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A method for imaging and spectroscopy using γ-rays and magnetic resonance


Magnetic resonance imaging (MRI) provides fine spatial resolution, spectral sensitivity and a rich variety of contrast mechanisms for diagnostic medical applications1,2. Nuclear imaging using γ-ray cameras offers the benefits of using small quantities of radioactive tracers that seek specific targets of interest within the body3. Here we describe an imaging and spectroscopic modality that combines favourable aspects of both approaches. Spatial information is encoded into the spin orientations of tiny amounts of a polarized radioactive tracer using pulses of both radio-frequency electromagnetic radiation and magnetic-field gradients, as in MRI. However, rather than detecting weak radio-frequency signals, imaging information is obtained through the detection of γ-rays. A single γ-ray detector can be used to acquire an image; no γ-ray camera is needed. We demonstrate the feasibility of our technique by producing images and spectra from a glass cell containing only about 4 × 1013 atoms (about 1 millicurie) of the metastable isomer 131mXe that were polarized using the laser technique of spin-exchange optical pumping4. If the cell had instead been filled with water and imaged using conventional MRI, then it would have contained more than 1024 water molecules. The high sensitivity of our modality expands the breadth of applications of magnetic resonance, and could lead to a new class of radioactive tracers.

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Figure 1: Example of polarized nuclear imaging.
Figure 2: Directional emission of 164-keV γ-rays from 131mXe nuclei.
Figure 3: Experimental apparatus and imaging pulse sequence.
Figure 4: Examples of polarized nuclear spectroscopy.


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This work was supported by The Ivy Biomedical Innovation Fund at the University of Virginia, and we are grateful to the Ivy Foundation for its support of this programme. We also thank J. Brookeman for early financial support and R. Bryant (both from the University of Virginia) for conversations, and M. Souza of Princeton University for glass-blowing. G.D.C. acknowledges support from the US Department of Energy, Office of Science, Office of Nuclear Physics under contract no. DE-FG02-01ER41168.

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Authors and Affiliations



The experiments were conceived by G.D.C. and G.W.M. as well as Y.Z. All authors contributed to developing the experimental methods, discussing the results, and contributed to the writing of the manuscript. Most of the data were obtained and analysed by Y.Z.

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Correspondence to Gordon D. Cates.

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The authors declare no competing financial interests.

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Nature thanks P. Berthault and R. Bowtell for their contribution to the peer review of this work.

Extended data figures and tables

Extended Data Figure 1 Apparent motional narrowing in frequency spectra from Rabi oscillations.

ac, Spectra obtained from the ‘middle’ cell representing the Fourier amplitudes of Rabi oscillations under three conditions corresponding to maximum RF field homogeneity (a), a somewhat inhomogeneous RF field (b) and an even greater RF field inhomogeneity (c). RF field inhomogeneity was increased by increasing the separation of the RF coil pair, which is normally in a Helmholtz configuration. The measurements in b and c were acquired after lowering the bottom coil by 1 and 2 inches, respectively, without moving the upper coil or the sample. The splitting that is clearly visible in a gets progressively less pronounced in b and c. This result is consistent with the phenomenon of motional narrowing, but not with the hypothesis that the splitting was due to magnetic field inhomogeneities.

Extended Data Figure 2 Example of k-space data from polarized nuclear imaging of the ‘middle’ cell.

a, b, Images showing the amplitudes (in arbitrary units) of the real (a) and the imaginary (b) parts of the k-space data matrix obtained from the longitudinal detector, resulting from one complete set of imaging data. The data shown were used to produce the image shown in Extended Data Fig. 3a.

Extended Data Figure 3 Images of the ‘middle’ cell from individual detectors.

Each image represents two complete averages. a, The image from the longitudinal detector, with the highest analysing power; b, c, the images from the two transverse detectors (see Fig. 3a). The image in b is from the transverse detector pointing at the sample from the left, and c is from the detector pointing at the sample from the right.

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Zheng, Y., Miller, G., Tobias, W. et al. A method for imaging and spectroscopy using γ-rays and magnetic resonance. Nature 537, 652–655 (2016).

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