de Sola, C.

Piñol i Margalef, F.

Infoscience - École polytechnique fédérale de Lausanne

Adaptive Predictive Coding of Ultrasound ImagesC. de Sola Fabregas and F. Pi~nol i MargalefaaSignal Processing Laboratory, Swiss Federal Institute of Technology,CH-1015 Lausanne , SwitzerlandUltrasonic imaging has become an important modality in the eld of medical imagingsystems, making necessary to develop an ecient method to compress and store theseimages, while retaining the image delity. We present a lossless compression approachwhich exploits the particular characteristics of the ultrasound echo-cardiographic instru-mentation based on a predictive adaptive coding method for compression [?].The philosophy underlying predictive coding techniques is to remove mutual redun-dancy between successive pixels and to transmit only the remaining (uncorrelated) infor-mation. This information is essentially the error resulting from the prediction, which leadsto a lower variance of the residual information than with JPEG method. The residualinformation is then entropy coded in order to achieve higher compression without furtherloss [?].A set of pixels is chosen for the linear prediction model, taking into account the in-terpolation method used in the scan conversion process [?]. The prediction is performedby tting a polynomial to the values of the neighboring pixels. The original value of thepixel is then subtracted from the predicted one. The error (for each pixel i) is dened as:e[i] = x[i]  x0[i]; (1)where x0[i] is the predicted value calculated as:x0[i] =j=NXj=1f [j]x[i  j] (with N : order of prediction): (2)For each one of the predicted pixels the coecients of the lter, f [j], are adaptivelycalculated by minimizing the error. Since the used prediction algorithm is known to thedecoder, there is no need to transmit the coecients, which are computed `on the y'during the decoding process.The algorithm has been applied to ultrasound echo-cardiography images, of size 720x576pixels. The results are compared to the JPEG lossless compression method. The perfor-mance of the proposed scheme can be seen within the numerical results: applying losslessJPEG a bit rate of 1.69 bits/pels is obtained for the best mode (out of seven); whereaswith the predictive adaptive lter we achieve a bit rate of 1.16 bits/pels, meaning a gainof 31.3%.REFERENCES1. Peter M. Clarkson, \Optimal and Adaptive Signal Processing\, Proceeding of theIEEE, Vol. 67, No. 4, April 1979.2. Roger J. Clarke, \Digital Compression of Still Images and Video". Academic Press.1995.3. Steven C. Leavitt, Barry F. Hunt and Hugh G. Larsen. \A scan Conversion Algorithmfor Displaying Ultrasound images\. Hewlett-Packard Journal, October 1983.

Adaptive predictive coding of ultrasound images

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Adaptive predictive coding of ultrasound images

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