Simultaneous Detection Of Multi-parameter During Cortical Spreading Depression Based On Multi-spectral Optical Intrinsic Signal Imaging

Cortical spreading depression (CSD) has been an important disease model of neural disorders, such as migraine, cerebral ischemia and trauma et.al, characterization of CSD in vivo, especially in the related hemodynamics and energy metabolism, could help us with the therapy of these neural disorders. Multi-spectral optical intrinsic signal (OIS) imaging is an in vivo imaging technique with high temporal and spatial resolution, and could offer multi-parameter changes (hemodynamics, mitochondrial metabolism and light scattering) by using proper data analyzing method. Thus, we use multi-spectral OIS imaging to simultaneously investigate changes in multi-parameter during CSD in vivo (in rats and mice). The main contents of our study are listed as following:(1) Firstly we introduced the Multi-spectral OIS imaging system. Then the modified Lambert-Beer law was derived. In most previous studies, OIS was employed to only characterize changes of hemoglobin during CSD in vivo by ignoring other related factors. To solve this problem, we analyzed a series of chromophores (hemoglobin, water, cytochrome c, cytochrome oxidase, NADH and FAD) which related to tissue absorption, and determined whether they will be included in the data analysis model through their absorption spectra. We offered the final data analysis equation of multi-spectral OIS, and established the data analysis model. Moreover, we simulated one important parameter of the data analysis model-the differential pathlength, and showed that the differential pathlength depends on the tissue optical properties. So we estimated the absorption and scattering properties of brain tissue, and then showed the differential pathlength as a function of wavelengths between450run and650nm.(2) Multi-spectral OIS imaging was used to simultaneously investigate changes in multi-parameter during CSD in rats, including:oxygen-hemoglobin (HbO), deoxygen-hemoglobin (HbR), cytochrome c, cytochrome oxidase, FAD and light scattering. The OIS responses at450,470,500,530,550and570nm showed a similar four-phasic pattern during CSD, while responses at600,630and650nm had a complex biphasic pattern. HbO showed a strong increase; HbR indicated decreased, increased and decreased triphasic change; light scattering showed a biphasic change that was characterized by a initial increase followed by a decrease; cytochrome c and cytochrome oxidase were strongly reduced at first and later shifted toward an oxidized state; FAD decreased and slowly recovered to baseline. The increase in HbR and reduction in cytochrome c and cytochrome oxidase suggested that the supply of oxygen was not sufficient once during CSD in rats. We showed that the hemodynamic changes during CSD may not be correctly estimated if the scattering and other chromophores (FAD, cytochrome c and cytochrome oxidase) are not included in the fitting model of multi-spectra data analysis. Cytochrome c was related to OIS at550nm; cytochrome oxidase was related to OIS at450,600and650nm; and FAD was related to OIS at450and470nm during CSD. Therefore, if utilizing OIS at these wavelengths to determine the hemoglobin changes during CSD, the corresponding chromophores should be taken into account to avoid inaccurate results.(3) Multi-spectral OIS imaging was used to investigate time-varying CSD in mice. Two CSD were induced respectively in30minutes in mice, and these two CSD indicated different responses:450,470,500,530,550and570nm OIS showed triphasic changes during1st CSD and was higher than baseline at last, while showed four-phasic pattern during2nd CSD;600,630and650nm OIS showed four-phasic changes during1st CSD and was lower than baseline at last, while600nm OIS was still with four-phasic changes during2nd CSD,630and650nm OIS indicated triphasic changes during2nd CSD; HbO and total hemoglobin (HbT) decreased in1st CSD but increased in2nd CSD; light scattering increased initially, then decreased and at last slowly decreased prolonged in1st CSD, but increased and recovered in2nd CSD; the pial arteries showed triphasic changes in1st CSD:constricted, then recovered and at last mildly constricted for a long time, but indicated four-phasic changes during2nd CSD:small dilation, constriction, large dilation and recovery. The increase of reduced cytochrome c and cytochrome oxidase and the decrease of FAD suggested that mitochondrial metabolism was in reduced state and hypoxia happened in brain tissue in both two CSD, but the hypoxia in1st CSD was severer than in2nd CSD. Moreover, the1st CSD could induce prolong ischemia in the mouse’s cortex, characterized by the prolong decrease of HbT and constriction of arteries.(4) We investigated two induced consecutive CSD in ischemic mice with right common carotid artery occlusion (CCAO), and observed the spontaneous CSD in ischemic mice with bilateral CCAO by using multi-spectral OIS imaging. We found that changes in all parameters were similar during1st CSD between ischemic mice and normal mice, expect the duration of changes was longer and the amplitude of reduced cytochrome c and cytochrome oxidase was larger in ischemic mice; that changes in all parameters during2nd CSD between ischemic mice and normal mice were also similar expect HbO, HbO strongly increased in normal mice while initially decreased and then mildly increased in ischemic mice. The spontaneous CSD in ischemic mice with bilateral CCAO showed identical increase in all wavelengths of multi-spectral OIS imaging, and this increase in OIS was caused by the increase in light scattering.