Digital modulation and 3 D printing-new techniques to be exploited in near-infrared spectroscopy of the brain

The brain, one of the main organs in the human body, has been extensively studied throughout the history of medicine. Some brain parameters, particularly the hemodynamic parameters, are associated to several brain disorders. Due to this connection, NIRS (Near infrared spectroscopy) techniques play a key role in brain research – they measure such parameters in order to potentially exploit the early-detection process. NIRS devices make use of near infrared spectrum, light between 650nm and 950nm, to measure various parameters non-invasively and changes of the tissue such as concentrations of oxy-(HbO2) and deoxyhaemoglobin (HbR) main absorbers of most tissues in this spectral range and related to blood oxygenation and volume changes. TM-NIRS, CW-NIRS and FD-NIRS combined with code-modulation techniques are commonly used for medical purposes. Nowadays, new modulation techniques for wireless communication are being developed and could be even used in NIRS techniques. Based on this fact, this thesis provides a review of existing NIRS modulations and discusses their strengths and weaknesses. The main aim was to build a new simple, affordable, and operative NIRS transmitter that can be utilised in digital modulation techniques focusing on human and mice measurements. In addition, this project was aimed to exploit 3D printing sensor design techniques and the testing process of the designed device. A 4kHz emitter with 4 high-power LEDs, a clock signal generator, decade counters and a receiver was designed and tested. Furthermore, PPG signal-NIRS optodes and a prototype of a phantom head were designed and 3D printed.