SQUID-detected microtesla MRI: a new modality for tumor detection?

We are investigating the use of low-field magnetic resonance imaging with enhanced longitudinal-relaxation-time (T$_{1})$-weighted contrast to detect tumors. Our technique involves prepolarizing the sample in a magnetic field up to 0.3 T and detecting the nuclear magnetic resonance (NMR) signal at microtesla fields using a superconducting quantum interference device. This technique enables us to obtain T$_{1}$ dispersion curves and T$_{1}$-weighted contrast images in fields from 1.4 $\mu $T to 0.3 T. We have shown that for materials such as agarose gel the T$_{1}$-weighted contrast is greatly enhanced in microtesla fields. To investigate the use of this enhancement for tumor imaging we measured the T$_{1}$ relaxation times of healthy and cancerous tissue specimens, maintained at 4\r{ }C, shortly after their surgical removal. To minimize artifacts we measured normal and cancerous tissues simultaneously and separated their NMR signals by applying a magnetic field gradient. We present T$_{1}$ dispersion curves for several sets of samples, and discuss the applicability of this technique to \textit{in vivo} imaging. Work supported by USDOE.