Modality for estimating NMR relaxation time using perturbed angular correlation in double-photon emission nuclides

Abstract

T2 relaxation time in magnetic resonance imaging (MRI), which is determined by magnetic dipole interactions, has been employed as a parameter for tumor detection. However, owing to the lack of MRI detection sensitivity, nuclear medicine imaging is currently the basic option for tracking low concentrations of chemical probes. Previous studies utilizing cascade radionuclides have focused on the relaxation due to electric quadrupole interactions. However, magnetic dipole interactions, which are crucial in MRI, remains to be elucidated. In this study, we determined the magnetic relaxation rate by using 111In, a cascade radionuclide used in clinical single-photon emission computed tomography (SPECT) scans. As the angle between the gamma rays from the nuclei is affected by the electrical and magnetic interactions acting on the nuclei, we measured the angular correlation ratio by using eight gadolinium gallium garnet (GAGG) multi-pixel photon counter (MPPC) 8 × 8 array detectors and extracted the magnetic relaxation rate. Consequently, we obtained a rate that increased with the Fe concentration, similar to the T2 relaxation rate, although it was influenced by the inhomogeneity of the external magnetic field. This study utilized low concentrations of the liquid-state radionuclide, which is commonly used in clinical nuclear medicine imaging scans and is expected to provide much higher sensitivity and more selective detection of tumors than conventional MRI.