Designing and Optimization of Continuous Electromagnetic RF Pulses for Studying CEST MRI by Numerical Solution to the Bloch-McConnell Equations

Rezaeian, Mohammad Reza; Hossein-Zadeh, Gholam Ali; Soltanian Zadeh, Hamid

doi:10.22041/ijbme.2014.13558

Document Type : Full Research Paper

Authors

¹ Ph.D Student, Control and Intelligent Processing Center of Excellence (CIPCE), School of Electrical and Computer Engineering, University of Tehran

² Associate Professor, Control and Intelligent Processing Center of Excellence (CIPCE), School of Electrical and Computer Engineering, College of Engineering, University of Tehran

³ Professor, Control and Intelligent Processing Center of Excellence (CIPCE), School of Electrical and Computer Engineering, College of Engineering, University of Tehran

10.22041/ijbme.2014.13558

Abstract

Chemical exchange saturation transfer (CEST) is a new mechanism of contrast generation in magnetic resonance imaging (MRI) which differentiates molecule biomarkers via chemical shift. CEST MRI contrast mechanism is very complex and depends on radio frequency (RF) power and RF pulse shape. Two approaches have been used to saturate contrast agent (CA) protons: continuous wave CEST (CW-CEST) and pulsed CEST. To find the optimal RF pulse, numerical solution of Bloch-McConnell equations (BME) may be used. In this paperwe find the optimum values of RF pulse parameters that maximize the CEST contrast. Discrete pulses have lower specific absorption ratio (SAR) than CW RF pulses. However, since discretization is performed on continuous RF pulses, optimizing the continuous RF pulses leads to the optimization of discrete RF pulses. Therefore, in this paper, Rectangular, Gaussian and Fermi pulses are investigated as CW RF pulses. In this investigation, in addition to considering the SAR limitation, 60 dB approximation for the RF pulse amplitude is used. To compare the efficiency of pulses, their resultant flip angles (FA) are assumed equal. Efficiency of CW-CEST is investigated using two parameters, CEST ratio and SAR. According to these parametres, rectangular, Fermi and Gaussian RF pulses have the best performance respectively. Since implementation of rectangular RF is harder than Gaussian and Fermi RF pulses, Fermi and Gaussian RF pulses are desired. Our results suggest that it is possible to maximize CEST ratio by optimizing parameters of rectangular (with an amplitude of 5.7μT), Gaussian (σ about 0.7s) and Fermi (a-value about 0.3s) pulses. Results are verified by empirical formulation of CEST ratio.

Keywords

Main Subjects

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Iranian Journal of Biomedical Engineering

Designing and Optimization of Continuous Electromagnetic RF Pulses for Studying CEST MRI by Numerical Solution to the Bloch-McConnell Equations

References

References

Volume 8, Issue 1 - Serial Number 1
March 2014
Pages 87-99

Designing and Optimization of Continuous Electromagnetic RF Pulses for Studying CEST MRI by Numerical Solution to the Bloch-McConnell Equations

References

References

Volume 8, Issue 1 - Serial Number 1March 2014Pages 87-99

Volume 8, Issue 1 - Serial Number 1
March 2014
Pages 87-99