Magnetic Resonance Imaging of Hyperpolarized $^{3}{hbox {He}}$ Detected With a High-${hbox {T}}_{rm c}$ SQUID in Microtesla Magnetic Field at Laboratory Environment Fields

摘要

Nuclear magnetic resonance and imaging (NMR/MRI) of optically pumped (OP) hyperpolarized $^{3}{hbox {He}}$ were studied by using a high- ${hbox {T}}_{rm c}$ SQUID magnetometer device in microtesla magnetic fields. The OP cell was filled with a few milligrams of Rb metal, 0.0798 bar ${hbox {N}}_{2}$ gas and 0.705 bar $^{3}{hbox {He}}$ gas. The $^{3}{hbox {He}}$ cell had been hyperpolarized at an optical pumping system for 5 $sim$ 6 hours first; then it was moved to the SQUID-detected nuclear magnetic resonance and imaging system to measure. An appropriate ${rm B}_{1}$ pulse level and time duration generated a 5$^{circ}$ low flip angle of polarization. The free induction decay NMR signals were measured. The spin-lattice relaxation time $({hbox {T}}_{1})$ of $^{3}{hbox {He}}$ was 4.7 hours. We improved the line width of NMR spectrum to 0.8 Hz by compensating the inhomogeneous gradient field of environment. The filtered back projection image of hyperpolarized $^{3}{hbox {He}}$ could show a clear image in one shot. The SQUID-detected NMR/MRI would be a great interest for biological imaging.