PURPOSE: To develop an analytically based algorithm for rapid optimization of the local radiofrequency magnetic (B1+) field intensity for a given radiofrequency power through a transmit array. The analytical nature of the method will yield insight to optimization requirements and provides a valuable reference for numerically based searches. METHODS: With the knowledge of the B1+ field distribution generated by each single coil of the array, both the phases and the amplitudes of each coil current are optimized to maximize the magnitude of the B1+ field in a specific location of the body per unit of power transmitted through the array and, consequently, minimizing the whole body specific absorption rate for a given pulse sequence. RESULTS: Simulations considering the human body show that the proposed method can reduce the whole-body specific absorption rate for a given B1+ magnitude at the location of interest by a factor of about 6.3 compared to the classic birdcage current configuration, and by a factor of 3.2 compared to phase-only shimming in a case with significant coupling between the elements of the array. CONCLUSION: The proposed method can rapidly provide valuable information pertinent to the optimization of field distributions from transmit arrays.
PURPOSE: To develop an analytically based algorithm for rapid optimization of the local radiofrequency magnetic (B1+) field intensity for a given radiofrequency power through a transmit array. The analytical nature of the method will yield insight to optimization requirements and provides a valuable reference for numerically based searches. METHODS: With the knowledge of the B1+ field distribution generated by each single coil of the array, both the phases and the amplitudes of each coil current are optimized to maximize the magnitude of the B1+ field in a specific location of the body per unit of power transmitted through the array and, consequently, minimizing the whole body specific absorption rate for a given pulse sequence. RESULTS: Simulations considering the human body show that the proposed method can reduce the whole-body specific absorption rate for a given B1+ magnitude at the location of interest by a factor of about 6.3 compared to the classic birdcage current configuration, and by a factor of 3.2 compared to phase-only shimming in a case with significant coupling between the elements of the array. CONCLUSION: The proposed method can rapidly provide valuable information pertinent to the optimization of field distributions from transmit arrays.
Authors: Thomas Vaughan; Lance DelaBarre; Carl Snyder; Jinfeng Tian; Can Akgun; Devashish Shrivastava; Wanzahn Liu; Chris Olson; Gregor Adriany; John Strupp; Peter Andersen; Anand Gopinath; Pierre-Francois van de Moortele; Michael Garwood; Kamil Ugurbil Journal: Magn Reson Med Date: 2006-12 Impact factor: 4.668
Authors: Cem Murat Deniz; Ryan Brown; Riccardo Lattanzi; Leeor Alon; Daniel K Sodickson; Yudong Zhu Journal: Magn Reson Med Date: 2012-06-19 Impact factor: 4.668
Authors: Cornelis A T Van den Berg; Bob van den Bergen; Jeroen B Van de Kamer; Bas W Raaymakers; Hugo Kroeze; Lambertus W Bartels; Jan J W Lagendijk Journal: Magn Reson Med Date: 2007-03 Impact factor: 4.668