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Introduction
Published in Bertil R. R. Persson, Freddy Ståhlberg, Health and Safety of Clinical NMR Examinations, 2019
Bertil R. R. Persson, Freddy Ståhlberg
Free induction decay (FID) sequences are based on the acquisition of one or more Rf pulses and on the subsequent detection of the free induction decay signal, i.e., the decay of the Mxy component of the magnetization vector .53 FID sequences are easy to design and were therefore used early on in NMR imaging, usually with a single Rf pulse corresponding to a 90° flip angle aligned with the x axis. A development of the FID sequence, where both the requirements of Equation 8 are met, is shown in Figure 5.28,36 It can be seen here that the signal is collected at the time when the dephasing effects of the readout gradient are canceled by the gradient reversal, and that the sequence is repeated, e.g., 128 or 256 times, each time with a new value of the strength of the phase-encoding gradient. In this sequence the signal has the form of a spin echo, usually known as a gradient echo. This type of FID sequence is characterized by simplicity and short sequence duration (the time between the Rf pulse and the gradient echo can be made as short as a few milliseconds).
Biomedical Imaging Magnetic Resonance Imaging
Published in Lawrence S. Chan, William C. Tang, Engineering-Medicine, 2019
which indicates that is always shorter than or equal to T2. The signal shown in Fig. 3d is subject to relaxation and decays exponentially. This signal, which is produced in the absence of magnetic field, is known as free induction decay (FID) (Brown et al. 2014). It is one of the major signals for image formation in MRI.
Acquisition Strategies
Published in Luisa Ciobanu, Microscopic Magnetic Resonance Imaging, 2017
RF pulses. In its simplest form, the echo is generated with only two RF pulses, a 90o pulse (excitation) followed by an 180o pulse (refocusing). The 90∘ pulse will tip the magnetization and the transverse plane. In practice the B0 field is never perfectly homogeneous and consequently spins at different positions will precess at slightly different frequencies. As a result, following the application of the 90∘ pulse, they will begin to dephase relative to each other. After a certain time interval, denoted TE/2 (Fig. 4.1), the 180º pulse is applied. The spins which have accumulated extra positive phase will now have the negative of that phase, such that the faster spins will “catch” the slower spins after another time interval TE/2 and an echo is formed. The total time between the application of the 90∘ pulse and with echo formation is called echo time and is typically denoted TE. The echo magnitude is a factor of smaller than the maximum amplitude of the free induction decay,a1 longer T2 is the transverse relaxation time. The popularity of spin echo sequences is justified by their robustness to B0 inhomogeneities.
Demonstration of ameliorating effect of vardenafil through its anti-inflammatory and neuroprotective properties in autism spectrum disorder induced by propionic acid on rat model
Published in International Journal of Neuroscience, 2022
Bahattin Özkul, Furkan Ertürk Urfalı, İbrahim Halil Sever, Mehmet Fatih Bozkurt, İbrahim Söğüt, Çağrı Serdar Elgörmüş, Mumin Alper Erdogan, Oytun Erbaş
T2 sequence was acquired by using the standard spin-echo imaging and the protocol was as follows: TR = 2690 ms, TE = 102 ms, slice thickness = 2 mm, distance factor = 0.2 mm, FOV = 33 × 33 mm2, 256 × 256 pixel matrix, bandwidth = 175 Hz/pixel, number of acquisitions = 2, number of slice = 12. The volume of interest was placed on the right corpus striatum of the control and PPA-injected groups, and 1H-MRS examination was performed in a volume of 16 µl with using the automated multi-voxel 3D chemical shift imaging sequence (TR/TE = 1000/35 ms; phase encoding x/y = 24/24; voxel volume = 2 × 2 × 4 mm3; FOV: 6 × 6 mm2, number of excitation pulses = 1). The respective peaks of lactate and creatine (lactate: 1.33 ppm and creatine: 3.02 ppm) were identified, and after that, relative amounts of these compounds were measured. The MRS acquired via measured signal of free induction decay was Fourier-transformed. The raw data was transferred to the dedicated workstation (Advantage Workstation, GE Healthcare Company, USA), and specific software (GE Software, Release 4.7, USA) was used to evaluate the raw data derived from spectroscopy (Figure 3).
Roux-en-Y gastric bypass surgery in Zucker rats induces bacterial and systemic metabolic changes independent of caloric restriction-induced weight loss
Published in Gut Microbes, 2021
Florian Seyfried, Jutarop Phetcharaburanin, Maria Glymenaki, Arno Nordbeck, Mohammed Hankir, Jeremy K Nicholson, Elaine Holmes, Julian R. Marchesi, Jia V. Li
Urine samples were prepared by combining 400 μL of urine with 250 μL of 0.2 M sodium phosphate buffer (100% D2O, 0.01% TSP, and 3 mM sodium azide (NaN3), pH 7.4). The mixture was vortexed and centrifuged at 16,000 x g for 10 min at 4°C and 600 μL of supernatant was transferred into NMR tube with an outer diameter of 5 mm pending for NMR analysis. 1H NMR spectra of all urinary samples were acquired using a 600 MHz spectrometer (Bruker Avance III, Bruker Biospin, Germany) with 5 mm broadband inverse configuration probe with a z axis magnetic field-gradient capability operating at 600.13 MHz for proton. D2O solvent in the sample buffer was used to lock the magnetic field. A standard 1-dimensional (1-D) NMR pulse [recycle delay (RD)-90°-t1-90°-tm-90°-acquire free induction decay (FID)] was employed at 300 K for the acquisition of urine spectra. A total of 128 scans were recorded into 64 k data points with a spectral width of 20 ppm.
Effects of mono- and dialkylglucosides on the characterisation and blood circulation of lipid nanoemulsions
Published in Journal of Microencapsulation, 2019
Shigehiko Takegami, Atsuko Konishi, Shizuno Okazaki, Mai Fujiwara, Tatsuya Kitade
At suitable time intervals, an analytical sample was prepared by adding a 300 µL mouse blood sample to 240 µL of D2O and 60 µL of a 1.0 mM TFMS-D2O stock solution to achieve a concentration of 0.1 mM. The samples were stirred and transferred into 5-mm-diameter NMR sample tubes. All 19F NMR spectra were measured using a UNITYINOVA spectrometer (Agilent Technologies, Inc., Santa Clara, CA, USA) operating at 376.21 MHz without proton decoupling. The set parameters were a 9.0-μs pulse width (90° for the flip angle), a relaxation delay of 10.0 s, and an acquisition time of 1.0 s. The probe temperature was 25 °C. The number of free induction decay (FID) accumulations required to improve the signal-to-noise (S/N) ratio was more than 1000, which corresponded to an accumulation time of approximately 3.0 h. 19F-TP concentrations were calculated from the ratio of the signal intensity of 19F-TP to the signal intensity of the trifluoromethyl group of 0.1 mM TFMS, the internal standard.