Abstract
We created and evaluated a preclinical, multimodality imaging, and software platform to assess molecular imaging of small metastases. This included experimental methods (e.g., GFP-labeled tumor and high resolution multispectral cryo-imaging), nonrigid image registration, and interactive visualization of imaging agent targeting. We describe technological details earlier applied to GFP-labeled metastatic tumor targeting by molecular MR (CREKA-Gd) and red fluorescent (CREKA-Cy5) imaging agents. Optimized nonrigid cryo-MRI registration enabled nonambiguous association of MR signals to GFP tumors. Interactive visualization of out-of-RAM volumetric image data allowed one to zoom to a GFP-labeled micrometastasis, determine its anatomical location from color cryo-images, and establish the presence/absence of targeted CREKA-Gd and CREKA-Cy5. In a mouse with >160 GFP-labeled tumors, we determined that in the MR images every tumor in the lung >0.3 mm2 had visible signal and that some metastases as small as 0.1 mm2 were also visible. More tumors were visible in CREKA-Cy5 than in CREKA-Gd MRI. Tape transfer method and nonrigid registration allowed accurate (<11 μm error) registration of whole mouse histology to corresponding cryo-images. Histology showed inflammation and necrotic regions not labeled by imaging agents. This mouse-to-cells multiscale and multimodality platform should uniquely enable more informative and accurate studies of metastatic cancer imaging and therapy.
Highlights
Today, primary tumor masses are clinically controlled with surgical, drug, and radiation therapies, but the ability to control metastatic cancer is limited and over 90% of cancer patients die from metastases
Since we wanted to understand the deformation process, we examined the result of freezing on computed tomography (CT) images, which readily show any changes in tissue density, before and after freezing (Figure 2)
The unique feature of our software platform is that it enables at a whole-body level and with high resolution the localization of micrometastases in the body by employing single cell resolution cryo-imaging as a key modality and provides tools for studying the targeting efficiency at each micrometastasis
Summary
Primary tumor masses are clinically controlled with surgical, drug, and radiation therapies, but the ability to control metastatic cancer is limited and over 90% of cancer patients die from metastases. We identified micrometastases GFP tumors, determined the presence of red fluorescent imaging agent using highly sensitive cryo-fluorescence, determined if there was detectable MR signal, and examined histology for identification of tumor heterogeneity. In this way, we were able to identify that CREKA-Gd labeled an abundance of small and micrometastases. CITP technologies include high resolution and sensitivity cryo-imaging, experimental treatments to aid registration, whole mouse nonrigid registration algorithms, interactive visualization/analysis software that can accommodate very large out-of-RAM image data sets, and a tape method and nonrigid registration to allow accurate registration of histology
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