++ =+ = , during the optimization, both the magnitude 1 || B + and phase φ are weighted differently in the target function for different frequencies/coils. We note that in this investigation, all the rung currents, including the empty case, are determined via the STIR method, instead of using any predefined values [7]. Simulations Using the STIR optimization algorithm, the source profiles of the birdcage coils can be determined within two minutes on a 3-GHz PC. Fig.2 shows comparative results in terms of B1 field distribution before and after the optimization. The results clearly indicate that the optimization is quite capable of improving the uniformity of the RF field. About 85% of the B1-inhomogeneity caused by loading effects can be compensated for by optimizing the rung drives. Discussions In this preliminary study, we restrict ourselves to 2D scenarios [10], but the formalism can be easily adapted to other situations including 3D volume resonators and phased array systems. Optimal RF pulse modulation schemes are also being investigated for use with these structures. In addition, the algorithm is being applied to transceiver phased-array coils. It is hoped that theses studies will offer insight into coil design and/or useful imaging schemes for high field MRI.

An object-oriented finite-difference time-domain (FDTD) simulator has been developed for electromagnetic study and design applications in Magnetic Resonance Imaging. It is aimed to be a complete FDTD model of an MRI system including all high and low-frequency field generating units and electrical models of the patient. The design method is described and MRI-based numerical examples are presented to illustrate the function of the numerical solver, particular emphasis is placed on high field studies.

In this paper we present a system for the automatic segmentation of the left ventricle (LV) of the heart from breath hold MRI images with subsequent ejection fraction (EF) calculations. The ventricular luminal contours in short and long-axis slices are enhanced with morphological image processing methods and extracted using a novel Global Optimal Closed Path algorithm. In this study, contours both including and excluding LV trabeculations and papillary muscles are considered. Ventricular 3D-reconstructions are based on the use of both short-axis and long-axis contours, with the long-axis contours also being used as an internal skeleton template of the LV to correct for through plane motion. A series of volumes of the reconstructed 3D ventricle is evaluated at different times during the cycle and the EF calculated. By comparing our numerical results with those derived from manual segmentations on eight normal subjects, we conclude that the automated system performance is reliable and consistent.

In this paper we present an algorithm as the combination of a low level morphological operation and model based global circular shortest path scheme to explore the segmentation of the right ventricle. Traditional morphological operations were employed to obtain the region of interest, and adjust it to generate a mask. The image cropped by the mask is then partitioned into a few overlapping regions. Global circular shortest path algorithm is then applied to extract the contour from each partition. The final step is to re-assemble the partitions to create the whole contour. The technique is deemed quite reliable and robust, as this is illustrated by a very good agreement between the extracted contour and the expert manual drawing output

We have recently introduced the concept of whole-body asymmetric MRI systems. In this theoretical study, we investigate the PNS characteristics of whole-body asymmetric gradient systems as compared to conventional symmetric systems. Recent experimental evidence supports the hypothesis of transverse gradients being the largest contributor of PNS due to induced electric currents. Asymmetric head gradient coils have demonstrated benefits in the past. The numerical results are based on an anatomically-accurate 2mm-human voxel-phantom NORMAN. The results of this study can facilitate the optimization of whole-body asymmetric gradients in terms of patient comfort/safety (less PNS), while prospering the use of asymmetric MRI systems for in-vivo medical interventions

A. Trakic, F. Liu, S. Crozier School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Queensland, Australia Synopsis We have recently introduced the concept of whole-body asymmetric MRI systems [1]. In this theoretical study, we investigate the PNS characteristics of whole-body asymmetric gradient systems as compared to conventional symmetric systems. Recent experimental evidence [2] supports the hypothesis of transverse gradients being the largest contributor of PNS due to induced electric currents. Asymmetric head gradient coils have demonstrated benefits in the past [3, 4]. The numerical results based on an anatomically-accurate 2mm-human voxel-phantom NORMAN [6], show that asymmetric y-gradient is superior, in terms of reduced field induction, to its symmetric counterpart for typical patient orientations within the coil.

A finite-difference time-domain (FDTD) thermal model has been developed to compute the temperature elevation in the Sprague Dawley rat due to electromagnetic energy deposition in high-field magnetic resonance imaging (MRI). The field strengths examined ranged from 11.75–23.5 T (corresponding to 1H resonances of 0.5–1 GHz) and an N-stub birdcage resonator was used to both transmit radio-frequency energy and receive the MRI signals. With an in-plane resolution of 1.95 mm, the inhomogeneous rat phantom forms a segmented model of 12 different tissue types, each having its electrical and thermal parameters assigned. The steady-state temperature distribution was calculated using a Pennes ‘bioheat’ approach. The numerical algorithm used to calculate the induced temperature distribution has been successfully validated against analytical solutions in the form of simplified spherical models with electrical and thermal properties of rat muscle. As well as assisting with the design of MRI experiments and apparatus, the numerical procedures developed in this study could help in future research and design of tumour-treating hyperthermia applicators to be used on rats in vivo.