Optimization of the Trade-Off Between Speckle Reduction and Axial Resolution in Frequency Compounding

We measured the reduction of speckle by frequency compounding using Gaussian pulses, which have the least time-bandwidth product. The experimental results obtained from a tissue mimicking phantom agree quantitatively with numerical simulations of randomly distributed point scatterers. For a fixed axial resolution, the amount of speckle reduction is found to approach a maximum as the number of bands increases while the total spectral range that they cover is kept constant. An analytical solution of the maximal speckle reduction is derived and shows that the maximum improves approximately as the inverse square root of the Gaussian pulse bandwidth. Since the axial resolution is proportional to the inverse of the pulse bandwidth, an optimized trade-off between speckle reduction and axial resolution is obtained. Considerations for the applications of the optimized trade-off are discussed.

I. Introduction

Ultrasound imaging is the lowest cost of all deep tissue medical imaging modalities and is becoming an increasingly important diagnostic tool. Advantages include compact, real-time continuous imaging that can be used to guide injection and surgical procedures with no exposure to ionizing radiation to patients or clinicians. In addition, imaging modes such as color Doppler, shear wave and contrast agent labeling offer valuable additional information that complements x-ray, CT and MRI imaging. However, ultrasound imaging suffers from the presence of significant speckle noise, and useful resolution is severely degraded.