not require ionizing radiation. Optical coherence tomography (OCT) is another NIR medical imaging technique capable of 3D imaging with high resolution on par with low-power microscopy. Using optical coherence to measure photon pathlength allows OCT to build images of live tissue and clear examinations of tissue morphology. Due to technique differences OCT is limited to imaging 1–2 mm below tissue surfaces, but despite this limitation OCT has become an established medical imaging technique especially for imaging of the retina and anterior segments of the eye, as well as coronaries. A type of neurofeedback, hemoencephalography or HEG, uses NIR technology to measure brain activation, primarily of the frontal lobes, for the purpose of training cerebral activation of that region. The instrumental development of NIRS/NIRI/DOT/OCT has proceeded tremendously during the last years and, in particular, in terms of quantification, imaging and miniaturization. Peripheral NIRS Peripheral microvascular function can be assessed using NIRS. The oxygen saturation of haemoglobin in the tissue (StO2) can provide information about tissue perfusion. A vascular occlusion test (VOT) can be employed to assess microvascular function. Common sites for peripheral NIRS monitoring include the thenar eminence, forearm and calf muscles. Particle measurement NIR is often used in particle sizing in a range of different fields, including studying pharmaceutical and agricultural powders. Industrial uses As opposed to NIRS used in optical topography, general NIRS used in chemical assays does not provide imaging by mapping. For example, a clinical carbon dioxide analyzer requires reference techniques and calibration routines to be able to get accurate CO2 content change. In this case, calibration is performed by adjusting the zero control of the sample being tested after purposefully supplying 0% CO2 or another known amount of CO2 in the sample. Normal compressed gas from distributors contains about 95% O2 and 5% CO2, which can also be used to adjust %CO2 meter reading to be exactly 5% at initial calibration. See also Chemical Imaging Hyperspectral imaging Rotational spectroscopy Vibrational spectroscopy Terahertz time-domain spectroscopy Functional near-infrared spectroscopy (fNIR/fNIRS) Infrared spectroscopy Fourier transform spectroscopy Fourier transform infrared spectroscopy Optical imaging Spectroscopy References Further reading Kouli, M.: "Experimental investigations of non invasive measuring of cerebral blood flow in adult human using the near infrared spectroscopy." Dissertation, Technical University of Munich, December 2001. Raghavachari, R., Editor. 2001. Near-Infrared Applications in Biotechnology, Marcel-Dekker, New York, NY. Workman, J.; Weyer, L. 2007. Practical Guide to Interpretive Near-Infrared Spectroscopy, CRC Press-Taylor &