A 16-Channel Receive, Forced Current Excitation Dual-Transmit Coil for Breast Imaging at 7T

Abstract

Purpose To enable high spatial and temporal breast imaging resolution via combined use of high field MRI, array coils, and forced current excitation (FCE) multi channel transmit. Materials and Methods A unilateral 16-channel receive array insert was designed for use in a transmit volume coil optimized for quadrature operation with dual-transmit RF shimming at 7T. Signal-to-noise ratio (SNR) maps, g-factor maps, and high spatial and temporal resolution in vivo images were acquired to demonstrate the utility of the coil architecture. Results The dual-transmit FCE coil provided homogeneous excitation and the array provided an increase in average SNR of 3.3 times (max 10.8, min 1.5) compared to the volume coil in transmit/receive mode. High resolution accelerated in vivo breast imaging demonstrated the ability to achieve isotropic spatial resolution of 0.5 mm within clinically relevant 90 s scan times, as well as the ability to perform 1.0 mm isotropic resolution imaging, 7 s per dynamics, with the use of bidirectional SENSE acceleration of up to R = 9. Conclusion The FCE design of the transmit coil easily accommodates the addition of a sixteen channel array coil. The improved spatial and temporal resolution provided by the high-field array coil with FCE dual-channel transmit will ultimately be beneficial in lesion detection and characterization.

Homogeneous B1+ for bilateral breast imaging at 7 T using a five dipole transmit array merged with a high density receive loop array

“…A homogeneous B 1 + field is particularly important for MR sequences such as turbo spin echo (TSE), which can still not compete with the clinical standard at 3 T . One approach to overcome B 1 inhomogeneity is forced current excitation as demonstrated in previous studies . Another approach is the use of a multi‐transmit setup where RF shimming can be used to improve transmit uniformity for every subject …”

“…still not compete with the clinical standard at 3 T. 4 One approach to overcome B 1 inhomogeneity is forced current excitation as demonstrated in previous studies. [5][6][7] Another approach is the use of a multi-transmit setup where RF shimming can be used to improve transmit uniformity for every subject. 1,8 A wide variety of breast MRI studies at 7 T have been presented with various RF coil setups.…”

A 32‐channel receive array coil for bilateral breast imaging and spectroscopy at 7T

“…The remaining parts of the coil (including the integrated balun, bias tee, and biasing signal) were kept consistent with previous designs that simplified the coil active-detuning network. 21,22,24 The volume coil dimensions and simplified version of the FCE configuration are shown in Figure 1A.…”

“…Size and placement of each element on the bilateral 32-channel receive array was based on the design of the previously reported unilateral 16-channel receive array, which used the "soccer-ball" configuration presented by Wiggins et al 22,26 The coil former for each breast was a hemispherical 3D-printed shell with a volume of 900 mL, designed to accommodate approximately 80% of the general female population. 27 Extruded cuts on the outer surface of the shell were designed to hold each element and passive detuning trap in place.…”

Improved fat suppression of the breast using discretized frequency shimming

“…However, magnetic field distortions in both breasts cannot be completely removed, even with the availability of third-order B 0 shimming, available on most 7T systems (16). Fortunately, the development of hardware for breast MRI at 7 T is an active field of research (17)(18)(19)(20)(21)(22). Although not widely available, recently developed 7T breast coils can make use of the possibilities that parallel transmit systems provide (ie, the transmitter for each breast is connected to a separate RF amplifier) (18).…”