Simultaneous visualization of nerves and blood vessels with multispectral photoacoustic imaging for intraoperative guidance of neurosurgeries.

Real-time intraoperative guidance during neurosurgeries are often limited to endoscopy or microscopy, which are suboptimal when locating underlying blood vessels and nerves. However, accidental damage to these hidden yet critical structures can have severe surgical complications. To overcome this challenge, we are developing a fast-tuning, multispectral photoacoustic approach to guiding neurological procedures. An ex vivo porcine sciatic nerve and ex vivo caprine carotid artery perfused with whole human blood were suspended in a water bath. A spectroscopic analysis with wavelengths 690 nm to 1260 nm was performed on each specimen with a constant optical energy of 1.5 mJ/pulse and 11 mJ/pulse utilizing a 1 mm diameter optical fiber and a 5 mm diameter fiber bundle, respectively. The contrast and signal-to-noise ratio of each target was calculated from photoacoustic images, with wavelength-dependent contrast values and signal-to-noise ratios that ranged from 0.41 to 21.8 dB and 10.12 to 25.6 dB, respectively. In particular, the blood vessel contrast (18.2 dB) was greater than the nerve contrast (0.61 dB) when excited with 750 nm light. However, the nerve contrast (10.7 dB) was greater than the blood vessel contrast (6.6 dB) when excited with 1230 nm light. These results indicate that simultaneous visualization of major vessels and nerves requires an imaging system that exploits the unique optical absorption peaks of both hemoglobin and lipids by fast-tuning between two excitation wavelengths (e.g., 750 and 1230 nm).