Off-resonance experiments and contrast agents to improve magnetic resonance imaging (original) (raw)
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Inorganic Chemistry, 2018
The relaxivity of Gd(HP-DO3A) was studied as a function of pH and buffer composition in order to identify the main factors of the observed relaxation enhancement due to the exchange of the coordinated hydroxyl proton. It was established that the paramagnetic relaxation time, T 1M , of the coordinated hydroxyl proton is about 50% shorter than that of the protons in the coordinated water molecule. The control of the pK of the coordinated alcoholic −OH moiety in the ligand is fundamental to utilize the proton exchange enhanced relaxivity under physio/pathologic conditions. A new derivative of Gd(HP-DO3A) was synthesized by replacing the −CH 3 group with a −CF 3 moiety. In this complex, the −OH group becomes more acidic. Consequently, the maximum contribution of the proton exchange to the relaxivity is shifted to a lower pH region with the fluorinated ligand.
Studies of factors affecting the design of NMR contrast agents: manganese in blood as a model system
Magnetic Resonance in Medicine, 1984
Some factors affecting the performance of paramagnetic ions as contrast agents for proton NMR imaging have been studied. It is demonstrated that the relaxation rate of an aqueous solution of the ion is not reliably predicted by its magnetic moment, but that significant relaxation enhancement may result when the ion is complexed with large molecules, which increases the dominant correlation time. This enhancement in turn can be altered by factors such as pH and competition for binding. Chelation of the paramagnetic ion, which may be implemented to lower its toxicity, can considerably reduce its efficacy by not only limiting its access to water but also by preventing the enhancement from associations and macromolecules. For manganese the ratio TI /T2 is a useful parameter which is sensitive to the degree of metal binding. These features of paramagnetic relaxation enhancement in tissue are demonstrated in a series of experiments on systems consisting of blood components and manganese.
European Journal of Radiology, 2008
We provide a brief overview of the chemistry and most relevant properties of paramagnetic and diamagnetic contrast agents (CAs) for Magnetic Resonance Imaging and Magnetic Resonance Spectroscopic Imaging. Paramagnetic CAs for MRI consist mainly of Gd(III) complexes from linear or macrocyclic polyaminopolycarboxylates. These agents reduce, the relaxation times T(1) and T(2) of the water protons in a concentration dependent manner, increasing selectively MRI contrast in those regions in which they accumulate. In most instances they provide anatomical information on the localization of lesions and in some specific cases they may allow to estimate some physiological properties of tissues including mainly vascular performance. Because of its ability to discriminate easily between normal and diseased tissue, extracellular pH (pH(e)) has been added recently, to the battery of variables amenable to MRI investigation. A variety of Gd(III) containing macrocycles sensitive to pH, endogenous or exogenous polypeptides or even liposomes have been investigated for this purpose, using the pH dependence of their relaxivity or magnetization transfer rate constant (chemical exchange saturation transfer, CEST). Many environmental circumstances in addition to pH affect, however, relaxivity or magnetization transfer rate constants of these agents, making the results of pH measurements by MRI difficult to interpret. To overcome these limitations, our laboratory synthesized and developed a novel series of diamagnetic CAs for Magnetic Resonance Spectroscopic Imaging, a new family of monomeric and dimeric imidazolic derivatives able to provide unambiguous measurements of pH(e), independent of water relaxivity, diffusion or exchange.
Trends in NMR studies of paramagnetic Gd(III) complexes as potential contrast agents in MRI
Magnetic Resonance Imaging, 1991
The paramagnetic Gd(II1) complexes with polyaminocarboxylate ligands are intensively studied as possible Contrast Agents for Magnetic Resonance Imaging (M.R.I.). Their ability to enhance the solvent proton relaxation rate is mainly determined by the molecular reorientational time (T,&. In order to increase vR we studied the formation of non-covalent interactions between functionalized Gd(III)-complexes and micelles. The N.M.R.D. (Nuclear Magnetic Relaxation Dispersion) profiles of aqueous solutions of these paramagnetic complexes with hexadecyltrimetbylammonium bromide (CTABr) were measured and the results could be accounted for by difference in negative charge and number of hydrophobic aromatic residues among the different complexes.
Investigation of magnetic properties of various complexes prepared as contrast agents for MRI
Journal of Molecular Structure, 2008
In this study, the relaxivities of various ferri-ferro and superparamagnetic particles in human serum and deionized water were determined by using MRI system operating at 1.5 T. For this purpose, the spin-lattice (1/T 1) and spin-spin (1/T 2) relaxation rates in serum and deionized water were measured versus increasing concentrations of the DyPO 4 , 5Fe 2 O 3 3Gd 2 O 3 + dextran, 5Fe 2 O 3 3Gd 2 O 3 + CMC, 5Fe 2 O 3 3Gd 2 O 3. The longitudinal relaxivity (r 1) and transverse relaxivity (r 2) of proton were determined from the slopes of fits between the relaxation rates and concentrations. T 1 and T 2 times in serum were decreased due to increased concentrations of the ions added to samples. The r 2 /r 1 values for ions added to serum ranged from 1 to 4, whereas the r 2 /r 1 for the ions added to water changed between 0.57 and 1 except that for 5Fe 2 O 3 3Gd 2 O 3. PRRE (proton relaxation rate enhancement) data reveals that, the ions added to serum are not bound to the proteins. The present results suggest that chemical compounds of iron oxide studied may have a potential that can be used as an alternative superparamagnetic MRI contrast agent.
Inorganic Chemistry, 2007
The amphiphilic gadolinium complex MS-325 ((trisodium-{(2-(R)-[(4,4-diphenylcyclohexyl) phosphonooxymethyl] diethylenetriaminepentaacetato) (aquo)gadolinium(III)}) is a contrast agent for magnetic resonance angiography (MRA). MS-325 consists of two slowly interconverting diastereoisomers, A and B (65:35 ratio), which can be isolated at pH > 8.5 (Tyeklár, Z.; Dunham, S. U.; Midelfort, K.; Scott, D. M.; Sajiki, H.; Ong, K.; Lauffer, R. B.; Caravan, P.; McMurry, T. J. Inorg. Chem. 2007, 46, 6621−6631). MS-325 binds to human serum albumin (HSA) in plasma resulting in an extended plasma half-life, retention of the agent within the blood compartment, and an increased relaxation rate of water protons in plasma. Under physiological conditions (37°C, pH 7.4, phosphate buffered saline (PBS), 4.5% HSA, 0.05 mM complex)