Correlation between the IVIM-MRI based tissue perfusion parameters and blood flow index measured by diffuse correlation spectroscopy

Intravoxel incoherent motion (IVIM) magnetic resonance imaging (MRI) technique evaluates the microstructure and microvascular blood perfusion of biological tissues. IVIM-derived pseudo-diffusion coefficient (D_fast) quantifies the perfusion-related motion of blood within the tissue microvascular and is related to the mean squared displacement of water molecules in time. Diffuse correlation spectroscopy (DCS) is a noninvasive optical technique to monitor the microvascular blood flow changes. DCS-derived blood flow index (BFI_DCS) is proportional to mean squared displacement of the red blood cells in time, thereby enabling comparison to D_fast. To evaluate the correlation between D_fast and BFI_DCS, controlled muscle-occlusion tests were performed on five healthy volunteers, with five leg and four forearm datasets. In response to muscle occlusion, the BFI_DCS decreased, whereas the mean D_fast increased, leading to no positive correlation between these parameters (r_rm: repeated measures correlation, r_rm=-0.219,95%CI:-0.724to0.438 in leg occlusion and r_rm=-0.567,95%CI:-0.894to0.155, in forearm occlusion). The IVIM data were of adequate quality (median voxelwise signal to noise ratio at b = 0: 25-57), however the voxelwise coefficient of variation CV_voxels of the D_fast (median within-subjects CV_voxels in the leg: 210.3% and in forearm: 160.9%) were imprecise. The disagreement between the IVIM- and DCS-derived parameter responses is therefore specific to the applied protocol, and its cause remains unresolved. Therefore, further studies with larger cohorts and different experimental protocols are required to better characterize the correlation between the IVIM- and DCS-derived parameters under varying perfusion conditions.