We have proposed a high-range-resolution ultrasound imaging method for human carotid artery using an adaptive beamforming technique based on frequency domain interferometry (FDI). The method assumes that the received signal consists of multiple echoes of targets and noise, where the waveform of each echo is similar to that of the reference signal. In this study, we examine the dependence of the echo waveform on the target depth, and investigate the proper measurement-range for the FDI imaging method using a reference signal. Furthermore, we propose a ROI-division process, where each sub-ROI has a proper measurement-range for the application of the FDI imaging method. Simulation and experimental results show the efficiency of the ROI-division process in improving the image quality of human carotid artery acquired using the FDI imaging method. We believe that the modified FDI imaging method with the ROI-division process has the potential to facilitate significant progress in the detection of vessel stenosis and in the assessment of cardiovascular disease risk.