Artikel
Multimodal non linear-optical microscopy: a novel tool for imaging of brain tumors
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Veröffentlicht: | 21. Mai 2013 |
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Gliederung
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Objective: Changes in tissue composition due to brain tumor growth involve a series of complex biochemical alterations. Biochemical composition as well as micromorphology can be imaged on unstained native tissue using multimodal non-linear optical microscopy (NLOM): Coherent anti-Stokes Raman scattering (CARS) imaging that resonantly excites the symmetric stretching vibration of CH2 groups at 2850 cm and visualizes lipid content in combination with imaging of endogenous two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) were investigated for their ability to discern different types of tumors from normal tissue in unstained, native brain samples.
Method: Different types of tumors were induced in brains of nude mice NMRI nu/nu (n = 25) by stereotactic implantation of glioblastoma (U87, NCH644, NCH421K), melanoma (A375) and breast cancer (MCF-7) cell lines. After development of intracranial tumors, brains were removed and cryosections were either subjected to NLO microscopy and consecutive H&E staining. Tumor proliferation indices and vascularization were addressed by anti-Ki67 and anti-CD31 immunohistochemistry. Additionally, NLO microscopy was tested on human glioblastoma samples (n = 6).
Results: NLO microscopy of cryosections provided exhaustive information of the tumor morphology. The tumor tissue could be discerned from the surrounding normal brain independent of the tumor's properties like vascularization or proliferation. The tumor border was defined with cellular resolution by reduction of CARS signal intensity to 52% (glioblastoma), 50% (melanoma) and 58% (breast cancer), reflecting the lower lipid content within the tumor. Micrometastases infiltrating normal tissue (size 50–200 µm) were identified in glioblastoma and melanoma. Relevant SHG signal visualizing collagen was detected in human samples and enabled to image variations in tumor associated vasculature.
Conclusions: All primary or secondary brain tumors investigated were characterized by a lower intensity of the CARS signal, therefore offering a simple tool for objective tumor detection. The combination of techniques allows retrieving a quantity of information on native unstained tissue which is comparable to H&E staining. NLO microscopy has the potential to become a technology routinely used intraoperatively for inspection and by neuropathology for frozen section equivalent assessment of brain tumors.