Magnetic Resonance Imaging For Nanoparticle-Mediated Tumor Photothermal Therapy

Photothermal therapy(PTT)has emerged as an important treatment modality.PTT uses light absorbing materials as transducers;these transducers,often in the form of nanoparticles,are delivered to tumors prior to the treatment and under photoirradiation,causing thermal ablation of cancer cells.Compared to conventional treatment modalities,PTT affords the advantages such as minimal invasiveness and high selectivity.Moreover,PTT can be applied repeatedly without causing cumulative toxicity.Successful PTT therapy requires(1)selective delivery of enough photothermal conducting nanoparticles to tumor tissue to mediate effective PTT of tumor cells without damaging the surrounding normal tissues,(2)noninvasive real-time monitoring of the spatiotemporal heat profile,and(3)therapy response monitoring in a given target volume.Previous research on PTT has focused on the exploration of new photothermal agents and targeted delivery.The early prognosis and noninvasive temperature monitoring of PTT,which is pivotal for the assessment of the treatment and the therapy stratification,however,has been rarely studied.Conventional MRI,CT and X-ray were commonly used for the evaluation of therapeutic effect.Changes in tumor morphology,however,often require a certain amount of time.Therefore,it is necessary to perform some other functional imaging to monitor the tumor cell response in function and metabolism.Diffusion-weighted MRI(DW-MRI),as a functional MRI technique,has been increasingly used in the clinic to assess the extent of cell apoptosis and tissue damage.In the second chapter,we investigated DW-MRI as a tool for therapy monitoring and early prognosis of PTT.According to our research,ADC value changes in tumor tissues of mice in different treatment groups can be used as a prognosis biomarker for efficient PTT.During PTT,the higher or lower temperature of tumor will lead to ineffective treatment or some side effects.In order to obtain effective and safe treatment,it is also necessary to monitor and control the spatiotemporal heat profile of tumor tissue in real-time.In the third chapter,we herein used magnetic resonance temperature imaging(MRTI)as the noninvasive method to monitoring the temperature distribution during laser irradiation.MRTI shows good stability and accuracy in 9.4T Bruker MRI system.The application of MRTI provides the foundation for in vivo photothermal therapy.Overall,this paper systematically describes the application of DW-MRI and MRTI in tumor photothermal therapy.Our research aims to establish noninvasive methods for in vivo monitor nanoparticle-mediated PTT and further promote clinical translation of PTT.