High-Power Radio Frequency Amplifier for 5-T MRI Whole-Body Scanner

Magnetic resonance imaging (MRI) at ultra-high field (UHF) requires radio-frequency power amplifiers (RFPA) with high power capability for whole-body imaging. Insufficient RF power restricts the peak transmit magnetic field (B1+) strength, thereby impeding the ability to achieve sufficient high flip angles for body imaging. This study presents an RFPA that can achieve a peak power capability of 64 kW, the highest reported value for UHF MRI systems. A novel impedance matching circuit design method was proposed to optimize the power capability of each RF transistor. The designed RFPA features an innovative transmit architecture that accommodates various applications by configuring independent transmit channels in 8-channel, 4-channel, or 2-channel modes. High gain linearity of 0.2 dB / 3.6°, 0.3 dB / 5.2°, and 0.2 dB / 4° were achieved across different operating modes. The B1+ maps and body images acquired using a 5 Tesla whole-body MRI scanner demonstrated that sufficient flip-angles for whole body imaging can be achieved with the proposed RFPA. The body images also exhibited good uniformity in contrast.