NONINVASIVE OPTICAL IMAGING OF THE SUBARACHNOID SPACE AND CEREBROSPINAL-FLUID PATHWAYS BASED ON NEAR-INFRARED FLUORESCENCE

The authors have developed a noninvasive optical method to image the s ubarachnoid space and cerebrospinal fluid pathways in vivo based on th e near-infrared fluorescence of indocyanine green (ICG). The ICG was b ound to purified lipoproteins (ICG-lipoprotein) and injected into the subarachnoid space of neonatal and adult rats. The ICG fluorescence wa s detected by a cooled charge-coupled device camera. After injection o f ICG-lipoprotein into the cerebral subarachnoid space of the neonatal rat, ICG fluorescence was clearly detected at the injection site thro ugh the skull and skin. The ICG fluorescence was observed in the cereb ellum and the lumbar spinal cord 1 and 8 hours postinjection, respecti vely. After injection of ICG-lipoprotein into the lumbar spinal subara chnoid space of an adult rat, ICG fluorescence was observed from the i njection site to the thoracic levels along the spinal subarachnoid spa ce. In addition, with the rat's head tilted downward, ICG fluorescence had extended to the cerebral subarachnoid space by 1 hour postinjecti on. The ICG fluorescence imaging of the cerebral subarachnoid space de monstrated an increase in fluorescence intensity around the lambdoid s uture and the forebrain. On dissection of the rat brain the former loc ation was identified as the supracerebellar cistern and the latter as the olfactory cistern. The results of this study are the first to demo nstrate that an optical technique is applicable to imaging of the suba rachnoid space and cerebrospinal fluid pathways in vivo. In addition, ICG-lipoprotein provides a sensitive optical tracer for imaging extrav ascular biological structures. Finally, ICG fluorescence imaging does not require an intricate imaging system because ICG is localized near the surface of the body.