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

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Abstract
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.