Breast sound speed tomography from B-mode data

Cancerous breast tumors have been shown to have higher sound speeds than healthy tissue; so accurate sound speed imaging is potentially valuable in cancer detection. We have constructed a volume breast ultrasound (VBUS) scanner that measures sound speed using standard B-mode technology. The objective of this study was to validate VBUS scanner sound speed measurements. Methods: The VBUS scanner automatically images the patient's pendant breast without compression, while a rotational motor acquires approximately 140 B-Mode images over 360 degrees in under 30 seconds using a commercially-available B-Mode transducer; a second motor sets the slice elevation. B-Mode images contain information from a reflector opposite the breast from the transducer that provide time delays for each RF A-line. Back-projection using a graphics processing unit (GPU) produces a 3-dimensional sound speed image. Scanner performance was measured using test phantoms and patient volunteers. Results: Sound speed reconstruction was 1 second per slice. Sound speed accuracy was within 98% and images were able to identify lesions down to 2.4 mm in the breast test phantoms. Sound speed images were also obtained from healthy volunteers as part of validating performance and determining that the scanner is ready for clinical evaluation. Conclusions: Our volume breast ultrasound (VBUS) scanner utilizes conventional US imaging technology to image sound speed. Our results show encouraging resolution and contrast that could potentially improve breast cancer detection and diagnosis, especially in women with dense breasts.