Sum Frequency Imaging During Vibro-acoustography of Tissue

Vibro-acoustography is an imaging method that uses the radiation force of two interfering ultrasound beams of slightly different frequency to probe an object. An image is formed using the resulting low-frequency acoustic emission from the object's vibration at the difference frequency. A previously unstudied information signal is present during vibro-acoustography, which is formed by the sum frequency of the two beams. This study explored the feasibility of imaging tissue at the sum frequency while concurrently forming the low-frequency vibro-acoustic image, thereby increasing the amount of information acquired during a single scan. Vibro-acoustic and sum frequency images were acquired from a commercial breast phantom and excised human prostate and thyroid tissues. The sum frequency image produces a high-resolution C-scan of the tissue with the usual speckle artifact and is relatively similar to images at the 2(nd) harmonic frequency of the driving beams. Summing all three images together reduces speckle and improves image contrast.