Dipole-lets: a new multiscale decomposition for MR phase and quantitative susceptibility mapping

TL;DR

This paper introduces Dipole-lets, a multiscale transform that improves susceptibility mapping by effectively identifying and suppressing streaking artifacts caused by non-dipolar phase contributions.

Contribution

The paper presents a novel multiscale decomposition method called Dipole-lets for detecting dipole incompatibilities in MRI phase data, enhancing artifact suppression in susceptibility mapping.

Findings

Dipole-lets can extract non-dipolar content from phase data.

Dipole-lets effectively localize streaking artifacts.

Implementation as a regularizer improves mapping quality.

Abstract

Identifying and suppressing streaking artifacts is one of the most challenging problems in quantitative susceptibility mapping. The measured phase from tissue magnetization is assumed to be the convolution by the magnetic dipole kernel; direct inversion or standard regularization methods tend to create streaking artifacts in the estimated susceptibility. This is caused by extreme noise and by the presence of non-dipolar phase contributions, which are amplified by the dipole kernel following the streaking pattern. In this work, we introduce a multiscale transform, called Dipole-lets, as an optimal decomposition method for identifying dipole incompatibilities in measured field data by extracting features of different characteristic size and orientation with respect to the dipole kernel's zero-valued double-cone surface (the magic cone). We provide experiments that showcase that non-dipolar content can be extracted by Dipole-lets from phase data through artifact localization. We also present implementations of Dipole-lets as a optimization functional regularizator, through simple Tikhonov and infinity norm.