ABSTRACT
Objective To investigate the potential values of magnetic resonance elastography (MRE)for evaluating the brain tumor consistency in vivo.Methods Fourteen patients with known solid brain tumor(5 male,9 female;age range:16-63 years)underwent brain MRE studies.Informed consent was obtained from all patients.A dedicated external force actuator for brain MRE study Was developed.The actuator was fixed to the head coil.During scan.one side of the actuator was attached to the patients'head.Low frequency oscillation Was produced by the actuator and caused shear waves propagating into brain tissue.The pulse sequence used in the study Writs phase-contrast gradient-echo sequence.Phase images of the brain were obtained and the shear waves within the brain were directly imaged.Phase images were processed with local frequency estimation (LFE) technique to obtain the elasticity image.Consistency of brain tumors Was evaluated at surgery and Was classified as soft,intermediate,or hard with comparison to the white matter of the brain.Correspondence of MRE evaluation with operative results was studied.Results The elastic modulus of the tumor Was lower than that of white matter in 1 patient,higher inll patients,and similar in 2 patients.At surgery,the tumor manifested a soft consistency in I patient,hard consistency in 11 patients,intermediate consistency in 2 patients.The elasticity of tumors in 14 patients evaluated by MRE was correlated with the tumor consistency on the operation.Conclusion MRE Can noninvasively display the elasticity of brain tumors in vivo,and evaluate the brain tumor consistency before operation.
ABSTRACT
Objective: To study magnetic resonance elastography (MRE) technique. Methods: An external force actuator was developed, the imaging pulse sequence of MRE was designed,and tissue simulating phantoms were constructed. The actuator controlled by the pulse sepuence produced shear waves at low frequency on the surface of the phantoms. A modified gradient echo sequence was developed with motion sensitizing gradient (MSG)imposed along X,Y or Z direction.Cyclic displacement within the medium induced by shear waves caused a measurable phase shift in the received MR signal.From the measured phase shift,the displacement at each voxel could be calculated,and the propatating shear waves within the medium were directly imaged. By adjusting the phase offsets,the dynamic propagation of shear waves in a wave cycle was obtained.The phase images were processed to aquire quantitative elasticity image using local frequency estimation(LFE)method. The experiments were implemented with 1.0% and 1.5% tissue simulating agarose gel. Shear waves at frequency of 150 Hz,200 Hz,250 Hz,and 300 Hz were applied. Results: The phase images of MRE directly imaged the propagating shear waves within the phantoms.The wavelength of shear waves varied with the change of exciting frequency and stiffness of the phantoms. The wavelength of shear waves was exactly proportional to the frequency and stiffness of the phantom. The contrast of elasticity in agarose gel with two concentrations was clearly demonstrated on elasticity images.Conclusion: The phase images of MRE can directly visualize the propagation of shear waves in the medium. The elasticity image of MRE can quantitatively image the elastic modulus of the medium