title: Estimation of pore size in a microstructure phantom using the optimised gradient waveform diffusion weighted NMR sequence.
abstract: There has been increasing interest in nuclear magnetic resonance (NMR) techniques that are sensitive to diffusion of molecules containing NMR visible nuclei for the estimation of microstructure parameters. A microstructure parameter of particular interest is pore radius distribution. A recent in silico study optimised the shape of the gradient waveform in diffusion weighted spin-echo experiments for estimating pore size. The study demonstrated that optimised gradient waveform (GEN) protocols improve pore radius estimates compared to optimised pulse gradient spin-echo (PGSE) protocols, particularly at shorter length scales. This study assesses the feasibility of implementing GEN protocols on a small bore 9.4 T scanner and verifies their additional sensitivity to pore radius. We implement GEN and PGSE protocols optimised for pore radii of 1, 2.5, 5, 7.5, 10 μm and constrained to maximum gradient strengths of 40, 80, 200 mT m(-1). We construct microstructure phantoms, which have a single pore radius for each phantom, using microcapillary fibres. The measured signal shows good agreement with simulated signal, strongly indicating that the GEN waveforms can be implemented on a 9.4 T system. We also demonstrate that GEN protocols provide improved sensitivity to the smaller pore radii when compared to optimised PGSE protocols, particularly at the lower gradient amplitudes investigated in this study. Our results suggest that this improved sensitivity of GEN protocols would be reflected in clinical scenarios.
authors: Centre for Medical Image Computing, Department of Computer Science, University College London (UCL), Gower Street, London WC1E 6BT, UK. b.siow@cs.ucl.ac.uk
authors: Bernard
authors: B
authors: Siow
authors: Ivana
authors: I
authors: Drobnjak
authors: Aritrick
authors: A
authors: Chatterjee
authors: Mark F
authors: MF
authors: Lythgoe
authors: Daniel C
authors: DC
authors: Alexander
mesh_terms: D003198:Computer Simulation; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005240:Feasibility Studies; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008422:Materials Testing / Q000379:methods*; D008956:Models, Chemical; D008958:Models, Molecular; D010316:Particle Size; D016062:Porosity