Improved Bloch‐Siegert based B1 mapping by reducing off‐resonance shift. (28th January 2013)

• Record Type: Journal Article
• Authors: Duan, Qi; van, Peter; Duyn, Jeff
• Is Part Of: NMR in biomedicine. Volume 26:Number 9(2013:Sep.)
• Page Start: 1070
• Page End: 1078
• Publication Date: 2013-01-28
• Subjects: Nuclear magnetic resonance -- Periodicals; Magnetic Resonance Spectroscopy -- Periodicals; 574
• DOI: 10.1002/nbm.2920
• Languages: English
• ISSNs: 0952-3480

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <p>An MRI method based on the Bloch‐Siegert (BS) shift phenomenon was recently proposed as a fast and precise way to map a radio frequency (RF) transmit field (<italic>B₁</italic>⁺ field). For MRI at high field, the mapping sensitivity of this approach was limited by tissue heating associated with a BS irradiation pulse. To mitigate this, we investigated the possibility of lowering the off‐resonance frequency of this pulse since theoretical analysis indicated that the sensitivity of Bloch‐Siegert based <italic>B₁</italic>⁺ mapping could be substantially improved when irradiating closer to resonance. Using optimized irradiation pulse shape and gradient crushers to minimize direct excitation effects, <italic>in vivo</italic> experiments on human brains at 7 T confirmed improved sensitivity with this approach. Improved sensitivity translated into an 80% reduction in <italic>B₁</italic>⁺ estimation errors without increasing tissue heating. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.</p> </abstract>