Abstract
Background. Magnetic resonance elastography (MRE) is used to non-invasively estimate biomechanical tissue properties via the imaging of propagating mechanical shear waves. Several factors including mechanical transducer design, MRI sequence design and viscoelastic reconstruction influence data quality and hence the reliability of the derived biomechanical properties.Purpose. To design and characterize a novel mechanical MRE transducer concept based on a rotational eccentric mass, coined the gravitational transducer.Materials and methods. Table top measurements were performed using accelerometers to characterize the frequency response of the new transducer concept at different driving frequencies (f VIB) and different rotating masses. These were compared to a commercially available pneumatically driven MRE transducer. MR data were acquired on a 3T scanner using a fractionally encoded gradient echo MRE sequence in three healthy volunteers. Acceleration and displacement spectra were plotted in units of g and mm, respectively, and visually compared, emphasizing the ratio between the peaks at f VIB and its 2nd harmonic, a known cause of error in the reconstruction of biomechanical properties as is explored in more detail in numerical simulations here. No formal statistical testing was performed in this proof-of-principle paper.Results. The new transducer concept shows—as expected from theory—a quadratic or linear increase of acceleration amplitude with increase in f VIB or mass, respectively. Furthermore, different versions of the transducer show markedly lower 2nd harmonic-to-f VIB ratios compared to the commercially available pneumatically driven transducer. Displacement was constant over a range of f VIB, in accordance with theory. Phantom and in vivo data show low nonlinearity and excellent data quality.Conclusion. The table top measurements are in concordance with the theory behind a transducer based on a rotational eccentric mass. The resulting constant displacement amplitude irrespective of f VIB and low 2nd harmonic-to-f VIB ratio result in low nonlinearity and high data fidelity in both phantom and in vivo examples.
Highlights
Magnetic resonance elastography (MRE) is a non-invasive MR imaging (MRI) technique, capable of quantifying soft tissue biomechanical properties by applying vibrations to the tissue of interest using an MRE transducer (Muthupillai et al 1995, Glaser et al 2012)
To design and characterize a novel mechanical MRE transducer concept based on a rotational eccentric mass, coined the gravitational transducer
The purpose of this study is to develop and demonstrate the principle of a new MRE transducer based on the concept of a rotational eccentric mass that addresses the aforementioned points
Summary
Magnetic resonance elastography (MRE) is a non-invasive MR imaging (MRI) technique, capable of quantifying soft tissue biomechanical properties by applying vibrations to the tissue of interest using an MRE transducer (Muthupillai et al 1995, Glaser et al 2012). MRE is FDA-approved (FDA) for liver fibrosis grading since 2009 (Loomba et al 2016) and has the potential to make a significant impact in other diagnostic areas, e.g. cancer staging and therapy response monitoring (Pepin et al 2015) To further facilitate this development, more reliable estimates of soft tissue biomechanical properties are desirable. This can be achieved (i) by mechanical transducers of higher fidelity to improve the quality of the source, (ii) by improved data acquisition methods providing more SNR and less motion artefacts from residual respiration for instance (Guenthner et al 2018), and (iii) by improved reconstruction algorithms for obtaining the complex shear modulus (Fovargue et al 2018). To design and characterize a novel mechanical MRE transducer concept based on a rotational eccentric mass, coined the gravitational transducer
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
