Angular scatter imaging: clinical results and novel processing

Human tissues exhibit variation in scattering magnitude as the angle between transmission and reception is changed. These angular scatter variations result from intrinsic acoustic properties and sub-resolution structure. We have developed a clinical imaging system that uses the translating apertures algorithm to obtain statistically reliable, local angular scatter measurements. The obtained data can be processed to yield novel images. A significant problem with angular scatter imaging is limited depth of field (DOF). We describe a new method to improve DOF by applying shift variant filters to the data obtained at each angle. We show that this approach is optimal in a minimum sum squared error sense. The filter coefficients used in the technique can be determined via experiment or simulation. Unlike prior methods, this approach does not assume a model for the source of decorrelation, rather it includes all sources of decorrelation implicitly. We present simulation results showing the improvements in DOF obtained using this technique. We present experimental angular scatter data from phantoms and human subjects. In one phantom, designed to mimic microcalcifications in soft tissue, experimental data shows the angular scatter from 500 um glass spheres falling off by 50% over a 20 degree range of interrogation angles. In the same phantom the angular scatter from 50 um sephadex spheres fell off by only 10% over the same range. In the human calf muscle, brightness fell off by 60% over 20 degrees, while tendon brightness dropped by only 20%. Interestingly, the brightest target in the phantom (glass spheres) exhibited the greatest angular scatter variation, while the brightest target in the calf (tendon) exhibited the least angular scatter variation. These results provide compelling evidence that angular scatter properties are uncorrelated to b-mode image brightness.