Clinical evaluation of irreversible compression of ultrasound images using the JPEG algorithm at approximately 9∶1

Abstract

A PRIOR ULTRASOUND compression study performed by our group considered a variety of factors, including frame-grabbed versus direct Digital Imaging and Communications in Medicine (DICOM) acquisition techniques, Joint Photographic Expert's Group (JPEG), and wavelet compression algorithms, the presence of "burned-in" text in the image, anda variety of compression ratios ranging from 10:1 to 25:1.1 The results of this prior study showed that grayscale ultrasound images compressed with the JPEG algorithm were preferable to those compressed with our wavelet techniques. The results also indicated that grayscale ultrasound images compressed with a quality factor of 70 (corresponding to a compression ratio of approximately 9:1) were of acceptable for diagnostic purposes. The purpose of this study was to formally validate that preliminary finding using a large number of grayscale and color ultrasound images. METHODSA frame-grabbed ultrasound image was selected from each of 300 patients by two of the authors (J.W.C. and E.M.J.) during the course of their routine clinical practice. These images were evenly distributed among four general anatomical regions (abdomen, pelvis, small parts, and vascular). A total of 36 of the 300 images were color. The images were processed on a PC using a cormnercial JPEG implementation. The quality factor was held fixed at values of 70 and 97 for the grayscale and color images, respectively. This resulted in compression ratios ranging from 6 to 13, with an average value of approximately 9:1. The images were then sent to a picture archiving and communication system (PACS) workstation via DICOM for evaluation. Tables 1 and 2 show a summary of the number of images, type of images, and resultant compression ratio range for this study.The images were presented as original/compressed pairs on a single cathode ray tube (CRT) monitor in a blinded fashion to a group of five radiologists practicing in three different departments. Radiologists were asked to pick which image (right or lefl) was preferred in terms of diagnostic utility, and to weight their preference from 1 to 5 (1 = slight preference, 5 = strong preference). The original image appeared on the right randomly in 50% of the cases. Care was taken to keep the CRT luminance and ambient light in tight control during all reading sessions.The data from all five radiologists were pooled and the rates at which the original and compressed images were preferred was computed. The number of image pairs and radiologist readings were chosen to assure that the 95% confidence intervals of the preference rates were approximately 2.5%. Average compression ratio (QF = 70) 8.6 9.3 9.1 8.4NOTE. Grayscale images were compressed using the JPEG algorithm at a quality factor (QF) of 70. This resulted in compression ratios ranging from 6.0 to 12.8 with an average of approximately 9 to 1.points also assured that if the preference rate of either the compressed or the original images was 45% or less, this would be detected using our experimental design 90% of the time. ...

Wavelet compression algorithm applied to abdominal ultrasound images

“…For US images, the compression ratios of 36.6:1 is acceptable for these types of images How does this compare with the literature? A compression ratio of 20:1 using Joint Photographic Experts Group (JPEG) format for echocardiographic images was reported by Karson et al 13 Persons et al 14 showed that a compression ratio of approximately 9:1 using a JPEG for both grey scale and colour US could be recommended for clinical use. Wu and Tai 15 developed a strategy to raise the compression ratio by exploiting spectra similarity while preserving good decoded quality.…”