High-resolution 3D proton MRI of hyperpolarized gas enabled by parahydrogen and Rh/TiO2 heterogeneous catalyst

Abstract

Several supported metal catalysts were synthesized, characterized, and tested in heterogeneous hydrogenation of propene with parahydrogen to maximize nuclear spin hyperpolarization of propane gas using parahydrogen induced polarization (PHIP). The Rh/TiO2 catalyst with a metal particle size of 1.6 nm was found to be the most active and effective in the pairwise hydrogen addition and robust, demonstrating reproducible results with multiple hydrogenation experiments and stability for ≥1.5 years. 3D (1) H magnetic resonance imaging (MRI) of 1 % hyperpolarized flowing gas with microscale spatial resolution (625×625×625 μm(3) ) and large imaging matrix (128×128×32) was demonstrated by using a preclinical 4.7 T scanner and 17.4 s imaging scan time.

Keywords: heterogeneous catalysis; hyperpolarized gas; magnetic resonance imaging; parahydrogen; supported catalysts.

Figure 1

a) Experimental setup diagram of propane hyperpolarization by PHIP with subsequent 3D MR imaging of letter-shaped phantoms shown in Figure 2. b) Molecular diagram of propene hydrogenation by parahydrogen over M/TiO₂ yielding hyperpolarized propane. c) ¹H NMR (9.4 T) spectra acquired with continuous flow of reaction products after propene hydrogenation with parahydrogen over different TiO₂-supported metal catalysts in Earth’s magnetic field with subsequent adiabatic transfer to the magnetic field of the NMR spectrometer (ALTADENA conditions). d) TEM image of the representative Rh/TiO₂ catalyst; arrows indicate the presence of deposited Rh nanoparticles.

Figure 2

3D gradient echo (GRE) ¹H MRI of flowing HP propane (a) and water reference (b) in “VU”-shaped phantom with three projections shown for each image. Both sets of 3D images have voxel size of 625 × 625 × 625 μm³ and total imaging time of 17.4 s with TR =4.2 ms, TE =2.1 ms. The field of view (FOV) was 80 × 80 × 20 mm³ with imaging matrix 128 × 128 × 32. A movie showing the full 3D rendering is available in the Supporting Information.