Magnetomotive optical coherence elastography using magnetic particles to induce mechanical waves

Abstract

Magnetic particles are versatile imaging agents that have found wide spread applicability in diagnostic, therapeutic, and rheology applications. In this study, we demonstrate that mechanical waves generated by a localized inclusion of magnetic nanoparticles can be used for assessment of the tissue viscoelastic properties using magnetomotive optical coherence elastography. We show these capabilities in tissue mimicking elastic and viscoelastic phantoms and in biological tissues by measuring the shear wave speed under magnetomotive excitation. Furthermore, we demonstrate the extraction of the complex shear modulus by measuring the shear wave speed at different frequencies and fitting to a Kelvin-Voigt model.

Quantitative assessment of corneal viscoelasticity using optical coherence elastography and a modified Rayleigh–Lamb equation

“…The phantoms were assumed to be homogeneous and isotropic with a negligible viscosity. 14 The agar phantoms were placed on a ring support such that the central part of the bottom surface was free of the contact. The excitation position was at the center of the top surface of the phantom and all OCE measurements were taken in the central region.…”

Optical coherence elastography – OCT at work in tissue biomechanics [Invited]

“…Since biological tissues are inherently conductive, this method makes possible a wide range of investigations using biocurrent and tissue conductivity to study not only biomechanical properties, but also electrophysiological properties. A related alternative, extensively investigated by the Boppart group, is the use of magnetic nanoparticles, incorporated into tissues placed in an external magnetic field, as internal transducers for magnetomotive vibration [125][126][127][128][129][130][131][132][133][134][135][136][137][138][139]. Thus, loading is highly localized, to individual or aggregations of nanoparticles, but distributed throughout the tissue, and dynamic, in the alternating-current magnetic field.…”

“…Nanoparticles can be functionalized to selectively target tissues of interest [127,136,138]. The particles can be used to induce elastic waves [133] or spectroscopic analysis can be performed by sweeping the excitation frequency and finding resonance modes for micro-rheological analysis [125,131]. To date, there has been limited uptake of this method by other groups [129], perhaps because of the challenges presented by the very small displacements that can be induced.…”

Volumetric full-range magnetomotive optical coherence tomography

“…The resulting signals can be processed to generate contrast and probe the viscoelastic properties of materials and biological specimens. 5,6 The availability of fast OCT systems has allowed threedimensional (3-D) datasets to be routinely acquired, which is especially beneficial for in vivo measurements or in clinical environments where rapid scanning over large tissue volumes can have numerous benefits. However, in techniques such as dynamic optical coherence elastography (OCE) [7][8][9] and MM-OCT, 1,10 where dynamic excitation in the form of sinusoidal waveforms are utilized, the acquisition time is limited by the number of modulation cycles within the B-mode image.…”