GammaMRI: towards high-resolution single photon imaging using highly-polarized gamma-emitting nuclei
Dr. Karolina Kulesz (CERN, Geneve)

GammaMRI project aims to develop a new medical imaging modality able to overcome the
limitations of existing imaging techniques and to combines their advantages. Gamma-MRI
introduces the spatial resolution of MRI, the sensitivity of nuclear medicine (PET and SPECT) and
possible clinical benefits of xenon isotopes [1,2]. At the same time, it eliminates drawbacks of the
above-mentioned techniques. Our team is at present working on a proof-of-concept experiment.
Gamma-MRI is based on the detection of asymmetric γ-ray emission of long-lived polarized
nuclear states in the presence of magnetic fields [2]. The nuclei used in our study are long-lived
nuclear isomers of Xe isotopes: 129mXe (T1/2 = 9 d),131mXe (T1/2 = 12 d) and 133mXe (T1/2 = 2 d)
produced at the ILL high flux reactor in Grenoble or at ISOLDE facility at CERN [3]. The isomers
of Xe are then hyperpolarized via collisions with laser-polarized rubidium vapor (Spin Exchange
Optical Pumping) [4]. Once polarized and placed inside a magnetic field, they emit γ-rays whose
direction of emission depends on the degree of spin polarization. Emitted radiation is acquired with
CeGAAG crystals coupled to Si photodetectors and readout electronics compatible with strong
magnetic fields, which are able to support very high count-rates. Once high polarization is
successfully acquired, similar procedure can be used to record the spins’ response to rf pulses in
gradient magnetic field, which is up to 105 more sensitive than usual signal pick-up in rf coils.

References:
[1] R. Engel, Master thesis 2018, https://cds.cern.ch/record/2638538.
[2] Y. Zheng et al., Nature 537, 652 (2016).
[3] M. Kowalska et al., Letter of Intent, CERN-INTC-2017-092 / INTC-I-205 (2017).
[4] T. G. Walker and W. Happer, Rev. Mod. Phys. 69, 629 (1997).