A quantitative study of susceptibility and additional frequency shift of three common materials in MRI.

Purpose: This work quantifies magnetic susceptibilities and additional frequency shifts derived from different samples. Methods: Twenty samples inside long straws were imaged with a multiecho susceptibility weighted imaging and analyzed with two approaches for comparisons. One approach applied our complex image summation around a spherical or cylindrical object method to phase distributions outside straws. The other approach utilized phase values inside each straw from two orientations. Both methods quantified susceptibilities of each sample at each echo time. The R-2(+) value of each sample was measured too. Uncertainty of each measurement was also estimated. Results: Quantified susceptibilities from complex image summation around a spherical or cylindrical object are consistent within uncertainties between different echo times. However, this is not the case for the other method. Nonetheless, most quantified susceptibilities are consistent between these two methods. Phase values due to additional frequency shifts in some of ferritin and nanoparticle samples have been identified. Only R-2(+) values quantified from low concentration nanoparticle samples agree with the predictions from the static dephasing theory. Conclusion: This work suggests that using the sample sizes and phase values only outside samples can correctly quantify the susceptibilities of those samples. With the presence of a possible additional frequency shift inside a material, it will not be suitable to obtain susceptibility maps without taking that into account. (V) 2015 Wiley Periodicals, Inc.