An integrated device combining detection of the change in oxygen saturation (SO 2) by near-infrared spectroscopy (NIRS) and cerebral blood flow by diffuse correlation spectroscopy comprising: a first optical waveguide configured to deliver light at a first wavelength towards a tissue; and wherein the first optical waveguide is configured to deliver light at a second wavelength towards the tissue or wherein the device contains a second optical waveguide configured to deliver the light at the second wavelength towards the tissue, wherein each of the lights of the first and second wavelengths are referred to as SO 2 lights; a third optical waveguide configured to deliver a light at a third wavelength that is different than the wavelengths of the SO 2 lights towards the tissue, the light at the third wavelength is referred to as CBF light, and where the third wavelength is either longer or shorter than each of the wavelengths of the SO 2 lights; a fourth optical waveguide configured to transmit one or more of the SO 2 lights scattered from the tissue; a fifth optical waveguide configured to transmit the CBF light scattered from the tissue; a probe tip coupled to the distal end of each of the first, third, fourth, and fifth optical waveguides, and of the second optical waveguide if the integrated device comprises the second optical waveguide, wherein the distal ends of all these waveguides are aligned linearly in a narrow probe area at the probe tip; a first detector, in optical communication with the fourth optical waveguide, configured to detect the SO 2 lights; a second detector in optical communication with the fifth optical waveguide, configured to detect the CBF light scattered from the tissue; a first filter located in front of the first detector, where the first filter allows the SO 2 lights to pass through and substantially attenuates the CBF light; wherein the integrated device is configured to detect the SO 2 and CBF lights simultaneously. a first optical waveguide configured to deliver light at a first wavelength towards a tissue; and wherein the first optical waveguide is configured to deliver light at a second wavelength towards the tissue or wherein the device contains a second optical waveguide configured to deliver the light at the second wavelength towards the tissue, wherein each of the lights of the first and second wavelengths are referred to as SO 2 lights; a third optical waveguide configured to deliver a light at a third wavelength that is different than the wavelengths of the SO 2 lights towards the tissue, the light at the third wavelength is referred to as CBF light, and where the third wavelength is either longer or shorter than each of the wavelengths of the SO 2 lights; a fourth optical waveguide configured to transmit one or more of the SO 2 lights scattered from the tissue; a fifth optical waveguide configured to transmit the CBF light scattered from the tissue; a probe tip coupled to the distal end of each of the first, third, fourth, and fifth optical waveguides, and of the second optical waveguide if the integrated device comprises the second optical waveguide, wherein the distal ends of all these waveguides are aligned linearly in a narrow probe area at the probe tip; a first detector, in optical communication with the fourth optical waveguide, configured to detect the SO 2 lights; a second detector in optical communication with the fifth optical waveguide, configured to detect the CBF light scattered from the tissue; a first filter located in front of the first detector, where the first filter allows the SO 2 lights to pass through and substantially attenuates the CBF light; wherein the integrated device is configured to detect the SO 2 and CBF lights simultaneously.