Speckle reduction using stepped-frequency continuous wave ultrasound

Medical Ultrasonography is a valuable imaging technology for medical diagnostics and to guide interventional procedures. Ultrasound imaging is particularly useful in breast cancer detection and diagnosis for women with dense breast tissue where traditional mammography may fail to detect suspicious areas. However, ultrasound imaging suffers from speckle noise, an inherent characteristic of all coherent imaging techniques due to the presence of sub-resolution scatterers. Speckle noise produces a reduction in contrast resolution which is responsible for the overall lower effective resolution of ultrasound compared to x-ray or MRI imaging. In the case of breast imaging, ultrasound speckle can mask small details such as low contrast tumors or micro-calcifications, which may be an early indication of breast cancer. This limitation prevents ultrasound from displacing mammography as the gold standard for breast cancer screening. In conventional pulsed ultrasound imaging systems, de-noising techniques are used to minimize the effect of speckle noise. However, research shows that there is a tradeoff between the effectiveness of speckle reduction techniques and image resolution. We introduce stepped-frequency continuous wave ultrasound imaging which provides a framework where speckle reduction techniques are particularly effective, resulting in higher quality images with an improved SNR and significantly lower speckle noise while maintaining the spatial resolution of the original scan so that small lesions of interest are visible to the radiologist.