High-'& SQUIDs for Low-Field NMR and MRI of Room Temperature Samples

Abstruct-he have constructed a high-T, SQUID spectrometer to detect NMR signals from samples at room temperature in magnetic fields up to 3 mT. The multiloop SQUID magnetometer has a system noise of about 30 ff/Hz'" at the relevant frequencies of 2 to 100 kHz. The magnetometer is operated in vacuum at 77 K, and is separated from the sample, which is less than 1.5 mm away, by a sapphire window. In a magnetic field of 2 mT we can detect the proton spin echo at 86 kHz without signal averaging. This sensitivity enables us to obtain one-dimensional images. In addition, we present data on hyperpolarized *'%e, which has an optically pumped polarization of several percent.