Low field nuclear magnetic resonance (NMR) presents a unique opportunity for adaptation into medical and industrial applications. Low field (B0 < 1 T) systems present the advantage of being small and low cost. While low field NMR presents challenges, such as lower signal to noise ratios (SNR), it offers the portability and functionality to be used for applications outside the normal laboratory and clinical environment. As low field NMR moves to less controlled environments, a thorough understanding of the behavior of certain materials is vital. Well-studied materials can be used as references to ensure a system is functioning properly when used in nonideal environments. Previous work has focused on characterizing, with high precision, arrays of NiCl2 and MnCl2 solutions at clinical fields (1.5 T and 3 T), for use as an MRI reference object. The NiCl2 array consisted fourteen solutions with T1 values ranging from 80 ms to 2500 ms and T2 values ranging from 5 ms to 600 ms, while the T1 and T2 values measured for the fourteen component MnCl2 array ranged from 20 ms to 2000 ms (T1) and 15 ms to 1500 ms (T2) [1]. This work expands the characterization of the NiCl2 and MnCl2 solutions to low field strengths. T1 and T2 relaxation times are measured, using two variable field electromagnets, at field strengths of 6.5 mT, 30 mT, 64 mT, and 0.55 T. The field strengths being studied were chosen based on the growing number of low field systems being developed and deployed worldwide. We investigate the dependence of T1 and T2 relaxation times on both field strength and temperature using a custom RF probe. The probe was specifically designed so that the sample and solenoid RF coil are housed in a fully contained fluorinert system that allows for temperature control. 1H relaxation values are measured via T1 inversion recovery and T2 Carr Purcell Meiboom Gill experiments for temperatures ranging from 10 ̊C to 50 ̊C. The data presented aims to provide low field reference data that can be used for technique development of applications in the continually growing low field regime. [1] Stupic KF, Ainslie M, Boss, MA, et al. A standard system phantom for magnetic resonance imaging. Mag Reson Med. 2021. https://doi.org/10.1002/mrm.28779
