Near Infrared Spectroscopy (NIRS) has been widely used to access the brain functional activity non-invasively. A
portable, multi-channel, continuous-wave (CW) NIR topography instrument we designed to measure the concentration
changes of each hemoglobin species and map cerebral cortex functional activation. The probe of instrument consists of 4
LEDs operating at three-wavelength (735 nm & 805 nm & 850 nm) surrounded with 10 photodiodes mounted on a
flexible PCB with the interoptode distance up to 2.88cm. On the basis of the modified Beer-Lambert law, the ratios of
optical density changes in a ftilly oxygenated and deoxygenated state are determined by varying blood volume and
hemoglobin oxygenation state in model experiment. The average ratios are 0.56. 1.74 and 0.45. Additionally, study on
the phantoms is carried out to investigate the penetration depth (13 mm) of the sensor array.
Developmental dyslexia, a kind of prevalent psychological disease, represents that dyslexic children have unexpected difficulties in phonological processing and recognition test of Chinese characters. Some functional imaging technologies, such as fMRI and PET, have been used to study the brain activities of the children with dyslexia whose first language is English. In this paper, a portable, 16-channel, continuous-wave (CW) NIRS instrument was used to monitor the concentration changes of each hemoglobin species when Chinese children did the task of phonological processing and recognition test. The NIRS recorded the hemodynamic changes in the left prefrontal cortex of the children. 20 dyslexia-reading children (10~12 years old) and 20 normal-reading children took part in the phonological processing of Chinese characters including the phonological awareness section and the phonological decoding section. During the phonological awareness section, the changed concentration of deoxy-hemoglobin in dyslexia-reading children were significantly higher (p<0.05) than normal-reading children in the left ventrolateral prefrontal cortex (VLPFC). While in the phonological decoding section, both normal and dyslexic reading children had more activity in the left VLPFC, but only normal-reading children had activity in the left middorsal prefrontal cortex. In conclusion, both dyslexic and normal-reading children have activity in the left prefrontal cortex, but the degree and the areas of the prefrontal cortex activity are different between them when they did phonological processing.