Department of Biomedical Engineering
Diffuse Optical Imaging of Tissue Lab
Diffuse Optical Imaging of Tissue Lab

The general idea of CHS

Coherent hemodynamics spectroscopy is a study of modulated hemodynamics. Hemodynamic modulation may occur spontaneously in tissues (for example as a result of respiration, heart beat, or low-frequency oscillations (LFO)) or may be induced, for example, by cyclic changes in arterial blood pressure. In the latter case of induced hemodynamics, it is possible to control the frequency of modulated hemodynamics, thus allowing for a study of the frequency dependence of local hemodynamic responses to systemic cyclical perturbations. The idea is that systemic hemodynamic perturbations elicit local hemodynamic responses in perfused tissues that can relay information about their physiological or pathological state. Figure 1 illustrates the key conceptual steps of CHS:

  1. Systemic hemodynamic perturbations are induced at a given frequency;
  2. The induced systemic hemodynamic perturbations at the selected frequency elicit local hemodynamic oscillations at the same frequency in the tissue of interest;
  3. The amplitude and phase of the local hemodynamic oscillations (for example [Hb] and [HbO2]) are measured;
  4. The three steps above are repeated at multiple frequencies to generate CHS spectra of amplitude and phase of elicited hemodynamic oscillations in the tissue of interest;
  5. A mathematical CHS model is used to fit the measured CHS spectra with fitting parameters that carry physiological information such as capillary transit time or effectiveness of cerebral autoregulation.
     
General approach of coherent hemodynamics spectroscopy (CHS). The systemic mean arterial pressure is modulated at a given frequency to drive oscillatory hemodynamics in tissues of interest.

Fig. 1. General approach of coherent hemodynamics spectroscopy (CHS). The systemic mean arterial pressure is modulated at a given frequency to drive oscillatory hemodynamics in tissues of interest (the brain in this example). Measurements of oscillatory tissue concentrations of oxy- ([HbO2]) and deoxyhemoglobin [Hb]) (which are usually denoted with O and D, respectively, in CHS, so that total hemoglobin concentration is T = O + D) at multiple frequency can be fit to a CHS model to yield physiological measurements such as capillary transit time or cerebral autoregulation.

The general idea of CHS (PDF)

See also:

  • S. Fantini, “Dynamic model for the tissue concentration and oxygen saturation of hemoglobin in relation to blood volume, flow velocity, and oxygen consumption: Implications for functional neuroimaging and coherent hemodynamics spectroscopy (CHS),” NeuroImage 85, 202-221 (2014).
  • M. L. Pierro, B. Hallacoglu, A. Sassaroli, J. M. Kainerstorfer, and S. Fantini, “Validation of a novel hemodynamic model for coherent hemodynamics spectroscopy (CHS) and functional brain studies with fNIRS and fMRI,” NeuroImage 85, 222-233 (2014).
  • S. Fantini, “NIRS brain studies with a new hemodynamic model: Coherent hemodynamics spectroscopy and functional neuroimaging,” OSA Topical Meeting on Biomedical Optics, Miami, FL, April 26-30, 2014. https://doi.org/10.1364/biomed.2014.bt5b.5.