Photodynamic therapy (PDT) is a promising and relatively new therapeutic modality for cancer treatment. With PDT, a tumor-localized photosensitizer is irradiated with visible light to generate reactive oxygen that efficiently kills cells and ablates tumors. PDT can be administered deep into tumors using minimally invasive techniques as only the small laser fiber that delivers the light to the tumor needs to be inserted into the lesions. PDT with Photofrin is US-FDA approved for treating early and advanced lung cancer, advanced esophageal cancer, and Barrett's esophagus. An important advantage of PDT is that both the photosensitizer and the light are inert by
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| Mouse registration. Image on the left is the coronal MR image. The white arrows indicate two tumors on the back of the mouse. Image at the center is the PET FDG image. The white arrows indicate two tumors. Image on the right is the overlay image. The tumors are registered well. |
themselves, and the light can be precisely focused onto a selected region, allowing extreme specificity in the localization of the photodynamic effect. Consequently, systemic toxicities are minimized.
We are investigating imaging techniques to study the tumor response to photodynamic therapy (PDT). PET can image the rapid biochemical and physiological responses of tumors to PDT; whereas MRI provides superior anatomical information, locations, and morphological changes within tumors. Combining PET and MRI has several advantages. (1) MRI scans provide anatomical reference for the PET images. (2) Fusion of MRI and PET images can enhance our ability to visualize the distribution of a radiolabeled pharmaceutical. (3) MRI provides tumor shape and size information that can be used to improve the accuracy of the PET data analysis, such as drawing regions of interests and performing quantitative analyses. (4) MRI can be used to correct PET data for partial volume effects to clarify that the PET-measured changes induced by PDT are due to metabolic and hemodynamic changes and not to artifacts of changes in tumor size. In this study, we acquired high-resolution MRI and microPET 18 F-fluorodeoxyglucose (FDG) images from C3H mice with RIF-1 tumors that were treated with PDT. We developed two registration methods for this application.
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