Adaptive compensation of TGC effects in contrast-free ultrasensitive ultrasound Doppler imaging for improved resistivity index map visualization

Ultrasensitive power Doppler (uPD) ultrasound has become an alternative for microcirculation imaging in which all the advantages offered by ultrasound-based methods in terms of noninvasiveness, cost, portability, lower complexity and temporal resolution can be exploited. A uPD acquisition can be used to calculate a uPD image and the resistivity index (RI) over the entire field of view, which could be of great importance in clinical applications. However, uPD in deep tissues, such as kidney and liver, is greatly affected by noise in the deeper areas, which makes it difficult to visualize blood vessels in these regions. Some solutions have been proposed to mitigate the effects of noise by estimating the background noise and then equalizing the uPD image. In this work, an alternative equalization method is proposed in which the background noise is estimated without assuming homogeneity over the channels, thus obtaining an improved uPD image that is used to obtain a RI map, where the concerns related to aliasing effects are addressed. The proposed method was tested in the clinic, and preliminary results showed that the uPD image obtained using the proposed strategy improved the visualization of small vessels, and with respect to RI measurements at certain points, since in the clinic it is not possible to obtain a RI map, relative errors of less than 10% were obtained with respect to clinical measurements.