Design of a Coil System for Hyperpolarized 3He Human Lung Imaging

Introduction: Clinic hyperpolarized He gas human lung imaging has been widely conducted in recent years. Multi-channel coil designed for human lung parallel imaging has been reported [1] to accelerate the imaging speed. Large asymmetric birdcage coil were also developed to replace the single loop coil for better B1 homogeneity [2]. This work presents a design of a coil system for hyperpolarized He gas human lung imaging that consists of a large asymmetric quadrature birdcage transmit coil and a receive coil array. The birdcage transmit coil occupies nearly the entire scanner bore for maximum patient comfort. Methods: The non-circular asymmetric profile coil was designed using the conformal transformation [3,4]. The circular coordinates z=r*exp(-iφ) was transformed into a non-circular profile, w=f(z), while still maintaining the homogeneity of the B1 field inside the coil volume. The overall dimension of the designed coil is W=58cm, H=43cm and L=65cm in order to fill the bore volume and cover the upper airway (the throat) and entire lung. The birdcage coil was designed as a 16-rung high pass coil (figure 1a). The open and unshield transmit coil provides ability of proton anatomy scanning without petiant movement. The end-ring frame structure is designed to split into top and bottom parts for easy patient access. To determine the capacitor value on the endring, the inductance and mutual inductance of each segment was calculated with empirical formula [5] with the consideration of the MRI scanner body coil RF shield and image current (figure 2a) [6]. The inductance and mutual inductance was also calculated by modeling with HFSS (Ansoft) (figure 2b) as well as to measure on the actual coil frame [7].