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

Abstract

While magnetic thermoseeds are often utilized in interstitial magnetic thermotherapy (iMT) to enable localized tumor ablation, we propose to extend their use as the perturbative source in magnetomotive optical coherence elastography (MM-OCE) so that the heat-induced elasticity alterations can be 'theranostically' probed. MM-OCE measurements were found to agree with indentation results. Tissue stiffening was visualized on iMT-treated porcine liver and canine soft tissue sarcoma specimens, where histology confirmed thermal damages. Additionally, the elasticity was found to increase exponentially and linearly with the conventional thermal dosage metrics and the deposited thermal energy, respectively. Collectively, a physiologically-meaningful, MM-OCE-based iMT dosimetry is feasible.

Biomechanical sensing of in vivo magnetic nanoparticle hyperthermia-treated melanoma using magnetomotive optical coherence elastography

“…A spectral domain OCT system with a superluminescent diode (wavelength 1325 ± 50 nm) light source provided an axial and transverse resolution of 8 µm and 16 µm, respectively, and was used with the magnetomotive setup for MM-OCT/MM-OCE measurements 35 . The main additional component was an electromagnetic coil (inner and outer diameter were 6 mm and 20 mm, respectively), enclosed in a chilled-water-filled chamber, that induced a maximum magnetic field strength of 170 G. The coil was placed in the sample arm of the OCT system, right above the MNP-laden tissue, to induce magnetomotion.…”

“…the breast tumor “felt” stiff when being palpated 28 ; melanoma tumor appears stiffer than the surrounding skin 29 ), tissue elasticity can potentially be correlated with cancer therapeutic outcomes as well. During thermotherapy, cell membrane integrity can deteriorate, and protein folding, unfolding, or irreversible denaturation may occur 8 , 9 , all of which can affect tissue biomechanics 30 - 35 . Observed on normal livers and muscles, tissue stiffness can change linearly with the thermal energy and exponentially with regard to conventional temperature-based dosage metrics 32 , 35 .…”

“…During thermotherapy, cell membrane integrity can deteriorate, and protein folding, unfolding, or irreversible denaturation may occur 8 , 9 , all of which can affect tissue biomechanics 30 - 35 . Observed on normal livers and muscles, tissue stiffness can change linearly with the thermal energy and exponentially with regard to conventional temperature-based dosage metrics 32 , 35 . Previously, ablative therapy was also shown to induce stiffening in prostate tumor and soft tissue sarcoma 33 , 35 .…”

“…Observed on normal livers and muscles, tissue stiffness can change linearly with the thermal energy and exponentially with regard to conventional temperature-based dosage metrics 32 , 35 . Previously, ablative therapy was also shown to induce stiffening in prostate tumor and soft tissue sarcoma 33 , 35 . Recently, an interesting finding of softened breast and colon tumors was observed after chemotherapy, where dystrophic, edema, and necrotic cells all contributed to the decrease in elasticity, making tissue biomechanics a potential predictor of a complete pathologic response 36 - 39 .…”

“…As a functional extension, the viscoelasticity of the specimen can be extracted as MM-OCE further analyzes the temporal characteristics of the magnetomotion (e.g. mechanical resonant frequency 44 , 50 , 51 , natural frequency 43 , 52 , or elastic wave propagation velocity 35 , 45 ).…”