title: Double Diffusion Encoded Magnetic Resonance Imaging: Compensation of Artifacts Arising from Concomitant Magnetic Fields by Means of Additional Oscillating Gradients
creator: Rauch, Julian
subject: ddc-530
subject: 530 Physics
description: Concomitant or Maxwell fields imprint additional phases on the transverse magnetization. This concomitant phase can cause severe image artifacts due to the induced intravoxel dephasing. In particular, double diffusion encoding (DDE) schemes consisting of two pairs of bipolar diffusion-weighting gradients separated by a refocusing radiofrequency pulse are prone to concomitant field artifacts that may distort determination of quantitative parameters such as microscopic tissue anisotropy. In this work, different compensation methods were developed using additional oscillating gradients that reduce the concomitant phase before signal readout without additional refocusing pulses in the context of DDE. It is shown that adding oscillating gradients to the bipolar gradient pairs is an efficient method to reduce the self-squared concomitant phase. In simulations, it is demonstrated that a pulse-width modulation of the diffusion-weighting waveforms enables a compensation of both the self-squared terms and cross terms of the concomitant field. Oscillating gradient pulses obtained by constrained optimization, added to the original gradient waveforms, reduce the overall accumulated concomitant phase without significant changes in the original sequence characteristics. In vivo measurements in the brain of a healthy volunteer exhibited an increase in the signal-to-noise ratio of up to 35 % for b = 750 s/mm2 for each weighting for a transversal slice that had an isocenter distance of 5 cm.
date: 2024
type: Dissertation
type: info:eu-repo/semantics/doctoralThesis
type: NonPeerReviewed
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/34439/1/Dissertation.pdf
identifier: DOI:10.11588/heidok.00034439
identifier: urn:nbn:de:bsz:16-heidok-344392
identifier:   Rauch, Julian  (2024) Double Diffusion Encoded Magnetic Resonance Imaging: Compensation of Artifacts Arising from Concomitant Magnetic Fields by Means of Additional Oscillating Gradients.  [Dissertation]     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/34439/
rights: info:eu-repo/semantics/openAccess
rights: http://archiv.ub.uni-heidelberg.de/volltextserver/help/license_urhg.html
language: eng