Ng, Thomas S. C. and Bading, James R. and Park, Ryan and Sohi, Hargun and Procissi, Daniel and Colcher, David and Conti, Peter S. and Cherry, Simon R. and Raubitschek, Andrew A. and Jacobs, Russell E. (2012) Quantitative, Simultaneous PET/MRI for Intratumoral Imaging with an MRI-Compatible PET Scanner. Journal of Nuclear Medicine, 53 (7). pp. 1102-1109. ISSN 0161-5505 http://resolver.caltech.edu/CaltechAUTHORS:20120806-140725812
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Noninvasive methods are needed to explore the heterogeneous tumor microenvironment and its modulation by therapy. Hybrid PET/MRI systems are being developed for small-animal and clinical use. The advantage of these integrated systems depends on their ability to provide MR images that are spatially coincident with simultaneously acquired PET images, allowing combined functional MRI and PET studies of intratissue heterogeneity. Although much effort has been devoted to developing this new technology, the issue of quantitative and spatial fidelity of PET images from hybrid PET/MRI systems to the tissues imaged has received little attention. Here, we evaluated the ability of a first-generation, small-animal MRI-compatible PET scanner to accurately depict heterogeneous patterns of radiotracer uptake in tumors. Methods: Quantitative imaging characteristics of the MRI-compatible PET (PET/MRI) scanner were evaluated with phantoms using calibration coefficients derived from a mouse-sized linearity phantom. PET performance was compared with a commercial small-animal PET system and autoradiography in tumor-bearing mice. Pixel and structure-based similarity metrics were used to evaluate image concordance among modalities. Feasibility of simultaneous PET/MRI functional imaging of tumors was explored by following ^(64)Cu-labeled antibody uptake in relation to diffusion MRI using cooccurrence matrix analysis. Results: The PET/MRI scanner showed stable and linear response. Activity concentration recovery values (measured and true activity concentration) calculated for 4-mm-diameter rods within linearity and uniform activity rod phantoms were near unity (0.97 ± 0.06 and 1.03 ± 0.03, respectively). Intratumoral uptake patterns for both ^(18)F-FDG and a ^(64)Cu-antibody acquired using the PET/MRI scanner and small-animal PET were highly correlated with autoradiography (r > 0.99) and with each other (r = 0.97 ± 0.01). On the basis of these data, we performed a preliminary study comparing diffusion MRI and radiolabeled antibody uptake patterns over time and visualized movement of antibodies from the vascular space into the tumor mass. Conclusion: The MRI-compatible PET scanner provided tumor images that were quantitatively accurate and spatially concordant with autoradiography and the small-animal PET examination. Cooccurrence matrix approaches enabled effective analysis of multimodal image sets. These observations confirm the ability of the current simultaneous PET/MRI system to provide accurate observations of intratumoral function and serve as a benchmark for future evaluations of hybrid instrumentation.
|Additional Information:||© 2012 Society of Nuclear Medicine, Inc. Received Oct. 25, 2011; revision accepted Mar. 5, 2012. First published June 1, 2012. We thank Dr. Kofi Poku for preparing the 64Cu-DOTANHS- M5A antibody and Dr. Andrey Demyanenko, Desiree Crow, Alex Poznak, Sonia Collazo, and Bita Alaghebandan for their technical assistance. Drs. YibaoWu and Scott Fraser gave helpful advice. The project was funded by NIBIB R01 EB000993, NCRR S10 RR015703, S10 RR019253, the Beckman Institute, USC Molecular Imaging Center, and the Caltech/City of Hope Biomedical Initiative.|
|Subject Keywords:||PET/MRI; multimodal imaging; tumor heterogeneity; quantitative molecular imaging; preclinical|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||06 Aug 2012 22:24|
|Last Modified:||06 Aug 2012 22:24|
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