Phase incremented echo train acquisition applied to magnetic resonance pore imaging

Abstract

Efficient phase cycling schemes remain a challenge for NMR techniques if the pulse sequences involve a large number of rf-pulses. Especially complex is the Carr Purcell Meiboom Gill (CPMG) pulse sequence where the number of rf-pulses can range from hundreds to several thousands. Our recent implementation of Magnetic Resonance Pore Imaging (MRPI) is based on a CPMG rf-pulse sequence in order to refocus the effect of internal gradients inherent in porous media. While the spin dynamics for spin-1/2 systems in CPMG like experiments are well understood it is still not straight forward to separate the desired pathway from the spectrum of unwanted coherence pathways. In this contribution we apply Phase Incremented Echo Train Acquisition (PIETA) to MRPI. We show how PIETA offers a convenient way to implement a working phase cycling scheme and how it allows one to gain deeper insights into the amplitudes of undesired pathways.

Experimental determination of pore shapes using phase retrieval from q -space NMR diffraction

“…The phase problem was overcome by modifying the temporal gradient profile: Laun et al replaced one of the narrow gradient pulses with a very long pulse of equal area and could thus preserve the phase information [25,26]. With the greater information content of the thus determinable 𝜌 �(𝒒), the direct reconstruction of arbitrary pore space functions was enabled so that the average pore shape in an imaging volume element could be measured [27][28][29][30][31]. This technique, known as diffusion pore imaging, potentially enables in-vivo estimations of histology-like parameters such as cell-size distributions.…”