Real time strain imaging and in-vivo applications in prostate cancer

Prostate tumors can have a higher mechanical hardness than the surrounding tissue. During the digital rectal exam this can be used not only to detect the hypertrophy but also localized hardenings. The examination by digital palpation is inaccurate and even in combination with PSA-value and a transrectal ultrasonic examination the result is often not reliable. Ultrasound strain imaging is able to measure and visualize the elastic properties of a tissue region and hence is an adequate supplement for commonly used diagnostic procedures. We have developed a real time system for elastographic mechanical tissue assessment of the prostate which can be used for the transrectal ultrasonic examination for navigation and diagnosis. During the examination a sequence of ultrasonic images is acquired while the organ is slightly compressed by the ultrasound probe. Using a numerical analysis of image pairs of the acquired sequence the tissue strain is calculated which represents the spatial elasticity distribution of a specific cross-section of the organ and which are able to distinguish hard areas in the tissue. We present results from several patients which show that real time strain imaging is able to detect tumor-like areas which are inconspicuous in the b-mode image. The results correspond to the histological specimens. After the evaluation of 170 patients using a prospective study we found the specificity for cancer detection to be approximately 84% and a sensitivity of approximately 76%. Furthermore the tumor location and extend was correctly predicted in most of the investigated patients using our real time strain imaging.