Comparison of B+1 Field and Specific Absorption Rate(SAR)between Birdcage, Transverse Electromagnetic and Microstrip Coil for Ultra High Field MRI at 9.4Tesla
The RF coil is an essential part of MRI systems.In ultra-high field(UHF)MRI,the design of RF coils is a challenging task.The RF coil should resonate at a particular frequency(the Larmor Frequency)and must provide a highly homogeneous B+1 field as well.It must be safe to use by maintaining a low specific absorption rate(SAR)value.Homogeneity of the B+1 is a supremely important factor in MRI systems.A homogenous B+1 allows the spin in different mediums having different electromagnetic properties to see the same B+1 field value.When the field-tissue interaction takes place,the spin interacts differently in a unique manner making it possible for materials to be imaged.Generally speaking,this allows higher resolutions images with high contrast increasing therefore the sensitivity of the MRI system.The specific absorption rate is a safety indicator.It is an indicator that reflects how much electromagnetic energy is absorbed in the biological tissue.SAR value must be kept as low as possible.The task of this paper is to provide a quantitative comparison between three common volume RF coils at 9.4Tesla.The comparison is held in terms of the homogeneity of the B+1 both in the loaded and unloaded cases and also as a function of the SAR.Additionally,a comparison with the performance of 7Tesla published earlier to quantify the gain of increasing the frequency.Before comparing the coils,the coils must be built first.A novel design for each type of coils is shown.Before comparing the coils,the coils must be first built.A novel design for each type of coils is shown.The S-parameter as a clue of resonance at the Larmor frequency is presented accompanied with a comparison with measurements performed.A quantitative approach to assess the interaction between the electromagnetic fields and phantoms is provided and discussed in the context of dielectric resonance.Additional visual clues are provided.A detailed statistical study of the local homogeneity/inhomogeneity is performed.This makes it possible to conduct local field corrections,increasing therefore the homogeneity and consequently the sensitivity of the MRI system.
J.Slim, B B.Abu Suheil D.Hoelscher D.Heberling
Institute of High Frequency Technology,RWTH Aachen University,Germany
国际会议
Progress in Electromagnetics Research Symposium 2014(2014年电磁学研究新进展学术研讨会)
广州
英文
1623-1627
2014-08-01（万方平台首次上网日期，不代表论文的发表时间）