MAGNETOMOTIVE OCE

Magnetomotive OCE (MM-OCE) is an internal OCE technique, which introduces magnetic nanoparticles (MNPs) in the medium to be probed, and by applying a small, controlled, external magnetic field, one gains access to the nano- to micro-level interactions between the MNPs and the surrounding microenvironmental matrix. By quantifying the spatiotemporal characteristics of the mechanically-perturbed tissue sample, one can extract the mechanical properties of the sample.     
 

Transient-responce MM-OCE

When excited by step waveform from the electromagnet, the natural frequency of oscillation of each sample was obtained from the time-resolved displacement of each scatterer, measured optically with the coherence ranging system. From the results, a linear relationship between the natural frequency of oscillation of a material and the square root of its elastic modulus is demonstrated.

Crecea V, Oldenburg AL, Liang X, Ralston TS, Boppart SA. Magnetomotive nanoparticle transducers for optical rheology of viscoelastic materials. Optics Express, 17:23114-23122 2009. 2009 n/a PDF
Crecea V, Ahmad A, Boppart SA.   Magnetomotive optical coherence elastography for microrheology of biological tissues.   J Biomedical Optics, 18:121504 2013. 2013 PubMed Abstract PDF

 

Spectroscopic MM-OCE

When excited by a broadband waveform (e.g. chirp) from the electromagnet, the MNP-laden tissue sample undergoes a forced vibration across a range of frequencies. The responding oscillation of the tissue reaches the maximum amplitude (termed 'resonance') when the excitation frequency hits the natural frequency of the sample. The resonant frequency can therefore be utilized to infer the elastic properties of the tissue sample.
 

Ahmad A, Huang P-C, Sobh N, Pande P, Kim J, Boppart SA.   Mechanical contrast in spectroscopic magnetomotive optical coherence elastography.   Phys MedBiol 60:6655-6668 2015. 2015 PubMed Abstract PDF

 

Shear-wave MM-OCE

Localized, highly concentrated MNPs can serve as a shear-wave mechanical exctiation source. By exciting a harmonic oscillation and acquire the OCT data in a M-B mode manner (i.e. M-mode data collected across a range of spatial locations), the shear-wave propagation speed can be quantified and used to extract the Young's modulus of the tissue sample.
 

Ahmad A, Kim J, Sobh NA, Boppart SA.   Magnetomotive optical coherence tomography using magnetic particles to induce mechanical waves. Biomedical Optics Express, 5:2349-2361 2014. 2014 PubMed Abstract PDF

 

MM-OCE for magnetic hyperthermia dosimetry

Other than being utilized in MM-OCE, MNPs have also been independently used for magnetic hyperthermia treatment, which is a therapeutic technique that uses localized tissue heating to kill tumors. The temperature elevation during magnetic hyperthermia treatment not only can damage the targeted tissue, but can also induce stiffness change. Therefore, we have proposed a novel dosimetric technique for magnetic hyperthermia treatment based on the alteration of mechanical properties detected by MM-OCE.

Huang P-C, Pande P, Ahmad A, Marjanovic M, Spillman DR, Odintsov B, Boppart SA. Magnetomotive optical coherence elastography for magnetic hyperthermia dosimetry based on dynamic tissue biomechanics . IEEE J Selected Topics in Quantum Electronics: NanoBiophotonics, 22:6802816, 2016. 2016 PubMed Abstract PDF