Calibration of RF transmitter voltages for hyperpolarized gas MRI

Abstract

MRI with hyperpolarized gases, 3He, 129Xe, 13C, and others, has the potential to become an important diagnostic technique for clinical imaging. Due to the nonreversible loss of magnetization in hyperpolarized gas imaging, the choice of the flip angle is a major factor that influences the signal intensity, and hence, the signal-to-noise ratio. Conventional automated radiofrequency (RF) calibration procedures for 1H imaging are not suitable for hyperpolarized gas imaging. Herein, we have demonstrated a simple procedure for RF calibration for magnetic resonance imaging (MRI) with hyperpolarized gases that is easily adaptable to clinical settings. We have demonstrated that there exists a linear relationship between the RF transmitter voltages required to obtain the same nutation angle for protons (V1H) and hyperpolarized gas nuclei (V3He). For our 1H and 3He coils we found that V3He = 1.937 V1H with correlation coefficient r2 = 0.97. This calibration can be done as a one-time procedure during the routine quality assurance (QA) protocol. The proposed procedure was found to be extremely robust in routine scanning and provided an efficient method to achieve a desired flip angle, thus allowing optimum image quality. © 2008 Wiley-Liss, Inc.