Dual-Source Parallel Radiofrequency Excitation Body MR Imaging Compared with Standard MR Imaging at 3.0 T: Initial Clinical Experience

Abstract

To prospectively compare the image quality and homogeneity of magnetic resonance (MR) images obtained by using a dual-source parallel radiofrequency (RF) excitation body MR imaging system with parallel transmission and independent RF shimming with the image quality and homogeneity of single-source MR images obtained by using standard sequences for routine clinical use in patients at 3.0 T. After institutional review board approval and informed patient consent were obtained, a dual-source parallel RF excitation 3.0-T MR system with independent RF shimming and parallel transmission technology was used to examine 28 patients and was compared with a standard 3.0-T MR system with single RF transmission. The RF power was distributed to the independent ports of the system body coil by using two RF transmission sources with full software control, enabling independent control of the phase and amplitude of the RF waveforms. Axial T2-weighted fast spin-echo (SE) and diffusion-weighted (DW) liver images, axial T2-weighted fast SE pelvic images, and sagittal T1- and T2-weighted fast SE spinal images were obtained by using dual- and single-source RF excitation. Two radiologists independently evaluated the images for homogeneity and image quality. Statistical significance was calculated by using the nonparametric Wilcoxon signed rank test. Interobserver agreement was determined by using Cohen kappa and Kendall tau-b tests. Image quality comparisons revealed significantly better results with dual-source rather than single-source RF excitation at T2-weighted liver MR imaging (P = .001, kappa = 1.00) and better results at DW liver imaging at a statistical trend level (P = .066, tau-b > 0.7). Owing to reduced local energy deposition, fewer acquisitions and shorter repetition times could be implemented with dual-source RF excitation pelvic and spinal MR imaging, with image acquisition accelerating by 18%, 33%, and 50% compared with the acquisitions with single-source RF excitation. Image quality did not differ significantly between the two MR techniques (P > .05, tau-b > 0.5). Dual-source parallel RF excitation body MR imaging enables reduced dielectric shading, improved homogeneity of the RF magnetic induction field, and accelerated imaging at 3.0 T.