A fast, analytically based method to optimize local transmit efficiency for a transmit array

• Published in: Magnetic resonance in medicine Vol. 71; no. 1; pp. 432 - 439
• Main Authors: Carluccio, Giuseppe, Collins, Christopher M., Erricolo, Danilo
• Format: Journal Article
• Language: English
• Published: United States Blackwell Publishing Ltd 01-01-2014; Wiley Subscription Services, Inc
• Subjects: Computer-Aided Design; Equipment Design; Equipment Failure Analysis; Humans; Image Enhancement - instrumentation; magnetic resonance imaging; Magnetic Resonance Imaging - instrumentation; power; radiofrequency; Reproducibility of Results; Sensitivity and Specificity; shimming; specific absorption rate; spectroscopy; Transducers; Whole Body Imaging - instrumentation; shimming; specific absorption rate; magnetic resonance imaging; power; spectroscopy; radiofrequency
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.24653

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. Magn Reson Med 71:432–439, 2014. © 2013 Wiley Periodicals, Inc.