Determination of the acceptable MPEG-4 quality for clinical real-time tele-echocardiography services.

The characteristics of Moving Picture Experts Group (MPEG-4) video compression, in particular its adaptability to narrowband channels and the elevated degree of compression obtainable, make it of interest for services of telemedicine that require instantaneous video transmission and interpretation. In this study we faced the problem of the minimum quality of service (QoS) in specific applications of tele-echocardiography (T-E). In the specifics we evaluated the clinical adequacy of MPEG-4 compression in the real time transmission of echocardiographic studies. Forty echocardiographic examinations consisting of standard projections of patients affected by ischemic heart disease were submitted to two observers expert in echocardiography, who made 4 separate evaluations as follows: 2 on the same equipment on which the original studies were performed; 1 after online MPEG-4 codification of the studies at 256 kb/s; 1 after online MPEG-4 codification of the studies at 128 kb/s. For each evaluation, the following data were collected: subjective opinion on the overall visual quality of the images; estimate of ejection fraction and level of impairment; wall Motion Score Index and percentage of asynergy; mitral failure. The results: 1) the subjective quality of the echocardiographic images was the same as that perceived in the video at Mpeg4/256 kb/s compression level while it was lower, as expected, in the video Mpeg4/128 kb/s; 2) the quality degradation did not produce a statistically significant difference in the evaluation of left ventricular function and regional wall motion impairments. These results confirm the feasibility of MPEG-4 compression for the transmission of echocardiographic studies for use in telemedicine and suggest that it is not necessary to seek transmission speeds higher than 256 kb/s for the semiquantitative reading of left venticular kinetics.