Noninvasive Visualization of In Vivo Drug Delivery of Paramagnetic Polymer Conjugates with MRI
Mansoor M. Amiji in Nanotechnology for Cancer Therapy, 2006
Longitudinal T1 relaxation involves the return of protons from the high energy state back to equilibrium by dissipating their excess energy to their surroundings. The process is also called spin-lattice relaxation. Transverse (T2) relaxation involves the transfer of the spin angular momentum among the protons via the interactions such as dipole–dipole interaction. The process is called spin–spin relaxation. In biological systems, the T2 relaxation time is typically shorter than T1 relaxation time. Because the main magnetic field of MRI scanners is not perfectly homogenous, the inhomogeneity of the magnetic field also causes dephasing of individual magnetizations of protons, resulting in more rapid loss of transverse magnetization. The process is called relaxation.
Contrast enhancement agents and radiopharmaceuticals
A Stewart Whitley, Jan Dodgeon, Angela Meadows, Jane Cullingworth, Ken Holmes, Marcus Jackson, Graham Hoadley, Randeep Kumar Kulshrestha in Clark’s Procedures in Diagnostic Imaging: A System-Based Approach, 2020
MR contrast agents work by altering the magnetic environment (magnetic susceptibility) of the local tissue and are not directly visualised. This is unlike iodinated contrast agents that function by their ability to directly alter the image, being additive to the normal tissue attenuation. Many substances exist that possess inherent magnetic characteristics and the choice has to be based on the ability to produce these compounds in a physiologically acceptable form. The criteria for such compounds is that they affect the following parameters: Proton density.Spin–lattice relaxation time, T1.Spin–spin relaxation time, T2.Flow.
Two-dimensional and Three-dimensional Dosimetry
W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald in Handbook of Radiotherapy Physics, 2021
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.
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).
Effect of Doxorubicin on Squamous Cell Carcinoma of Skin: Assessment by MRI Relaxometry at 4.7T
Published in Cancer Investigation, 2019
Ashok Sharma, Uma Sharma, N. R. Jagannathan, Ruma Ray, Moganty Raja Rajeswari
MRI experiments were performed on normal, saline treated tumor (Control) and doxorubicin treated tumor (Test) mice groups respectively (19,20). All MR studies were carried out using 4.7 T Bruker–Biospec MRI scanner (Bruker Corp., Billerica, MA, USA), using 72-mm diameter volume resonator transmitter/receiver coils. Animals were anesthetized with a combination of thiopentone (40 mg/kg) and diazepam (8 mg/kg) i.p. and placed head first and supine on a positioning sled. Orthogonal 3-plane (axial, coronal and sagittal plane) scout images were initially acquired to confirm animal positioning. Following the pilot scan, T-2 weighted (T2W) images using Rapid Acquisition with Relaxation Enhancement (RARE) sequence were acquired in the axial plane for characterization of tumors. The parameters used for T2W imaging were as follow: TR/TE = 3000/56 ms, RARE factor = 8, slice thickness = 2 mm, interslice distance = 2 mm, averages = 4 and matrix size = 256 × 256. Spin-lattice relaxation time (T1) and spin-spin relaxation time (T2) were measured for all mice at different time points.
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].
Related Knowledge Centers
- Nuclear Magnetic Resonance
- Magnetic Resonance Imaging
- Spin–Lattice Relaxation
- Beat
- Rotational Correlation Time
- Spin Echo
- Steady-State Free Precession Imaging
- Relaxation