMR flow cell that is equipped with a solenoidal radiofrequency coil where the NMR signal is acquired. The whole flow path of the reactants is thermostatted using the liquid FC-43 (perfluorotributylamine) so that exothermic and endothermic reactions can be studied under almost isothermal conditions. The set-up enables kinetic investigation of reactions with time constants of only a few seconds. Non-reactive mixing experiments carried out with the new probe head demonstrate that it facilitates the acquisition of constant highly resolved NMR signals suitable for quantification of different species in technical mixtures. Reaction kinetic measurements on a test system are presented that prove the applicability of the novel NMR probe head for monitoring fast reactions.

Excite and receive solenoid radiofrequency coil for MRI-guided breast interventions.

A radiofrequency coil based on a solenoid design was developed and integrated with a novel device for MR-guided breast interventions using a circumferential approach. The transmit/receive tapered solenoid design conforms to the shape of the pendent breast, and provides open circumferential needle access to breast tissue under rotational symmetry. Phantom and in vivo studies using a healthy volunteer demonstrated a superior uniformity using the tapered solenoid coil compared with a commercial 8-channel diagnostic imaging coil. The solenoid coil design has important advantages due to localized transmit/receive such as B(1) -homogeneity and reduced specific absorption ratio (SAR) especially at high-field strengths. Because it provides open access and a rotationally symmetric local field, the tapered solenoid design can easily be adapted for bilateral imaging and 3D MR-guided breast interventions.

Sensitivity of Cryogenic Solenoidal Probe for Split-Pair Superconducting Magnet With Cross-Bore

By using a split-pair superconducting magnet with cross-bore, one can implement a solenoidal radio frequency (RF) coil for solution nuclear magnetic resonance (NMR). We expect the solenoidal RF coil to give us higher sensitivity than an ordinary saddle-shaped RF coil. We have developed both room temperature and cryogenic NMR probes with a solenoidal RF coil for a split-pair superconducting magnet. The probes and the solenoidal RF coils were evaluated using a sensitivity test with standard 0.1% ethylbenzene. The sensitivity tests of the room temperature probes indicated that the signal-to-noise ratio (SNR) of the solenoidal RF coil was higher than that of an ordinary saddle-shaped RF coil. In the sensitivity test of the cryogenic probe, we compared a four-turn solenoidal RF coil with a two-turn one. As a result, the SNR of the one of two-turn RF coil was higher than that of the one of the four-turn one. It is believed that the reason is that the SNR depends on the quality factor of the specimen Qs and, furthermore, Qs depends on the shape of the RF coil.

TU‐E‐BRC‐05: First MR Images Obtained During Megavoltage Photon Irradiation From An Integrated Linac‐MR System

Purpose: To prove whether our hybrid linac‐MR design can sufficiently decrease mutual magnetic and radio frequency (RF) interferences to produce a MR image during linac‐irradiation that has similar geometric accuracy and image contrast to an MR image obtained without linac‐irradiation. Method and Materials: A hybrid prototype has been built consisting of a 6 MV linac mounted on the open end of a bi‐planar 0.2 T permanent‐magnet MR system. Both the linac waveguide and the MR system are mounted onto a single gantry that would rotate around a subject. The permanent magnet poles (82×82 cm2) are rigidly held apart to give 27.9cm pole‐to‐pole opening with flat gradients (40 mT/m max) running under a TMX NRC console (Canada). The linac components are comprised of salvaged magnetron‐based Varian 6 MV 600C decommissioned system. The distance from linac target to MR isocentre is 80 cm. Magnetic and RF shielding calculations were performed by finite element analysis and confirmed with appropriate measurements. Faraday cage shielding, typical of all MR installations, was also provided. The testing phantom was an acrylic rectangular cube, 15.95 × 15.95 × 25.4 mm with holes of diameters 2.52 mm, 3.45 mm and 4.78 mm drilled parallel to the length (25.4 mm) of rectangular cube. The cube was immersed in a 10 mM solution of within a plastic container 22.5 mm inner diameter. The container with the cube insert were placed inside an inductively tuned solenoid RF coil with an integrated pin‐diode transmit/receive switch. Results: Images (128×128) were obtained in about 38 secs using raw gradient echo sequences. Compared to no‐radiation, MR images during linac‐radiation had no geometric distortion but slightly reduced SNR. Conclusion: Our linac‐MR design produces MR images obtained during or without linac irradiation that are sufficiently similar to implement real‐time MR‐guided radiotherapy.

Development of a solenoid RF coil for animal imaging in 3 T high‐magnetic‐field MRI

The purpose of this study was to develop a solenoid coil for use with small animals in a 3 Tesla horizontal magnetic resonance imaging (MRI) system, and to investigate image quality by examination of parameters such as signal-to-noise ratio (SNR) and Q-factor. A receiver solenoid coil was formed by winding three separate coils of copper tape around an acryl cylinder. The cylinder was supported at each end. A euthanized rat weighing 240 g was used as a subject animal for imaging. A cylindrical plastic tube containing a solution of 0.7 g/L CuSO(4) was used as a phantom. Measured SNRs were 985 in the phantom image 995 in the rat. The Q-factor was 89 in the phantom and 84 in the rat, in the loaded condition. The homogeneity of the radiofrequency (RF) field was good and the resolution of the image was sufficient to distinguish internal organs from one another in the abdomen of a rat. This study has demonstrated that a solenoid coil may be used to produce good quality images of small animals.

