How to design ¹³C para‐hydrogen‐induced polarization experiments for MRI applications

Abstract

The application of hyperpolarization techniques for MRI purposes is gathering increasing attention, especially for nuclei such as (13)C or (129)Xe. Among the different proposed methods, ParaHydrogen Induced Polarization requires relatively cheap equipment. The setup of an MRI experiment by means of parahydrogen requires the application of skills and methodologies that derive from different fields of knowledge. The basic theory and a practical insight of this method are presented here. Parahydrogenation of alkynes, having a labelled (13)CO group adjacent to the triple bond, catalyzed by Rh(I) complexes containing a chelating phosphine, represents the best choice for producing and maintaining high heteronuclear polarization effect. In order to transform anti-phase into in-phase (net) (13)C polarization for MRI application it is necessary to set up the described magnetic field cycle procedure. In vitro and in vivo images have been acquired using fast imaging sequences (RARE and trueFISP).

Para‐hydrogen induced polarization of Si‐29 NMR resonances as a potentially useful tool for analytical applications

“…The PHIP results for these compounds were analogous to those previously reported for mono‐trimethylsilylacetylene . In both cases highly enhanced, 29 Si resonances of the alkene (–9.86 ppm for 1a and –8.21 ppm for 2a , respectively) and the alkane (3.27 ppm for 1b and 2.56 ppm for 2b , respectively) products were observed in the 29 Si NMR spectra acquired immediately after para‐hydrogenation and application of a field cycling procedure, which is necessary for generating an in‐phase 29 Si resonance . Figure shows the 29 Si NMR spectrum of hyperpolarized 1a , obtained by para‐hydrogenation of 1 .…”

Use of Labile Precursors for the Generation of Hyperpolarized Molecules from Hydrogenation with Parahydrogen and Aqueous‐Phase Extraction

“…To tackle the issue associated to the non‐biocompatibility of the hydrogenation catalyst, its removal through a passage on a ion‐exchange resin has been proposed 13. However this step may cause a dramatic polarization loss, as the temporary immobilization of the substrate on the resin may result in markedly enhanced relaxation rates.…”

Synthesis and testing of a p‐H2 hyperpolarized 13C probe based on the pyrazolo[1,5‐a]pyrimidineacetamide DPA‐713, an MRI vector to target the peripheral benzodiazepine receptors

“…The latter consists of quickly taking the sample to a quasi-zero magnetic field and then slowly bringing it back to earth magnetic field. [2,26] A strong signal enhancement (approximately 4500 times with respect to the equilibrium signal intensity) was observed for the 13 C carbonyl resonance of the alkene molecule at 166.18 ppm (Fig. 2) due to polarization transfer from the added protons to the 13 C nucleus via scalar couplings.…”