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DCS Analysis

Diffuse Correlation Spectroscopy (DCS) analyzes the rapid temporal fluctuations of near-infrared light scattered deeply through biological tissues (e.g., the brain or muscle) to measure microvascular blood flow.

DCS represents the third physics model overlay built on top of the Multi-Tau Correlator (CORM). The background C++ thread fits the semi-infinite medium diffusion approximation to the measured g²(τ) decay curve, outputting critical metrics like the Blood Flow Index (BFI).

Function Reference

Function	Parameters (In/Out)	Returns	Description
nexatom_tt_enable_dcs_analysis	[In] nexatom_tt_handle device [In] bool enable	nexatom_error_code_t	Enables host DCS analysis. An available selected result has analysis_type == 3; enabling alone does not guarantee it.
nexatom_tt_set_dcs_tissue_properties	[In] nexatom_tt_handle device [In] double mu_a [In] double mu_s_prime [In] double source_detector_separation_cm	nexatom_error_code_t	Defines the macroscopic tissue optics: absorption coefficient (μa), reduced scattering coefficient (μs’), and the physical source-detector separation in centimeters.
nexatom_tt_set_dcs_model_parameters	[In] nexatom_tt_handle device [In] double anisotropy_g [In] double tissue_n [In] double wavelength_nm	nexatom_error_code_t	Defines microscopic optics: tissue scattering anisotropy (g), tissue refractive index (n), and the near-infrared laser wavelength (e.g., 785 nm or 850 nm).
nexatom_tt_set_dcs_fit_range	[In] nexatom_tt_handle device [In] uint32_t start_index [In] uint32_t end_index	nexatom_error_code_t	Restricts the Levenberg-Marquardt solver to a specific temporal region of the 80-bin CORM lag curve to bypass early hardware afterpulsing.
nexatom_tt_set_dcs_fitting_control	[In] nexatom_tt_handle device [In] double tolerance [In] int max_iterations [In] double initial_beta [In] double initial_db	nexatom_error_code_t	Seeds the curve fitter with starting estimates for the coherence factor (β) and diffusion coefficient (Db) to optimize convergence speed.

Data Structures: nexatom_dcs_analysis_result_t

An available DCS result is exported when analysis_type == 3. Enabling analysis alone does not guarantee selection, fit convergence or computed values. General fit quality and beta are in the parent fit_result; uncomputed fields can be NaN or zero. The representation below does not establish clinical validity or instrument qualification for a biological measurement.

Field	Type	Description
blood_flow_index	float	Primary diagnostic output: BFI = α × DB (in cm²/s).
brownian_diffusion_cm2_s	float	Tissue diffusion coefficient (DB).
alpha	float	The fraction of moving scatterers (assumed active red blood cells).
decorrelation_time_us	float	Characteristic decorrelation time (τc).
penetration_depth_mm	float	Effective optical measurement depth based on the source-detector separation.
absorption_coefficient_per_cm	float	μa absorption coefficient (echoes input).
reduced_scattering_per_cm	float	μs’ reduced scattering (echoes input).
tissue_refractive_index	float	Tissue refractive index (echoes input).
mean_square_displacement_um2	float	⟨Δr²⟩ at τc.
flow_velocity_mm_s	float	Directed flow velocity component (if active flow models are fitted).
shear_rate_per_s	float	Shear flow rate across the sampled microvascular bed.
decay_rate_per_s	float	1/τc.
perfusion_units	float	Model output when computed; not a calibrated clinical unit or proof of clinical validity.
relative_flow_change_percent	float	For monitoring applications comparing baseline vs. current.
photon_path_length_cm	float	Average photon path length through the tissue.
mu_eff	float	Effective attenuation coefficient (reserved/currently NaN when not computed).

C Example: Configuring a DCS Tissue Measurement

// Fragment: illustrative model inputs, not prescribed tissue properties.
// Check every return and preserve the complete acquisition owner's cleanup.
double mu_a = 0.15;       // Absorption (1/cm)
double mu_s_prime = 10.0; // Reduced scattering (1/cm)
double separation = 2.5;  // 2.5 cm between laser and detector

nexatom_tt_set_dcs_tissue_properties(my_device, mu_a, mu_s_prime, separation);

// 2. Configure the physical constants
double anisotropy_g = 0.9;
double tissue_n = 1.4;    // Refractive index of tissue
double wavelength = 785.0; // 785nm NIR laser

nexatom_tt_set_dcs_model_parameters(my_device, anisotropy_g, tissue_n, wavelength);

// 3. Exclude very fast lags to bypass detector afterpulsing
nexatom_tt_set_dcs_fit_range(my_device, 3, 80);

// 4. Activate the DCS physics pipeline
nexatom_tt_enable_dcs_analysis(my_device, true);

Use the analysis validity guide and appropriate experimental validation before interpreting any derived quantity.