Visual quality assessment of H.264/AVC compressed laparoscopic video

Abstract

The digital revolution has reached hospital operating rooms, giving rise to new opportunities such as tele-surgery and tele-collaboration. Applications such as minimally invasive and robotic surgery generate large video streams that demand gigabytes of storage and transmission capacity. While lossy data compression can offer large size reduction, high compression levels may significantly reduce image quality. In this study we assess the quality of compressed laparoscopic video using a subjective evaluation study and three objective measures. Test sequences were full High-Definition videos captures of four laparoscopic surgery procedures acquired on two camera types. Raw sequences were processed with H.264/AVC IPPP-CBR at four compression levels (19.5, 5.5, 2.8, and 1.8 Mbps). 16 non-experts and 9 laparoscopic surgeons evaluated the subjective quality and suitability for surgery (surgeons only) using Single Stimulus Continuous Quality Evaluation methodology. VQM, HDR-VDP-2, and PSNR objective measures were evaluated. The results suggest that laparoscopic video may be lossy compressed approximately 30 to 100 times (19.5 to 5.5 Mbps) without sacrificing perceived image quality, potentially enabling real-time streaming of surgical procedures even over wireless networks. Surgeons were sensitive to content but had large variances in quality scores, whereas non-experts judged all scenes similarly and over-estimated the quality of some sequences. There was high correlation between surgeons' scores for quality and "suitability for surgery". The objective measures had moderate to high correlation with subjective scores, especially when analyzed separately by camera type. Future studies should evaluate surgeons' task performance to determine the clinical implications of conducting surgery with lossy compressed video.

Selecting stimuli parameters for video quality assessment studies based on perceptual similarity distances

“…The SS experiments conducted with bit-rates chosen in the parameter selection step indicate that the selected stimuli were approximately equally distributed in the Quality (DMOS) space, but fit better to non-experts' than surgeons' scores. As discussed in [2], surgeons scores may have had larger variability compared to non-experts due to their inexperience with subjective quality experiments and the use of quality scales, or differing understanding of quality criteria between subjects. This in turn may have affected the goodness of fit to the perceptual difference predictions.…”

“…For the laparoscopic video compression experiment, non-experts and surgeons were asked to rate the overall quality ("Quality") of each sequence using a continuous scale from 0 (Poor) to 100% (Excellent quality). The experimental procedure and results are explained in [2].…”

“…1). Details regarding the conversion from the raw image acquisition format to the reference and H.264/AVC compressed sequences may be found in [2]. The PS experiment was conducted on scene D from [2].…”

“…For the SS experiment, four perceptually equidistant compression levels selected from the PS experiment were applied to four laparoscopic surgery scenes and presented to 9 laparoscopic surgeons and 16 non-experts (see [2] for details).…”

The Relative Impact of Ghosting and Noise on the Perceived Quality of MR Images

“…In addition, ROC is usually measured for a specific (detection) task; yet, MR imaging can produce a large variety of image contrasts, each with a large variety of clinical questions and each clinical question may link to a rather wide variety of relevant image-patterns. Hence, perceived image quality is considered as a measure that addresses performance averaged over all these (potential) diagnostic questions, and therefore is more and more studied in medical imaging [40]- [42]. Research linking perceived image quality to diagnostic performance, however, is very limited.…”