MR temperature imaging of nanoshell mediated laser ablation

Abstract

Minimally invasive thermal therapy using high-power diode lasers is an active area of clinical research. Gold nanoshells (AuNS) can be tuned to absorb light in the range used for laser ablation and may facilitate more conformal tumor heating and sparing of normal tissue via enhanced tumor specific heating. This concept was investigated in a xenograft model of prostate cancer (PC-3) using MR temperature imaging (MRTI) in a 1.5T scanner to characterize the spatiotemporal temperature distribution resulting from nanoparticle mediated heating . Tumors with and without intravenously injected AuNS were exposed to an external laser tuned to 808 nm for 180 sec at 4W/cm2 under real-time monitoring with proton resonance frequency shift based MRTI. Microscopy indicated that these nanoparticles (140–150 nm) accumulated passively in the tumor and remained close to the tumor microvasculature. MRTI measured a statistically significant (p<0.001) increase in maximum temperature in the tumor cortex (mean=21±7°C) in +AuNS tumors versus control tumors. Analysis of the temperature maps helped demonstrate that the overall distribution of temperature within +AuNS tumors was demonstrably higher versus control, and resulted in damage visible on histopathology. This research demonstrates that passive uptake of intravenously injected AuNS in PC-3 xenografts converts the tumor vasculature into a potent heating source for nanoparticle mediated ablation at power levels which do not generate significant damage in normal tissue. When used in conjunction with MRTI, this has implications for development and validation of more conformal delivery of therapy for interstitial laser ablations.

Design Maps for the Hyperthermic Treatment of Tumors with Superparamagnetic Nanoparticles

“…This approach, known as photothermal therapy , has been applied to the treatment of different tumor types, leading to complete tumor regression in animal models [17], [18], [19], [20], [21]. Although AuNPs can generate locally high temperatures, well above 50°C [22], they suffer by two major limitations: the maximum penetration depth of nIR light in a biological tissue is of the order of a few millimeters, making this approach quite inefficient for the treatment of deep tumors; the lack of clinical imaging modalities for the in vivo detection of AuNPs. Carbon-based materials, such as fullerenes and carbon nanotubes, have shown very promising heating behaviors in nIR light and RF fields [23], [24].…”

Optimization in interstitial plasmonic photothermal therapy for treatment planning

“…Although the development of interstitial PPTT is still in its early stage, it can be anticipated that interstitial PPTT may become as popular as LITT in the near future. 11 Numerical modeling of the laser-tissue interaction process is an important and effective way to facilitate the evaluation of a wide range of parameters for a desired outcome without extensive in vivo trials. A number of early studies have sought to model the hyperthermic and coagulative responses of tissues during surface-irradiation 12,13 and laser interstitial thermal therapy processes 14,15 without the use of nanoparticles.…”

Molecular thermometers for potential applications in thermal ablation procedures

“…We chose this range to interrogate the sensitivity of the molecular thermometers to clinically relevant temperatures of thermal ablations. [16][17][18] The UV/Vis spectrum of the conjugate 7 is shown in Fig. 4.…”