Mustafa Çavuşoğlu1, Benjamin Emanuel Dietrich2, David Otto Brunner2, Markus Weiger2, Klaas Paul Pruessmann2. 1. Information Technology and Electrical Engineering Department, Institute for Biomedical Engineering, University and ETH Zürich, Swiss Federal Institute of Technology, ETZ F 64.1, Gloriastrasse 35, 8092, Zurich, Switzerland. cavusoglu@biomed.ee.ethz.ch. 2. Information Technology and Electrical Engineering Department, Institute for Biomedical Engineering, University and ETH Zürich, Swiss Federal Institute of Technology, ETZ F 64.1, Gloriastrasse 35, 8092, Zurich, Switzerland.
Abstract
OBJECTIVES: The accuracy and precision of the parallel RF excitations are highly dependent on the spatial and temporal fidelity of the magnetic fields involved in spin excitation. The consistency between the nominal and effective fields is typically limited by the imperfections of the employed hardware existing both in the gradient system and the RF chain. In this work, we experimentally presented highly improved spatially tailored parallel excitations by turning the native hardware accuracy challenge into a measurement and control problem using an advanced field camera technology to fully correct parallel RF transmission experiment. MATERIALS AND METHODS: An array of NMR field probes is used to measure the multiple channel RF pulses and gradient waveforms recording the high power RF pulses simultaneously with low frequency gradient fields on equal time basis. The recorded waveforms were integrated in RF pulse design for gradient trajectory correction, time imperfection compensation and introduction of iterative RF pre-emphasis. RESULTS: Superior excitation accuracy was achieved. Two major applications were presented at 7 Tesla including multi-dimensional tailored RF pulses for spatially selective excitation and slice-selective spoke pulses for [Formula: see text] mitigation. CONCLUSION: Comprehensive field monitoring is a highly effective means of correcting for the field deviations during parallel transmit pulse design.
OBJECTIVES: The accuracy and precision of the parallel RF excitations are highly dependent on the spatial and temporal fidelity of the magnetic fields involved in spin excitation. The consistency between the nominal and effective fields is typically limited by the imperfections of the employed hardware existing both in the gradient system and the RF chain. In this work, we experimentally presented highly improved spatially tailored parallel excitations by turning the native hardware accuracy challenge into a measurement and control problem using an advanced field camera technology to fully correct parallel RF transmission experiment. MATERIALS AND METHODS: An array of NMR field probes is used to measure the multiple channel RF pulses and gradient waveforms recording the high power RF pulses simultaneously with low frequency gradient fields on equal time basis. The recorded waveforms were integrated in RF pulse design for gradient trajectory correction, time imperfection compensation and introduction of iterative RF pre-emphasis. RESULTS: Superior excitation accuracy was achieved. Two major applications were presented at 7 Tesla including multi-dimensional tailored RF pulses for spatially selective excitation and slice-selective spoke pulses for [Formula: see text] mitigation. CONCLUSION: Comprehensive field monitoring is a highly effective means of correcting for the field deviations during parallel transmit pulse design.
Entities:
Keywords:
Correction; Excitation; Field imperfection; Field monitoring; Parallel transmission
Authors: David O Brunner; Benjamin E Dietrich; Mustafa Çavuşoğlu; Bertram J Wilm; Thomas Schmid; Simon Gross; Christoph Barmet; Klaas P Pruessmann Journal: NMR Biomed Date: 2015-08-13 Impact factor: 4.044
Authors: William Grissom; Chun-yu Yip; Zhenghui Zhang; V Andrew Stenger; Jeffrey A Fessler; Douglas C Noll Journal: Magn Reson Med Date: 2006-09 Impact factor: 4.668