Soy lecithin: A beneficial substance for adjusting the ADC in aqueous solutions to the values of biological tissues

Abstract

To test soy lecithin as a substance added to water for the construction of MRI phantoms with tissue-like diffusion coefficients. The performance of soy lecithin was assessed for the useable range of adjustable ADC values, the degree of non-Gaussian diffusion, simultaneous effects on relaxation times, and spectral signal properties.Methods: Aqueous soy lecithin solutions of different concentrations (0%, 0.5%, 1%, 2%, 3% … , 10%) and soy lecithin-agar gels were prepared and examined on a 3 Tesla clinical scanner at 18.5 • ± 0.5 • C. Echoplanar sequences (b values: 0-1000/3000 s/mm 2 ) were applied for ADC measurements. Quantitative relaxometry and MRS were performed for assessment of T 1 , T 2 , and detectable spectral components. Results:The presence of soy lecithin significantly restricts the diffusion of water molecules and mimics the nearly Gaussian nature of diffusion observed in tissue (for b values <1000 s/mm 2 ). ADC values ranged from 2.02 × 10 −3 mm 2 /s to 0.48 × 10 −3 mm 2 /s and cover the entire physiological range reported on biological tissue. Measured T 1 /T 2 values of pure lecithin solutions varied from 2685/2013 to 668/133 ms with increasing concentration. No characteristic signals of soy lecithin were observed in the MR spectrum. The addition of agar to the soy lecithin solutions allowed T 2 values to be well adjusted to typical values found in parenchymal tissue without affecting the soy lecithin-controlled ADC value. Conclusion:Soy lecithin is a promising substance for the construction of diffusion phantoms with tissue-like ADC values. It provides several advantages over previously proposed substances, in particular a wide range of adjustable ADC values, the lack of additional 1 H-signals, and the possibility to adjust ADC and T 2 values (by adding agar) almost independently of each other.