Implementation of the QRAPMASTER data analysis using dictionary matching and quantitative evaluation of the magnetization transfer effect

Abstract

PurposeTo clarify the magnetization transfer (MT) effect on T1 and T2 values obtained with the QRAPMASTER sequence. MethodsA phantom consisting of MnCl2 aqueous solution with various proton relaxation times and a chicken breast sample was imaged with the QRAPMASTER sequence and a multislice multiple spin-echo (MSMSE) sequence that was the basis of the QRAPMASTER sequence using a 1.5 T MRI system. T1 values were calculated by data matching using the dictionary dataset created by a Bloch image simulation of the QRAPMASTER sequence. T2 values were calculated by data matching using the dictionary dataset created by a Bloch image simulation of the MSMSE sequence. The MT effect on the images acquired with the QRAPMASTER and MSMSE sequences was calculated by numerically solving Bloch equations using a two-pool model. ResultsThe linearity and accuracy of the regression lines between the T1 values measured by the QRAPMASTER sequence and those measured by the standard method excluding the T1 values of the chicken breast sample was excellent (R = 0.9969–0.9986, slope = 1.0065–1.016) for consecutive four slices including the central slice. The linearity of the regression lines for the T2 values of all samples was good (R = 0.963–0.985) for the four slices. The accuracy of the regression line was not good (slope = 0.674–0.758), which was mainly due to the effect of eddy currents. The large deviation of the T1 values of the chicken breast sample from the regression line was semi-quantitatively reproduced by the Bloch simulation for the two-pool model. ConclusionThis study demonstrated that the T1 value of a biological sample obtained by the QRAPMASTER sequence was shortened by the MT effect.