Magnetic Resonance Imaging Protocol Optimization for Evaluation of Hyaline Cartilage in the Distal Interphalangeal Joint of Fingers

To identify a single magnetic resonance imaging (MRI) protocol that will provide optimal signal-to-noise ratio, resolution, and image contrast with minimal susceptibility artifacts and that will allow clear delineation and visualization of cartilage, fluid, bone, tendons, and ligaments within the distal interphalangeal (DIP) joint of the human hand. A highly optimized 2.4 T MRI system was constructed from a 31-cm horizontal bore magnet, using a solenoid radiofrequency coil. This was used to study the DIP joints of 16 healthy, asymptomatic volunteers. A range of image contrast protocols were explored, including spin-echo T1 and T2, field echo, chemical shift suppression to give water only images, and magnetization transfer. Susceptibility variations were explored by changing the field strength from 0.6 to 2.4 T. A spin-echo protocol with TR = 1500 msec and TE = 30 msec can routinely produce images with resolution 0.075 x 0.150 for a slice thickness of 1 mm in 13 minutes. That protocol can visualize simultaneously compact and trabecular bone, two layers of cartilage, synovial fluid, and synovium within the joint, tendons and ligaments, and the volar plate. Although the contrast is not fully optimized for any one tissue, the spin echo protocol (TR = 1500, TE = 30) provides sagittal MR images, which clearly delineate the major structures of interest within the DIP joint, and which will be used in future studies to compare changes in the DIP joint because of aging or osteoarthritis. Experience gained by applying the above methods to a total of 16 healthy, asymptomatic volunteers has enabled a single sequence to be identified, which although not optimized for any one tissue, nevertheless visualized simultaneously and clearly delineated compact and trabecular bone, two layers of cartilage, synovial fluid, and synovium within the joint.

Fingers: three-dimensional MR imaging and angiography with a local gradient coil.

The authors interfaced a 12-cm-diameter local gradient coil with a solenoid radio-frequency coil (2.2-cm internal diameter, 1.4-cm long) to a recalibrated clinical magnetic resonance imaging system. Three-dimensional gradient-echo imaging and phase-contrast angiography were performed on the fingers of five healthy volunteers (four men and one woman, aged 23-33 years). Data sets (256 x 256 x 28) were acquired with spatial resolution of 100 x 100 x 500 microns in 6 minutes 51 seconds. The angiograms clearly delineated blood vessels that were less than 1 mm in diameter.

Electromagnetic field focusing (EFF) probe in aneurysm thrombosis

Due to its capability of producing a well localized intense heat field of predictable dimensions, the electromagnetic field focusing probe was evaluated experimentally as a surgical tool in aneurysm thrombosis. Aneurysm models were created by anastomosing a segment of vein to the abdominal aorta. Seventy-five such aneurysms were created in seventy-five animals. The aneurysms were then placed under the solenoidal radiofrequency coil and the tip of the field focusing probe was inserted into them. Intense heat was delivered with well defined, effective and quick thrombosis and shrinkage of the aneurysm. Nineteen of the aneurysms were followed for up to one week. Histological studies were conducted showing complete thrombosis of the aneurysm with good preservation of the aorta. With further refinement of this technique, it is hoped that stereotaxic aneurysm thrombosis might be possible.

The deuterium quadrupole coupling constants of di- and trihalomethanes

There have recently been published a number of papers reporting the deuterium quadrupole coupling constants (QCC) of small molecules dissolved in liquidcrystalline media (1-5). The results presented show, in many instances, wide variations in QCC values determined by different groups. These differences can be mainly attributed to the presence of different solvent-solute interactions in different liquid-crystal phases. Other causes of the range of values found arise from the difficulty in choosing appropriate bond lengths and making vibrational corrections to the dipolar couplings. Such uncertainties have led to some puzzling anomalies. For example, with the deuterohalomethanes, tribromomethane appears to have a considerably larger QCC than either trichloromethane or triiodomethane. These results have prompted us to determine the QCC values for deuterotrihalomethanes, C!HX3 (X = Cl, Br, or I), and dideuterodihalomethanes, C2H2X2, using solid-state deuterium quadrupole spin-echo techniques (6). Such measurements, at least for the di- and trihalomethanes, do not suffer so severely from uncertainties due to solvent effects, arising, for example, from the use of various liquid crystals containing aromatic and other more polar groups, or to uncertainties in bond lengths, vibrational averaging, and unknown electric field gradient asymmetry parameters. Spectra were obtained on a “home-built” spectrometer at 55.3 MHz using an 8.‘45 T, 3.0 in. bore Oxford Instruments (Qsney Mead, Oxford, U.K.) superconducting so’lenoid, a Nicolet (Madison, Wise.) 1180 computer and 1290 transient recorder, together with a variety of other digital and radiofrequency electronics. We also used a home-built solenoidal radiofrequency coil probe (sample volume -0.8 cm3), together with a quadrupole spin-echo sequence (6), for data acquisition. The 90” pulse width used was 3.3 ps. All samples (except [2H]triiodomethane) were obtained from Merck, Sharpe, and Dohme (Canada), and were used without further purification. [2H]Triiodomethane was prepared from [2H]trichloromethane and iodoethane, as reported in the literature (7). A typical experimental spectrum (displayed for the convenience of the reader as a “mirrored” on-resonance single-phase detected spectrum), together with its com