%0 Journal Article %J Journal of Magnetic Resonance %D 2006 %T SQUID-detected microtesla MRI in the presence of metal %A Mossle, M. %A Han, S. I. %A Myers, W. R. %A Lee, S. K. %A Kelso, N. %A Hatridge, M. %A Pines, A. %A Clarke, J. %K nmr %X

In magnetic resonance imaging performed at fields of I T and above, the presence of a metal insert can distort the image because of susceptibility differences within the sample and modification of the radiofrequency fields by screening currents. Furthermore, it is not feasible to perform nuclear magnetic resonance (NMR) spectroscopy or acquire a magnetic resonance image if the sample is enclosed in a metal container. Both problems can be overcome by substantially lowering the NMR frequency. Using a microtesla imaging system operating at 2.8 kHz, with a superconducting quantum interference device as the signal detector, we have obtained distortion-free images of a phantom containing a titanium bar and three-dimensional images of an object enclosed in an aluminum can; in both cases high-field images are inaccessible. (c) 2005 Elsevier Inc. All rights reserved.

%B Journal of Magnetic Resonance %V 179 %P 146-151 %8 Mar %@ 1090-7807 %G English %U ://WOS:000236977600019 %N 1 %M WOS:000236977600019 %! SQUID-detected microtesla MRI in the presence of metal %R Doi 10.1016/J.Jmr.2005.11.005 %0 Journal Article %J Ieee Transactions on Applied Superconductivity %D 2005 %T SQUID-detected in vivo MRI at microtesla magnetic fields %A Mossle, M. %A Myers, W. R. %A Lee, S. K. %A Kelso, N. %A Hatridge, M. %A Pines, A. %A Clarke, J. %K nmr %X

We use a low transition temperature (T(c)) Super-conducting Quantum Interference Device (SQUID) to perform in vivo magnetic resonance imaging (MRI) at magnetic fields around 100 microtesla, corresponding to proton Larmor frequencies of about 5 kHz. In such low fields, broadening of the nuclear magnetic resonance lines due to inhomogeneous magnetic fields and susceptibility variations of the sample are minimized, enabling us to obtain high quality images. To reduce environmental noise the signal is detected by a second-order gradiometer, coupled to the SQUID, and the experiment is surrounded by a 3-mm thick Al shield. To increase the signal-to-noise ratio (SNR), we prepolarize the samples in a field up to 100 mT. Three-dimensional images are acquired in less than 6 minutes with a standard spin-echo phase-encoding sequence. Using encoding gradients of similar to 100 mu T/m we obtain three-dimensional images of bell peppers with a resolution of 2 x 2 x 8 mm(3). Our system is ideally suited to acquiring images of small, peripheral parts of the human body such as hands and arms. In vivo images of an arm, acquired at 132 mu T, show 24-mm sections of the forearm with a resolution of 3 x 3 mm(2). and a SNR of 10. We discuss possible applications of MRI at these low magnetic fields.

%B Ieee Transactions on Applied Superconductivity %V 15 %P 757-760 %8 Jun %@ 1051-8223 %G English %U ://WOS:000229765300170 %N 2 %M WOS:000229765300170 %! SQUID-detected in vivo MRI at microtesla magnetic fields %R Doi 10.1109/Tasc.2005.850043