2.4. Low-Field Nuclear Magnetic Resonance (LF-NMR) and Magnetic Resonance Imaging (MRI)

The water distribution and states of large yellow croakers were determined by a MesoMR23-060H.I LF-NMR analyzer (Niumag Corporation, Shanghai, China) according to a previously described method [13,14]. Thawed samples (2.0 cm × 2.0 cm × 1.0 cm) were taken from the dorsal muscles of the croaker, dried to remove surface water, and wrapped with fresh-keeping film. Each sample was examined in a 70 mm diameter cylindrical probe with a working temperature of 32 °C. Acquisition parameters were as follows: receiver bandwidth frequency (SW) = 100 kHz; analog gain (RG1) = 20.0 dp; P1 = 19.00 μs; digital gain (DRG1) = 6; TD = 400,068; preamplifier gain (PRG) = 1; duration between successive scans (TW) = 2000 ms; number of the scans (NS) = 4; P2 = 38.00 μs; time echo (TE) = 0.500 ms; and NECH = 8000. The MRI imaging software and MSE spin-echo imaging sequence acquisition were used to generate the proton density weighted images of the samples.