Gradient-Free Frequency Encoded MRI

Motivation: Eliminating conventional gradients can help miniaturize and lower costs of MRI significantly. No method using RF-gradients has been able to achieve frequency encoding, the fastest encoding mechanism in MRI. Goal(s): Develop a Simultaneous-Transmit-and-Receive (STAR) system and perform RF Frequency encoding using the Bloch Siegert shift. Approach: A novel injection transformer, 2MHz/47.5mT RF coil setup and pulse sequence was developed to enable STAR to prevent the RF encoding signal from overwhelming the receiver while frequency encoding MR signal without conventional gradients. Results: The novel STAR system achieved 99.75% cancellation of RF encoding signal, enabling the first-ever acquisition of frequency encoded MR images using RF-gradients. Impact: We have demonstrated, for the first time ever, frequency encoded MRI using RF field gradients in place of conventional B0 gradients. This is a fundamental requirement to make RF encoded-MR imaging as fast as conventional gradient encoding.