Introduction: RF field non-uniformities caused by shortened RF wavelengths in human tissue significantly affect the image quality, especially for high-field MRI [1]. Spiral coils [2, 3] have been put forth to improve field homogeneity. In addition, RF shimming based on a TEM coil [4] or an RF transmit array [5] is an efficient method to address such non-uniformities. In this work, we combine th...

The cardiac magnetic resonance (CMR) of children at 3.0 T presents a unique set of technical challenges because of their small cardiac anatomical structures, fast heart rates, and the limited ability to keep motionless and hold breathe, which could cause problems associated with field inhomogeneity and degrade the image quality. The aim of our study was to evaluate the effect of dual-source par...

Introduction Achieving given homogeneity and SAR constraints in RF shimming process is an important problem in high field MRI. There are different studies in the literature which dealt with the optimization of these parameters by using non-convex optimization techniques. In a previous work whole body SAR constrained RF shimming problem was solved in order to achieve whole slice transmit homogen...

PURPOSE To improve the homogeneity of transmit volume coils at high magnetic fields (> or =4 T). Due to radiofrequency (RF) field/tissue interactions at high fields, 4 T to 8 T, the transmit profile from head-sized volume coils shows a distinctive pattern with relatively strong RF magnetic field B(1) in the center of the brain. MATERIALS AND METHODS In contrast to conventional volume coils at...

In a multimodal volume coil, only one mode can generate homogeneous Radiofrequency (RF) field for Magnetic Resonance Imaging. The existence of other modes may increase the volume coil design difficulties and potentially decreases coil performance. In this study, we introduce common-mode resonator technique to high and ultrahigh field volume coil designs to reduce the resonant mode while maintai...

Introduction: Because of the inherent advantage of improved SNR, ultra-high field (3T~9.4T) MRI technology and applications have been accelerated these years. However many engineering challenges have arisen from high-operation frequencies. One major challenge is the difficulty of designing large-size RF coils with high-resonance frequencies. In addition, it has been shown that the homogeneity o...

BACKGROUND The purpose of this study was to establish the feasibility of three-dimensional (3D) balanced steady-state-free-precession (bSSFP) myocardial perfusion cardiovascular magnetic resonance (CMR) at 3T using local RF shimming with dual-source RF transmission, and to compare it with spoiled gradient echo (TGRE) acquisition. METHODS Dynamic contrast-enhanced 3D bSSFP perfusion imaging wa...

For body dimensions at 3T and head dimensions at 7T and above the RF wavelength in dielectric tissue is comparable or smaller than the dimensions of the human anatomy. This in turn leads to RF phase related traveling time differences, prominent wave behavior and the potential for a significant difference between transmit B1 + and receive B1 fields [5-10]. It is possible to correct some of the r...

Background As shown at 7T Time-of-Flight (TOF) angiography significantly benefits from ultra high field (UHF) [1,2], because of shorter T1 relaxation constant and increased SNR. However, significant challenges have to be overcome before using 7T TOF in clinical applications: I) RF induced specific absorption rate (SAR) substantially increases at UHF, preventing the use of standard RF pulses (ve...

In high and ultrahigh field magnetic resonance imaging (MRI) research, computational electromagnetic techniques are now taking an important role in the design and evaluation of MRI radiofrequency (RF) coils. This paper focuses on the RF power requirements and specific absorption rate (SAR) associated with the MRI operation at different field strength. This paper also presents new techniques for...