Experimental design for MRI by greedy policy search

Tim Bakker, Herke van Hoof, Max Welling

Spotlight presentation: Orals & Spotlights Track 15: COVID/Applications/Composition
on 2020-12-09T08:20:00-08:00 - 2020-12-09T08:30:00-08:00
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on 2020-12-09T09:00:00-08:00 - 2020-12-09T11:00:00-08:00
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Abstract: In today’s clinical practice, magnetic resonance imaging (MRI) is routinely accelerated through subsampling of the associated Fourier domain. Currently, the construction of these subsampling strategies - known as experimental design - relies primarily on heuristics. We propose to learn experimental design strategies for accelerated MRI with policy gradient methods. Unexpectedly, our experiments show that a simple greedy approximation of the objective leads to solutions nearly on-par with the more general non-greedy approach. We offer a partial explanation for this phenomenon rooted in greater variance in the non-greedy objective's gradient estimates, and experimentally verify that this variance hampers non-greedy models in adapting their policies to individual MR images. We empirically show that this adaptivity is key to improving subsampling designs.

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