Similar to functional magnetic resonance imaging (fMRI), functional near-infrared spectroscopy (fNIRS) detects the changes of hemoglobin species inside the brain, but via differences in optical absorption. Within the near-infrared spectrum, light can penetrate biological tissues and be absorbed by chromophores, such as oxyhemoglobin and deoxyhemoglobin. What makes fNIRS more advantageous is its portability and potential for long-term monitoring. This paper reviews the basic mechanisms of fNIRS and its current clinical applications, the limitations toward more widespread clinical usage of fNIRS, and current efforts to improve the temporal and spatial resolution of fNIRS toward robust clinical usage within subjects. Oligochannel fNIRS is adequate for estimating global cerebral function and it has become an important tool in the critical care setting for evaluating cerebral oxygenation and autoregulation in patients with stroke and traumatic brain injury. When it comes to a more sophisticated utilization, spatial and temporal resolution becomes critical. Multichannel NIRS has improved the spatial resolution of fNIRS for brain mapping in certain task modalities, such as language mapping. However, averaging and group analysis are currently required, limiting its clinical use for monitoring and real-time event detection in individual subjects. Advances in signal processing have moved fNIRS toward individual clinical use for detecting certain types of seizures, assessing autonomic function and cortical spreading depression. However, its lack of accuracy and precision has been the major obstacle toward more sophisticated clinical use of fNIRS. The use of high-density whole head optode arrays, precise sensor locations relative to the head, anatomical co-registration, short-distance channels, and multi-dimensional signal processing can be combined to improve the sensitivity of fNIRS and increase its use as a widespread clinical tool for the robust assessment of brain function.

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An interleaved gradient-echo (GE) / spin-echo (SE) EPI sequence was used to acquire images during the first pass of a susceptibility contrast agent, in patients with brain tumors. Maps of 1) GE (total) rCBV (relative cerebral blood volume), 2) SE (microvascular) rCBV, both corrected for T 1 leakage effects, and 3) (R 2 */R 2), a potential marker of averaged vessel diameter, were determined. Both GE rCBV and R 2 */R 2 correlated strongly with tumor grade (P 0.01, P 0.01, n 15), while SE rCBV did not (P 0.24, n 15). When the GE rCBV data were not corrected for leakage effects, the correlation with tumor grade was no longer significant (P 0.09, n 15). These findings suggest that MRI measurements of total blood volume fraction (corrected for agent extravasation) and R 2 */R 2 , as opposed to maps of microvascular volume, may prove to be the most appropriate markers for the evaluation of tumor angiogenesis (the induction of new blood vessels) and an-tiangiogenic therapies.

CSF volume is widely variable between individuals. The decreased CSF volume that results from increased abdominal pressure, such as with obesity or pregnancy, may produce more extensive neuraxial blockade through diminished dilution of anesthetic. The mechanism by which increased abdominal pressure decreases CSF volume is probably inward movement of soft tissue in the intervertebral foramen, which displaces CSF.

Fast GRE MR imaging can be reliably used to demonstrate diaphragmatic motion and may prove useful in the investigation of normal and abnormal respiratory mechanics.