Fig. 2.

Removal of bulk motion from voxels within each B-frame segment. (A) Decorrelation due to bulk motion (D_BM) is modeled as a function of logarithmic reflectance R based linear regression coefficients m_k and n_k from the regression analysis of the k^th frame segment. Voxels with decorrelation value below threshold D_TH set at the 97.5 percentile of bulk motion (assuming normal distribution) are classified as non-flow voxels (D set to zero). The bulk motion-induced decorrelation in blood D_BM,blood is calculated using the reflectance of blood$R_{blood}$obtained from the median reflectance of flow voxels (voxel with D above D_TH). Bulk motion velocity v_BM is obtained from D_BM,blood using Eq. (2). (B) The bulk motion velocity is subtracted from a voxel with uncorrected decorrelation value D₀ and corresponding velocity v₀ that is high relative to the saturation velocity according to the nonlinear curve relating flow signal D to velocity. Therefore subtracting v_BM from v₀ to obtained corrected velocity v₁and corrected flow signal D₁ has little effect. (C) The bulk motion velocity is subtracted from a voxel with uncorrected decorrelation value D₀ and corresponding velocity v₀ that is lower than the saturation velocity. Here subtracting v_BM from v₀ to obtained corrected velocity v₁and corrected flow signal D₁ has a larger effect than the previous example.