SQUID‐detected MRI at 132 μT with T1‐weighted contrast established at 10 μT–300 mT

T1-weighted contrast MRI with prepolarization was detected with a superconducting quantum interference device (SQUID). A spin evolution period in a variable field between prepolarization and detection enabled the measurement of T1 in fields between 1.7 μT and 300 mT; T1 dispersion curves of agarose gel samples over five decades in frequency were obtained. SQUID detection at 5.6 kHz drastically reduces the field homogeneity requirements compared to conventional field-cycling methods using Faraday coil detection. This allows T1 dispersion measurements to be easily combined with MRI, so that T1 in a wide range of fields can be used for tissue contrast. Images of gel phantoms with T1-weighted contrast at four different fields between 10 μT and 300 mT demonstrated dramatic contrast enhancement in low fields. A modified inversion recovery technique further enhanced the contrast by selectively suppressing the signal contribution for a specific value of the low-field T1. Magn Reson Med 53:9–14, 2005. Published 2004 Wiley-Liss, Inc.