Optimization of external driver amplitude in magnetic resonance elastography of the liver. Relationship between appropriate external driver amplitude and indicators of physical constitution

Magnetic resonance elastography (MRE) of the liver was performed to examine the appropriate external driver amplitude according to the physique of the subject and the index useful for determining the physique. For 60 subjects who underwent MRE examination, we measured the unmeasurable elastic modulus area in the liver based on the stiffness map obtained from MRE. The external driver amplitude with the smallest unmeasurable elastic modulus area was taken as the appropriate external driver amplitude for the subject. The receiver operating characteristic (ROC) analysis was performed on the indicators of physical constitution (abdominal depth, waist circumference, body weight and body mass index (BMI)) and external driver amplitude of 30%, 50% and 70%. BMI was the most appropriate tool for the comparison of indicators of physical constitution. The appropriate external driver amplitude was 30% when the cutoff value of BMI was less than 25.3 kg/m², 70% when it was 31.0 kg/m² or more, and 50% when it was between them. It is considered that an accurate elastic modulus can be obtained by setting an appropriate indicator of physical constitution and external driver amplitude according to physique in MRE. (author)