## 4 Discussion  
The results of Figure 3A,B show that there were different curve distributions between dilution volume percentage and image grayscale. The distribution presented the interaction between the contrast agent and the hydrogen nucleus, possibly relating to the chemical exchange saturation transfer [24; 25]. To understand the differences clearly, the statistical data of Gd-DTPA-BMEA and fervator-tran with different attributes were subjected to linear and exponential regression analysis. The volume percentage of Gd-DTPA-BMEA contrast agent with D.D. water decreased from the highest weight percentage of 2.3% to 0% pure water, with 24 dilution points in total. The results of linear regression statistical analysis showed that the coefficient of determination R\({}^{2}\) = 0.9349, with 93.49% reliability, and the grayscale of the image was negatively correlated with the dilution concentration of the contrast agent, showing a trend of linear normal probability. There was a total of 12 dilution points in the dilution ratio of iron oxide contrast agent to D.D. water, starting from the highest dilution weight percentage of 0.1% and decreasing progressively to 0.00025%. The results of exponential regression analysis showed that R\({}^{2}\) = 0.9885, with a reliability of only 98.9%, and the grayscale of the image showed an exponential distribution relationship with contrast agent dilution concentration. The results suggested that the two types of contrast agents with different properties have completely different presentation characteristics [26; 27; 28]. OptiMARK is a paramagnetic MRI contrast agent, which belongs to Gd-DTPA-BMEA metal ion chelating agent [29]. Gd\({}^{3+}\) has a large magnetic moment, which is distributed in the space of blood vessels and extracellular fluids after injection into animals, but cannot penetrate the intact BBB under normal circumstances. The statistical results in Figure 5A are consistent with the literature [30]. Figure 5A shows that although there are significant differences in grayscale numerical statistics after injection of diluted contrast agent in normal mice (***, \(p\) < 0.001), only the brain grayscale value before injection was greater than that after injection, while other values were smaller. This confirmed the result in the literature that Gd-DTPA-BMEA could not penetrate the intact BBB. Figure 5: (**A**) T1W pulse sequence imaging. (**B**) T2W pulse sequence imaging. The visualized grayscale numerical statistics of the brain, heart, liver and mesentery before and after injection of diluted paramagnetic contrast agent Gd-DTPA-BMEA and superparamagnetic contrast agent iron oxide were analyzed and compared, and one-way ANOVA grayscale statistical analysis was conducted. All \(p\) values less than 0.001 are summarized with three asterisks. oxide microparticle preparation of ferroarbotran and is a superparamagnetic contrast agent for MRI in organ-specific imaging [31]. Comparison of statistical results in Figure 5B also shows this phenomenon, i.e., the grayscale numerical statistics before injection were all higher than those after injection, especially in the liver. The results verified that the optimal dilution ratios of Gd-DTPA-BMEA and ferroarbotran contrast agents can be quantified by visualized grayscale numerical statistics and applied in in vivo experiments. Paramagnetic contrast agent Gd-DTPA-BMEA and superparamagnetic contrast agent ferucarbotran are two types of contrast agents with different properties commonly used in clinical practice. Although Gd-DTPA-BMEA and Fercarbotran contrast agents have different pharmacokinetics (PK) responses, both of them are suitable for liver indications [32]. Comparing grayscale statistics of brain, heart, liver and mesentery before and after the contrast agent injection in Figure 5, the ratios are 1.14, 0.62, 0.75 and 0.77 for Gd-DTPA-BMEA and 2.45, 4.60, 5.32 and 1.91 for iron oxide, respectively.