Category Archives: Overhauser MRI

Dynamic nuclear polarisation of liquids at one microtesla using circularly polarised RF with application to millimetre resolution MRI

Hilschenz, Ingo, Sangwon Oh, Seong-Joo Lee, Kwon Kyu Yu, Seong-min Hwang, Kiwoong Kim, and Jeong Hyun Shim. “Dynamic Nuclear Polarisation of Liquids at One Microtesla Using Circularly Polarised RF with Application to Millimetre Resolution MRI.” Journal of Magnetic Resonance 305 (August 2019): 138–45.

Magnetic resonance imaging in ultra-low fields is often limited by mediocre signal-to-noise ratio hindering a higher resolution. Overhauser dynamic nuclear polarisation (O-DNP) using nitroxide radicals has been an efficient solution for enhancing the thermal nuclear polarisation. However, the concurrence of positive and negative polarisation enhancements arises in ultra-low fields resulting in a significantly reduced net enhancement, making O-DNP far less attractive. Here, we address this issue by applying circularly polarised RF. O-DNP with circularly polarised RF renders a considerably improved enhancement factor of around 150,000 at 1.2 lT. A birdcage coil was adopted into an ultra-low field MRI system to generate the circularly polarised RF field homogeneously over a large volume. We acquired an MR image of a nitroxide radical solution with an average in-plane resolution of 1 mm. De-noising through compressive sensing further improved the image quality.

Oxygen-induced leakage of spin polarization in Overhauser-enhanced magnetic resonance imaging: Application for oximetry in tumors #DNPNMR

Gorodetskii, Artem A., Timothy D. Eubank, Benoit Driesschaert, Martin Poncelet, Emily Ellis, Valery V. Khramtsov, and Andrey A. Bobko. “Oxygen-Induced Leakage of Spin Polarization in Overhauser-Enhanced Magnetic Resonance Imaging: Application for Oximetry in Tumors.” Journal of Magnetic Resonance 297 (December 2018): 42–50.

Overhauser-enhanced Magnetic Resonance Imaging (OMRI) is a double resonance technique applied for oxygen imaging in aqueous samples and biological tissues. In this report, we present an improved OMRI approach of oxygen measurement using the single line ‘‘Finland” trityl spin probe. Compared to a traditional approach, we introduced an additional mechanism of leakage of spin polarization due to an interaction of a spin system with oxygen. The experimental comparison of the new approach with an oxygendependent leakage factor to a traditional approach performed in phantom samples in vitro, and mouse tumor model in vivo, shows improved accuracy of determination of oxygen and contrast agent concentrations.

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