A prior ultrasound study indicated that images with low to moderate levels of JPEG and wavelet compression were acceptable for diagnostic purposes. The purpose of this study is to validate this prior ®nding using the Joint Photographic Experts Group (JPEG) baseline compression algorithm, at a compression ratio of approximately 10:1, on a suf®ciently large number of grayscale and color ultrasound images to attain a statistically signi®cant result. The practical goal of this study is to determine if it is feasible for radiologists to use irreversibly compressed images as an integral part of the day to day ultrasound practice (ie, perform primary diagnosis with, and store irreversibly compressed images in the ultrasound PACS archive). In this study, 5 Radiologists were asked to review 300 grayscale and color static ultrasound images selected from 4 major anatomic groups. Each image was compressed and decompressed using the JPEG baseline compression algorithm at a ®xed quality factor resulting in an average compression ratio of approximately 9:1. The images were presented in pairs (original and compressed) in a blinded fashion on a PACS workstation in the ultrasound reading areas, and radiologists were asked to pick which image they preferred in terms of diagnostic utility and their degree of certainty (on a scale from 1 to 4). Of the 1,499 total readings, 50.17% (95% con®dence intervals at 47.6%, and 52.7%) indicated a preference for the original image in the pair, and 49.83% (95% con®dence intervals at 47.3%, and 52.0%) indicated a preference for the compressed image. These ®ndings led the authors to conclude that static color and gray-scale ultrasound images compressed with JPEG at approximately 9:1 are statistically indistinguishable from the originals for primary diagnostic purposes. Based on the authors laboratory experience with compression and the results of this and other prior studies JPEG compression is now being applied to all ultrasound images in the authors radiology practice before reading. No image quality±related issues have been encountered after 12 months of operation (approximately 48,000 examinations).KEY WORDS: Compression, Joint Photographic Experts Group, ultrasound, medical images, PACS, teleradiology, archive W ith the rapidly dropping cost of digital storage and conservative use of standards-based irreversible (lossy) compression techniques, it is becoming practical to maintain large volumes of clinical images online, and distribute them eciently over networks.A prior ultrasound compression study was performed by our group to evaluate the eects of irreversible wavelet compression on ultrasound images and to determine how much compression can be applied, and still have the images be``acceptable for diagnostic purposes.'' 1 That study focused speci®cally on grayscale ultrasound images and considered a variety of factors including wavelet compression at several compression levels, different acquisition techniques (frame-grabbed v directly digitally acquired) and the eects of text that is`b ur...

The purpose of the study was to evaluate the effects of Iossy compression on grayscale ultrasound images to determine how much compression can be applied while still maintaining images that are acceptable for diagnostic purposes. The study considered how the acquisition technique (video frame-grabber versus directly acquired in digital forro) influences how much compression can be applied. For directly acquired digital images, the study considered how text (that is burned into the image) affects the compressibility of the image. The Iossy compression techniques that were considered include JPEG and a Wavelet algorithm using set partitioning in hierarchical trees (SPIHT).

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. ...