A new method for grating lobe reduction for 3D synthetic aperture imaging with ultrasound computer tomography

Our 3D Ultrasound Computer Tomograph for breast imaging uses unfocused transducers grouped on a large non-planar aperture and synthetic aperture focusing in 3D. Technical feasibility limits the number of transducer positions to a sparse aperture, causing artifacts due to grating lobe effects in the resulting images. To suppress the artifacts, a median filter is applied to special pressure distributions, which are derived for each image point. After filtering the distributions are summed up for reconstruction. This approach reduces the artifacts significantly. For a phantom of ten nylon threads (0.2 mm diameter) an increase of contrast (SDNR) from 7.6 to 35.9 could be achieved. Also more complex phantoms showed significant reduction. The presented approach is simple and very effective, and can be easily integrated into the applied synthetic aperture focusing technique.