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Magnetic Nanoparticles for Cancer Diagnosis
Published in D. Sakthi Kumar, Aswathy Ravindran Girija, Bionanotechnology in Cancer, 2023
R. G. Aswathy, D. Sakthi Kumar
T1 longitudinal relaxation (spin-lattice relaxation) signifies the speed of magnetization that is parallel to static magnetic field recovery after inducing a disruption. Rapidly relaxing protons (short T1) recover complete magnetization along the longitudinal axis and yield high intensity signal. Complete magnetization on the longitudinal axis is not redeemed for protons that relax slowly (long T1) before successive RF pulses, and generally produce a low intensity signals [32]. T2 transverse relaxation (spin-spin relaxation) signifies how fast magnetization in the plane perpendicular to static magnetic field losses the phase coherence. When RF pulse is applied, proton nuclei spin in phase and after the pulse, the magnetic fields of all the nuclei interact and the energy is exchanged. The nuclei lose their phase coherence and spin in random manner [33].
Two-dimensional and Three-dimensional Dosimetry
Published in W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald, Handbook of Radiotherapy Physics, 2021
Mark Oldham, Devon Godfrey, Titania Juang, Andrew Thomas
MRI (see Section 33.2) was the first imaging modality used for 3D gel dosimeter readout and can be used to image both Fricke gels and polymer gels (Maryanski et al. 1994; Baldock et al. 2010). In Fricke gel dosimetry, spin-lattice relaxation rate (R1 = 1/T1) is the MRI parameter most often used. The R1 relaxation for water protons is perturbed differently due to the different paramagnetic characteristics of neighbouring Fe2+ and Fe3+ ions and thus varies depending on the concentration of the two ion species. These mechanisms are described in detail in the literature. For polymer gel dosimetry, spin-spin relaxation rate (R2 = 1/T2) is the MRI parameter measured most frequently due to high sensitivity, a large dynamic range and linear response to dose. Recommendations on MRI imaging sequences for use in polymer gel dosimetry have been published by De Deene (De Deene 2013) and are reproduced here in Table 18.1.
Physical Principles of BOLD fMRI—What Is Important for the Clinician
Published in Andrei I. Holodny, Functional Neuroimaging, 2019
The three major tissue contrast mechanisms important for our discussion of BOLD fMRI are T1, T2, and T2*. T1 is the longitudinal relaxation time or spin-lattice relaxation time, caused by the interaction between the spin and its environment. T2 is the transverse relaxation time or spin-spin relaxation time in a homogeneous local magnetic field, caused by the interaction between the spin and other nearby spins. T2* is the transverse relaxation time or spin-spin relaxation time in a nonhomogeneous local magnetic field. Usually T1- and T2-weighted images are used for anatomical studies, i.e., displaying tissue and/or tumor structures in the brain. T2*-weighted images are used in BOLD fMRI to investigate brain function.
Multifunctional MIL-Cur@FC as a theranostic agent for magnetic resonance imaging and targeting drug delivery: in vitro and in vivo study
Published in Journal of Drug Targeting, 2020
Sadegh Dehghani, Maryam Hosseini, Soheila Haghgoo, Vahid Changizi, Hamid Akbari Javar, Mehdi Khoobi, Nader Riahi Alam
Since FC coating reduced the porosity of the MIL-Cur@FC NPs, the water molecules diffusion into the MIL-Cur@FC NPs was restricted [38] resulting in lower T1 relaxation time of protons in the water molecules surrounding the MIL-Cur@FC compared to MIL NPs. Moreover, the spin-spin relaxation time of water molecules was lower affected by the magnitude of magnetic spins of MIL due to increasing the distance between them induced by FC thickness leading in T2 relaxation time reduction [39]. The pH effect on T1 and T2 contrast was noteworthy. Strongest bright contrast was demonstrated in T1-weighted images at pH 5.0 for MIL and MIL-Cur@FC NPs (r1=4.5 and 3.9 mM−1.S−1, respectively), which might be due to the decomposition of the NPs improving accessibility of the detached paramagnetic iron ions to the water molecules. These data are in consistent with the theory that the separated Fe3+ as a paramagnetic centre can produce T1-weighted images through releasing from decomposed NPs and meeting sufficient water molecules [40]. On the other hand, the decomposition of MIL and MIL-Cur@FC NPs significantly reduced the T2 contrast at pH 5.0 (r2=0.5 and 0.6 mM−1.S−1, respectively) that could be due to decreased magnetisation saturation (MS) of NPs [38,40].
Preparation of curcumin self-micelle solid dispersion with enhanced bioavailability and cytotoxic activity by mechanochemistry
Published in Drug Delivery, 2018
Qihong Zhang, Nikolay E. Polyakov, Yulia S. Chistyachenko, Mikhail V. Khvostov, Tatjana S. Frolova, Tatjana G. Tolstikova, Alexandr V. Dushkin, Weike Su
1H NMR spectra were recorded on Bruker Avance III 500 MHz spectrometer, and the spin–spin relaxation time T2 was measured using the Carr-Purcell–Meiboom-Gill (CPMG) pulse sequence from Avance version of Bruker pulse sequence library: P1 (90°) – (τ – P2 (180°) – τ)n – registration, where τ = 0.5 ms – fixed time delay, and n varied from 0 to 2000. The compositions prepared mechanochemically and by physical mixing of components were investigated in D2O and CD3OD (Aldrich, St. Louis, MO, 99.8%) solutions as well as in their mixture. Spin–spin relaxation times (T2) are sensitive to molecular motions. The T2 value is closely related to the mobility of a molecule and is inversely proportional to the rotational correlation time. Thus, using T2 data, one can probe changes in the environment or state (free/bound) of the molecules (Deese et al., 1982).
Superparamagnetic lipid-based hybrid nanosystems for drug delivery
Published in Expert Opinion on Drug Delivery, 2018
E. Millart, S. Lesieur, V. Faivre
In this equation, Ri(obs) and 1/Ti(obs) are the global relaxation rates in an aqueous system, Ti(dia) is the relaxation time of the system before addition of the contrast agent, C is the concentration of the paramagnetic center expressed in mmol.L−1, and ri is the relaxivity (s−1.mmol−1.L). The effectiveness of a T1 or T2 contrast agent is defined by the r2/r1 ratio: the higher the ratio r2/r1, the more efficient the T2 agent and the better the contrast. The magnetic relaxation characteristics can be measured by studying the nuclear magnetic resonance dispersion (NMRD) profile, which finally yields information about the mean crystal size, the specific magnetization, and the Néel relaxation time [24]. The dipolar interactions between the superparamagnetic cores and surrounding solvent protons result in an increase in both longitudinal (spin-lattice) and transverse (spin-spin) relaxation rates and thus to an upgrade in the relaxivity; that is to say the effectiveness of the contrast agent. As examples, the r1 values of commercial Resovist and Endorem are 25 mM−1.s−1 and 40 mM−1.s−1, respectively, at 0.47 T while their r2 values was found to be 164 mM−1.s−1 and 160 mM−1.s−1 at the same magnetic field strength. Thus, the r2/r1 ratios of Resovist and Endorem are 6.2 and 4, respectively [25]. Interesting properties have also been obtained with non-commercial SPION [26,27].