Clinical Cardiac MR at 3.0 Tesla using parallel RF transmission with patient-adaptive local RF shimming: initial experience

Purpose: The use of high-field MRI scanners has introduced new challenges for cardiac imaging, associated with B1- and B0-field inhomogeneities. A dual – source RF transmission system may help reduce dielectric effects, thus improving image contrast and reducing local SAR peaks of cardiac TSE and SSFP sequences, thereby allowing a shorter minimum TR and TE of SSFP sequences. Thus, the aim of our study was to evaluate the impact of dual – source parallel RF transmission with patient adaptive RF-shimming on image quality and diagnostic confidence for routine clinical CMR using a 3.0 T dual – channel transmit whole – body MRI system.

Materials and Methods: A clinical 3.0 T MRI system (Achieva 3.0T-TX, Philips Healthcare, Best, Netherlands), equipped with a dual-source RF transmission system was used. The effect of parallel RF transmission with patient adaptive B1 shimming (multi transmit=MTx) vs. conventional (single transmit=STx) RF transmission on SSFP sequences and TSE Black-Blood (TSE BB) sequences was evaluated. Images were analyzed independently by two experienced readers for homogeneity and diagnostic confidence on a 4-point grading-scale. Also, the presence of off-resonance artefacts in the SSFP images was rated on a 4-point grading scale. CNR between interventricular septum and blood pool was determined.

Results: A total of 21 patients were included into the study. For both, TSE BB and SSFP -images, the use of MTx resulted in a significant improvement of image homogeneity and diagnostic confidence in the left and right ventricle. As a side effect, off-resonance artefacts were significantly reduced in the acquired SSFP images. Interrater agreement for all ratings was very good. The quantitative measurements revealed a significant increase of CNR in the RF shimmed images using MTx compared to the images acquired with STx.((BR))Conclusions: Patient adaptive local RF-shimming using parallel dual source RF-transmission significantly improves image homogeneity, diagnostic confidence and contrast of cardiac SSFP and TSE BB sequences.