Practical error bounds for ultrasonic strain estimation using coded excitation

Ultrasound-based strain imaging is an exciting new medical imaging technique that is capable of revealing soft tissue regions that stiffen early in the development of disease processes. In one important application, breast imaging, lesion visibility is limited primarily by decorrelation noise. Accumulating measurements from many small compressions was found to be most effective at reducing decorrelation noise without reducing contrast or spatial resolution provided that we also applied coded pulse excitation to the probing ultrasonic transmission. Improvements were greatest when the echo signal-to-noise ratio (eSNR) was low. To predict the quality of strain estimates when designing systems, generalized coherence functions and the corresponding displacement variance bounds were derived. The contribution of this paper is to extend that treatment to include coded excitation and multi-compression techniques. The advantages of coded excitation/multi-compression techniques are demonstrated by imaging tissue-like phantoms and comparing results with conventional short pulse/single compression methods.