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

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.