In vivo determination of hepatic stiffness using steady-state free precession magnetic resonance elastography

Objective: The objective of this study was to introduce an magnetic resonance elastography (MRE) protocol based on fractional motion encoding and planar wave acquisition for rapid measurements of in vivo human liver stiffness. Materials and Methods: Vibrations of a remote actuator membrane were fed by a rigid rod to the patient's surface beneath the right costal arch resulting in axial shear deflections of the liver. Data acquisition was performed using a balanced steady-state free precession (bSSFP) sequence incorporating oscillating gradients for motion sensitization. Tissue vibrations of frequency f(v) = 51 Hz were tuned by twice the sequence repetition time (1/f(v) = 2TR). Twenty axial images acquired by time-resolved through-plane wave encoding were used for planar elasticity reconstruction. The MRE data acquisition was achieved within 4 breathholds of 17 seconds each. The method was applied to 12 healthy volunteers and 2 patients with diffuse liver disease (fibrosis grade 3). Results: MIZE data acquisition was successful in all volunteers and patients. The elastic moduli were measured with values between 1.99 +/- 0. 16 and 5.77 +/- 0.88 kPa. Follow-up studies demonstrated the reproducibility of the method and revealed a difference of 0.74 +/- 0.47 kPa (P < 0.05) between the hepatic stiffness of 2 healthy male volunteers. Conclusion: bSSFP combined with fractional MRE enables rapid measurement of liver stiffness in vivo. The used actuation principle supports a 2-dimensional analysis of the strain wave field captured by axial wave images. The measured data indicate individual variations of hepatic stiffness in healthy volunteers.