Magnetomotive Optical Coherence Elastography for Magnetic Hyperthermia Dosimetry Based on Dynamic Tissue Biomechanics

Abstract

Magnetic nanoparticles (MNPs) have been used in many diagnostic and therapeutic biomedical applications over the past few decades to enhance imaging contrast, steer drugs to targets, and treat tumors via hyperthermia. Optical coherence tomography (OCT) is an optical biomedical imaging modality that relies on the detection of backscattered light to generate high-resolution cross-sectional images of biological tissue. MNPs have been utilized as imaging contrast and perturbative mechanical agents in OCT in techniques called magnetomotive OCT (MM-OCT) and magnetomotive elastography (MM-OCE), respectively. MNPs have also been independently used for magnetic hyperthermia treatments, enabling therapeutic functions such as killing tumor cells. It is well known that the localized tissue heating during hyperthermia treatments result in a change in the biomechanical properties of the tissue. Therefore, we propose a novel dosimetric technique for hyperthermia treatment based on the viscoelasticity change detected by MM-OCE, further enabling the theranostic function of MNPs. In this paper, we first review the basic principles and applications of MM-OCT, MM-OCE, and magnetic hyperthermia, and present new preliminary results supporting the concept of MM-OCE-based hyperthermia dosimetry.

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.…”

Review of optical coherence tomography in oncology

“…In addition to the academic efforts to utilize OCT for breast cancer detection, scientists from industry have also been contributing to the same goal. 32,42 Unlike the previously reported OCT studies that rely on the structural analysis of breast tissue, optical coherence elastography (OCE) probes tissue mechanical contrast in tissues 35,[43][44][45][46][47] and polarization-sensitive OCT (PS-OCT) is sensitive to form birefringence in human breast tissue. 48,49 A dynamic spectraldomain OCE imaging technique with improved acquisition and processing speed has been reported.…”

Interstitial magnetic thermotherapy dosimetry based on shear wave magnetomotive optical coherence elastography

“…Magnetomotive optical coherence elastography (MM-OCE) is a branch of dynamic OCE that vibrates tissue with an oscillating magnetic force and probes the temporal tissue displacements for further mechanical assessment [20][21][22][23][24][25]. Magnetic nanoparticles (MNPs), acting as internal mechanical perturbative sources, can be delivered to the tissues uniformly and induce motions when exposed to an external magnetic field gradient.…”

“…Magnetic nanoparticles (MNPs), acting as internal mechanical perturbative sources, can be delivered to the tissues uniformly and induce motions when exposed to an external magnetic field gradient. Subsequently, either the natural or resonant frequency can be extracted from the induced "magnetomotion" and be utilized to infer the elasticity of the homogeneous or heterogenous tissues [20][21][22][23][24]. In addition, by confining the MNPs to a small cylindrical region at high concentration, a more localized magnetic force can be exerted to induce shear waves, where the wave propagation velocity can be utilized for stiffness quantification [25].…”

“…A mechanical actuator can also be attached to an RFA electrode or microwave antenna to induce shear waves for mapping the elasticity of the treated tissue [31]. Using OCE, our group has previously proposed and demonstrated the use of MNPs for both magnetic fluid hyperthermia and MM-OCE, where a significant shift in resonant frequency was observed in the mechanical spectrum of the treated tissue specimen, qualitatively indicating tissue stiffening [24]. Here, the theranostic function is implemented with a thin embedded magnetic rod, which can be utilized in both iMT as a highly localized heating source (therapeutic), and in shear wave MM-OCE as an internal vibrating source for quantitative elastic measurements (dosimetric/diagnostic).…”