## 3 Optical Imaging Modalities to Develop and Verify Diagnosis/Treatment Techniques of Stroke  
### Fluorescence Imaging  
Fluorescence imaging is a modality that measures biological, chemical, or biophysical information and its time-varying changes by imaging fluorescence indicators that emit fluorescent signals including required information. Moreover, it has an advantage of noninvasive acquisition of functional and specific bio-information without destroying any biomaterials, for instance, cells [37; 38; 39; 40; 41]. For this reason, fluorescence imaging is utilized in both in vitro and in vivo preclinical assays for understanding their causes and verifying diagnostic/ therapeutic techniques of stroke by imaging the fluorescent markers that display biochemical and biophysical information related to strokes and its consequent brain damages. In particular, structural neuroplasticity [42; 43], axonal regrowth and sprouting [44; 45], a regeneration of dendrites [46] in recovery and rehabilitation after stroke were understand by high-resolution fluorescence imaging techniques. In this section, several studies on in vivo animal studies on stroke using fluorescence imaging were explored. Confocal and two-photon fluorescence microscopy are some of the advanced fluorescence imaging techniques that overcome limits of penetration depth in general fluorescence imaging with a higher resolution [47; 48; 49; 50]. Therefore, these have been employed to analyze stroke-induced in vivo animal models and conduct preclinical tests of stroke-related medical devices. [PERSON] et al. identified blood clots, which were generated by photothrombiosis, in arteries penetrating the longitudinal axis, and changes in blood clots  
Figure 2: Two-photon high-resolution fluorescence images used to observe variations in cerebral blood micro-vessels and dendrites before and after 30 min of stroke induction in a large area (\(>\)0.40 mm\({}^{2}\)). They indicate that dendrites do not recover from stroke and its consequent brain damages in a large area. Reprinted with permission from Ref. [35]. Copyright 2007 Public Library of Science. and surrounding blood vessels by observing fluorescein/dextran labeled plasmas using two-photon microscopy [51]. [PERSON] et al. obtained fluorescence images of blood clots formed inside a cerebral blood vessel beyond a thinned skull of mice [52]. In this study, thrombosis in cerebral blood vessels was confirmed by obtaining fluorescence images of injected fluorescein/dextran in the vessels using a confocal fluorescence microscope. Brain damages from a generation of thrombosis were also verified by 2,3,5-triphenyltetrazolzolium chloride (TTC) staining after an extraction of the brain. [PERSON] et al. conducted a study to analyze a transient progression of a distribution of the cerebral blood vessels and blood flows using optical speckle and two-photon fluorescence microscopes [53]. The multi-exposure optical speckle imaging used in this study showed a possibility of a long-term analysis of cerebral blood vessels in stroke-induced animal models through its comparison with the two-photon fluorescence imaging. Studies that analyze strokes and a resultant brain damage using fluorescence imaging of in vivo brain of animal models mainly employed near-infrared probes, which correspond to one of the highest transmission windows [54]. [PERSON] et al. developed an optical imaging system and technique to acquire a near-infrared image of a distribution of blood vessels in a mouse brain without removing a skull using a carbon nanotube indicator that emits functionalized optical signals between 1300 and 1400 nm [55]. This imaging technique can obtain arterial and venous veins in the mouse brain with minimal invasiveness up to a depth of approximately 2 mm. Moreover, an experiment to observe vascular loss in a local brain region, which is caused by middle cerebral artery occlusion (MCAO) induced stroke, confirmed its applicability as a stroke research tool. [PERSON] et al.