System Combines Optical Microscopy, MRI
MUNICH, June 8, 2015 — Combining optical and MRI techniques, a new imaging system aims to uncover the complexities of tumors to help better tailor cancer treatment.
The preclinical and intravital molecular imaging system houses a window for tissue observation in addition to a larger imaging chamber. Together they are being used to peer into the microenvironment of tumors and other tissues while learning about the coregistration of multiple lines of imaging data.
"Understanding the physiology behind multimodal imaging is very challenging due to discrepancies between macroscopic and microscopic images, and between images of extracted or transplanted tissues versus images of a live subject," said Zhen Liu, a doctoral candidate from the department of nuclear medicine at the Technical University of Munich. "This establishment of high-resolution, multimodal intravital imaging can bridge these discrepancies and offer a tool for the long-term observation of underlying physiology."
In a study, a tumor cell line was transplanted into a rat and imaged with each of the following: conventional MRI, the radiotracer carbon-13 (C-13) pyruvate and hyperpolarized MRI at a resolution of 2.5 mm, Medipix positron detector, luminescence sensor, and a fluorescence microscope.
Each of the imaging techniques has its advantages, Liu and colleagues said.
Direct positron imaging is a nuclear medicine technique that allows researchers to gain physiological information from radiolabeled imaging agents that bind to targets in the body. The hybrid system applies both conventional and hyperpolarized MRI.
The conventional MRI is suitable for soft-tissue contrast. Hyperpolarized MRI provides fine imaging resolution thanks to dynamic nuclear spin polarization technology, which is used to track minute biochemistry in the body, such as the transition of the naturally occurring chemical pyruvate to lactate. This exchange, which takes place throughout the body, has been found to be an excellent biomarker for disease.
Finally, luminescence, fluorescence and optical imaging are all state-of-the-art imaging techniques that can be used to paint targets as small as a strand of DNA with glowing substances to make them stand out when scanned or observed under a very powerful microscope.
Results of the study showed that increased lactate production was detected by hyperpolarized MRI in areas of hypoxia, or low-oxygenation, and higher levels of FDG binding represented areas of hypermetabolic activity surrounding the hypoxic areas. These are indications that areas of diseased tissue may be dying, while other parts of a tumor could be rapidly growing or becoming more aggressive.
These details tell researchers about the heterogeneity of tumors, which is essential for developing appropriate research and drug protocols that can navigate all the inherent complexity of not just the anatomy and physiology being imaged, but also how imaging technologies intersect to capture as much information as possible.
"This technology allows us to obtain in-depth knowledge of molecular imaging techniques, how to optimize them, and how to leverage data with statistical analysis while advancing new radiotracers and contrast agents for the imaging and treatment of a range of diseases," Liu said.
The research was to be presented during the annual meeting of the Society of Nuclear Medicine and Molecular Imaging in Baltimore.
For more information, visit www.snmmi.org.
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