A Novel Preprocessing Method for Common Carotid Artery Ultrasound Images Based on Phase Asymmetry Metric and Non-subsampled Shearlet Transform

The intima media thickness (IMT) of the common carotid artery (CCA) is helpful for the diagnosis of atherosclerosis. The CCA ultrasound image segmentation methods can be used for the IMT measurements. However, the speckle noise and the blurred edges can reduce the accuracy of the IMT measurements. To address this issue, a preprocessing method based on non-subsampled shearlet transform (NSST) and Phase Asymmetry Metric is proposed for the CCA ultrasound images. First, the CCA ultrasound image is decomposed into the NSST domain with a low-frequency sub-band and several high-frequency sub-bands. Next, the high frequency sub-band image is despeckling using an adaptive threshold method. Then, the processed image is reconstructed through NSST. Finally, an edge enhancement method based on the phase asymmetry (PAS) metric is used for enhancing the edges in the reconstructed CCA ultrasound images. In the simulated CCA ultrasound image experiments, the CNR value of proposed method is 1.8191 dB, which is the highest among four state-of-the-art methods. In the clinical CCA ultrasound image experiments, the average CNR values of proposed method is 1.5457 ± 0.6595 (mean ± std in dB), which is the best among four advanced methods. In the real application of IMT measurements, the average absolute error of intima-media thickness measurements of proposed method is 0.0790 ± 0.0588 (mean ± std in mm), which is the lowest among four advanced methods. In conclusion, the proposed approach has improved performance in suppressing the speckle noise and enhancing the intima media complex (IMC) regions, and it is a potential method for preprocessing of the CCA ultrasound images in clinical application.