China
Africa
Explore chapters and articles related to this topic
Principles behind Magnetic Resonance Imaging (MRI)
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
Effectively, it is the magnetic field of the RF pulse that causes the effect on , and this time-varying magnetic field can, equivalently, be described as the vector sum of two vectors of magnitude rotating, with the resonance frequency, in opposite directions in the xy-plane (cf. linear polarization). These two vectors are sometimes referred to as (clockwise rotation) and (counter-clockwise rotation). Often, a rotating coordinate system or rotating frame (with axes denoted x’, y’, z’) is introduced, rotating with the Larmor frequency around the z-axis (i.e. the z’ axis equals the z axis). In the rotating frame, will exhibit a precession around (Figure 32.3), according to Eq. 32.12:
Magnetic Resonance Imaging
Published in Shoogo Ueno, Bioimaging, 2020
and is called the Larmor frequency or magnetic resonance frequency. Because of the above gyromagnetic ratio, when a 1-T static magnetic field is applied externally to hydrogen, resonance occurs because of irradiation with electromagnetic waves with a frequency of 42.58 MHz.
Magnetic Resonance Imaging
Published in Suzanne Amador Kane, Boris A. Gelman, Introduction to Physics in Modern Medicine, 2020
Suzanne Amador Kane, Boris A. Gelman
The Larmor frequency is proportional to both the strength of the applied magnetic field and the value of the nuclear magnetic moment : where the quantity is called the nucleus's gyromagnetic ratio, and is the Planck constant. For protons the gyromagnetic ratio is given by, where we used Equation 8.1, and the value where of the nuclear magneton. The quantity gives the Larmor frequency per one Tesla of the magnetic field. The expression in Equation (8.5) holds true for protons; for another nuclear species, the factor of 2.79, which determines the value of the nuclear magnetic moment in units of the nuclear magneton (see Equation 8.1), would be replaced by an appropriate value.
Ranking mAb–excipient interactions in biologics formulations by NMR spectroscopy and computational approaches
Published in mAbs, 2023
Chunting Zhang, Steven T. Gossert, Jonathan Williams, Michael Little, Marilia Barros, Barton Dear, Bradley Falk, Ankit D. Kanthe, Robert Garmise, Luciano Mueller, Andrew Ilott, Anuji Abraham
All pseudo-2D STD NMR experiments and T1 measurement experiments of BMSmAb-excipient samples were acquired at 283 K and 293 K on a Bruker NEO 700 MHz (16.4 T) spectrometer equipped with a 3 mm probe head. The Larmor frequency was 700.1 MHz for 1H. 1H chemical shift was referenced with respect to the internal standard TSP at 0.0 ppm. For STD NMR experiments, typical 90° pulse length was 8.71 µs for 1H, and the recycle delay was 12 s and an STD-pulse train saturation period of 10 s. A total of 64 scans were recorded. Selective on- and off-resonance frequencies were set at 0.4 and −10 ppm, respectively. The saturation pulse trains were composed of selective Gaussian pulses of 50 ms duration and 200 Hz amplitude. All STD NMR spectra were processed and analyzed in Bruker TopSpin (version 4.1.3) and ACD Spectrus software. Proton T1-measurements were performed in samples containing ~0.18 mM of excipients using the inversion recovery method.
Protective Effect of Tunisian Flaxseed Oil against Bleomycin-Induced Pulmonary Fibrosis in Rats
Published in Nutrition and Cancer, 2020
Anouar Abidi, Nadia Kourda, Moncef Feki, Saloua Ben Khamsa
Following sacrifice, the abdominal cavity and chest were opened. The right lung lobe was used for the analysis of Balf metabolites. Balf samples were obtained by intratracheal injections of saline (4–5 mL) via a catheter and re-aspiration of the liquid between two fractions of Balf. Balf samples (1:10, 550 µL) were placed in a 5 mm NMR tube to be analyzed by 1H-NMR. Measurements were performed using an Avance 500 spectrometer (Bruker Corporation, Billerica, MA) at a magnetic field of 11.75 T, corresponding to a Larmor frequency of 500 MHz (25). The lock signal (deuterium) was obtained, and the optimization of static field homogeneity was performed to correct in homogeneities in the magnetic field. The sample was rotated to homogenize the signal at the time of acquisition. A first pulse sequence was used to determine the exact resonance frequency of the protons in water molecules that would, in the second pulse sequence, selectively saturate the resonance and minimize water molecule signals. For the Balf samples, characterized by their high dilution, 128 scans were needed to determine the exact resonant frequency of the protons of the water molecule, which will subsequently allow the signal of the water to be minimized. Once the electrical signals were recorded, a Fourier transformation was applied to switch the function of time into the frequencies that make it up.
Systematic review of pre-clinical and clinical devices for magnetic resonance-guided radiofrequency hyperthermia
Published in International Journal of Hyperthermia, 2020
Fatemeh Adibzadeh, Kemal Sumser, Sergio Curto, Desmond T. B. Yeo, Amir A. Shishegar, Margarethus M. Paulides
Another approach, designated as ‘thermal MR’, allows RF heating and MR imaging application using the same antenna array and the power amplifier of the MR system. Here, part of the regular imaging sequence time, e.g., the last 10%, is used to apply RF for heating. This approach is particularly effective in MR scanners at ultra-high magnetic fields (≥ 7 T) for which the Larmor frequency approaches the optimum frequency for semi-deep heating [76,77]. The advantage of the pulse modulated signal used for RF HT and MRT is the ability to modify the imaging technique in order to perform RF HT and MRI at the same frequency without the need for electronic switching which further reduces the dead time for contemporaneous operation. In addition, the electric fields for imaging and heating are equal, thus, in vivo quality assurance can be applied using B1+ imaging as a surrogate for the electric field induced in the patient. One such device is an 8-channel transmit/receive (Tx/Rx) hybrid RF applicator consisting of bow-tie dipole antennas (‘dual function bowtie array’) that generate an E-field pattern for RF heating and a circular polarized H-field for MRI [76]. Each channel has independent control of phase and amplitudes. The applicator was connected to the MR system via a coil interface comprising 8 Tx/Rx switches.