de Sola, C.

Dejean, C.

Infoscience - École polytechnique fédérale de Lausanne

COMPRESSION BASED ON A GEOMETRIC TRANSFORMATION OFECHOCARDIOGRAPHIC ULTRASOUND IMAGESCarmen de Solà and Cedric DejeanSignal Processing LaboratorySwiss Federal Institute of Technology, CH-1015 LausanneIntroduction:Ultrasound echo-cardiographic imaging has become an important modality in the field of medicalimaging system. This emphasizes the growing need to develop an efficient method to compressand store these images, while preserving image fidelity. Due to the nature of the transducerand the sampling methods, images obtained from an echocardiography show a strong circularcomponent. Therefore, the use of polar coordinates (radius ρ and angle α) should be moresuited for this kind of images.Method:In echo-cardiographic images, the region of interest (ROI) that contents most clinicalinformation does not occupy the whole image. In fact the ROI represents a sector of a circle.This ROI is scanned from top to bottom, by increasing the length of the radius (ρ) and thescanning angle(α), and vice versa. The new pixel value, expressed in polar coordinates isinterpolated from the four closest pixels of the original image. Images obtained with thepolar transformation exploit the fact that correlation among pixels is higher along the arcsand radius than along vertical and horizontal lines.Results:The classic JPEG compression algorithm has been applied to the transformed image and theresults were compared to those obtained with the original data (size of 640X480 pixels). Thetransformed image takes into account only the region of clinical interest, yielding a smallerimage. Numerical results show the performance of the proposed transformation. For a fixedquality of 38dB of the decompressed image, the compression ratio obtained with the originalimage is 16:1 (Q=35), while for the transformed image, it becomes 19:1 (Q=75) when scanningalong the radius, and  18:1 (Q=75) when scanning along the arcs.Conclusion:In this work a new way of interpreting the information given by an echocardiography image ispresented. The image is scanned taking into account the way in which it has been obtained fromthe transducer output data (i.e. in polar coordinates), and stored as the Cartesianrepresentation in order to exploit the specific correlation inherent to ultrasound images.

Compression based on a geometric transformation of echocardiographic ultrasound images

http://infoscience.epfl.ch/record/86505/files/de%20Sola1997_443.pdf

Compression based on a geometric transformation of echocardiographic ultrasound images

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Infoscience - École polytechnique fédérale de Lausanne