Philipp Ehses1,2, Jonas Bause2, G Shajan2, Klaus Scheffler1,2. 1. Department of Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany. 2. High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.
Abstract
PURPOSE: Standard gradient-echo sequences are often prohibitively slow for T2*-weighted imaging as long echo times prolong the repetition time of the sequence. Echo-shifting offers a way out of this dilemma by allowing an echo time that exceeds the repetition time. The purpose of this work is to present a gradient-echo sequence that is optimized for multislice T2*-weighted imaging applications by combining echo-shifting with an interleaved slice excitation order. THEORY AND METHODS: This combined approach offers two major advantages: First, it combines the advantages of both concepts, that is, echo time and pulse repetition time can be significantly increased without affecting scan time. Second, there is no echo-shifting related signal loss associated with this concept as only a single radiofrequency pulse is applied per pulse repetition time and slice. RESULTS: A 9.4 Tesla high-resolution T2*-weighted anatomical brain scan of the proposed sequence is compared to a standard gradient-echo. Furthermore, results from 9.4 Tesla blood oxygen level dependent functional magnetic resonance imaging experiments with an in-plane resolution of 0.8 × 0.8 mm(2) are presented. CONCLUSION: The proposed sequence allows for efficient generation of T2*-weighted contrast by combining echo-shifting with an interleaved slice excitation order.
PURPOSE: Standard gradient-echo sequences are often prohibitively slow for T2*-weighted imaging as long echo times prolong the repetition time of the sequence. Echo-shifting offers a way out of this dilemma by allowing an echo time that exceeds the repetition time. The purpose of this work is to present a gradient-echo sequence that is optimized for multislice T2*-weighted imaging applications by combining echo-shifting with an interleaved slice excitation order. THEORY AND METHODS: This combined approach offers two major advantages: First, it combines the advantages of both concepts, that is, echo time and pulse repetition time can be significantly increased without affecting scan time. Second, there is no echo-shifting related signal loss associated with this concept as only a single radiofrequency pulse is applied per pulse repetition time and slice. RESULTS: A 9.4 Tesla high-resolution T2*-weighted anatomical brain scan of the proposed sequence is compared to a standard gradient-echo. Furthermore, results from 9.4 Tesla blood oxygen level dependent functional magnetic resonance imaging experiments with an in-plane resolution of 0.8 × 0.8 mm(2) are presented. CONCLUSION: The proposed sequence allows for efficient generation of T2*-weighted contrast by combining echo-shifting with an interleaved slice excitation order.
Authors: Joana R Loureiro; Gisela E Hagberg; Thomas Ethofer; Michael Erb; Jonas Bause; Philipp Ehses; Klaus Scheffler; Marc Himmelbach Journal: Hum Brain Mapp Date: 2016-09-23 Impact factor: 5.038