Transcranial Photoacoustic Detection of Blood-Brain Barrier Disruption Following Focused Ultrasound-Mediated Nanoparticle Delivery
Blood-brain barrier disruption (BBBD) is of interest for treating neurodegenerative diseases and tumors by enhancing drug delivery. Focused ultrasound (FUS) is a powerful method to alleviate BBB challenges; however, the detection of BBB opening by non-invasive methods remains limited. The purpose of this work is to demonstrate that 3D transcranial color Doppler (3DCD) and photoacoustic imaging (PAI) combined with custom-made nanoparticle (NP)-mediated FUS delivery can detect BBBD in mice.
We use MRI and stereotactic ultrasound-mediated BBBD to create and confirm four openings in the left hemisphere and inject intravenously indocyanine green (ICG) and three sizes (40 nm, 100 nm, and 240 nm in diameter) of fluorophore-labeled NPs. We use PAI and fluorescent imaging (FI) to assess the spatial distribution of ICG/NPs in tissues.
A reversible 41 ± 12 % (n = 8) decrease in diameter of the left posterior cerebral artery (PCA) relative to the right after FUS treatment is found using CD images. The spectral unmixing of photoacoustic images of the in vivo (2 h post FUS), perfused, and ex vivo brain reveals a consistent distribution pattern of ICG and NPs at *FUS locations. Ex vivo spectrally unmixed photoacoustic images show that the opening width is, on average, 1.18 ± 0.12 mm and spread laterally 0.49 ± 0.05 mm which correlated well with the BBB opening locations on MR images. In vivo PAI confirms a deposit of NPs in tissues for hours and potentially days, is less sensitive to NPs of lower absorbance at a depth greater than 3 mm and too noisy with NPs above an absorbance of 85.4. FI correlates well with ex vivo PAI to a depth of 3 mm in tissues for small NPs and 4.74 mm for large NPs.
3DCD can monitor BBBD over time by detecting reversible anatomical changes in the PCA. In vivo 3DPAI at 15 MHz combined with circulating ICG and/or NPs with suitable properties can assess BBB opening 2 h post FUS.
Key wordsPhotoacoustic Nanostructures Blood-brain barrier Focused ultrasound therapy Color Doppler Fluorescence microscopy
We would like to acknowledge Yin, Rideout-Gros, and Nghiem for their help with animal care, So for histology, Mikloska and Seerala for MRI, and FUS and Heinmiller for PAI.
JLF and FSF were funded by TFRI under grant number 1022 and CIHR grant FDN148367. RKP was funded by Princeton SEAS Blaire/Pyne and Old Guard. KH was funded by NIH under grant number R01-EB003268 and CRC.
Compliance with Ethical Standards
Conflict of Interest
FSF consults for and receives grant funding from Fujifilm VisualSonics Inc.
All experimental procedures were approved by the Animal Care Committee at Sunnybrook Research Institute, University of Toronto.
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