The inhomogeneous backscattering distribution of low-coherent light in blood vessels, which appears as waisted double fan-shaped intensity pattern, is investigated in an in vivo mouse model and flow phantom measurements using high resolution spectral domain optical coherence tomography in the 1.3 μm wavelength region. Based on a predicted orientation of the red blood cells towards laminar flow, an angular modulation of the corresponding backscattering crosssection inside the vessels is assumed. In combination with the signal attenuation in depth by absorption and scattering, a simple model of the intravascular intensity modulation is derived. The suitability of the model is demonstrated exemplarily at the saphenous artery of the mouse during different states of the heart cycle as well as at phantom measurements with well known flow characteristics. The obtained data and the predicted model show good correspondence to each other which leads to the conclusion that the red blood cell orientation seems to be the reason for the observed intensity distribution inside the blood vessels. Therefore, the analysis of the intravascular intensity pattern might be useful for the evaluation of flow characteristics. Additional investigations of the precise angular backscattering of the complex shaped red blood cells are necessary for further model refinement.