Calibrated parametric medical ultrasound imaging

The goal of this study was to develop a calibrated on-line technique to ext ract as much diagnostically-relevant information as possible from conventio nal video-format echograms. The final aim is to improve the diagnostic pote ntials of medical ultrasound. Video-output images were acquired by a frame grabber board incorporated in a multiprocessor workstation. Calibration ima ges were obtained from a stable tissue-mimicking phantom with known acousti c characteristics. Using these images as reference, depth dependence of the gray level could fairly be corrected for the transducer performance charac teristics: for the observer-dependent equipment settings and for attenuatio n in the examined tissues. Second-order statistical parameters still displa yed some nonconsistent depth dependencies. The results obtained with two ec hoscanners for the same phantom were different; hence, an a posteriori norm alization of clinical data with the phantom data is indicated. Prior to pro cessing of clinical echograms, the anatomical reflections and echoless void s were removed automatically. The final step in the preprocessing concerned the compensation of the overall attenuation in the tissue. A 'sliding wind ow' processing was then applied to a region of interest (ROI) in the 'back- scan converted' images. A number of first and second order statistical text ure parameters and acoustical parameters were estimated in each window and assigned to the central pixel. This procedure results in a set of new 'para metric' images of the ROI, which can be: inserted in the original echogram (gray value, color) or presented as a color overlay. A clinical example is presented for illustrating the potentials of the developed technique. Depen ding on the choice of the parameters, four Full resolution calibrated param etric images can be calculated and simultaneously displayed within 5 to 20 seconds. In conclusion, an on-line technique has been developed to estimate acoustic and texture parameters with a reduced equipment dependence and to display acoustical and textural information that is present in conventiona l echograms.