gms | German Medical Science

Objective: The difficulty in visualizing glioma margins intraoperatively remains a major issue in the achievement of gross total tumor resection and, thus, the better outcome of glioma patients. Fluorescence guided surgery with the use of 5-aminolevulinic acid as a contrast agent has become the standard of care in Europe, but suffers from low sensitivity, specificity as well as limited spatial resolution and imaging depth. We opted to test the potential of a new optical imaging strategy with the use of gold nanostars as a dual-modality contrast agent combining the specificity and -sensitivity of Raman spectroscopy with the complemental tissue depth multispectral optoacoustic tomography (MSOT) provides in real-time.

Methods: Four week old Nestin-tv-a/Ink4a-arf^-/-/Pten^fl/fl mice were stereotactically implanted with RCAS-Pdgfb and RCAS-Cre transfected DF-1 cells to induce glioblastoma in the forebrain. Four weeks later surface-enhanced resonance Raman scattering nanoparticles featuring a star-shaped gold core and a Raman reporter resonant in the near-infrared were intravenously injected. Sequential 2D MSOT imaging was performed prior and post injection in vivo and followed by streamline Raman imaging for image comparison. Subsequent histological examination served as a reference standard. The pharmacokinetics of the nanostars were assessed by both modalities. The in vitro limit of detection as well as the photostability of the nanostars were assessed in a brain tissue mimicking phantom.

Results: In vitro the limit of detection of the nanostars was found to be in the low picomolar (<1 pM) by MSOT as well as even up to the low femtomolar range (1.5 fM) by Raman imaging. When exposed to high energy laser light they were found to be photostable. We found the nanostars to be cleared from the blood stream within a few hours and to sufficiently accumulate in the glioblastoma tumor tissue. MSOT was able to well depict the glioblastoma up to a centimeter in tissue depth with high specificity in vivo and found to correspond well to the Raman images proven to be ultrasensitive and –specific in the depiction of the accumulated nanostars.

Conclusion: The surface enhanced Raman scattering nanostars reported here were shown to be suitable to serve as dual-modality contrast agent in the depiction of glioblastoma by Raman and MSOT imaging in the near-infrared in a mouse model. Far beyond the limits of fluorescence imaging this complemental novel imaging strategy allowed for the ultrasensitive and –specific detection of glioblastoma up to a centimeter in tissue depth at high resolution.